Input Impedance Management and Leakage Current Detection

Abstract

The present invention discloses a system for a power distribution network, the system comprising an electrical device configured to monitor or control one or more aspects of the power distribution network, the electrical device including a contact switch configured to open and close. The system further includes an input device. The input device includes: an impedance module; and an input interface electrically connected to the impedance module and the contact switch of the electrical device. The input interface is configured to have one of a plurality of input impedances, the plurality of input impedances including at least a first input impedance and a second input impedance lower than the first input impedance, and when the contact switch of the electrical device is open, the input interface has the second input impedance. The input device may include a plurality of leakage current detection modules.

Description

Technical Field

[0001] This disclosure relates to input impedance management and leakage current detection. Background Art

[0002] Switching devices, including reclosers, can be used in a power distribution network to protect the network from electrical fault conditions. Fault conditions are detected by monitoring current and voltage through switching devices on the power distribution network. Fault conditions include transient or steady-state amplitude faults and frequency or phase relationship faults. Under normal operating conditions, the recloser is closed and current flows through the recloser. In response to detecting a fault condition, the recloser trips or opens to prevent current from flowing through the recloser, and then opens and closes multiple times to attempt to clear the fault. If the fault condition still exists, the recloser remains open. If this fault condition is cleared, the recloser closes and the distribution network resumes normal operation. A voltage regulator can be used to monitor and control the voltage level in the distribution network. Summary of the Invention

[0003] In one general aspect, a system for a power distribution network includes electrical devices configured to monitor or control one or more aspects of the power distribution network, the electrical devices including a contact switch configured to open and close. The system further includes an input device. The input device includes: an impedance module; and an input interface electrically connected to the impedance module and the contact switch of the electrical device. The input interface is configured to have one of a plurality of input impedances, the plurality of input impedances including at least a first input impedance and a second input impedance lower than the first input impedance, and when the contact switch of the electrical device is open, the input interface has the second input impedance.

[0004] The embodiments may include one or more of the following features. The input interface may include a first impedance element, and the impedance module may include a second impedance element, and when the contact switch of the electrical device is open, current may flow through the first impedance element and the second impedance element such that the input interface has the second input impedance. The impedance module may further include an electronic switch associated with a first state and a second state, the electronic switch conducting current in the first state and the electronic switch not conducting current in the second state. In these embodiments, current flows in the second impedance element only when the electronic switch is in the first state. The input device may further include an electronic processor configured to provide a signal to the electronic switch, the signal being sufficient to transition the electronic switch to the first state such that the input interface has the second input impedance even when the contact switch of the electrical device is closed. The electronic processor coupled to the impedance module may be configured to generate the signal prior to an expected opening of the contact switch. After the expected opening of the contact switch, the electronic processor may be further configured to cause the electronic switch to transition to the second state such that if the contact switch of the electrical device is closed, the input interface has the first input impedance.

[0005] In some embodiments, the control cable includes a conductor electrically connecting the input interface and the contact switch. In these embodiments, the control system may further include a leakage current detection module electrically coupled to the impedance module, the leakage current detection module being configured to provide an indication of the amount of current flowing in the conductor. The electrical device may include a plurality of contact switches, the control cable may include a plurality of conductors, each of the conductors being connected to one of the plurality of contact switches, the input device may include a plurality of impedance modules and a plurality of input interfaces, each of the input interfaces being electrically connected to one of the conductors, each of the impedance modules being electrically connected to one of the plurality of input interfaces, and all of the impedance modules being electrically connected to the leakage current detection module. The electrical device may include a plurality of contact switches, the control cable may include a plurality of conductors, each of the conductors may be connected to one of the plurality of contact switches, the input device may include a plurality of impedance modules and a plurality of input interfaces, each of the input interfaces being electrically connected to one of the conductors, each of the impedance modules being electrically connected to one of the plurality of input interfaces, the input device may include a plurality of leakage current detection modules, and each of the impedance modules may be electrically connected to one of the leakage current detection modules.

[0006] The electrical device may be, for example, a recloser or a voltage regulator.

[0007] In another general aspect, an input device includes a plurality of input interfaces, each of the input interfaces being configured to be electrically connected to a contact switch of an electrical device that monitors or controls one or more aspects of a power distribution network. Each of the input interfaces is configured to have one of a plurality of impedances, the plurality of impedances including at least a first input impedance or a second input impedance, the second input impedance being lower than the first input impedance. The input device further includes a plurality of impedance modules, each impedance module being connected to one of the plurality of input interfaces. When current flows through the impedance module connected to each input interface, the input interface has the second input impedance.

[0008] Embodiments may include one or more of the following features. The input device may further include one or more leakage current detection modules, where each of the one or more leakage current detection modules is electrically connected to one of the impedance modules and is configured to measure the amount of current flowing out of the one impedance module among the impedance modules. The input interface may be configured to receive N conductors, where N is an integer greater than 1, the input device may include N leakage current detection modules, and each of the N leakage current detection modules may be configured to measure the leakage current flowing in one of the N conductors. In some embodiments, the input interface is configured to receive N conductors, where N is an integer greater than 1, the input device includes one leakage current detection module, and the leakage current detection module is configured to measure the leakage current flowing in any one of the N conductors.

[0009] In another general aspect, measure the amount of leakage current flowing in a cable of an input device that connects an electrical device and a control system; analyze the measured amount of leakage current to determine one or more characteristics of the leakage current; determine whether there is moisture in the cable based on the analysis; and if it is determined that there is moisture in the cable, generate an indication of an error.

[0010] Embodiments of any of the techniques described herein may include an electrical device and an input device, an input device, an input circuit, an input circuit and a leakage current detection module, a leakage detection module, software stored on a non-transitory computer-readable medium (the software, when executed, monitors and / or analyzes leakage current), a method and / or kit for retrofitting a recloser or a voltage regulating device. Details of one or more embodiments are set forth in the drawings and the following description. Other features will be apparent from the description and drawings, and from the claims. Description of the Drawings

[0011] Figure 1A and Figure 1B are block diagrams of examples of a power system.

[0012] Figure 2 are block diagrams of examples of an input device.

[0013] Figure 3A are schematic diagrams of examples of an input circuit.

[0014] Figure 3B are schematic diagrams of examples of a trigger module.

[0015] Figure 3C are schematic diagrams of examples of a leakage current detection module.

[0016] Figure 4 is a flowchart of an example of a process for measuring leakage current.

[0017] Figure 5 are schematic diagrams of another example of an input circuit.

[0018] Figure 6 are schematic diagrams of another example of an input circuit. Detailed Description

[0019] Figure 1A is a block diagram of an example of a power system 100. The power system 100 includes a power distribution network 101 that transmits power from a power source 102 to a power load 103 through a distribution path 104 and an electrical device 110. The electrical device 110 is a switching device, such as a recloser or a voltage regulator or any other device capable of controlling and / or monitoring the power flow on the distribution path 104. The power distribution network 101 can be, for example, a power grid, an electrical system, or a polyphase electrical network that supplies power to commercial and / or residential customers. The power distribution network 101 can have, for example, an operating voltage of at least 1 kilovolt (kV), at most 34.5 kV, at most 38 kV, or 69 kV or higher, and can operate at a fundamental frequency of, for example, 50 hertz to 60 hertz (Hz). The distribution path 104 can include, for example, one or more transmission lines, cables, and / or any other means for transmitting power.

[0020] The electrical device 110 is installed on the structure 115. The structure 115 can be, for example, a telephone pole, a substation installation frame, or other large structures for supporting electrical equipment. The electrical device 110 is electrically connected to the control system 120 via the cable 131. The control system 120 monitors the state of the electrical device 110 and controls the electrical device 110. The cable 131 is connected to the electrical device 110 at the socket 114, and the cable 131 is connected to the control system 120 at the socket 121. The sockets 114 and 121 are any type of electrical interfaces capable of holding the cable 131 and electrically connecting one or more conductors in the cable 131 to the electrical device 110 and the control system 120. The control system 120 is also installed on the structure 115 but is separated from the electrical device 110. The cable 131 is relatively long, for example, 20 feet to 100 feet (6.10 meters to 30.84 meters) long or more than 240 feet (73.15 meters) long.

[0021] The control system 120 includes an input device 130 and a leakage current detection module 170. The control system 120 also includes an electronic processor 122, an electronic storage device 124, and an input / output (I / O) interface 126. The length of the cable 131 can cause noise, which affects the ability to monitor the state of the electrical device 110. As described below, the input impedance of the input device 130 is controllable, and this allows the control system 120 to reduce or eliminate false readings of the state of the electrical device 110.

[0022] In addition, the leakage current detection module 170 measures or gauges the current in the cable 131. Moisture entering the cable 131 can cause leakage current between the ground and the pins in the socket 121 and / or 114, between the pins within the socket 121, or between the pins within the socket 114. The presence of moisture can lead to suboptimal performance or failure of the electrical device 110, the cable 131, and / or the control system 120. The control system 120 and / or the monitoring station 180 communicating with the control system 120 via the data link 181 coupled to the I / O interface 126 use the amount of leakage current measured by the leakage current detection module 170 to determine whether moisture is present.

[0023] When it is determined that moisture is present, the control system 120 can issue an alarm to alert the operator to perform maintenance and / or replace the cable 131, the control system 120, and / or the electrical device 110. Thus, the control system 120 having the input device 130 and the leakage current detection module 170 is capable of monitoring and early detecting moisture intrusion. Such monitoring and early detection can reduce the failure rate of the electrical device 110, thereby improving the performance of the power distribution network 101. In addition, the capabilities of the leakage current detection module 170 can be further extended during operation to measure the current of the reclosing coil. Then, these current measurement results can be used to determine the health of the electrical device 110 and / or the control system 120. In addition, data from the current measurements can be used for diagnostic information and predictive analysis.

[0024] Reference is also made to Figure 1B , which is also a block diagram of the power system 100, where the electrical device 110 is discussed in more detail. In Figure 1B 's example, the electrical device 110 and the control system 120 are part of the system 105. The electrical device 110 includes a mechanism 111 and a contact switch 112, which controls whether power flows through the electrical device 110 (and thus through the distribution path 104) and / or controls the manner in which power flows through the electrical device, and the contact switch monitors the state of the mechanism 111. The contact switch 112 is also referred to as the status contact 112. The electrical device 110 can include more than one contact switch 112. The contact switch 112 has more than one state, and the state of the contact switch 112 provides the state of the mechanism 111. For example, when the mechanism 111 is open, the contact switch 112 is open, and when the mechanism 111 is closed, the contact switch 112 is closed. The contact switch 112 can be a mechanical contact or a solid-state switch, such as, for example, an open-drain metal oxide semiconductor field effect transistor (MOSFET) output or an open-collector transistor output that provides an indication of the state of the mechanism 111. The electrical device 110 also includes a drive device 113, which controls the mechanism 111 by, for example, causing all or a part of the mechanism 111 to move so that the electrical device 110 performs an operation. The drive device 113 includes various electrical, mechanical, and / or electromechanical devices (such as, for example, coils and / or motors) that control the mechanism 111.

[0025] The electrical device 110 can be any device or equipment that can be used to monitor and / or control the power distribution network 101. For example, the electrical device 110 can be any device, equipment, or system capable of controlling and / or monitoring one or more aspects of the power flowing in the distribution path 104. The electrical device 110 can be a recloser that controls the power flow in the distribution path 104 by opening (disconnecting) and closing (connecting) contacts that are part of the mechanism 111, and the state (open or closed) of these contacts is monitored by one or more contact switches 112. During normal operating conditions, the mechanism 111 of the recloser is closed so that power flows through the recloser and into the distribution path 104. The mechanism 111 opens during abnormal events such as lightning strikes to stop the power flow in the distribution path 104. The electrical device 110 can be a voltage regulator that controls the voltage at the distribution path 104. In these embodiments, the mechanism 111 can be, for example, a tap changer, and the position of the tap determines the voltage output by the voltage regulator, where the contact switch 112 provides the state of the tap.

[0026] The cable 131 houses conductors 134 for each of the contact switches 112, where each conductor 134 electrically connects the contact switch 112 to the input device 130. For simplicity, Figure 1B only one conductor 134 is shown. As described above, the cable 131 is relatively long, for example, 20 feet to 100 feet (6.10 meters to 30.84 meters) long or longer than 100 feet (30.84 meters). The length of the cable 131 can cause noise that affects the ability to monitor the state of the contact switch 112.

[0027] The input device 130 includes one or more input circuits 132 that are configured to have an input impedance that depends on the state of the contact switch 112. For example, when the contact switch 112 is open, the input circuit 132 can have a relatively low input impedance, and when the contact switch 112 is closed, the input circuit can have a relatively high input impedance. The input circuit 132 provides greater noise immunity by having a low input impedance when the contact switch 112 is open than an input circuit 132 that has a high impedance when the contact switch 112 is open. Thus, the state indicating that the contact switch 112 is open from the input device 130 can be more accurate than the state from a system that has a high input impedance when the contact switch 112 is open. Additionally, when the contact switch 112 is closed, the input circuit 132 provides a high input impedance, resulting in reduced power consumption during typical operation when the contact switch 112 is closed. Thus, the input device 130 provides the beneficial effect of a low input impedance when the contact switch 112 is open and a high input impedance at other times.

[0028] Figure 2 、Figure 3A , Figure 5 and Figure 6 illustrate examples of embodiments of the input circuit 132. Figure 3C illustrates an example of the leakage current detection module 170. Figure 4 is a flowchart of a process for measuring and / or analyzing leakage current.

[0029] Refer to Figure 2 , which shows a block diagram of the input device 230. The input device 230 is an example of an embodiment of the input device 130 ( Figure 1A and Figure 1B ). The input device 230 includes N input circuits 232_1, 232_2... 232_N, where N is an integer one (1) or greater. Each of the input circuits 232_1, 232_2... 232_N is configured to have one of a plurality of different input impedances. In Figure 2 example, each of the input circuits 232_1, 232_2... 232_N is configured to have a first input impedance or a second input impedance. The first input impedance and the second input impedance are different impedances, where the second input impedance is a smaller impedance than the first input impedance.

[0030] Each of the N input circuits 232_1, 232_2... 232_N includes a corresponding input interface 235_1, 235_2... 235_N. Each input interface 235_1, 235_2... 235_N is electrically connected to a corresponding contact switch 212_1, 212_2... 212_N via electrical conductors 234_1, 234_2... 234_N. The contact switches 212_1, 212_2... 212_N are part of the electrical device 210. The electrical conductors 234_1, 234_2... 234_N may be included in a single cable (not shown) connecting the input device 230 and the electrical device 210.

[0031] All the input circuits 232_1, 232_2... 232_N are configured and function in the same way. For simplicity, only the input circuit 232_1 is discussed in detail.

[0032] The input circuit 232_1 includes an input interface 235_1 and an impedance module 237_1. The input interface 235_1 is electrically connected to the contact switch 212_1 via a conductor 234_1. The input interface 235_1 includes an impedance element 239_1. The impedance element 239_1 can be a collection of any type of electronic component having resistance, for example. For example, the impedance element 239_1 may include resistors arranged in series and / or in parallel. The impedance module 237_1 also includes any type of electronic component having resistance. The impedance module 237_1 may include resistors and / or current sources in any configuration. Figure 6 An example of an impedance module including a current source is shown.

[0033] The input circuit 232_1 is configured such that current does not always flow through the impedance module 237_1. When current cannot flow through the impedance module 237_1, the input impedance of the input circuit 232_1 is the same as the impedance of the impedance element 239_1. When current can flow through the impedance module 237_1, the impedance module 237_1 and the impedance element 239_1 are in parallel with each other, and the impedance of the input circuit 232_1 is the parallel combination of the impedance module 237_1 and the impedance element 239_1. Equation 1 provides the relationship between the impedance values of the impedance module 237_1 and the impedance element 239_1 and the parallel combination of the components:

[0034] Equation (1),

[0035] where Z1 is the impedance of the impedance element 239_1 and Z2 is the impedance of the impedance module 237_1. The parallel combination (Ztotal) is less than the impedance of the impedance element 239_1 and less than the impedance of the impedance module 237_1. Thus, when current can flow through the impedance module 237_1, the input circuit 232_1 has a lower input impedance than when current cannot flow through the impedance module 237_1.

[0036] Therefore, the input circuit 232_1 has two possible input impedances: a first input impedance, which is the impedance of the impedance element 239_1; and a second input impedance, which is the impedance of the impedance element 239_1 in parallel with the impedance module 237_1. The second input impedance is a lower impedance than the first input impedance.

[0037] When the contact switch 212_1 is open, current can flow in the impedance module 237_1. Thus, when the contact switch 212_1 is open, the input circuit 232_1 has a second input impedance (a lower input impedance). For example, the impedance module 237_1 may be connected to a control element 238_1 (such as, Figure 3Aof transistor 338 or another type of switch). The state of control element 238_1 determines whether current can flow in impedance module 237_1. In some embodiments, input circuit 232_1 may be configured such that when control element 238_1 is in an on state, current can flow in impedance module 237_1, and when the transistor is in an off state, current cannot flow in impedance module 237_1. In these embodiments, opening contact switch 212_1 causes control element 238_1 to transition to a state where current can flow in impedance module 237_1.

[0038] Additionally, impedance module 237_1 may be configured to conduct current based on a trigger or command from electronic processor 240. Electronic processor 240 can be any type of electronic processor and may or may not include a general-purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), and / or an application-specific integrated circuit (ASIC). In addition to generating a trigger for impedance module 237_1, electronic processor 240 may also perform other actions. For example, electronic processor 240 can be used with or instead of electronic processor 122 of control system 120 and can generate command signals that cause contact switch 212_1 to open or close or cause mechanism 211_1 of electrical device 210 to operate.

[0039] A trigger from electronic processor 240 is sufficient to cause control element 238_1 to transition to a state that allows current to flow in impedance module 237_1 even when contact switch 212_1 is closed. For example, electronic processor 240 can provide a trigger signal to control element 238_1 just before contact switch 212_1 is expected to open (or just before mechanism 211_1 operates) to ensure that when contact switch 212_1 opens (or when mechanism 211_1 operates), input circuit 232_1 has a second input impedance (a lower input impedance). Additionally, electronic processor 240 can provide a trigger signal sufficient to cause control element 238_1 to transition to a state that prevents current from flowing in impedance module 237_1, such that input circuit 232_1 has a first input impedance (a higher input impedance).

[0040] Each of the other input circuits 232_2 to 232_N is configured and functions in the same manner as input circuit 232_1. Specifically, each of the input circuits 232_2 to 232_N includes a corresponding input interface 235_2 to 235_N and a corresponding impedance module 237_2 to 237_N. Each of the input interfaces 235_2 to 235_N includes a corresponding impedance element 239_2 to 239_N. Each of the input interfaces 235_2 to 235_N is electrically connected to a corresponding contact switch 212_2 to 212_N. When any one of the contact switches 212_2 to 212_N is open, current can flow through the corresponding impedance modules 237_2 to 237_N, thereby reducing the input impedance of the corresponding input interfaces 235_2 to 235_N. Additionally, the electronic processor 240 is configured to provide a trigger signal to any one of the impedance modules 237_2 to 237_N such that the corresponding input circuits 232_2 to 232_N have a lower input impedance regardless of whether the corresponding contact switches 212_2 to 212_N are open or closed.

[0041] The impedance modules 237_1, 237_2... 237_N are electrically connected to the leakage current detection module 170. When the corresponding switches 212_1, 212_2... 212_N are open, leakage current can be formed in the conductors 234_1, 232_4... 234_N and flow through the impedance modules 237_1, 237_2... 237_N. The leakage current is measured by the leakage current detection module 170. Figure 3C An example of an embodiment of the leakage current detection module 170 is provided.

[0042] In Figure 2 the example, all of the impedance modules 237_1, 237_2... 237_N are connected to the leakage current detection module 170. Thus, the leakage current measured at the leakage current detection module 170 is the sum of all of the leakage currents in the conductors 234_1, 234_2... 234_N connected to the open contact switches. Other embodiments are possible. For example, instances of the leakage current detection module 170 can be electrically connected to each of the impedance modules 237_1, 237_2... 237_N such that the leakage current can be measured on each of the conductors 234_1, 234_2... 234_N.

[0043] In addition, the input device 230 can be connected to more than one electrical device 210. In Figure 2In the example shown, each of the contact switches 212_1, 212_2... 212_N is part of the same electrical device 210. In other embodiments, at least some of the contact switches 212_1, 212_2... 212_N are part of one or more electrical devices that are separate and distinct from the electrical device 210, where some of the input interfaces 235_1, 235_2... 235_N are connected to the electrical device 210, and other input interfaces are connected to the separate and distinct electrical devices. Thus, the input device 230 can monitor leakage currents from different electrical devices and can provide input impedance management to more than one electrical device 210.

[0044] Figure 3A is a schematic diagram of the input circuit 332. The input circuit 332 can be used as any one or all of the input circuits 232_1, 232_2... 232_N. The input circuit 332 includes an input interface 335 that is electrically connected to the contact switch 312 through a cable (such as, Figure 1A and Figure 1B cable 131). The cable is not shown in Figure 3A . The length of the cable, which can be at least 20 feet, is represented as a crack 325 in Figure 3A . The contact switch 312 is shown in Figure 3A in the open position. The contact switch 312 is part of an electrical device 310, which can be, for example, a recloser or a voltage regulator. The electrical device 310 includes a housing, a base, or other support frame 311. The housing 311 is grounded. When the contact switch 312 is open, the input circuit 332 provides a low input impedance, and when the contact switch 312 is closed, the input circuit provides a high input impedance. Thus, the input circuit 332 is a dual-input impedance input circuit. The input circuit 332 is self-powered, which means that the state (open or closed) of the contact switch 312 is detected by the input circuit 332 without using an external power source.

[0045] When the contact switch 312 is open, the impedance element 339 pulls up the input interface 335 to V1. Current flows through the resistor R7 to the capacitor C4, which charges to V1. V1 can be, for example, 15 volts (V). In Figure 3A example, the impedance element 339 is the resistor R5. The resistor R5 can have an impedance of, for example, 1.5 kiloohms (kΩ). The resistor R5 is shown as a single resistor, but any combination or arrangement of electronic components can be used to form the resistor R5.

[0046] The input circuit 332 also includes a comparator U1. In Figure 3AIn the example, comparator U1 is an operational amplifier. However, comparator U1 can be any collection or arrangement of electronic components capable of comparing more than one voltage at the input terminals and producing an output indicating the relative difference between the voltages. For example, comparator U1 can be any configuration of electronic components that compares two voltages at the input terminals and produces a binary output (e.g., high or low) indicating which of the two input voltages is greater.

[0047] The positive input terminal of comparator U1 is labeled as pin 3, the negative input terminal of comparator U1 is labeled as pin 4, and the output terminal of comparator U1 is labeled as pin 1. A resistor network including resistors R6, R8, and R10 forms a voltage divider that biases the positive input of comparator U1. When the voltage at the negative input terminal of comparator U1 is less than the voltage at the positive input terminal of comparator U1, the output of comparator U1 is high. When the voltage at the negative input terminal of comparator U1 is greater than the voltage at the positive input terminal of comparator U1, the output of comparator U1 is low.

[0048] The state of the output of comparator U1 affects the total resistance of the voltage divider formed by resistors R6, R8, and R10. When the output of comparator U1 is low, the total impedance of the voltage divider formed by resistors R6, R8, and R10 is lower than the total impedance when the output of comparator U1 is high. Therefore, the bias voltage at the positive input terminal of comparator U1 is greater than the bias voltage when the output terminal of comparator U1 is high. For example, in an embodiment where resistor R6 is 100 kΩ, resistor R8 is 205 kΩ, resistor R10 is 49.9 kΩ, and V1 is 15 V, when the output of comparator U1 is high, the bias voltage at the positive input terminal is 6.39 V, and when the output of comparator U1 is low, the bias voltage at the positive input terminal is 4.30 V. The values of resistors R6, R8, and R10 (and V1) can be selected to control the voltage at which the output of comparator U1 changes state.

[0049] Voltage V1 is selected such that V1 is greater than the bias voltage at the positive input terminal of comparator U1. Therefore, after capacitor C4 is charged to V1, the voltage at the negative input terminal of comparator U1 is higher than the voltage at the positive input terminal of comparator U1. Therefore, the output of comparator U1 is low. The low output of comparator U1 forward biases diode D1 (shown at pin 5). Diode D1 turns control element 338 into a state where it conducts current. In the example of FIG. 3, control element 338 is a P-channel metal-oxide-semiconductor field-effect transistor (MOSFET) that turns into an on state and conducts current when the gate node 346 is pulled low. The gate node 346 is pulled low by the low output of comparator U1 through diode D1.

[0050] When the control element 338 is turned on, current can flow through the control element 338 and through the impedance module 337 connected to the drain of the control element 338, thereby pulling the impedance module 337 to V1. By pulling the impedance module 337 to V1, the impedance module 337 is set to be in parallel with the impedance element 339. Thus, when the control element 338 is turned on, the input impedance of the input circuit 332 is the parallel combination of the impedance module 337 and the impedance element 339. In Figure 3A the example, the impedance module 337 includes a resistor R2 and a resistor R3 in parallel with the resistor R2. The resistors R2 and R3 can each be, for example, 430 Ω. Thus, the parallel combination of the impedance module 337 and the impedance element 339 can be approximately 188 Ω, which is less than the impedance of the impedance element 339 and less than the impedance of the impedance module 337.

[0051] Thus, in response to the contact switch 312 being opened, the input impedance of the input circuit 332 becomes the lower of two possible input impedances. When the contact switch 312 is opened, the capacitor C4 remains charged to V1, causing the output of the comparator U1 to remain low, causing the control element 338 to remain in the on state. Thus, when the contact switch 312 is opened, the input impedance of the input circuit 332 remains low.

[0052] The input circuit 332 includes other components. For example, the input circuit 332 also includes an optocoupler U2. When the output of the comparator U1 is low, current flows through the optocoupler U2 and turns on the transistor 347. An optocoupler is an electronic component or circuit assembly that transfers an electrical signal between two isolated circuits using light. In Figure 3A the example, the optocoupler U2 isolates the digital ground terminal of the input circuit 332 from the ground terminal.

[0053] In addition, the input circuit 332 can provide an indication that the contact switch 312 is open. For example, the output of the comparator U1 or the optocoupler U2 can be used to provide a perceptible indication of the state of the contact switch 312. The perceptible and / or measurable signal can be, for example, the voltage across a resistor network connected to pin 10 of the transistor 347, or the light emitted from a light-emitting diode connected to pin 10 of the transistor 347.

[0054] Also referring to Figure 3B , the trigger module 352 is connected to the diode D1 at pin 6 (labeled as node 348 in Figure 3A and Figure 3B ). The trigger module 352 is used to force the input circuit 332 to have a lower input impedance by turning on the control element 338. The trigger module includes a control element 349 electrically connected to the electronic processor 240. The electronic processor 240 controls the state of the control element 349. The trigger module 352 can be connected to more than one instance of the input circuit 332.

[0055] During the steady-state operation of the electrical device 310, the contact switch 312 is closed. The electronic processor 240 is ready to operate the electrical device 310 that includes the contact switch 312. In other words, the electronic processor 240 is ready to generate a command signal that, when provided to the electrical device 310, will cause the contact switch 312 to open. In anticipation of opening the contact switch 312, the electronic processor 240 forces the input impedance of the input circuit 332 to be low to minimize the effect of noise on the conductors that electrically connect the input interface 335 to the contact switch 312.

[0056] To force the input impedance of the input circuit 332 to be low before the contact switch 312 is opened, the electronic processor 240 triggers the control element 349 to conduct. For example, the control element 349 can be an N-channel MOSFET, and the electronic processor 240 can cause a voltage sufficient to turn on the control element 349 to be provided to the gate of the MOSFET.

[0057] The electronic processor 240 turns on the control element 349, and the control element 349 forward biases the diode D1 at the node 348, thereby forcing the control element 338 to conduct. As a result, current can flow through the impedance module 337, causing the input impedance of the input circuit 332 to be low.

[0058] After the operation is completed (e.g., after the electrical device 310 has operated and the contact switch 312 has been opened), the electronic processor 240 disconnects the control element 349. As described above, the electronic processor 240 and the control element 349 can be electrically connected to more than one instance of the input circuit 332. Each instance of the input circuit 332 is electrically connected to at least one contact switch. Although the electronic processor 240 commands the electrical device 310 to operate such that the contact switch 312 is opened, some other contact switches in the electrical device 310 can remain closed. In an embodiment where all instances of the input circuit 332 are connected to the control element 349, when the control element 349 conducts, all input circuits 332 have a low impedance regardless of the state of the contact switches connected to the input circuits.

[0059] After the electronic processor 240 disconnects the control element 349, the input circuits connected to the open contact switches continue to have a low input impedance because current continues to flow through the impedance module 337. Specifically, when the contact switch 312 is opened, the output of the comparator U1 is low regardless of the state of the control element 349. The low output of the comparator U1 forward biases the diode D1 at the pin 5 and causes the control element 238 to remain conducting, allowing current to flow through the impedance module 337. Additionally, the low output of the comparator U1 causes the output of the transistor 347 to produce an indication of the open contact switch.

[0060] When the control element 349 is turned off, the input circuit connected to the closed contact switch has a high input impedance. Return Figure 3A As an example, when the contact switch 312 is closed, a current (e.g., about 70 milliamperes) flows through the contact switch 312. The resistor R7 discharges the capacitor C4 from V1 to zero (0) V. The negative input terminal ( Figure 3A pin 4 in the example) of the comparator U1 drops below the positive input terminal (pin 3) of the comparator U1, which causes the output of the comparator U1 to go high. When the output of the comparator U1 is high, the optocoupler U2 and the diode D1 at pin 5 are turned off. If the control element 349 ( Figure 3B ) is turned off or turned off by the electronic processor 240, the resistor R1 pulls the gate node of the control element 338 to V1, which causes the control element 338 to turn off. Therefore, current cannot flow through the impedance module 337, and current only flows through the impedance element 339. Therefore, the input impedance of the input circuit 332 is the impedance of the impedance element 339.

[0061] Also refer to Figure 3C , a schematic diagram of the leakage current detection module 370 is shown. The leakage current can be the current flowing to the ground terminal in the input wire (such as the wire at the input interface 335). The leakage current is the stray current that is not intended to be in the cable connecting the input circuit 332 to the electrical device 310. The presence of the leakage current can indicate existing or potential problems with the cable and / or the electrical device 310. For example, when moisture is in the cable, there may be a leakage current.

[0062] The leakage current detection module 370 is an example of an implementation of the leakage current detection module 170 (FIG. 1 and Figure 2 ). The leakage current detection module 370 is electrically connected to the input circuit 332 at the leakage current detection (LCD) node 372. In Figure 3A the input circuit 332 shown in the example, the node 372 corresponds to the source of the P-channel MOSFET 338. Although Figure 3A only one input circuit 332 is shown, more than one input circuit 332 can be used. In an implementation using more than one input circuit 332, the leakage current detection module 370 can be electrically connected to the LCD node 372 (the source of the P-channel MOSFET 338) of each input circuit 332. In other words, a single leakage current detection module 370 can be electrically connected to more than one instance of the input circuit 332. Other implementations are also possible. For example, in some implementations including more than one input circuit 332, each input circuit 332 is electrically connected to a separate leakage current detection module 370.

[0063] Refer to Figure 3A andFigure 3C In the example shown, when the contact switch 312 is open, the control element 338 conducts current. If there is a leakage current, the leakage current flows through the impedance module 337, through the LCD node 372, and into the leakage current detection module 370. The leakage current is measured at the output node 375 of the leakage current detection module 370.

[0064] The leakage current detection module 370 includes an electronic amplifier U3. In Figure 3C the example, the electronic amplifier U3 is an operational amplifier. However, the electronic amplifier U3 can be any electronic component or collection of electronic components associated with a gain and configured to amplify an input signal by the gain to produce an amplified output signal. The electronic amplifier U3 can be an analog electronic component that produces an amplified analog electrical output signal based on an analog electrical input signal.

[0065] The electronic amplifier U3 has an output terminal at pin 11, a positive input terminal at pin 12, and a negative input terminal at pin 13. The negative input terminal of the electronic amplifier U3 is connected to the LCD node 372 through a resistor R16 such that a leakage current detection voltage is sensed at the negative input terminal of the electronic amplifier U3. The output terminal of the electronic amplifier U3 is connected to the base 351 of a transistor Q3, which is an NPN bipolar junction power transistor (BJT) in Figure 3C the example. The positive input terminal of the electronic amplifier U3 is connected to V1 (e.g., 15V). The voltage of V1 is regulated by the electronic amplifier U3 and the transistor Q3. The electronic amplifier U3 senses the voltage of V1 on the left side of R16 and provides a bias to the transistor Q3 such that Q3 operates in class A mode to regulate the voltage of V1 to the same voltage level (V_f) as pin 12 of the electronic amplifier U3. In Figure 3B the example, the voltage level of pin 12 of the electronic amplifier U3 is labeled V_f and is +15V.

[0066] The voltage provided to the base of the transistor Q3 is sufficient to cause the transistor Q3 to operate in class A mode. In class A mode or in class A operation, the signal input to the base of the BJT is reproduced exactly at the emitter of the BJT. In Figure 3C the example, the emitter of the transistor Q3 is labeled 353. The leakage current detection module 370 further includes resistors R17 and R19, which are in parallel with each other and electrically connected to the LCD node 372. The parallel combination of the resistors R17 and R19 is also connected to the positive input terminal of an electronic amplifier U4 through resistors R22 and R23. In Figure 3CIn the example, the electronic amplifier U4 is an operational amplifier. However, the electronic amplifier U4 can be any electronic component or collection of electronic components associated with a gain and configured to amplify an input signal by the gain to produce an amplified output signal.

[0067] When the contact switch 312 is open and there is a leakage current from the input interface 335 to the base 311 due to moisture in the cable represented by the crack 325, current flows out of the node 372, through the resistor 337 to Figure 3A the base 311. This leakage current also flows from the emitter of Q3 through Figure 3B the resistors R17 and R19. This leakage current causes a voltage drop across R17 and R19, which is sensed by the electronic amplifier U4. The output signal of the electronic amplifier is converted to an appropriate offset and range such that an analog-to-digital (A / D) converter (not shown) can meter the leakage current at the node 375.

[0068] The current that flows as leakage current through the resistors R17 and R19 originates from the LCD node 372. The resistors R20, R18, R22, and R23 are configured such that the output of the electronic amplifier U4 fluctuates between a minimum voltage (0V) and a maximum voltage (V2) based on the amount of leakage current flowing through the parallel combination of the resistors R17 and R19. V2 can be, for example, 5V. When no current or very little current flows through the parallel combination of the resistors R17 and R19, the output of the electronic amplifier U4 is at V2. When a relatively large amount of leakage current flows through the parallel combination of the resistors R17 and R19, the output of the electronic amplifier U4 is 0V. Thus, an output of 0V from the electronic amplifier U4 indicates the presence of a leakage current. In some embodiments, an output of 0V from the electronic amplifier U4 indicates a leakage current of approximately 517 milliamperes (mA) flowing out of the LCD node 372. When the output of the electronic amplifier U4 is V2, there is no leakage current. An output value between 0V and V2 indicates the presence of an amount of leakage current greater than 0A but less than 517 mA.

[0069] The output of the electronic amplifier U4 can be provided to an analog-to-digital (A / D) converter (not shown) at the node 375. The A / D converter produces a digital signal having a value indicative of the amount of leakage current detected at the output of the electronic amplifier U4. The analog-to-digital converter can be, for example, a 12-bit analog-to-digital converter that produces a digital signal that can have 2048 different values to represent the amount of leakage current detected at the output of the electronic amplifier U4 as a function of time.

[0070] The leakage current detection module 370 also includes elements that do not directly participate in detecting the leakage current. In Figure 3CIn the example, the leakage current detection module 370 further includes a resistor network that includes resistors R11, R12, R13, and R14 connected in parallel. The resistor network is used for power dissipation.

[0071] Reference Figure 4 , a flowchart of an exemplary process 400 for metering leakage current is shown. Process 400 may be performed by the electronic processor 122 ( Figure 1A and Figure 1B ) and / or by the monitoring station 180 ( Figure 1A and Figure 1B ). Process 400 may be implemented as instructions stored at or downloaded to the control system 120 and / or the monitoring station 180 or may be a computer program. Process 400 is discussed for an example of nine instances where the leakage current detection module 370 ( Figure 3C ) is connected to the input circuit 332 ( Figure 3A ). The leakage current detection module 370 may be connected to more or fewer instances of the input circuit 332.

[0072] Each of the nine instances of the input circuit 332 is electrically connected to a contact switch in the three-phase recloser via a cable (such as, Figure 1A and Figure 1B cable 131). In other words, in the Figure 4 example, the electrical device 330 is a three-phase recloser. The three phases are referred to as phase A, phase B, and phase C. Each phase has three contact switches: switch 1, switch 2, and switch 3. Therefore, there are nine contact switches in the electrical device 330. The states (open or closed) of the contact switches for the Figure 4 example are shown in Table 1.

[0073] Phase Switch 1 Switch 2 Switch 3 A Closed Open Closed B Closed Open Open C Closed Open Closed

[0074] Process 400 begins by determining whether any of the input circuits in the input circuit 332 has a low impedance (405). An input circuit having a low impedance may be referred to as being in a low impedance mode. The input circuit 332 is in a low impedance mode when current can flow through the impedance module 337. The input circuit 332 is also in a low impedance mode when the contact switch connected to the input circuit 332 is open. The input circuit 332 is in a low impedance mode when the output of the comparator U1 is low. Therefore, it may be determined that the input circuit 332 is in a low impedance mode by measuring the output of the comparator U1 or by determining whether current is flowing in the impedance module 337.

[0075] In the example of Table 1, four instances of the input circuit 332 are in the low impedance mode. Specifically, the input circuits electrically connected to the contact switches 2_A, 2_B, 2_C, and 3_B are in the low impedance mode. When determining whether the input circuit 332 is in the low impedance mode, process 400 may also determine how many input circuits 332 are in the low impedance mode. In Figure 4 the example, four input circuits 332 are in the low impedance mode.

[0076] As described above, leakage current from the cable can be detected in the conductors connected to the open contact switches. If no contact switch is open, no leakage current is detected, and process 400 continues to determine whether any of the input circuits in the input circuit are in the low impedance mode and waits until a contact switch is open. In this example, four contact switches are open, and leakage current flows from the four input circuits connected to the open contact switches to the LCD node 372. A voltage value (410) associated with the leakage current flowing out of the LCD node 372 is obtained. For example, the voltage at the output of the electronic amplifier U4 can be measured. In another example, a signal from an analog-to-digital converter connected to the output of the electronic amplifier U4 is obtained.

[0077] Based on the obtained voltage value, the amount of leakage current is determined (415). The obtained voltage value can be any voltage value that depends on the amount of leakage current flowing in the leakage current detection module 370. For example, the output of the electronic amplifier U4 can be obtained. As described above, the output of the electronic amplifier U4 has a continuous range of possible voltage values, where each voltage value corresponds to the amount of leakage current. In another example, the output voltage of the electronic amplifier U4 can be provided to an analog-to-digital converter, which quantifies the analog voltage at the output of the electronic amplifier U4 into discrete voltage values. Each discrete voltage value in the discrete voltage values corresponds to the amount of leakage current. The correspondence between the voltage measured at the output of the electronic amplifier U4 and the amount of leakage current is known in advance and is based on the configuration of the leakage current detection module 370. For example, the values of the resistors R17 and R19 and the characteristics of the electronic amplifier U4 determine how the output voltage of the electronic amplifier U4 is related to the amount of leakage current flowing out of the LCD node 372.

[0078] In Figure 4 the example, the leakage current flowing out of the LCD node 372 is the leakage current from four conductors in the cable. Therefore, the leakage current determined based on the obtained voltage is the total leakage current originating from four instances of the input circuit 332. The total leakage current can be divided by the number of input circuits in the low impedance mode to determine the average leakage current per conductor. The amount of leakage current determined can be the total leakage current or the average leakage current per conductor.

[0079] Analyze the amount of leakage current (420) that has been determined. One or more characteristics of the leakage current can be determined. For example, the amplitude of the leakage current can be determined at a specific time or over a period of time. The average amount of leakage current can be determined over a period of time.

[0080] In some embodiments, the determined amount of leakage current is analyzed by comparing the amount of leakage current with a threshold. The threshold is a pre-determined value corresponding to the amount of leakage current, where it is known that the amount of leakage current indicates that the cable has a maintenance problem or will soon develop a maintenance problem. Additionally, the threshold can be a threshold based on the average amount of leakage current per conductor. The threshold can be stored on the electronic storage device 124 of the control system 120 ( Figure 1A and Figure 1B ). The electronic storage device 124 can be any type of electronic memory capable of storing data, and the electronic storage device 124 can include volatile and / or non-volatile components. The electronic storage device 124 is coupled to the electronic processor 122 such that the electronic processor 122 can access or read data from the electronic storage device 124 and can write data to the electronic storage device 124.

[0081] The analysis (420) of the determined amount of leakage current can include other techniques. For example, the amount of leakage current measured over a limited period of time (such as a day, a week, or a month) can be used for the analysis. Each amount of leakage current obtained at different times is a sample of the amount of leakage current measured at a specific time. In these embodiments, the analysis can include determining that a sufficient number of samples of the measured amount of leakage current exceed a pre-determined threshold and / or that the measured amount of leakage current repeatedly exceeds the pre-determined threshold within a predefined period of time. In some embodiments, pattern recognition or template matching techniques are used to identify a specific type of fault. For example, the leakage current over time can be analyzed to determine characteristics of the problem, such as an arc or a recurring maximum current with increasing frequency and amplitude (which indicates a blockage fault). These characteristics can be stored in the electronic storage device 124 of the control system 120 or at the monitoring station 180. The leakage current collected over time can be compared with these characteristics such that potential faults or maintenance problems can be detected and resolved early before damage occurs.

[0082] The determined amount of leakage current can be analyzed at the control system 120, or the determined amount of leakage current can be provided to the monitoring station 180 ( Figure 1A and 1B ) for analysis.

[0083] Regardless of the technique used to analyze the leakage current, if the analysis does not indicate that the amount of leakage current indicates the presence of moisture (e.g., if the determined amount of leakage current is less than a threshold), process 400 continues to monitor the leakage current and returns to (405). If the analysis indicates the presence of moisture (e.g., if the determined amount of leakage current is equal to or greater than the threshold), an error indication is generated (430). The error indication can be generated by, for example, electronic processor 240 and / or electronic processor 122 of control system 120, and can be presented at I / O interface 126 ( Figure 1A and Figure 1B ). I / O interface 126 can be any interface that allows a human operator and / or an autonomous process to interact with control system 120. I / O interface 126 can include, for example, a display, a keyboard, audio input and / or output (such as speakers and / or microphones), serial or parallel ports, universal serial bus (USB) connections, and / or any type of network interface, such as, for example, Ethernet. I / O interface 126 can also allow contactless communication, for example, via IEEE 802.11, Bluetooth, or near field communication (NFC) connections.

[0084] The error indication can be any type of perceptible warning, such as a sound, a flashing light, or a visual display presented on a computer screen that is part of I / O interface 126. In some embodiments, the error indication can be provided to a machine remote from input circuit 332. For example, the error indication can be in the form of an email or text message that is transmitted to a mobile device used by an operator of electrical device 330.

[0085] Reference Figure 5 shows a schematic diagram of input circuit 532. Input circuit 532 is Figure 3A another example of an embodiment of input circuit 332 of Figure 2 . Input circuit 532 can be used as any one or all of input circuits 232_1, 232_2... 232_N in input device 230 of Figure 1A and Figure 1B . Input circuit 532 can be used with or without one or more leakage current detection modules, such as leakage current detection module 170 ( Figure 3C and

[0086] Input circuit 532 is similar to that described above with respect to Figure 3AThe input circuit 332 described above. V1 in the input circuit 532 can be 24V. Instead of the optocoupler U2, the input circuit 532 includes an inverter U7, which is electrically connected to the output of the comparator U1 through a resistor network formed by resistors R21, R30, and R32. When the output of the comparator U1 is low, the output of the inverter U7 is high. When the output of the comparator U1 is high, the output of the inverter U7 is low. Therefore, when the contact switch 312 is open, the output of the inverter U7 is high, and the high output on the inverter U7 should indicate that the contact switch 312 is open. However, transient events (such as electromagnetic interference) can cause the output of the comparator U1 to erroneously go low and the inverter U7 to erroneously go high.

[0087] To reduce the false output, the inverter U7 is connected to a field-programmable gate array (FPGA) 544. The FPGA 544 includes logic programmed to evaluate whether the detected opening of the contact is due to an actual event on the distribution path 104 or a false reading. This logic can be referred to as a "debounce function". The debounce function samples the output of the inverter U7 at periodic intervals. For example, the FPGA 544 can sample the output value of the inverter U7 every 250 microseconds (µs). This logic compares the sample value with a pattern representing the actual transition value of the contact switch 312. A valid transition is one in which the contact switch 312 is open. A valid transition causes the output of the inverter U7 to go high (e.g., to 1) and remain 1 for a certain number of consecutive samples. On the other hand, an output of the inverter U7 that erroneously indicates that the contact switch 312 is open can appear as a single high reading followed by multiple consecutive zeros.

[0088] Immediately after obtaining the first sample that is high from the inverter U7, the debounce function starts a counter to track a predetermined number of subsequent values of the output of the inverter U7 and compares the sampled output values with a known pattern. Additionally, the FPGA 544 causes the electronic processor 240 to place the input circuit 532 in a low-impedance mode when the debounce function counter is enabled. In some embodiments, the FPGA 544 places the input circuit 532 directly in a low-impedance mode without using the electronic processor 240. As described with respect to Figure 3A and Figure 3BAs described, the trigger module 352 places the input circuit 532 in a low impedance mode by causing the control element 338 to conduct. Placing the input circuit 532 in a low impedance mode when collecting and analyzing the output of the inverter U7 allows the analysis of the output of the inverter U7 to be performed with minimal noise. The electronic processor 240 or the FPGA 544 places the input circuit 532 in a low impedance mode for at least a certain amount of time to determine whether the transition is a valid transition, and this certain amount of time is determined by the sampling rate and the number of samples collected. For example, in an embodiment where the sampling rate is 1 sample per 250 µs and the pattern of a valid transition is 1 followed by 11 consecutive 0s, the time for the bounce function to execute is (250 µs * 11) = 2.75 ms. The electronic processor 240 can extend the time during which the input circuit 532 is held in the low impedance mode for a longer time.

[0089] Figure 6 is a schematic diagram of the input circuit 632. The input circuit 632 is another example of an embodiment of the input circuit 132 ( Figure 1B ), and the input circuit 632 can be used as any one or all of the input circuits 232_1, 232_2... 232_N ( Figure 2 ). The input circuit 632 includes an input interface 635 electrically connected to the contact switch 612 via a cable 631. The contact switch 612 provides the state of an electrical device such as Figure 1A and Figure 1B the electrical device 110. When the contact switch 612 is open, the input circuit 632 provides a low input impedance, and when the contact switch 612 is closed, the input circuit provides a high input impedance. The input circuit 632 includes an impedance element 639 and an impedance module 637. The impedance element 639 is connected to the input interface represented as a single resistor 639. However, the impedance element 639 can be a collection of more than one resistor element arranged in any manner. When the contact switch 612 is closed, current flows into the input interface 635 (labeled as node 635) and into the impedance element 639. Therefore, when the contact switch 612 is closed, the input impedance of the input circuit 632 is the same as the impedance of the impedance element 639.

[0090] The input circuit 632 is similar to the input circuit 332 ( Figure 3A ) in that when current flows in the impedance module 637, the input impedance of the input circuit 632 decreases. When current flows in the impedance module 637, the impedance element 639 and the impedance module 637 are in parallel, and thus, the input impedance of the input circuit 632 decreases and the input circuit 632 is in a low impedance mode. However, in the input circuit 632, the impedance module 637 uses a constant current source and provides a variable impedance.

[0091] Figure 6 The impedance module 637 shown includes two resistors R63 and R64 connected in series with each other. Resistor R63 is connected to the drain 667 of transistor 638. In Figure 6 the example shown, transistor 638 is a P-channel MOSFET. The gate of transistor 638 is connected to diode arrangement D60. Pin 2 of diode arrangement D60 is connected to output pin 12 of inverter 670. Pin 1 of diode arrangement D60 is connected to trigger module 352 ( Figure 3B ). To place the input circuit 632 in the low impedance mode, the voltage at gate 646 is controlled such that transistor 638 operates in class A mode (or in linear mode) and current flows through impedance module 637. In this configuration, transistor 638 forms a constant current source with an impedance that depends on the voltage at gate 646.

[0092] When contact switch 612 is open, the input circuit 632 is placed in the low impedance mode. When contact switch 612 is open, impedance module 637 pulls node 635 up to V1, and current flows through resistor R60, which charges capacitor C61 to V1. Inverter 670 has the characteristic that when pin 13 is at V1, the output of inverter 670 is low. The low output of inverter 670 forward-biases the diode at pin 2, which causes transistor 638 to transition from off to class A or linear mode. Thus, current flows in transistor 638 and through impedance module 637. Additionally, current also flows in impedance element 639, which is arranged in parallel with impedance module 637 when transistor 638 is not in the off state. Thus, the input impedance of input circuit 632 is reduced to impedance module 637, which is in series with the variable impedance of transistor 638, which is in parallel with impedance element 639. Additionally, even when contact switch 612 is closed by providing a trigger from trigger module 352, transistor 638 can be forced from the off state into class A mode.

[0093] Other embodiments are within the scope of the claims.

Claims

1. A system for an electric power distribution network, the system comprising: an electrical device configured to monitor or control one or more aspects of the electric power distribution network, the electrical device including a contact switch configured to open and close; an input device, the input device including: an impedance module; and an input interface electrically connected to the impedance module and the contact switch of the electrical device, wherein the input interface is configured to have one of a plurality of input impedances, the plurality of input impedances including at least a first input impedance and a second input impedance lower than the first input impedance, and wherein the input interface has the second input impedance when the contact switch of the electrical device is open; a control cable including a conductor electrically connecting the input interface and the contact switch; and a leakage current detection module electrically coupled to the impedance module, the leakage current detection module configured to provide an indication of the amount of current flowing in the conductor.

2. The system according to claim 1, wherein the input interface includes a first impedance element and the impedance module includes a second impedance element, and when the contact switch of the electrical device is open, current flows through the first impedance element and the second impedance element such that the input interface has the second input impedance.

3. The system according to claim 2, wherein the impedance module further includes an electronic switch associated with a first state and a second state, the electronic switch conducting current in the first state and not conducting current in the second state, wherein current flows in the second impedance element only when the electronic switch is in the first state.

4. The system according to claim 3, wherein the input device further includes an electronic processor configured to provide a signal to the electronic switch, the signal sufficient to transition the electronic switch to the first state such that the input interface has the second input impedance even when the contact switch of the electrical device is closed.

5. The system according to claim 4, wherein the electronic processor coupled to the impedance module is configured to generate the signal prior to an expected opening of the contact switch.

6. The system according to claim 5, wherein, after the expected opening of the contact switch, the electronic processor is further configured to cause the electronic switch to transition to the second state such that if the contact switch of the electrical device is closed, the input interface has the first input impedance.

7. The system according to claim 1, wherein the electrical device includes a plurality of contact switches, the control cable includes a plurality of conductors, each of the conductors connected to one of the plurality of contact switches, The input device includes a plurality of impedance modules and a plurality of input interfaces, each of the input interfaces being electrically connected to one of the conductors, each of the impedance modules being electrically connected to one of the plurality of input interfaces, and all of the impedance modules are electrically connected to the leakage current detection module.

8. The system according to claim 1, wherein the electrical device includes a plurality of contact switches, the control cable includes a plurality of conductors, each of the conductors being connected to one of the plurality of contact switches, the input device includes a plurality of impedance modules and a plurality of input interfaces, each of the input interfaces being electrically connected to one of the conductors, each of the impedance modules being electrically connected to one of the plurality of input interfaces, the input device includes a plurality of leakage current detection modules, and each of the impedance modules is electrically connected to one of the leakage current detection modules.

9. The system according to claim 1, wherein the electrical device is a recloser or a voltage regulator.

10. The system according to claim 1, wherein an indication of the amount of current flowing in the conductor includes the measured amount of leakage current flowing in the conductor, and the system further includes an electronic processor configured to: analyze the measured amount of leakage current to determine one or more characteristics of the leakage current; determine whether moisture is present in the cable based on the analysis; and generate an indication of an error if it is determined that moisture is present in the cable.

11. An input device, the input device comprises: a plurality of input interfaces, each of the input interfaces being configured to be electrically connected to a contact switch of an electrical device that monitors or controls one or more aspects of a power distribution network, wherein each of the input interfaces is configured to have one of a plurality of impedances, the plurality of impedances including at least a first input impedance or a second input impedance, the second input impedance being lower than the first input impedance; a plurality of impedance modules, each impedance module being connected to one of the plurality of input interfaces, wherein when current flows through the impedance module connected to each input interface, the input interface has the second input impedance; and one or more leakage current detection modules, wherein each of the one or more leakage current detection modules is electrically connected to one of the impedance modules and is configured to measure the amount of current flowing out of the one impedance module of the impedance modules.

12. The input device according to claim 11, wherein: the input interface is configured to receive N conductors, N is an integer greater than 1, the input device includes N leakage current detection modules, and each of the N leakage current detection modules is configured to measure the leakage current flowing in one of the N conductors.

13. The input device according to claim 11, Wherein: The input interface is configured to receive N conductors, where N is an integer greater than 1, the input device includes a leakage current detection module, and the leakage current detection module is configured to measure a leakage current flowing in any one of the N conductors.

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