Electrical power disconnection circuit and method

Abstract

An electrical power disconnection circuit to disconnect from a power source a plurality of power lines, comprises a disconnection switch, an earthing switch, a current source, an input device, a current sensor, and a control device to, in response to receiving a disconnection command from one or more input device(s): - control the disconnection switch to disconnect each of the plurality of power lines from the power source; - control the earthing switch to connect each of the plurality of power lines to the protective earth; - control the current source to generate the verification current in at least one of the plurality of power lines, - control the current sensor to measure the electrical current through the earthing switch, - compare a measurement value of the electrical current through the earthing switch as measured by the current sensor to a value of the verification current as generated by the current source, - determine, using the comparison, if the power lines are disconnected from the power source, and - output a verification message in case the determining establishes that the power lines are disconnected from the power source.

Description

[0001] Title: Electrical power disconnection circuit and method

[0002] The present invention relates to an electrical power disconnection circuit configured to disconnect from a power source a plurality of power lines, an electrical power installation comprising such electrical power disconnection circuit, an assembly of an electrical apparatus and the electrical power installation, and a method of disconnecting from a power source a plurality of power lines.

[0003] The electrical standard e.g. EN 50110-1 discloses a method to safely disconnect an electrical load from an electrical power source. The load may be at a remote distance from the power source. The power source may be connected to the load via a switchboard. The switchboard may be controlled via an auxiliary circuit from the remote distance. The described method may require two operators in communication with each other. One of the operators is at the electrical load while the other operator is at the switchboard. The operator at the electrical (remote) load side switches off via an auxiliary circuit and thereby communicates the request to disconnect the load from the power source to the operator at the switchboard. The operator at the switchboard operates the power switch or switches to disconnect the load from the power source, secures the disconnection, for example by removing switchgear from the switchboard to prevent unintended or unexpected re-powering, and transmits a confirmation to the operator at the load. The operator at the load may then e.g. lock the switch in off position to perform maintenance, repair, cleaning, etc. The two operators may be the same person, moving between the remote locations of the switchboard and the load.

[0004] A problem associated with the safety methods is that the one operator at the switchboard could re-establish the supply of power by the power source to the electrical load in the case of mis-communication, misunderstanding, confusion, thus imposing a safety risk on the other operator at the load who may not be aware of the fact that the power is switched on.

[0005] The invention seeks to provide a safe disconnection of the electrical load from the power source.

[0006] According to an aspect of the invention, there is provided an electrical power disconnection circuit configured to disconnect from a power source a plurality of power lines, comprising: a disconnection switch for disconnecting each of the plurality of power lines from the power source; an earthing switch for connecting each of the plurality of power lines to a protective earth; a current source configured to generate a verification current in a respective one of the plurality of power lines; an input device configured to generate a disconnection command; a current sensor configured to measure an electrical current through the earthing switch; and a control device operationally connected to the disconnection switch, the earthing switch, the current source, the current sensor and the input device and configured to, in response to receiving a disconnection command from the input device: a) control the disconnection switch to disconnect each of the plurality of power lines from the power source; b) control the earthing switch to connect each of the plurality of power lines to the protective earth; c) control the current source to generate the verification current in at least one of the plurality of power lines, d) control the current sensor to measure the electrical current through the earthing switch, e) compare a measurement value of the electrical current through the earthing switch as measured by the current sensor to a value of the verification current as generated by the current source, f) determine, using the comparison, if the power lines are disconnected from the power source, and g) output a verification message indicative that the power lines are disconnected from the power source in case the determining at f) establishes that the power lines are disconnected from the power source.

[0007] The power source may comprise any source that provides or is configured to provide electrical power. The power source may comprise any electrical power source, such as an electrical generator, a solar panel installation, an electrical mains, or a high voltage power supply electrical network. The load may comprise any electrical load, such as a machine, a heating device, a transformer, a motor, a power converter, or any other load. The machine may for example comprise a semiconductor manufacturing apparatus, a paper manufacturing apparatus, a packaging apparatus, a metal manufacturing apparatus, or any other machine. The power lines may for example comprises a power line and a neutral line or 3 power lines of a 3 phase power supply, e.g. plus a neutral line, or any other combination of power lines.

[0008] The disconnection switch may comprise any suitable electrical power switch. The disconnection switch may comprise multiple contact pairs, e.g. each for a respective power line of the plurality of power lines.

[0009] The earthing switch may comprise any suitable electrical power switch. The earthing switch may comprise multiple contact pairs, e.g. each for a respective power line of the plurality of power lines. One side of the earthing switch may be connected to the protective earth, e.g. the ground or an electrical ground connector.

[0010] The disconnection switch is configured to, in a conductive state thereof, electrically connect the plurality of power lines to the power source, and in a non-conductive state thereof, electrically disconnect the plurality of power lines from the power source. The earthing switch is configured to, in a conductive state thereof, electrically connect the plurality of power lines to the protective earth, and in a non-conductive state thereof, electrically disconnect the plurality of power lines from the protective earth.

[0011] When the disconnection switch is electrically conductive and the earthing switch is non- conductive, the power lines are in a power-on state, wherein the power lines may (e.g. directly) transfer electrical power between the power source and the load. When the disconnection switch is disconnecting the power lines from the power source, i.e. the disconnection switch is electrically non-conductive, and the earthing switch is connecting the power lines to the protective earth, i.e. the earthing switch is conductive, the power lines are in a power-off state, wherein the power lines may not transfer electrical power between the power source and the load. As the earthing switch connects, in the conductive state thereof, each of the plurality of power lines to protective earth, it follows that the power lines are electrically connected to each other and connected to protective earth. The power-on state and the power-off state may be steady states, i.e. the control device may be configured to retain the disconnection switch in the conductive state and the earthing switch in the non-conductive state to retain the power lines in the power-on state until the control device receives, from the input device a disconnection command, e.g. inputted by an operator. Similarly, the control device may be configured to retain the disconnection switch in the non-conductive state and the earthing switch in the conductive state to retain the power lines in the power-off state until the control device receives, from the input device a connection command, e.g. inputted by an operator, to connected the power lines to the power source.

[0012] The input device may be configured to be in a locked state after a disconnection command has been inputted, i.e. the input device may be configured to require an unlocking by the operator to be brought into an unlocked state again, before the input device is able to, responsive to operator input, transmit the connection command to the control device. Thereby, safety is enhanced, in that inadvertent or un-authorized operator input leading to inadvertent or unauthorized transitioning from the power-off state to the power-on state, may be prevented. The un-locking may be performed by any suitable means, such as by a key switch, a PIN-code, a password, a key-tag, etc.

[0013] As in the power-off state the power lines are electrically connected to protective earth and to each other, safety is enhanced, in that, in case for example an electrical contact of the disconnection switch would malfunction, resulting in an unintended electrical connection of (one of) the power lines to the power source, an overcurrent protection of the power source (such as a fuse) would be triggered, causing the un-intended powering of (the one of) the power lines to be interrupted by the overcurrent protection.

[0014] The power lines may be brought into the power-off state for the purpose of powering down, switching off a load (i.e. an electrical load) connected to the power lines, and / or for the purpose of powering down the power lines themselves. The power lines and / or the load connected to the power lines, i.e. any electrical conductor and / or any electrical load at the switched-off side of the disconnection switch, may be powered down for any purpose, such as powering off, service, maintenance, inspection, replacement, etc.

[0015] The current source may be configured to generate the verification current, the verification current may e.g. have a pre-determined electrical current value. The verification current may be a Direct Current (DC) or an Alternating Current (AC), The current source may be configured to generate a plurality of verification currents, e.g. a verification current per power line. Alternatively, a current source connecting switch may be provided, the current source connecting switch configured to connect the current source to a respective one of the plurality of power lines so as to direct the verification current to the respective one of the plurality of power lines. The current source may be configured to inject the verification current. The verification current may be a direct current, an alternating current, a pulsed current, a current encoded with data by any suitable encoding scheme. In an embodiment, a spectral content of the verification current differs from a spectral content of the power provided by the power source. For example, in case the power source provides electrical power at an AC mains frequency, such as 50 Hz or 60 Hz, the verification current may be a direct current or a current having a frequency or pulse repetition rate different from 50 Hz, so as to enable the control device, when measuring the current by the current sensor, to distinguish between (a remainder) of a current due to the power source and the verification current. In the context of the present document, the term current source may be understood as a current injector, configured to inject the verification current. The current source, thus the current injector, may form a low impedance connection for other electrical currents, e.g. other than the injected verification current, thus to retain a low impedance path via the current source, e.g. to protective earth, for safety purposes. This feature of low impedance may enable the current source to be connected in e.g. the connection from the earthing switches to protective earth, which connection is aimed to provide a low impedance path to protective earth for safety purposes. The input device may be an operator operable device, such as a switch, a push button or other user interface. The disconnection command may be an analogue signal or a digital signal, and may be transmitted by the input device by any suitable means, such as by wire, by optical fiber, by wireless communication or by any other suitable means of communication. Plural remote input devices may be connected to the control device, which may enable the switching off of the power lines from plural remote locations. The input devices may further comprise a signalling means, configured to signal to the operator if the power lines are disconnected. The signalling means may signal to the operator that the power lines are disconnected from the power source, in response to receiving the verification message from the control device. Thus, the operator may receive feedback indicating if the power lines are safely disconnected from the power source and / or if the power lines are safely connected to protective earth, and may proceed to access the load for maintenance, repair, cleaning, etc, in response to such indication.

[0016] The current sensor may comprise any suitable sensor configured to sense an electrical current. The current sensor may comprise a single sensor or a sensor per power line of the plurality of power lines. In order for the current sensor to measure the electrical current through the earthing switch, the current sensor may for example be connected in series with the earthing switch. The current sensor may for example comprise a current transformer, a Hall-generator, an inductive coil, or operate on the basis of for example a capacitive, a thermal or a magneto strictive current measurement. The control device may comprise any suitable control device, such as a microcontroller provided with suitable program instructions, a microprocessor provided with suitable program instructions, a an embedded Programmable Logic Controller, PLC, provided with suitable program instructions, or a state machine configured to perform the actions as described.

[0017] Upon receiving a disconnection command from the input device, the control device may initiate the following: a) control the disconnection switch to disconnect each of the plurality of power lines from the power source. The disconnection switch may for example comprise a multi pole switch or comprise plural switches, one per power line. The power lines may accordingly be disconnected from the power supply voltage provided by the power source. b) control the earthing switch to connect each of the plurality of power lines to the protective earth. As e.g. a safety provision, the power lines are connected to the protective earth. The earthing switch may comprise a multi pole switch or plural switches, one per power line. By controlling the disconnection switch to disconnect each of the plurality of power lines from the power source and controlling the earthing switch to connect each of the plurality of power lines to the protective earth, the power lines are brought from the power-on state to a power-off state. The term “connect to” or “electrically connected to” may be understood as electrically connected by a low impedance connection. Thus, the earthing switch, when connecting each of the plurality of power lines to protective earth, provides for a low impedance electrical connection of each of the plurality of power lines to protective earth. As each of the plurality of power lines is connected to protective earth by a low impedance electrical connection, it follows that the power lines are electrically interconnected in the power-off state by the low impedance electrical connection. c) control the current source to generate the verification current in at least one of the plurality of power lines, The current source may generate the verification current, which may be employed in order to verify an electrically safe state of the power lines as described below: d) control the current sensor to measure the electrical current through the earthing switch. The electrical current through the earthing switch may be responsive to the verification current generated by the current source. The electrical current through the earthing switch is measured while the disconnection switch is controlled to disconnect each of the plurality of power lines from the power source and the earthing switch is controlled to connect each of the plurality of power lines to the protective earth. e) compare a measurement value of the electrical current through the earthing switch as measured by the current sensor to a value of the verification current as generated by the current source. The verification current may have a pre-determined electrical current value, i.e. a pre-determined electrical current magnitude. Accordingly, the measurement value of the electrical current through the earthing switch as measured by the current sensor may be compared to the pre-determined electrical current value of the verification current. Typically, at the power line or power lines in which the verification current is fed by the current source, the electrical current measured would be expected to substantially correspond to the verification current. However, in the case of a malfunction of the one or more contacts of the disconnection switch or a malfunction of the earthing switch the measured electrical current may deviate from a value of the electrical current as would be expected on the basis of the measurement current. A malfunction may result from one or more of various causes, such as for example a corroded contact(s) of the earthing switch providing for a relatively high contact resistance or a short circuit between two or more of the power lines. As another example, the disconnection switch itself may malfunction. The comparison of the measurement value of the electrical current to the value of the verification current may be performed for one of the power lines or for plural ones of the power lines, thus to verify, for the respective power line or power lines, if the measured current matches the current that would be expected in a safe situation of the basis of the feeding in of the verification current. f) determine, using the comparison, if the power lines are disconnected from the power source by the disconnection switch (and connected to the protective earth by the earthing switch), e.g. for the purpose of switching of the load e.g. for the purpose of powering down or service, such as maintenance, repair, cleaning, etc. For the power line or power lines in which the verification current is fed, it is to be expected that the value of the measured current substantially corresponds to the value of the verification current. A larger current value may indicate an error condition, such as a malfunction of the disconnection switch. A smaller current value may likewise indicate an error condition, such as a too high contact resistance of the earthing switch. Thus, using the comparison, it may be determined if the power lines are disconnected from the power source by the disconnection switch and connected to protective earth by the earthing switch. Once it has been determined, using the comparison, that the power lines are disconnected from the power source by the disconnection switch and connected to the protective earth by the earthing switch, the power lines may be considered safe, as high electrical voltages from the power source may have been removed and as high electrical currents from the power source via the power lines to the electrical load may have been halted. The electrical voltages of the power lines may be proximate to protective earth as the power lines are electrically connected to protective earth by the earthing switch. The electrical voltage and / or electrical current to the power lines are subjected by the current source may be at least one order of magnitude lower, i.e. at least a factor 10 lower, preferably at least two orders of magnitude lower, i.e. at least a factor 100 lower, than the electrical voltage and / or electrical current to which the power lines are subjected by the power source. The current source may be a low voltage, low electrical power source, providing into the power lines a verification current and associated voltage which is harmless if touched by a human, e.g. the electrical voltage at the power lines due to the current source, in the power-off state of the power lines, being at least one order of magnitude lower than the electrical voltage injected into the power lines in the power-on state, i.e. when electrically connected to the power source to be powered by the power source. For the power line or power lines in which no verification current is fed, a measurement of the current may also be performed, whereby an expected value of the current in the power line(s) in which no verification current is fed, may be substantially zero. In case the value of the current measured in the power lines in which no verification current is fed, is too high, this may likewise indicate the presence of an error, such as a short circuit towards another one of the power lines (in which a verification current is fed) or a malfunctioning of the disconnection switch. g) output a verification message indicative that the power lines are disconnected from the power source by the disconnection switch (and are connected to protective earth by the earthing switch) in case the determining at f) establishes that the power lines are disconnected from the power source (and connected to protective earth by the earthing switch). The verification message confirms that the power lines are in the power-off state. The verification message may for example be output at a user interface of the input device, thus to confirm to the operator which operates the input device, that the disconnection has been performed and that the power lines and possibly the equipment electrically connected to the power lines to be powered by the power source, can be safely accessed, e.g. for maintenance, repair, cleaning, etc. In order to indicate to an operator that the power lines are in the power-off state and may be safely accessed, the control device may be configured to control the disconnection switch and the earthing switch to maintain the power lines in the power-off state, i.e. to control the disconnection switch to maintain each of the plurality of power lines disconnected from the power source, and to control the earthing switch to maintain each of the plurality of power lines connected to the protective earth, while controlling the input device to maintain outputting the verification message at the user interface thereof. For example, the control device may be configured to, in the power-off state of the plurality of power lines, maintain outputting the verification message at the user interface, control the disconnection switch to maintain each of the plurality of power lines disconnected from the power source and control the earthing switch to maintain each of the plurality of power lines connected to the protective earth. The operator may accordingly be provided safe access to the power lines and any load electrically connected to the power lines during the power-off state. The power-on state and the power-off state may be steady states. The power-off state may e.g. extend over a time period of at least ten seconds, preferably at least a minute, more preferably at least ten minutes, enabling service such as cleaning, maintenance or repair.

[0018] One operator may control the disconnection of the power from the power lines and load. The operator may provide an input at the input device, and may receive a feedback on the basis of the verification message that the power has been safely disconnected. The switching off of the power is performed by the disconnection switch under control of the control device, thereby requiring a minimum of human on site intervention. The earthing of the power lines to protective earth by the earthing switch may provide for an additional safety, in that the disconnected power lines are electrically connected to protective earth to further reduce a risk of exposure to electrical voltages at the power lines. The connection to protective earth via the earthing switches is tested by the feeding in of the verification current(s) thus verifying if the power lines are indeed connected to protective earth via a low impedance connection. A risk of reestablishing the supply of power by the power source as a result of an interrupt of power from the power source or a glitch is reduced, as the control device not only disconnects the power lines from the power supply, however also connects the power lines to protective earth by means of the earthing switches. Moreover, the disconnection switch and earthing switch are controlled by the control device, reducing a risk of inadvertent switching to an undesired state. The control device is responsive to an input from the input device only, which input device may be connected to the control device via an optical fiber connection, a shielded wire connection, and / or make use of a data protocol enhancing a robustness of data communication, thereby reducing a susceptibility for disturbances such as spikes, glitches, etc. .

[0019] In an embodiment, the control device is configured to perform a ) and b) for each one of the power lines simultaneously and perform c) - e) for each one of the power lines sequentially. Accordingly, the power lines are switched off and connected to protective earth at the same time to establish a power off state of the load connected to the power lines and to enhance a safety by connecting the power lines to protective earth. Then the steps c), d) and e) may be performed per power line. For example the verification current is fed by the current source into one of the power lines and the current measurement by the current sensor is performed for the particular one of the power lines. Accordingly, it may be verified if the value of the current measured by the current source matches the value of the verification current as fed into the one of the power lines. The process of feeding the verification current, measuring by the current sensor and comparing may be repeated per power line.

[0020] Furthermore, the control device may be configured to, when performing c), and d) for one of the power lines, further control the current sensor to measure the electrical current through the earthing switch at at least one other of the power lines. When performing c) and d) for one of the power lines, the measuring of the electrical current through the earthing switch may be performed for each one of the other power lines, one by one, thus providing a measurement result per pair of power lines. All combinations of power lines, i.e. all pairs may thus be measured by feeding the verification current in one of the power lines and measuring in each one of the other power lines. A source of error may accordingly be determined by identification of a pair providing a measurement result that deviates from an expected measurement result. The electrical current at the other one of the power lines is expected to be zero or near zero, as the power line in question is disconnected from the power source, connected to protective earth and not supplied with a verification current. An error, such as a short circuit or a finite contact resistance between the power line that is subject to the verification current and the other one of the power lines may result in the occurrence of a current in the other one of the power lines. The current measured at the at least one other of the power lines may be compared to zero or a threshold value lower than the verification current. In case the threshold value is exceeded, this may signal the presence of an error condition. The error condition may be established on the basis of the comparison of the current measured in the other one of the power lines (i.e. not subject to the verification current) or on the basis of a combination with one or more other comparisons: for example: the measurement of a (too high) current in the other power line in which no verification current is fed at the moment of the current measurement, may be associated with the measurement of a (too low) current in the power line in which the verification current is fed: such combination may signal the occurrence of an electrical impedance between the power line in which the verification current is fed and the other power line, resulting in the verification current to partly divert to the other one of the power lines.

[0021] As a further example, the control device is configured to determine, at f), if a measurement value of the electrical current through the earthing switch at at least one other of the power lines as measured when performing c), d) and e) for the one of the power lines, exceeds a safety threshold. The exceeding of the safety threshold may indicate a parasitic impedance (or short circuit) between the power lines or may indicate a defect of the disconnection switch for the power line in which the safety threshold is exceeded, leading to an unintended supply of power from the power supply to the power line that is intended to have been disconnected from the power supply. In an embodiment, the control device is configured to determine that the power lines are disconnected from the power source by determining if the measurement value of the electrical current through the earthing switch as measured by the current sensor equals the current value of the verification current as generated by the current source within a verification window. In an normal situation, it would be expected that the measurement of the current at the power line in which the verification current is fed, yields a substantially the same value as the verification current, indicating that no current is diverted away, indicating e.g. the absence of a too high contact resistance to protective earth, e.g. in the earthing switch or in an earthing contact. According, the comparison of the measured current to the verification current may provide an efficient determination indicating that the electrical power disconnection circuit operates safely and as intended.

[0022] In an embodiment, the control device is further configured to control the earthing switch to open while controlling the current source to generate a contact cleaning current. The contact cleaning current may be a current having a higher value than the verification current and may be applied to enable the earthing switch to be cleaned by the application of the electrical current having the relatively high value at the moment that the earthing switch opens, which may generate an electrical spark at electrical contacts of the earthing switch, which may provide for a cleaning of the electrical contacts of the earthing switch.

[0023] The current source may be connected in different ways. For example, in an embodiment, the current source is electrically connected between the protective earth and the respective one of the plurality of power lines, preferably in an electrical series connection with the earthing switch. Thereby, a reliable indication that the earthing switch provides a low impedance connection to protective earth may be provided, as the verification current is fed into the circuit is series with the earthing switch.

[0024] Alternatively, the current source may be electrically connected in an electrical path to protective earth parallel to earthing switch). Consequently, the current source may be away from a conductive path that may carry a high current in the case of a short circuit, etc, accordingly being less susceptible to damage from high currents, current spikes, etc. The verification current may be measured directly through the earthing contact to be tested.

[0025] In an embodiment, the current sensor is electrically connected in series with the earthing switch, such as between the earthing switch and the protective earth. By connecting the current sensor in series with the earthing switch, such as between the earthing switch and the protective earth, a reliable indication of the electrical current through the earthing switch may be obtained, which may provide a reliable monitoring of the earthing switch and the connection of the power line to protective earth. In another embodiment, the current sensor is electrically connected in series in an electrical path to protective earth parallel to the earthing switch. Accordingly, the current sensor may be away from a conductive path that may carry a high current in the case of a short circuit, etc, consequently the current sensor being less susceptible to damage from high short circuit currents, current spikes, etc.

[0026] In an embodiment, for each one of the power lines, a wiring length from the earthing switch to protective earth is substantially the same. As the wiring length from the earthing switch to protective earth is substantially the same, the electrical resistance from the earthing switch to protective earth may be substantially the same for each power line, enabling to compare the current measurements at the power lines to each other. In case of substantially the same value of the verification current for each power, line and substantially the same contact resistance of the earthing switch, substantially the same current would be expected to be measured in each one of the power lines.

[0027] In an embodiment, for each one of the power lines, a wiring impedance from the earthing switch to protective earth is lower than twice a wiring impedance from the earthing switch via the power lines to a load powered via the power lines. As the power line is disconnected from the power source by the disconnecting switch, the power line may remain connected to the load. Upon feeding the verification current into the power line, the verification current may in divert between the earthing switch and the load that is still connected to the power line. Accordingly, in case of a low load impedance, a lower value of the current could be measured by the current sensor, compared to the value of the verification current, as the load impedance may e.g. be effectively electrically parallel to the earthing switch, hence reducing an accuracy of the determination. As the load is connected via the power line, a relatively high wiring impedance of the power line compared to the wiring impedance from the earthing switch to protective earth, may reduce an effect of the parallel path via the load, due to the series impedance of the power line wiring.

[0028] In an embodiment, the current source is arranged in a vicinity of the earthing switch, i.e. at or near the earthing switch, hence enabling a low impedance electrical connection of the current source to the earthing switch, which may similarly as above reduce an effect of a parallel electrical path via the power line and the load.

[0029] In an embodiment, the electrical power disconnection circuit further comprises an operator console operationally connected to the control device, wherein the operator console comprises the input device and wherein the control device is configured to output the message indicative if the power lines are disconnected from the power source to the operator console. The operator at the operator console may provide an input, e.g. via a user interface, initiating the disconnection of the power lines from the power source, and verify that the power lines are disconnected from the power source by the message indicative of the disconnection.

[0030] In an embodiment, the electrical power disconnection circuit further comprises a voltage sensor configured to measure a voltage at the power lines, wherein the control device is operationally connected to the voltage sensor and configured to control the voltage sensor to measure the voltage at the power lines and wherein the control device is configured to use in g) a determination if the voltage measured at the power lines is below a voltage threshold. A voltage at one or more of the power lines above such voltage threshold may be indicative of the occurrence of an error, such as a malfunctioning of the disconnection switch resulting in an undesired connection to the power source, or a too high resistance towards protective earth, resulting via the verification current fed by the current source into a too high voltage at the respective one of the power lines.

[0031] In an embodiment, the disconnection switch and the earthing switch each comprise a bistabile switch, thereby the switches remaining in the state in which they are driven, in the case of an absence of further control signals, in case of a voltage sag on the power lines, or in case of a blackout on one or more of the electrical phases on the respective power lines.

[0032] A defined and safe power-up behaviour may be provided in that, in an embodiment, the disconnection switch is configured to be in a non-conductive state and the earthing switch is configured to be in a conductive state at a power-up of the control device. The control device may, at a power up of the control device, a restart of the control device or a reset of the control device, drive the disconnection switch to be in a non-conductive state and the earthing switch to be in a conductive state, hence starting from a safe, power down situation. Once the control device receives a power up command from the input device (e.g. in response to the user operating the input device to initiate power up), the control device may de-activate the current source if activated, may disconnect the current source switches if present, may disconnect the earthing switch to disconnect the power lines from protective earth, and may drive the disconnection switch to connect the power lines to the power source thus providing power via the power lines to the load.

[0033] According to a further aspect of the invention, there is provided an electrical power installation configured to power a load from a power source, the electrical power installation comprising a plurality of power lines electrically connected to the load and the electrical power disconnection circuit according to the present invention to disconnect the plurality of power lines from the power source. The electrical power disconnection circuit may be remote from the load, e.g. at a power distribution switchboard, at which the power lines are to be connected to the power source, respectively disconnected from the power source.

[0034] In an embodiment, the electrical power installation further comprises further comprises a control panel, such as a power distribution panel where incoming power from the power source is switched to power lines that are connected to a load to power the load. The power lines may extend from the control panel to the load. The disconnection switch, the earthing switch, the current source, and the current sensor of the electrical power disconnection circuit are arranged at the control panel. Accordingly, a verification if the power line is safely disconnected from the power source may be performed at the control panel.

[0035] In an embodiment, the input device is arranged at the load. Accordingly, in case the load is to be disconnected from the power source, e.g. for maintenance or repair of the load, an operator present at the load may operate the input device, and receive feedback on the basis of the signal indicating that the power lines are safely disconnected from the power source, enabling the operator to safely access the load.

[0036] According to a further aspect of the invention, there is provided an assembly of an electrical apparatus and the electrical power installation according to the invention, wherein the electrical apparatus is comprised in the load powered by the electrical power installation. Examples of the electrical apparatus may comprise a packaging machine for the packaging industry, a paper manufacturing or paper processing machine for the paper manufacturing / processing industry, a semiconductor manufacturing or semiconductor processing machine for the semiconductor industry.

[0037] According to a further aspect of the invention, there is provided a method to disconnect from a power source a plurality of power lines, the method comprising, in response to receiving a disconnection command from an input device: a) disconnecting, by a disconnection switch, each of the plurality of power lines from the power source; b) connecting, by an earthing switch, each of the plurality of power lines to the protective earth; c) generating, by a current source, a verification current in at least one of the plurality of power lines, d) measuring, by the current sensor, the electrical current through the earthing switch, e) comparing a measurement value of the electrical current through the earthing switch as measured by the current sensor to a current value of the verification current as generated by the current source, f) determining from the comparison, if the power lines are disconnected from the power source, and g) outputting a message indicative that the power lines are disconnected from the power source, in case the determining at f) establishes that the power lines are disconnected from the power source.

[0038] With the method according to the invention, the same effects may be achieved as described above in respect of the electrical power disconnection circuit according to the invention. Furthermore, the same or similar embodiments may be provided as described with reference to the electrical power disconnection circuit, the embodiments achieving the same or similar effects as described with reference to the electrical power disconnection circuit according to the invention.

[0039] Further features, advantages and effects will follow from the appended drawing, showing non-limiting embodiments of the present invention, wherein:

[0040] Figure 1 depicts a schematic diagram of a remote lock out arrangement;

[0041] Figure 2 depicts an electrical schematic diagram of a disconnection circuit according to an embodiment of the invention;

[0042] Figure 3 depicts an electrical schematic diagram of a disconnection circuit according to a first alternative embodiment of the invention;

[0043] Figure 4 depicts an electrical schematic diagram of a disconnection circuit according to a second alternative embodiment of the invention;

[0044] Figure 5 depicts an electrical schematic diagram of a disconnection circuit according to a third alternative embodiment of the invention;

[0045] Figure 6 depicts an electrical schematic diagram of a disconnection circuit according to a fourth alternative embodiment of the invention;

[0046] Figure 7 depicts an electrical schematic diagram of a disconnection circuit according to a fifth alternative embodiment of the invention;

[0047] Figure 8 depicts an electrical schematic diagram of a disconnection circuit according to a sixth alternative embodiment of the invention;

[0048] Figure 9 depicts an electrical schematic diagram of a disconnection circuit according to a seventh alternative embodiment of the invention; and Figure 10 depicts an electrical schematic diagram of an electrical power installation according to an embodiment of the invention.

[0049] Figure 1 depicts a highly schematic illustrative diagram based on which the switching off of a load according to the prior art will be illustrated. A load LD, such as in the present example a machine, is powered from a power source PS, such as in the present example a mains power connection. At a control panel CP, the mains power connection is switched to power lines PL, such as 3 phase power lines, which extend from the control panel to the load. Upon maintenance of the load, it is desired to switch off the power from the load. According to the prior art, an operator console may be provided at the load. A first person, i.e. a first operator, operates the operator console to input a command to switch off the power, for example by operating a power control switch at the operator console. The operator console is connected to the control panel via a suitable control line. At the control panel, the control line is connected to a remotely activatable switch, SW1, which connects the power lines to the power source, and which is driven via the control line to disconnect the power lines from the power source. An accidental or inadvertent switching on of the remotely activatable switch SW1 , e.g. due to miscommunication, misunderstanding or an electrical malfunctioning, could cause a risk for operator 1, when performing maintenance on the load. As an additional safety measure, in order to prevent such an accidental or inadvertent switching on of the remotely activatable switch SW1, one or more a - licensed operator(s) with a permit(s) to switch electrical gear may disconnect a module comprising the remotely activatable switch SW1 from the control panel, as schematically depicted in Figure 1. Operator OP1 may then lock the operator console from being put back in the active state, and operator OP2 may lock the disconnected module from being connected, thereby enhancing a safety.

[0050] The above described procedure may require to presence of two operators, communication between the operators, and may impose a risk on the first operator that performs maintenance or repair at the load, for example as a result of miscommunication between the operators, or by any other cause. The operators OP1, OP2 may be the same person, which would require the person to alternate between the two remote locations, and which would require the actions by operator OP1 , OP2, to be performed by a person with the above mentioned permit to switch electrical gear at the switchboard.

[0051] Figure 2 depicts a schematic diagram of an electrical power disconnection circuit according to an embodiment of the present invention. Three phase power lines PL are indicated by L1, L2 and L3 and are configured to connect a load LD to a power source PS, such as in the present example a three phase mains power supply network. Additionally, a neutral line is indicated by N and a protective earth line connected to protective earth by PE, providing neutral and protective earth to the load. As both the power lines and the mains power supply network are provided with the 3 phase power lines, the neutral and protective earth, these denominations are provided at both the mains power supply network as well as the power lines which connect to the load. Disconnection switch SW1 is electrically connected between the power source and the power lines which connect to the load. In an electrically conductive state, the switch SW1 connects the power lines and the load to the power source. In an electrically non-conductive state, the disconnection switch disconnects the power lines from the power source. Figure 2 further depicts an earthing switch such as in the present example the switches SW2, which, when conductive, electrically connect the power lines L1 , L2, L3 as well as the Neutral N to protective earth. In an operative state of the load, the disconnection switch is electrically conductive, thus connecting the power source to the power lines, while the earthing switch is electrically non-conductive, thus not connecting the power lines to protective earth. The disconnection circuit further comprises an input device ID configured to transmit a disconnection command and a control device CD configured to be connected to the input device to receive the disconnection command and to be connected to the disconnection switch SW1 and the earthing switch SW2. Upon receiving a disconnection command from input device, the control device drives the disconnection switch SW1 to the non-conductive state and, after the disconnection switch has disconnected the power lines from the power source, the control device drives the earthing switch SW2 to the conductive state so as to connect the power lines to the protective earth for the purpose of safety. Thus, the power lines should have been disconnected from the power source and should have been connected to protective earth to create a safe situation. A malfunction of the disconnection switch and / or the earthing switch could nevertheless result in a dangerous situation, as follows: a malfunction of the disconnection switch could provide that one of more of the power lines could still be connected to the power source, A malfunction of the earthing switch could result in one or more of the power lines being disconnected from protective earth.

[0052] According to the present invention, a current source CUR is provided, which, in the present example, is formed by an auxiliary voltage source supply (in the present example a 24V supply) and electrical resistors connected between the 24V voltage source supply and the power line, at least in the present example, the power lines L1, L2, L3 as these lines may carry a voltage in normal operation. The 24 V power source and the resistors provide for a verification current from the 24V power source, via the resistors, via the power lines, and via the earthing switch to protective earth. A current measurement may be performed by the current sensors CS, e.g. Hall sensors, in a series connection with the earthing switches. The current is measured while the disconnection switches are controlled to disconnect the power lines from the power source and the earthing switches are controlled to connect the power lines to protective earth. A verification current may be measured by the current sensors, representative of a current from the power lines via the earthing switch to protective earth. The current measured by the current sensors may be compared to a value of the verification current, as determined in the present example by the 24V power source and the impedance of the resistors. In case the disconnection switch, the earthing switch, earthing contact etc. operate as intended, and in the absence of short circuits between electrical conductors, the electrical current measured by the current sensors would substantially be the same as the verification current. Based on the comparison of the measured current with the value of the verification current, it may be decided if the measured value corresponds to an expected value based on the verification current, and in case of a positive determination, an output signal may be provided, such as to the operator console, indicating that the power to the load is safely disconnected.

[0053] A further verification may be performed by voltage measurement of the voltage on the power lines at VD. When the power lines should have been disconnected from the power source by the disconnection switch and should have been connected to protective earth by the earthing switch, so to create a safe situation, a further verification may be performed by measurement of a voltage at the power lines. The measurement of the voltage may for example be performed simultaneously with the feeding in of the verification current. Ideally, i.e. in the case that the disconnection switch and the earthing switch operate as desired, establishing a low ohmic connection of the power lines to protective earth, the voltage to be measured at the disconnected power lines would be approximately zero Volts. The feeding of the verification current into the power lines would, in case of the low ohmic connection of the power lines to protective earth, retain the power lines at such a low voltage. Similarly, a defect in the disconnection switch could raise the voltage on one or more of the power lines, thus the measurement of the voltage providing an additional verification of a safe state of the power lines. An auxiliary power supply, such as the switched mode power supply SMPS, may provide electrical power to the control device, input device, current source and current sensors. In the event that a check would be carried out only on the basis of a voltage measurement on the power lines, the disconnection circuit would not work reliably in all cases. For example, when the load forms a connection to zero or ground. Such a risk may come into existence, for example, in the event of an insulation fault in the connected load LD or a low-impedance connection between two phase(s). In such a situation, an unclosed contact SW2 may not be detected, as the verification current may flow to ground (PE) via the low impedance load or via the short circuit. Therefore, a current injection and detection as described should also be performed. In case the verification current would difficult to detect due to the low value of the current, a pulse-shaped verification current signal may offer a solution. In case the earthing switch SW2 would not function, there would be a risk that the injection of a verification current could lead to high voltages at the power lines. Such high voltages may be detected by the voltage detection performed by VD. Furthermore, the impedance of the contacts of the earthing switch may not be accurately determined by the influence of the impedance of the connected load which may form a parallel connection to protective earth. Various alternative embodiments are described with reference to Figures 3 - 8.

[0054] Figure 3 depicts an alternative embodiment of the invention, in which a different embodiment of the current source is depicted. Instead of the auxiliary power supply and the series resistors to feed a verification current into the power lines, a verification current loop is formed, in the present example using the current source switches CSS to protective earth. In the present example, the verification current is injected in the connection to protective earth, i.e. in the connection to protective earth. For example, a primary winding of a transformer, such as a toroidal transformer may be connected in the connection to protective earth, a verification current being fed into a secondary winding of the transformer. In general, the verification current may be a DC current or an AC current. In case the earthing switches provide for a low impedance connection to protective earth, the verification current may flow via a loop comprising the earthing switches, at least part of the power lines, the current source switches and the protective earth. The current sensors are arranged in the loop. In the present example, the current sensors are arranged between the earthing switches and the protective earth. The feeding in of the verification current in the loop and the measurement of the current by the current sensors, may be followed by a comparison of the value of the measured current with the value of the verification current. Based on such comparison, it may be decided if the circuit is safe, i.e. if the power lines and thus the load connected via the power lines, are safely disconnected from the power source and if the connection with the protective earth has still a controlled very low impedance. In case the circuit provides, via the earthing switches a low impedance connection to protective earth, and in case of no further potential risks such as short circuits or a malfunction of the disconnection switch, the value of the current measured by the current sensors will be substantially the same as the value of the verification current, which may indicate that the circuit is safe. Similarly as described above with reference to Figure 2, the voltage at the power lines may further be measured and evaluated.

[0055] By switching on the current source switches CSS (one after another in time or simultaneously), a verification current injection into the return path is realized with the current source CUR. As a result, verification currents flow through the contacts of the earthing switch SW2 that can be detected and / or measured by current sensor(s) CS in the individual contacts of SW2. This allows the condition of the SW2 short-circuit contacts to be assessed.

[0056] The present embodiment may provide a high degree of reliability because the verification current may be much higher than the verification current in the embodiment according to Figure 2, where the verification current is limited by the power supply with series resistors. Also, by comparing the measured currents across the different contacts, the condition of the contacts of the earthing switch SW2 may be assessed. By injecting current with, for example, a transformer with one or a lower number of windings, the voltage at the load LD may remain very low under all conditions.

[0057] When applying the Neutral (Phase), it may be advisable to include a fuse to obtain a proportional impedance for the circuit.

[0058] In the event of an incorrect operation of the system, a short-circuit current may flow through SW2 if SW1 is switched on incorrectly. This will cause SW1 to be switched off. This short-circuit current generates a counter-electromotive force in the current source CUR. Therefore, a low impedance connection to protective earth may be provided. For example, a large cross-section of the wire / copper strip of the current source CUR (e.g. a thick strip through a toroidal transformer of the current source). It is advisable to carry out the detection of a closure of the earthing switch with hall generators. The detection carried out with current transformers can lead to high counter-EMFs where appropriate measures may be necessary.

[0059] In the event that the current source switch CSS would get stuck, it may be necessary to avoid negative influence on the grid (voltage dip). For example rapid fuse cartridges or a motor protection switch may be used.

[0060] In the embodiment as described with reference to Figures 2 and 3, the controlling of the disconnection switch, the earthing switch, the current source, the current sensors, the current source switches, may be performed by control device CD, such as a microcontroller, microcomputer or PLC. The control device may initiate these actions in response to receiving a disconnection command, e.g. from an input device such as an input device (e.g. a switch, touchscreen input, etc.) at the operator console OC depicted in Figure 1. Responsive to the determination that the power lines are disconnected from the power source, the control device may output a verification message, such as verification data, which may be transmitted to the operator console for providing an output signal at the operator console indicating that the power lines are disconnected. The operator may, responsive to receiving the indication at the operator console, proceed to perform maintenance or repair, etc. at the power lines and / or at the load connected to the power lines.

[0061] The opening of the disconnection switch to disconnect the power lines from the power source may be performed for the plural power lines simultaneously. Likewise, the closing of the earthing switch to connect the power lines to protective earth may be performed for the plural power lines simultaneously. The feeding of the verification current and the measurement of the current by the current sensor may be performed per power line, i.e. sequentially per power line or may be performed for the power lines simultaneously. In the sequential case, the current in all power lines may be measured, i.e. the current in the power line in which the verification current is fed as well as in the remaining power lines. In the power line in which the verification current is fed, the measured current may be compared to the verification current, while in the remaining power lines, the measured current may be compared to a current value of substantially zero. In case the current in the remaining power lines deviates from the value of substantially zero, e.g. exceeding a safety threshold, this may signal a defect, such as a short circuit between the power line in which the verification current is fed and the power line where the measured current exceeds the safety threshold.

[0062] The earthing switch may be cleaned as follows: the control device may control the current source to generate a contact cleaning current and control the earthing switch to open. As a result of the contact cleaning current, a spark may be generated when opening the contact(s) of the earthing switch, the spark promoting a contact cleaning of the contact(s) of the earthing switch. Although Figure 3 depicts a specific arrangement of the current source and the current sensors, the current source, current sensors and the current source switches may be arranged in various ways. Examples of alternative arrangements are schematically depicted in Figures 4 - 8, as briefly described below.

[0063] It is noted that the below description only refers to the differences of the alternative embodiments. Thus, the description in respect of Figures 2 and 3 above as well as the remainder of the present document, apply to the alternative embodiments as well.

[0064] In Figure 4, the current source is at the same location as in Figure 3, i.e. between the earthing switches and protective earth. The current sensors have been arranged, i.e. electrically connected, in series with the current source switches, i.e. between the current source switches and protective earth. By including current sensors CS in the return test path of SW2, a simpler set-up with smaller current transformers or other detectors can be achieved. By switching on the current source switches CSS (per contact one after another in time or simultaneously), a verification current injection into the return path may be realized with the current source CUR. The disadvantage of the location of the current source switches CSS may be that it is not certain that the injected current also flows through the individual contacts of SW2.

[0065] Mutual short circuits (between any of L1 , L2, L3, N and PE) or low load resistances (e.g. due to large motors) may lead to incorrect measurements with the current sensors CS. This may be the case if, for example, one of the contacts of SW2 would not work. As a result, the verification current may still flow through the current source switch CSS partly due to the load LD or short circuit (in L1 , L2, L3, N or PE).

[0066] The latter can be solved by controlling the contacts of the current source switches CSS to close one after the other, i.e. separately in time.

[0067] In Figure 5, the current source has been arranged, i.e. electrically connected, between the earthing switches and protective earth. The current sensors have been arranged, i.e. electrically connected, in series with the current source switches, namely in the present embodiment between the current source switches and the power lines. By including both current measurement and current injection in a test return path of the earthing switch SW2, one or more of the following may be achieved; for example, a more compact design, smaller current sensing components, easy adjustment of the required measurement current, etc.

[0068] By switching on the current source switches CSS (per contact one after another in time or simultaneously), a current injection into the return path may be realized with a current source CUR. A disadvantage of the location of the current source switches CSS may be that it is not certain that the injected current also flows through the individual contacts of SW2.

[0069] A mutual short circuit (between any of L1 , L2, L3, N and PE) or a low load resistance (e.g. due to a large motor) may lead to incorrect measurements with the current sensors CS. This may be the case if, for example, one of the contacts of SW2 does not work. As a result, the current may still flow through the CSS partly due to the load LD or short circuit (in L1 , L2, L3, N or PE). However, this may not be solvable as indicated in the explanation of Figure 4, however the present embodiment may be easier to implement in a switchboard, namely providing a low impedance connection to the current source switch CSS,

[0070] In Figure 6, the current source has been arranged, i.e. electrically connected between the earthing switches and protective earth. The current sensors have been arranged, i.e. electrically connected, in series with the earthing switches, namely in the present embodiment between the earthing switches and the protective earth. By placing the current sensors CS directly in series with either end of the contacts of the earthing switch SW2, it may be determined with a high degree of certainty whether a test current is flowing through the relevant contact, even in the event of faults in the connected loads. By switching on the short-circuit power relays CSS (per contact one after another in time or simultaneously), a verification current injection into the return path may realized with a current source CUR. As a result, currents flow through the contacts of earthing switch SW2 that can be detected and / or measured by the current sensor(s) CS in the individual contacts of the earthing switch SW2. This may allow the condition of the contacts of the earthing switch SW2 to be assessed.

[0071] Mutual short circuits (between any of L1 , L2, L3, N and PE) or low load resistances (e.g. due to large motors) can lead to incorrect measurements with the current sensors CS. This may be the case if, for example, one of the contacts of earthing switch SW2 would not work. As a result, the current may still flow through the current switches CSS partly due to the load LD or short circuit (in L1 , L2, L3, N or PE). However, this is not solvable in a way as indicated in the explanation of Figure 4, however the present embodiment may be easier to implement in a switchboard panel, e.g. the diameter of a conductor to the current source switches CSS. The electrical connection from current source switches CSS to protective earth PE may be adapted to achieve a desired verification current value.

[0072] In Figure 7, likewise to Figure 6, the current source has been arranged, i.e. electrically connected between the earthing switches and protective earth. The current sensors have been arranged, i.e. electrically connected, in series with the earthing switches, namely in the present embodiment between the earthing switches and the protective earth. In the embodiment, the disconnection switch and the earthing switch each comprise multiple or plural single bi- or monostable circuit breaker(s) with auxiliary contacts. As a result, more faults may be detected and thus a reliability may be increased. The circuit breakers may provide a disconnector that may be available with a high overvoltage category. By switching on the mono-stable or bi-stable short-circuit circuit breaker, i.e. the current source switches CSS (separately per contact one after the other or simultaneously), a current injection into the return path may be realized with the current source CUR. A requirement for controlling the disconnection switch SW1 to switch to the conductive state may be that it is verified that all contacts of the current source switches CSS and the earthing switch SW2 are open. As a result, currents through the contacts of the earthing switch SW2 may be detected and / or measured by current sensor(s) CS in the individual contacts of the earthing switch SW2. This may allow the condition of the SW2 short- circuit contacts to be assessed.

[0073] When applying a TN earthing system where the neutral has earth potential, it may also be possible to connect SW1 and / or SW2 three poles and thus only short circuit and ground the phases to each other.

[0074] The system may also be used for DC grids with a plus, minus and / or middle connection, and / or IT systems or other systems, one, two, and / or three phases where an active conductor is connected to earth, for example one phase . It does not rule out the applicability of future and other systems.

[0075] Mutual short circuits (between any of L1 , L2, L3, N and PE, if present) or a low resistance of the load (e.g. due to large motors) may lead to incorrect measurements with the current sensors CS. This is the case if, for example, one of the contacts of the earthing switch SW2 would not work. As a result, the current may still flow through the current source switch CSS partly due to the load LD or short circuit (in L1 , L2, L3, N or PE). However, this may not be solvable in a way as indicated in the explanation of Figure 4. However the present embodiment may be easier to implement in a switchboard panel, in particular the diameter of a conductor to the current source switches CSS. The CSS to ground PE conduit may be easy to adjust to achieve a correct current value.

[0076] In Figure 8, likewise to Figure 5, the current source has been arranged, i.e. electrically connected, between the earthing switches and protective earth. The current sensors have been arranged, i.e. electrically connected, in series with the current source switches, namely in the present embodiment between the current source switches and the power lines. Including both current measurement and current injection in a test return path of the earthing switch SW2 may, for example, provide a more compact design, smaller current sensing components, easy adjustment of the required measurement current, etc. By switching on the mono or bi-stable current source switches CSS (one by one per contact or simultaneously), a current injection into the return path may be realized with a current source CUR. A requirement for enabling the disconnection switch SW1 is that it is verified that all contacts of the current source switches CSS and the earthing switch SW2 are open. The disadvantage of the location of the CSS in Figure 8 is that it is not certain that the injected current also flows through the individual contacts of SW2.

[0077] When applying a TN earthing system where the Neutral has earth potential, it may also be possible to perform a three pole switching of the disconnection switch SW1 and / or the earthing switch SW2 and thus only short circuit and ground the phases to each other.

[0078] The system can also be used for DC grids with a plus, minus and / or middle connection, and / or IT systems or other systems, one, two, and / or three phases where an active conductor is connected to earth, for example one phase. It does not rule out the applicability of future and other systems. Mutual short circuits (between any of L1 , L2, L3, N and PE, if present) or a low resistance of the load (e.g. due to large motors) may lead to incorrect measurements with the current sensors CS. This may be the case if, for example, one of the contacts of SW2 does not work. As a result, the current can still flow through the CSS partly due to the load LD or short circuit (in L1 , L2, L3, N or PE, if present). However, this may not be solvable as indicated in the explanation of Figure 4, however the present embodiment may be more easy to implement in a panel, specifically, the diameter of a conductor to the current source switches CSS.

[0079] The current source switch CSS to protective earth PE conduit may easy be adjusted to achieve the correct current value

[0080] In the examples described with reference to Figures 3 - 8, use is made of a single current source, which feeds a verification current into the loop from the protective earth, via the earthing switch, the power lines (or part thereof), the current source switches, back to the protective earth. One such loop may be provided per power line, i.e. providing earthing switches and current source switches per power line, as depicted in Figures 3 - 8. The single current source may accordingly be connected to each of the loops and may be arranged in a common part of the loop, namely in the depicted examples in a common connection to protective earth, either a common connection from the earthing switches to protective earth or a common connection from the current source switches to protective earth. By means of the current source switches, the verification current fed by the current source may be fed into one or more of the loops, by closing the respective one or more of the current source switches.

[0081] Alternatively, each one of the loops may be provided with a respective current source, individually addressable by the control device. The individually controllable current sources may for example be activated one by one, whereby the respective current sensor associated with the activated one of the current sources, is controlled to measure the verification current. Optionally, in line with the embodiments described above, the remaining current sensors may be driven to measure the currents in the remaining loops.

[0082] For example, Figure 9 depicts an embodiment with a current source and a current sensor per power line. The current sources may be individually switchable by the current source switches CSS. The current sensor may be combined with the current source, e.g. a current transformer with a current sensor. By switching on one of the current sources at a time and then measuring the current by the current sensor associated with the current source that has been switched on, as well as measuring the current in the other two phases, the check may be further completed, and may be carried out sequentially by switching on the current sources one by one. Thereby, all contact transitions may be measured in pairs and a check for deviations may be performed. This may allow the condition of the earthing switch SW2 short-circuit contacts to be assessed. When using a four-pole switching of SW2, it may be advisable to further include a fuse in the neutral phase of the current source switches CSS in order to obtain a proportional impedance for the circuit.

[0083] By applying (more sophisticated) current transformers possibly with multiple windings, the current source for verification current injection and the current sensor for current measurement may be integrated into a single unit. This may require a slightly different method of control by the control device, however may result in a simpler and more compact design. Design requirements on the combined current source and current sensor may be raised, for example measures must be taken to ensure that the combined current source and current sensor is able to withstand SW1 fault conditions.

[0084] In the event of incorrect operation of the system, a short-circuit current may flow through the earthing switch SW2 if SW1 is switched on incorrectly. This may cause SW1 to be switched off. Such a short-circuit current may generate a counter Electro Motive Force in the combined current sensor CS and current source CUR, namely in one element, i.e. one of the combined current sensor and current source. This may be solved by sufficient cross-section of the wire / copper strip of the current sensor and current source, CS+CUR (e.g. by a thick conductive strip through the toroidal transformer.

[0085] The embodiment as described with reference to Figure 9 may be amended, e.g. combinations with any of the previous embodiments in accordance with Figures 2 - 8 may be possible. Furthermore, the current injections may be performed by other means (e.g. capacitive, inductive, etc.).

[0086] Preferably, the wiring lengths and impedances for each of the loops are substantially the same to provide comparable current readings in each one of the loops. An impedance of the load connected to the power lines may be in a parallel connection to a part of the loop or provide for impedances between two or more of the power lines. The wiring impedance of the wiring impedance from the earthing switch to protective earth is lower, e.g. preferably at least a factor 2 lower, than the wiring impedance of the power line, thus to provide that the impedance of a parallel path via the power line(s) and the load, is higher than the impedance of the path via the earthing switch that is to be tested, namely via the earthing switches to protective earth.

[0087] The switches SW1 , SW2 may comprise bi-stable switches, thus remaining in an open or closed state when not driven, and switch SW1 may be configured to initially be in the non- conductive state, while switch SW2 may be configured to initially be in the conductive state upon power up independent of the status of the (remote) switch. Only when the ID is set to off (or in a off-state) AND a manual invoked reset signal to the controller, will initiate the previously mentioned status if the SW1 switch is in the conductive state and the SW2 switch is in the non- conductive state. The disconnection circuit as described with reference to Figures 2 - 9 may be provided in an electrical power installation, as schematically depicted in Figure 10. Figure 10 depicts a load LD, such as in the present example a machine, is powered from the power source PS, such as in the present example the mains power connection. At the control panel CP, the mains power connection is switched to power lines PL, such as 3 phase power lines, which extend from the control panel to the load. Upon cleaning, adjustment, process changeover, maintenance, repair, etc. at the load side, it is desired to switch off the power from the load. An operator console may be provided at the load. An operator, operates the operator console to input a disconnection command to switch off the power, for example by operating the input device, such as a power control switch at the operator console. The operator console is connected to the control panel via a suitable control line, such as a digital wired connection, an analogue wired connection, an optical fiber connection, or a wireless connection, such as a radio frequency or optical (e.g. Infrared) connection. Also more operator consoles may be attached to the disconnection circuit in case of e.g. a larger machine(s) or production line(s). The disconnection circuit DSC as described above with reference to Figures 2 - 9 may be arranged at the control panel to disconnect the power lines from the power source. The disconnection switch, the earthing switch, the current source, the current source connecting switch (if present) and the current sensor of the electrical power disconnection circuit are arranged at the control panel, while the input device is arranged at the operator console at the load.

Claims

CLAIMS1 . An electrical power disconnection circuit configured to disconnect from a power source a plurality of power lines, comprising: a disconnection switch for disconnecting each of the plurality of power lines from the power source; an earthing switch for connecting each of the plurality of power lines to a protective earth; a current source configured to generate a verification current in a respective one of the plurality of power lines; an input device configured to generate a disconnection command; a current sensor configured to measure an electrical current through the earthing switch; and a control device operationally connected to the disconnection switch, the earthing switch, the current source, the current sensor and the input device and configured to, in response to receiving a disconnection command from the input device: a) control the disconnection switch to disconnect each of the plurality of power lines from the power source; b) control the earthing switch to connect each of the plurality of power lines to the protective earth; c) control the current source to generate the verification current in at least one of the plurality of power lines, d) control the current sensor to measure the electrical current through the earthing switch, e) compare a measurement value of the electrical current through the earthing switch as measured by the current sensor to a value of the verification current as generated by the current source, f) determine, using the comparison, if the power lines are disconnected from the power source, and g) output a verification message indicative that the power lines are disconnected from the power source in case the determining at f) establishes that the power lines are disconnected from the power source.

2. The electrical power disconnection circuit according to claim 1 , wherein the control device is configured to perform a ) and b) for each one of the power lines simultaneously and perform c) - e) for each one of the power lines sequentially.

3. The electrical power disconnection circuit according to claim 2, wherein the control device is configured to, when performing c), and d) for one of the power lines, furthercontrol the current sensor to measure the electrical current through the earthing switch at at least one other of the power lines.

4. The electrical power disconnection circuit according to claim 3, wherein the control device is configured to determine, at f), if a measurement value of the electrical current through the earthing switch at at least one other of the power lines as measured when performing c), d) and e) for the one of the power lines, exceeds a safety threshold.

5. The electrical power disconnection circuit according to any one of the preceding claims, wherein the control device is configured to determine that the power lines are disconnected from the power source by determining if the measurement value of the electrical current through the earthing switch as measured by the current sensor equals the current value of the verification current as generated by the current source within a verification window.

6. The electrical power disconnection circuit according to any one of the preceding claims, wherein the control device is further configured to control the earthing switch to open while controlling the current source to generate a contact cleaning current.

7. The electrical power disconnection circuit according to any one of the preceding claims, wherein the current source is electrically connected between the protective earth and the respective one of the plurality of power lines.

8. The electrical power disconnection circuit according to any one of claims 1 - 6, wherein the current source is electrically connected in an electrical path to protective earth parallel to the earthing switch, such as between the protective earth and the current sensor.

9. The electrical power disconnection circuit according to any one of the preceding claims, wherein the current sensor is electrically connected between the earthing switch and the protective earth or in an electrical path to protective earth parallel to the earthing switch.

10. The electrical power disconnection circuit according to any one of the preceding claims, wherein, for each one of the power lines, a wiring length from the earthing switch to protective earth is substantially the same.

11. The electrical power disconnection circuit according to any one of the preceding claims, wherein, for each one of the power lines, a wiring impedance from the earthing switch toprotective earth is lower than twice a wiring impedance from the earthing switch via the power lines to a load powered via the power lines.

12. The electrical power disconnection circuit according to any one of the preceding claims, wherein the current source is arranged at or near the earthing switch.

13. The electrical power disconnection circuit according to any one of the preceding claims, further comprising an operator console operationally connected to the control device, wherein the operator console comprises the input device and wherein the control device is configured to output the message indicative if the power lines are disconnected from the power source to the operator console.

14. The electrical power disconnection circuit according to any one of the preceding claims, further comprising a voltage sensor configured to measure a voltage at the power lines, wherein the control device is operationally connected to the voltage sensor and configured to control the voltage sensor to measure the voltage at the power lines and wherein the control device is configured to use in g) a determination if the voltage measured at the power lines is below a voltage threshold.

15. The electrical power disconnection circuit according to any one of the preceding claims, wherein the disconnection switch and the earthing switch each comprise a bi-stabile switch.

16. The electrical power disconnection circuit according to any one of the preceding claims, wherein the disconnection switch is configured to be in a non-conductive state and the earthing switch is configured to be in a conductive state at a power-up an initial state of control of the control device.

17. An electrical power installation configured to power a load from a power source, the electrical power installation comprising a plurality of power lines electrically connected to the load and the electrical power disconnection circuit according to any one of the preceding claims to disconnect the plurality of power lines from the power source.

18. The electrical power installation according to claim 17, further comprising a control panel, wherein the power lines extend from the control panel to the load and wherein the disconnection switch, the earthing switch, the current source, and the current sensor of the electrical power disconnection circuit are arranged at the control panel.

19. The electrical power installation according to claim 17 or 18, wherein the input device is arranged at the load.

20. An assembly of an electrical apparatus and the electrical power installation according to any one of claims 17 - 19, wherein the electrical apparatus is comprised in the load powered by the electrical power installation.

21. A method to disconnect from a power source a plurality of power lines, the method comprising, in response to receiving a disconnection command from an input device: a) disconnecting, by a disconnection switch, each of the plurality of power lines from the power source; b) connecting, by an earthing switch, each of the plurality of power lines to the protective earth; c) generating, by a current source, a verification current in at least one of the plurality of power lines, d) measuring, by the current sensor, the electrical current through the earthing switch, e) comparing a measurement value of the electrical current through the earthing switch as measured by the current sensor to a current value of the verification current as generated by the current source, f) determining from the comparison, if the power lines are disconnected from the power source, and g) outputting a message indicative that the power lines are disconnected from the power source, in case the determining at f) establishes that the power lines are disconnected from the power source.

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