Method and system for use in operating a service disconnect switch

Abstract

A method is disclosed for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply. The method comprises controlling the discharge of a service disconnect capacitor in a discharge direction through an actuator for actuating the service disconnect switch. The method further comprises sensing an electrical discharge signal which is dependent on the discharging of the service disconnect capacitor through the actuator, and determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction based on the electrical discharge signal sensed during discharging of the service disconnect capacitor through the actuator in the discharge direction. An associated system for use in operating the service disconnect switch is also disclosed.

Description

[0001] METHOD AND SYSTEM FOR USE IN OPERATING A SERVICE DISCONNECT SWITCH

[0002] FIELD

[0003] The present disclosure relates to a method and system for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply and, in particular though not exclusively, to a method and system for use in operating a service disconnect switch of an electricity meter.

[0004] BACKGROUND

[0005] It is known to use a service disconnect (SD) switch in an electricity meter for electrically isolating a load from a power supply, wherein the service disconnect (SD) switch is driven by a DC motor in response to a Disconnect or Reconnect command. However, the service disconnect (SD) switch may not move between a closed state and an open state to complete its switching action reliably, for example in cold temperatures where the viscosity of motor lubricant may be excessively high. Consequently, it would be desirable to know whether the service disconnect (SD) switch has completed its switching action when a Disconnect or Reconnect command is issued. In this regard, the current flowing through the SD switch from the power supply to the load may not accurately reflect the state of the SD switch because the current flowing through the SD switch is not just dependent on the state of the SD switch, but is also dependent on the status of the power supply and the condition of the line from the power supply to the SD switch. Consequently, measuring a change in the current flowing through the SD switch from the power supply to the load during driving of the SD switch is not a reliable indicator of the operation of the SD switch.

[0006] In an attempt to ensure that the service disconnect (SD) switch has completed its switching action when a Disconnect or Reconnect command is issued, it is also known to routinely drive or pulse the DC motor twice with all of the energy stored in a large SD capacitor. However, if discharging the SD capacitor through the DC motor for the first time results in actuation of the SD switch between the closed and open states, then discharging the SD capacitor through the DC motor for the second time may actually be unnecessary. Moreover, discharging the SD capacitor through the DC motor causes large currents to flow through windings of the DC motor and the drive circuitry and may contribute to degradation of the windings or degradation of the SD capacitor. Consequently, it would be desirable to avoid any unnecessary discharging of the SD capacitor through the DC motor.

[0007] SUMMARY

[0008] According to an aspect of the present disclosure there is provided a method for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply, the method comprising: controlling the discharge of a service disconnect capacitor in a discharge direction through an actuator for actuating the service disconnect switch, wherein the discharge direction is selected from an opening discharge direction for driving the actuator to open the service disconnect switch and a closing discharge direction for driving the actuator to close the service disconnect switch; sensing an electrical discharge signal which is dependent on the discharging of the service disconnect capacitor through the actuator; and determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction based on the electrical discharge signal sensed during discharging of the service disconnect capacitor through the actuator in the discharge direction.

[0009] Such a method may be used to reliably confirm operation of the service disconnect switch between the closed and open states without measuring a change in current flowing through the service disconnect switch from the power supply to the load during driving of the service disconnect switch and without having to routinely drive or pulse the actuator with all of the energy stored in the service disconnect capacitor more than once.

[0010] Optionally, controlling the discharge of the service disconnect capacitor comprises selecting the discharge direction and controlling the timing of the discharge of the service disconnect capacitor through the actuator.

[0011] Optionally, the method comprises determining whether the service disconnect switch is in the open state or the closed state based at least in part on the selected discharge direction and based at least in part on determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction.

[0012] Optionally, the method comprises determining that the service disconnect switch is in the open state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction.

[0013] Optionally, the method comprises determining that the service disconnect switch is in the closed state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction.

[0014] Optionally, the method comprises: responsive to determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for a first time, recharging the service disconnect capacitor; discharging the service disconnect capacitor through the actuator in the opening discharge direction for a second time; determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time; and determining that the service disconnect switch is in the open state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time, else determining that the service disconnect switch is not operating correctly.

[0015] Optionally, the method comprises: responsive to determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for a first time, recharging the service disconnect capacitor; discharging the service disconnect capacitor through the actuator in the closing discharge direction for a second time; determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for the second time; and determining that the service disconnect switch is in the closed state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for the second time, else determining that the service disconnect switch is not operating correctly.

[0016] Optionally, the method further comprises determining the switch time taken to actuate the service disconnect switch between the closed and open states based on the electrical discharge signal sensed during discharging of the service disconnect capacitor through the actuator, and optionally storing the determined switch time for analysis at a later time and / or outputting the determined switch time to a user.

[0017] Optionally, the method comprises sensing a temperature of the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator and / or sensing a temperature of an environment surrounding the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator.

[0018] Optionally, the method comprises storing the temperature sensed for analysis at a later time and / or outputting the temperature sensed to a user.

[0019] Optionally, an instantaneous value of the electrical discharge signal is proportional to the charge stored in the service disconnect capacitor during the discharging of the service disconnect capacitor through the actuator.

[0020] Optionally, the electrical discharge signal comprises a voltage across the service disconnect capacitor as a function of time during the discharging of the service disconnect capacitor through the actuator.

[0021] Optionally, the method comprises determining that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time, where a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the first dip is less than a first predetermined threshold value and a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the second dip is less than a second predetermined threshold value.

[0022] Optionally, the method further comprises determining the time taken to actuate the service disconnect switch between the closed and open states based on the voltage across the service disconnect capacitor as a function of time, for example determining the time taken to actuate the service disconnect switch between the closed and open states based on the time between first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time.

[0023] Optionally, an instantaneous value of the electrical discharge signal is proportional to a rate of discharge of the service disconnect capacitor through the actuator during the discharging of the service disconnect capacitor through the actuator Optionally, the electrical discharge signal comprises a discharge current from the service disconnect capacitor through the actuator as a function of time during the discharging of the service disconnect capacitor through the actuator.

[0024] Optionally, the method comprises determining that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second peaks in the discharge current from the service disconnect capacitor through the actuator as a function of time, wherein a value of the discharge current associated with the first peak is greater than a first predetermined threshold value and a value of the discharge current associated with the second peak is greater than a second predetermined threshold value.

[0025] Optionally, the method further comprises determining the time taken to actuate the service disconnect switch between the closed and open states based on the discharge current from the service disconnect capacitor through the actuator as a function of time, for example determining the time taken to actuate the service disconnect switch between the closed and open states based on the time between first and second peaks in the discharge current.

[0026] Optionally, the method comprises discharging the service disconnect capacitor through the actuator in the discharge direction for a fixed time period, the fixed time period being selected to be greater than a time period required for the actuator to actuate the service disconnect switch between the closed and open states.

[0027] Optionally, the method comprises monitoring the sensed electrical discharge signal during discharging of the service disconnect capacitor through the actuator in the discharge direction and discharging the service disconnect capacitor through the actuator in the discharge direction until it is determined that the service disconnect switch is actuated between the closed and open states based on the monitored electrical discharge signal.

[0028] According to an aspect of the present disclosure there is provided a system for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply, the system comprising: an actuator for actuating the service disconnect switch; a service disconnect capacitor; a discharge switch arrangement for controlling the discharge of the service disconnect capacitor through the actuator in a discharge direction selected from an opening discharge direction for driving the actuator to open the service disconnect switch and a closing discharge direction for driving the actuator to close the service disconnect switch; an electrical discharge sensor for sensing an electrical discharge signal which is dependent on the discharging of the service disconnect capacitor through the actuator; and a processing resource which is configured to determine whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction based on the electrical discharge signal sensed by the electrical discharge sensor during discharging of the service disconnect capacitor through the actuator in the discharge direction.

[0029] Optionally, the processing resource is configured to control the discharge switch arrangement so as to select the discharge direction and control the timing of the discharge of the service disconnect capacitor through the actuator.

[0030] Optionally, the service disconnect system comprises driving circuitry for driving the discharge switch arrangement, wherein the processing resource is configured to control the driving circuitry and thereby control the discharge switch arrangement so as to select the discharge direction and control the timing of the discharge of the service disconnect capacitor through the actuator in the discharge direction.

[0031] Optionally, the processing resource is configured to determine whether the service disconnect switch is in the open state or the closed state based at least in part on the selected discharge direction and based at least in part on whether the processing resource determines that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction.

[0032] Optionally, the processing resource is configured to determine that the service disconnect switch is in the open state if the processing resource determines that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction.

[0033] Optionally, the processing resource is configured to determine that the service disconnect switch is in the closed state if the processing resource determines that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction.

[0034] Optionally, the service disconnect system comprises a charge arrangement such as a current source for charging the service disconnect capacitor.

[0035] Optionally, the processing resource is configured so that, in response to the processing resource determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for a first time, the processing resource controls the charge arrangement to re-charge the service disconnect capacitor, the processing resource controls the discharge switch arrangement to discharge the service disconnect capacitor through the actuator in the opening discharge direction for a second time, the processing resource determines whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time, and the processing resource determines that the service disconnect switch is in the open state if the processing resource determines that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time, else the processing resource determines that the service disconnect switch and / or the system is not operating correctly.

[0036] Optionally, the processing resource is configured so that, in response to the processing resource determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for a first time, the processing resource controls the charge arrangement to re-charge the service disconnect capacitor, the processing resource controls the discharge switch arrangement to discharge the service disconnect capacitor through the actuator in the closing discharge direction for a second time, the processing resource determines whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for the second time, and the processing resource determines that the service disconnect switch is in the closed state if the processing resource determines that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for the second time, else the processing resource determines that the service disconnect switch and / or the system is not operating correctly.

[0037] Optionally, the processing resource is configured to determine the switch time taken to actuate the service disconnect switch between the closed and open states based on the electrical discharge signal sensed by the electrical discharge sensor during discharging of the service disconnect capacitor through the actuator.

[0038] The switch time may be indicative of the condition or health of the actuator and / or of the service disconnect switch. Thus, determining the switch time may allow the condition or health of the actuator and / or of the service disconnect switch to be determined and, optionally, allow a user to decide whether to take any action in response to the determined condition or health of the actuator and / or of the service disconnect switch e.g. allow a user to decide whether to perform any preventative maintenance on the actuator and / or the service disconnect switch and / or whether to replace the actuator and / or the service disconnect switch.

[0039] Optionally, the processing resource is configured to store the determined switch time for analysis at a later time and / or to output the determined switch time to a user.

[0040] Optionally, the service disconnect system comprises a temperature sensor for sensing a temperature of the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator and / or a temperature sensor for sensing a temperature of an environment surrounding the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator.

[0041] Optionally, the processing resource is configured to store the temperature sensed by the temperature sensor for analysis at a later time and / or to output the temperature sensed by the temperature sensor to a user, for example together with the determined switch time.

[0042] The switch time may be temperature dependent. Thus, sensing the temperature in addition to the switch time may allow the condition or health of the actuator and / or of the service disconnect switch to be determined and, optionally, allow a user to decide whether to take any action in response to the determined condition or health of the actuator and / or of the service disconnect switch e.g. allow a user to decide whether to perform any preventative maintenance on the actuator and / or the service disconnect switch and / or whether to replace the actuator and / or the service disconnect switch.

[0043] Optionally, an instantaneous value of the electrical discharge signal is proportional to the charge stored in the service disconnect capacitor during the discharging of the service disconnect capacitor through the actuator.

[0044] Optionally, the electrical discharge signal comprises a voltage across the service disconnect capacitor as a function of time during the discharging of the service disconnect capacitor through the actuator.

[0045] Optionally, the processing resource is configured to determine the time taken to actuate the service disconnect switch between the closed and open states based on the voltage across the service disconnect capacitor as a function of time.

[0046] Optionally, the processing resource is configured to determine that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time, where a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the first dip is less than a first predetermined threshold value and a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the second dip is less than a second predetermined threshold value.

[0047] Optionally, the processing resource is configured to determine the time taken to actuate the service disconnect switch between the closed and open states based on the time between the first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time.

[0048] Optionally, an instantaneous value of the electrical discharge signal is proportional to a rate of discharge of the service disconnect capacitor through the actuator during the discharging of the service disconnect capacitor through the actuator.

[0049] Optionally, the electrical discharge signal comprises a discharge current from the service disconnect capacitor through the actuator as a function of time during the discharging of the service disconnect capacitor through the actuator.

[0050] Optionally, the processing resource is configured to determine the time taken to actuate the service disconnect switch between the closed and open states based on the discharge current from the service disconnect capacitor through the actuator as a function of time. Optionally, the processing resource is configured to determine that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second peaks in the discharge current from the service disconnect capacitor through the actuator as a function of time, wherein a value of the discharge current associated with the first peak is greater than a first predetermined threshold value and a value of the discharge current associated with the second peak is greater than a second predetermined threshold value.

[0051] Optionally, the processing resource is configured to determine the time taken to actuate the service disconnect switch between the closed and open states based on the time between the first and second peaks in the discharge current.

[0052] Optionally, the processing resource is configured to control the discharge switch arrangement so that the service disconnect capacitor is discharged through the actuator in the discharge direction for a fixed time period, the fixed time period being selected to be greater than a time period required for the actuator to actuate the service disconnect switch between the closed and open states.

[0053] Optionally, the processing resource is configured to monitor the sensed electrical discharge signal during discharging of the service disconnect capacitor through the actuator in the discharge direction and to control the discharge switch arrangement so that the service disconnect capacitor discharges through the actuator in the discharge direction until the processing resource determines that the service disconnect switch is actuated between the closed and open states based on the monitored electrical discharge signal.

[0054] Optionally, the discharge switch arrangement comprises an H-bridge switch arrangement.

[0055] Optionally, the actuator comprises a DC motor or a solenoid.

[0056] Optionally, at least one of the processing resource, the electrical discharge sensor and the driving circuitry constitute, or form part of, a controller such as a microcontroller.

[0057] According to an aspect of the present disclosure there is provided an electricity meter comprising the system as described above and the service disconnect switch, wherein the electricity meter is configured for measuring one or more electrical quantities associated with the supply of electrical power from the power supply to the load.

[0058] It should be understood that any one or more of the optional features of any one of the foregoing aspects of the present disclosure may be combined with any one or more of the other foregoing aspects of the present disclosure or the optional features of any one or more of the other foregoing aspects of the present disclosure.

[0059] BRIEF DESCRIPTION OF THE DRAWINGS

[0060] A service disconnect system and an electricity meter incorporating the service disconnect system and associated methods will now be described by way of non-limiting example only with reference to the drawings of which:

[0061] FIG. 1 is a schematic block diagram of a system for use in operating a service disconnect (SD) switch for electrically isolating a load from a power supply;

[0062] FIG. 2 is a circuit diagram of part of the system of FIG. 1 ;

[0063] FIG. 3 is a plot of voltage across a SD capacitor of the system of FIGS. 1 and 2 as a function of time, the current flowing through the SD switch as a function of time from the power supply to the load, and the first derivative of the voltage across the SD capacitor as a function of time during discharging of the SD capacitor through a DC motor of the system in an opening discharge direction to cause the SD switch to open;

[0064] FIG. 4 is a flow chart illustrating a method for use in opening the SD switch using the system of FIGS. 1 and 2;

[0065] FIG. 5 is a flow chart illustrating a method for use in closing the SD switch using the system of FIGS. 1 and 2; and

[0066] FIG. 6 is a plot of switch time of an SD switch using the system of FIGS. 1 and 2 as a function of SD cycles.

[0067] DETAILED DESCRIPTION OF THE DRAWINGS

[0068] Referring initially to FIG. 1 there is shown a system generally designated 2 for use in operating a service disconnect (SD) switch 10 between a closed state in which the SD switch 10 electrically connects a power supply 12 to a load 14, and an open state in which the SD switch 10 electrically isolates the load 14 from the power supply 12. It should be understood that the system 2 and the SD switch 10 may both be incorporated into, or form part of, an electricity meter which is configured for measuring one or more electrical quantities associated with the supply of electrical power from the power supply 12 to the load 14.

[0069] The system 2 further includes an actuator in the form of a DC motor 22 for actuating the SD switch 10 between the closed and open states, a SD capacitor 24, a discharge switch arrangement in the form of an H-bridge switch arrangement 26 for selectively discharging the SD capacitor 24 through the DC motor 22, and a controller in the form of a microcontroller 30. As represented by dashed line 29, the DC motor 22 is linked mechanically to the SD switch 10 for actuation of the SD switch 10 between the closed and open states during discharging of the SD capacitor 24 through the DC motor 22.

[0070] The microcontroller 30 includes an electrical discharge sensor 32 for sensing an electrical discharge signal in the form of a voltage signal across the SD capacitor 24 during discharging of the SD capacitor 24 through the DC motor 22, and a processing resource 34 which is configured to determine whether the SD switch 10 is actuated between the closed and open states during discharging of the SD capacitor 24 through the DC motor 22 based on the voltage signal sensed by the electrical discharge sensor 32.

[0071] The microcontroller 30 also includes driving circuitry 36 for driving the H-bridge switch arrangement 26, wherein the processing resource 30 is configured to control the driving circuitry 36 and thereby control the H-bridge switch arrangement 26 so as to select a direction of the discharge of the SD capacitor 24 through the DC motor 22 and control the timing of the discharge of the SD capacitor 24 through the DC motor 22.

[0072] The system 2 also includes a charge arrangement in the form of a current source 44 for charging the SD capacitor 24 before the SD capacitor 24 is discharged. Although not shown in FIG. 1 , it should be understood that the system 2 also includes a flyback arrangement for converting power from the power supply 12 into a 24 V DC voltage supply for powering the current source 44 and the microcontroller 30. Also, although not shown in FIG. 1 , the microcontroller 30 may be configured to control operation of the current source 44 for controlling charging of the SD capacitor 24.

[0073] The system 2 further includes a output arrangement 50 such as a display for outputting information to a local user or a transmitter for outputting information to a remote user. The system 2 also includes a temperature sensor 52 for sensing a temperature of the DC motor 22 before, during and / or after discharging of the SD capacitor 24 through the DC motor 22 and / or for sensing a temperature of an environment surrounding the DC motor 22 before, during and / or after discharging of the SD capacitor 24 through the DC motor 22.

[0074] FIG. 2 shows a winding L1 of the DC motor 22, the SD capacitor 24, the circuit components of the H-bridge switch arrangement 26, the circuit components of the current source 44, and the connectivity therebetween. The voltage V3 is the 24 V DC voltage generated by the flyback arrangement (not shown). As will be described in more detail below, the voltages V1 and V2 are voltage signals generated by the driving circuitry 36 for controlling the H-bridge switch arrangement 26 so as to select a direction of the discharge of the SD capacitor 24 through the DC motor 22 and control the timing of the discharge of the SD capacitor 24 through the DC motor 22.

[0075] In use, the processing resource 34 controls the driving circuitry 36 and thereby control the H-bridge switch arrangement 26 so as to select a direction of the discharge of the SD capacitor 24 through the through the DC motor 22 and control the timing of the discharge of the SD capacitor 24 through the DC motor 22. When it is desired to open the SD switch 10, the processing resource 34 controls the driving circuitry 36 so as to control the H-bridge switch arrangement 26 and cause the SD capacitor 24 to discharge through the DC motor 22 in an opening discharge direction. Conversely, when it is desired to close the SD switch 10, the processing resource 34 controls the driving circuitry 36 so as to control the H-bridge switch arrangement 26 and cause the SD capacitor 24 to discharge through the DC motor 22 in a closing discharge direction which is opposite to the opening discharge direction.

[0076] Specifically, when it is desired to open the SD switch 10, the processing resource 34 controls the driving circuitry 36 so as to apply a 400 ms voltage pulse at V2 whilst applying 0 V at V1 . The 400 ms voltage pulse applied at V2 is of a sufficient voltage to cause transistor switches M2 and M4 to turn ON for the duration of the 400 ms voltage pulse and the application of 0 V at V1 causes transistor switches M1 and M3 to remain OFF, thereby causing the SD capacitor 24 to discharge through the DC motor 22 in an opening discharge direction from M4 towards M2.

[0077] FIG. 3 corresponds to the case when the SD switch 10 is initially closed and shows the voltage 102 across the SD capacitor 24 as sensed by the electrical discharge sensor 32 as a function of time, the current 104 flowing through the SD switch 10 flowing from the power supply 12 to the load 14 as a function of time, and a first derivative 106 of the voltage 102 as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction and opening of the SD switch 10. At time t = 0 s, the SD capacitor 24 is fully charged and the SD capacitor voltage is approximately 20 V. The processing resource 34 controls the driving circuitry 36 so as to apply a 400 ms voltage pulse at V2 starting at around time t = 0.15 s whilst applying 0 V at V1 causing the SD capacitor 24 to discharge through the DC motor 22 in the opening discharge direction from around time t = 0.15 s to around time t = 0.35 s. As may be appreciated from the current 104 flowing through the SD switch 10 as a function of time, the discharge of the SD capacitor 24 through the DC motor 22 in the opening discharge direction causes the SD switch 10 to open around time t = 0.2 s. As may be appreciated from the voltage 102 as a function of time and the first derivative 106 of the voltage 102 as a function of time during a first discharge of the SD capacitor 24 through the DC motor 22 in the opening discharge direction shown in FIG. 3, the first derivative 106 of the voltage 102 as a function of time exhibits a first dip 106a corresponding to the start of the discharge of the SD capacitor 24 around time t = 0.15 s and a second dip 106b around time t = 0.23 s. It has been discovered that the second dip 106b in the first derivative 106 of the voltage 102 as a function of time corresponds to the point at which the DC motor 22 is no longer converting the electrical energy provided by the discharge of the SD capacitor 24 into motion, for example because the DC motor 22 and / or the SD switch 10 reach the end of their travel or a mechanical end stop of some kind. This causes laminations of the DC motor 22 to saturate and the impedance associated with the DC motor 22 to be reduced to the resistance of the windings of the DC motor 22. Consequently, the second dip 106b in the first derivative 106 of the voltage 102 as a function of time may serve as a signature which may be used to confirm that the SD switch 10 was opened during discharge of the SD capacitor 24 through the DC motor 22 in the opening discharge direction. Specifically, the processing resource 34 determines that the SD switch 10 was opened during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction based on detecting the first and second dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time, where the value of the first derivative 106 of the voltage 102 as a function of time associated with the first dip 106a is less than a first predetermined threshold value and the value of the first derivative 106 of the voltage 102 as a function of time associated with the second dip 106a is less than a second predetermined threshold value. Moreover, one of ordinary skill in the art will understand that the first and second predetermined threshold values are selected based at least in part on the level of noise on the first derivative 106 of the voltage 102 as a function of time, or the size of any random variations in the first derivative 106 of the voltage 102 as a function of time, so that the presence of the first and second dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time may be detected in the presence of noise on the first derivative 106 of the voltage 102 as a function of time.

[0078] It should be understood that when the SD switch 10 is initially open and the SD capacitor 24 is discharged through the DC motor 22 in the closing discharge direction to close the SD switch 10, the voltage across the SD capacitor 24 as sensed by the electrical discharge sensor 32 as a function of time and the first derivative of the voltage as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction are similar or identical to the voltage 102 as a function of time and the first derivative 106 of the voltage 102 as a function of time shown in FIG. 3. In contrast to the current 104 flowing through the SD switch 10 flowing from the power supply 12 to the load 14 as a function of time shown in FIG. 3, however, when the SD switch 10 is initially open, there is initially no current flowing through the SD switch 10 until the SD switch 10 closes, whereupon there is a step increase in the current flowing through the SD switch 10 from the power supply 12 to the load 14.

[0079] Consequently, when it is desired to close the SD switch 10, the processing resource 34 controls the driving circuitry 36 so as to apply a 400 ms voltage pulse at V1 whilst applying 0 V at V2. The 400 ms voltage pulse applied at V1 is of a sufficient voltage to cause transistor switches M1 and M3 to turn ON for the duration of the 400 ms voltage pulse and the application of 0 V at V2 causes transistor switches M2 and M4 to remain OFF thereby causing the SD capacitor 24 to discharge through the DC motor 22 in a closing discharge direction from M3 towards M1 . When discharging the SD capacitor 24 through the DC motor 22 in the closing discharge direction, the first derivative of the voltage across the SD capacitor 24 through the DC motor 22 as a function of time also exhibits a first dip, like dip 106a, corresponding to the start of the discharge of the SD capacitor 24 in the closing discharge direction and a second dip, like dip 106b, corresponding to the end of motion of the DC motor 22 and / or the SD switch 10 and indicating that the SD switch 10 was closed during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction. Specifically, the processing resource 34 determines that the SD switch 10 was closed during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction based on detecting the first and second dips in the first derivative of the voltage as a function of time, where the value of the first derivative of the voltage as a function of time associated with the first dip is less than a first predetermined threshold value and the value of the first derivative value of the voltage as a function of time associated with the second dip is less than a second predetermined threshold value.

[0080] In view of the foregoing description it will be appreciated that the system 2 may be used to reliably confirm whether the SD switch 10 is operated between the closed and open states without measuring a change in current flowing through the SD switch 10 from the power supply 12 to the load 14 during driving of the SD switch 10.

[0081] With reference to FIG. 4, one of ordinary skill in the art will appreciate that the foregoing description of the method of determining that the SD switch 10 was opened during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the first time requires the processing resource 34 to not only control the driving circuitry 36 to operate the H-bridge switch arrangement 26 so that the SD capacitor 24 is discharged through the DC motor 22 in the opening discharge direction at step 200, but to also check at step 202 for first and second dips 106a, 106b in the first derivative 106 of the voltage 102 across the SD capacitor 24 as a function of time as sensed during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the first time. If first and second dips 106a, 106b are detected at step 202 in the first derivative 106 of the voltage 102 as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the first time, it may be concluded at step 204 that the SD switch 10 was opened during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction at step 200. However, if the processing resource 34 fails to detect first and second dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time at step 202, it may be concluded that the SD switch 10 was not opened during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction at step 200. This may occur for example in cold temperatures where the viscosity of motor lubricant could be excessively high. Consequently, if the processing resource 34 fails to detect first and second dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time at step 202, the processing resource 34 controls or allows the current source 44 to re-charge the SD capacitor 24 at step 206 and then attempts to open the SD switch 10 for a second time by discharging the SD capacitor 24 through the DC motor 22 in the opening discharge direction for a second time at step 208 and checks at step 210 for opening of the SD switch 10 based on detection of first and second dips in the first derivative of the voltage as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the second time at step 208. If opening of the SD switch 10 is detected at step 210 during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the second time at step 208, it may be concluded at step 212 that the SD switch 10 was opened when the SD capacitor 24 was discharged through the DC motor 22 in the opening discharge direction for the second time at step 208.

[0082] If, however, first and second dips 106a, 106b are not detected at step 210 in the first derivative 106 of the voltage 102 as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction for the second time at step 208, it may be concluded at step 214 that the system 2 and / or the SD switch 10 is not operating correctly. Under these circumstances, the processing resource 34 may generate an error message and / or raise an alarm via the output arrangement 50.

[0083] Conversely, with reference to FIG. 5, one of ordinary skill in the art will appreciate that the foregoing description of the method of determining that the SD switch 10 was closed during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the first time requires the processing resource 34 to not only control the driving circuitry 36 to operate the H-bridge switch arrangement 26 so that the SD capacitor 24 is discharged through the DC motor 22 in the closing discharge direction at step 300, but to also check at step 302 for first and second dips in the first derivative of the voltage across the SD capacitor 24 as a function of time as sensed during discharge of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the first time. If first and second dips are detected at step 302 in the first derivative of the voltage as a function of time as sensed during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the first time, it may be concluded at step 304 that the SD switch 10 was closed during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction at step 300. However, if the processing resource 34 fails to detect first and second dips in the first derivative of the voltage as a function of time at step 302, it may be concluded that the SD switch 10 was not opened during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction at step 300. This may occur for example in cold temperatures where the viscosity of motor lubricant could be excessively high. Consequently, if the processing resource 34 fails to detect first and second dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time at step 302, the processing resource 34 controls or allows the current source 44 to re-charge the SD capacitor 24 at step 306 and then attempts to close the SD switch 10 for a second time by discharging the SD capacitor 24 through the DC motor 22 in the closing discharge direction for a second time at step 308 and checks at step 310 for closing of the SD switch 10 based on detection of first and second dips 106a, 106b, in the first derivative 106 of the voltage 102 as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the second time at step 308.

[0084] If closing of the SD switch 10 is detected at step 310 during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the second time at step 308, it may be concluded at step 312 that the SD switch 10 was closed when the SD capacitor 24 was discharged through the DC motor 22 in the closing discharge direction for the second time at step 308.

[0085] If, however, first and second dips are not detected at step 310 in the first derivative of the voltage as a function of time during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction for the second time at step 308, it may be concluded at step 314 that the system 2 and / or the SD switch 10 is not operating correctly. Under these circumstances, the processing resource 34 may generate an error message and / or raise an alarm via the output arrangement 50.

[0086] In addition to determining whether the SD switch 10 is opened or closed during discharge of the SD capacitor 24, the processing resource 34 may be configured to determine the time taken to actuate the SD switch 10 between the closed and open states based on the electrical discharge signal sensed by the electrical discharge sensor 32 during discharging of the SD capacitor 24 through the DC motor 22. For example, referring back to FIG. 3, the processing resource 34 may be configured to determine the time taken to open the SD switch 10 based on the time between the dips 106a, 106b in the first derivative 106 of the voltage 102 as a function of time across the SD capacitor 24 as sensed by the electrical discharge sensor 32 during discharging of the SD capacitor 24 through the DC motor 22 in the opening discharge direction. Conversely, the processing resource 34 may be configured to determine the time taken to close the SD switch 10 based on the time between the dips in the first derivative of the voltage as a function of time across the SD capacitor 24 as sensed by the electrical discharge sensor 32 during discharging of the SD capacitor 24 through the DC motor 22 in the closing discharge direction.

[0087] The time taken to actuate the SD switch 10 between the closed and open states - i.e. the switch time - may be indicative of the condition or health of the DC motor 22 and / or of the SD switch 10, with longer switch times indicating a deterioration in performance of the DC motor 22 and / or of the SD switch 10. For example, FIG. 6 shows an increase in switch time as a function of SD cycles illustrating a deterioration in the performance of the DC motor 22 and / or of the SD switch 10 as the number of SD cycles increases. Thus, determining the switch time may allow the condition or health of the DC motor 22 and / or of the SD switch 10 to be determined and, optionally, allow a user to decide whether to take any action in response to the determined condition or health of the DC motor 22 and / or of the SD switch 10 e.g. allow a user to decide whether to perform any preventative maintenance on the DC motor 22 and / or the SD switch 10 and / or whether to replace the DC motor 22 and / or the SD switch 10.

[0088] The switch time may also be temperature dependent. Thus, the processing resource 34 may also be configured to store the temperature sensed by the temperature sensor 52 together with the determined switch time for analysis at a later time and / or to output the temperature sensed by the temperature sensor 52 together with the determined switch time to a user. Sensing the temperature and determining the switch time may allow the condition or health of the DC motor 22 and / or of the SD switch 10 to be determined and, optionally, allow a user to decide whether to take any action in response to the determined condition or health of the DC motor 22 and / or of the SD switch 10 e.g. allow a user to decide whether to perform any preventative maintenance on the DC motor 22 and / or the SD switch 10 and / or whether to replace the DC motor 22 and / or the SD switch 10.

[0089] One of ordinary skill in the art will also understand that various modifications are possible to the system 2 or to any of the associated methods described above. For example, the processing resource 34 may be configured to control the H-bridge switch arrangement 26 so that the SD capacitor 24 is discharged through the actuator in the discharge direction for a fixed time period, the fixed time period being selected to be greater than a time period required for the DC motor 22 to open or close the SD switch 10. Alternatively, the processing resource 34 may be configured to monitor the sensed voltage signal during discharging of the SD capacitor 24 through the DC motor 22 in the discharge direction and to control the H-bridge switch arrangement 26 so that the SD capacitor 24 discharges through the DC motor 22 in the discharge direction until the processing resource 34 determines that the SD switch 10 has been opened or closed based on the monitored electrical discharge signal e.g. based on the detection of first and second dips 106a, 106b in the first derivative 106 of the sensed voltage 102 as a function of time.

[0090] In the foregoing embodiments, the electrical discharge sensor 32 senses an electrical discharge signal in the form of voltage across the SD capacitor 24 as a function of time and the processing resource 34 determines whether the SD switch 10 is closed or opened during discharge of the SD capacitor 24 through the DC motor 22 based on the sensed voltage across the SD capacitor 24 as a function of time. In other embodiments, the electrical discharge sensor 32 may sense an electrical discharge signal of any kind which is dependent on the discharging of the SD capacitor 24 through the DC motor 22. For example, the electrical discharge signal may be such that an instantaneous value of the electrical discharge signal is proportional to the charge stored in the SD capacitor 24 during discharging of the SD capacitor 24 through the DC motor 22. The electrical discharge signal may be such that an instantaneous value of the electrical discharge signal is proportional to a rate of discharge of the SD capacitor 24 through the DC motor 22 during discharging of the SD capacitor 24 through the DC motor 22. For example, the electrical discharge signal may comprise a discharge current signal from the SD capacitor 24 through the DC motor 22 during discharging of the SD capacitor 24 through the DC motor 22. The processing resource 34 may be configured to determine the time taken to actuate the SD switch 10 between the closed and open states based on the discharge current signal. The processing resource 34 may be configured to determine that the SD switch 10 is actuated between the closed and open states during discharging of the SD capacitor 24 through the DC motor 22 based on detecting first and second peaks in the discharge current signal, wherein the discharge current signal value associated with the first peak is greater than a first predetermined threshold value and the discharge current signal value associated with the second peak is greater than a second predetermined threshold value. The processing resource 34 may be configured to determine the time taken to actuate the SD switch 10 between the closed and open states based on the time between the first and second peaks in the discharge current signal.

[0091] In the foregoing embodiments, the actuator was described as a DC motor. In alternative embodiments, the actuator may be a solenoid or any other kind of electrically actuated actuator.

[0092] Although the system 2 and associated methods have been described in terms of preferred embodiments as set forth above, it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments. Those skilled in the art will be able to make modifications and alternatives to the described embodiments in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in any embodiment, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein. In particular, one of ordinary skill in the art will understand that one or more of the features of the embodiments of the present disclosure described above with reference to the drawings may produce effects or provide advantages when used in isolation from one or more of the other features of the embodiments of the present disclosure and that different combinations of the features are possible other than the specific combinations of the features of the embodiments of the present disclosure described above.

[0093] The skilled person will understand that in the preceding description and appended claims, positional terms such as ‘above’, ‘along’, ‘side’, etc. are made with reference to the accompanying drawings. These terms are used for ease of reference but are not intended to be of limiting nature. These terms are therefore to be understood as referring to an object when in an orientation as shown in the accompanying drawings.

[0094] Use of the term "comprising" when used in relation to a feature of an embodiment of the present disclosure does not exclude other features or steps. Use of the term "a" or "an" when used in relation to a feature of an embodiment of the present disclosure does not exclude the possibility that the embodiment may include a plurality of such features.

[0095] The use of reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

CLAIMS1 . A method for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply, the method comprising: controlling the discharge of a service disconnect capacitor in a discharge direction through an actuator for actuating the service disconnect switch, wherein the discharge direction is selected from an opening discharge direction for driving the actuator to open the service disconnect switch and a closing discharge direction for driving the actuator to close the service disconnect switch; sensing an electrical discharge signal which is dependent on the discharging of the service disconnect capacitor through the actuator; and determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction based on the electrical discharge signal sensed during discharging of the service disconnect capacitor through the actuator in the discharge direction.

2. The method as claimed in claim 1 , wherein controlling the discharge of the service disconnect capacitor comprises selecting the discharge direction and controlling the timing of the discharge of the service disconnect capacitor through the actuator.

3. The method as claimed in claim 1 , comprising determining whether the service disconnect switch is in the open state or the closed state based at least in part on the selected discharge direction and based at least in part on determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction.

4. The method as claimed in claim 1 , comprising determining that the service disconnect switch is in the open state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction.

5. The method as claimed in claim 1 , comprising determining that the service disconnect switch is in the closed state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction.

6. The method as claimed in claim 1 , comprising: responsive to determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for a first time, recharging the service disconnect capacitor; discharging the service disconnect capacitor through the actuator in the opening discharge direction for a second time; determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time; and determining that the service disconnect switch is in the open state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the opening discharge direction for the second time, else determining that the service disconnect switch is not operating correctly.

7. The method as claimed in claim 1 , comprising: responsive to determining that the service disconnect switch is not actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for a first time, recharging the service disconnect capacitor; discharging the service disconnect capacitor through the actuator in the closing discharge direction for a second time; determining whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the closing discharge direction for the second time; and determining that the service disconnect switch is in the closed state if it is determined that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in theclosing discharge direction for the second time, else determining that the service disconnect switch is not operating correctly.

8. The method as claimed in claim 1 , further comprising determining the switch time taken to actuate the service disconnect switch between the closed and open states based on the electrical discharge signal sensed during discharging of the service disconnect capacitor through the actuator, and optionally storing the determined switch time for analysis at a later time and / or outputting the determined switch time to a user.

9. The method as claimed in claim 1 , comprising sensing a temperature of the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator and / or sensing a temperature of an environment surrounding the actuator before, during and / or after discharging of the service disconnect capacitor through the actuator and, optionally, storing the temperature sensed for analysis at a later time and / or outputting the temperature sensed to a user.

10. The method as claimed in claim 1 , wherein an instantaneous value of the electrical discharge signal is proportional to the charge stored in the service disconnect capacitor during the discharging of the service disconnect capacitor through the actuator.1 1. The method as claimed in claim 1 , wherein the electrical discharge signal comprises a voltage across the service disconnect capacitor as a function of time during the discharging of the service disconnect capacitor through the actuator.

12. The method as claimed in claim 1 1 , comprising determining that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time, where a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the first dip is less than a first predetermined threshold value and a value of the first derivative of the voltage across the service disconnect capacitor as a function of time associated with the second dip is less than a second predetermined threshold value.

13. The method as claimed in claim 11 , further comprising determining the time taken to actuate the service disconnect switch between the closed and open states based on the voltage across the service disconnect capacitor as a function of time, for example determining the time taken to actuate the service disconnect switch between the closed and open states based on the time between first and second dips in the first derivative of the voltage across the service disconnect capacitor as a function of time.

14. The method as claimed in claim 1 , wherein an instantaneous value of the electrical discharge signal is proportional to a rate of discharge of the service disconnect capacitor through the actuator during the discharging of the service disconnect capacitor through the actuator15. The method as claimed in claim 1 , wherein the electrical discharge signal comprises a discharge current from the service disconnect capacitor through the actuator as a function of time during the discharging of the service disconnect capacitor through the actuator.

16. The method as claimed in claim 15, comprising determining that the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator based on detecting first and second peaks in the discharge current from the service disconnect capacitor through the actuator as a function of time, wherein a value of the discharge current associated with the first peak is greater than a first predetermined threshold value and a value of the discharge current associated with the second peak is greater than a second predetermined threshold value.

17. The method as claimed in claim 15, further comprising determining the time taken to actuate the service disconnect switch between the closed and open states based on the discharge current from the service disconnect capacitor through the actuator as a function of time, for example determining the time taken to actuate the service disconnect switch between the closed and open states based on the time between first and second peaks in the discharge current.

18. The method as claimed in claim 1 , comprising discharging the service disconnect capacitor through the actuator in the discharge direction for a fixed time period, the fixedtime period being selected to be greater than a time period required for the actuator to actuate the service disconnect switch between the closed and open states, or monitoring the sensed electrical discharge signal during discharging of the service disconnect capacitor through the actuator in the discharge direction and discharging the service disconnect capacitor through the actuator in the discharge direction until it is determined that the service disconnect switch is actuated between the closed and open states based on the monitored electrical discharge signal.

19. A system for use in operating a service disconnect switch between a closed state in which the service disconnect switch electrically connects a power supply and a load, and an open state in which the service disconnect switch electrically isolates the load from the power supply, the system comprising: an actuator for actuating the service disconnect switch; a service disconnect capacitor; a discharge switch arrangement for controlling the discharge of the service disconnect capacitor through the actuator in a discharge direction selected from an opening discharge direction for driving the actuator to open the service disconnect switch and a closing discharge direction for driving the actuator to close the service disconnect switch; an electrical discharge sensor for sensing an electrical discharge signal which is dependent on the discharging of the service disconnect capacitor through the actuator; and a processing resource which is configured to determine whether the service disconnect switch is actuated between the closed and open states during discharging of the service disconnect capacitor through the actuator in the discharge direction based on the electrical discharge signal sensed by the electrical discharge sensor during discharging of the service disconnect capacitor through the actuator in the discharge direction.

20. An electricity meter comprising: the system of claim 19; and the service disconnect switch, wherein the electricity meter is configured for measuring one or more electrical quantities associated with the supply of electrical power from the power supply to the load.

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