Power receiving system and ground fault overcurrent relay

Abstract

To avoid an unnecessary operation of a ground fault overcurrent relay while reducing component cost and design man hour.SOLUTION: A power reception system comprises: a disconnector 89R_2; a grounding device ES; and a ground fault overcurrent relay 51GR. The ground fault overcurrent relay 51GR detects ground fault overcurrent on a distribution line DL. The ground fault overcurrent relay 51GR comprises: first input; second input; and a signal output circuit. The first input receives a first signal showing a detection result of unbalanced current on the distribution line DL. The second input receives a second signal showing an opening / closing state of the disconnector 89R_2. The signal output circuit generates an output signal having a first logical value showing detection of ground fault overcurrent, or a second logical value showing non-detection of ground fault overcurrent according to the first signal and the second signal. The signal output circuit generates an output signal having the first logical value when the first signal shows presence of unbalanced current and the second signal is the one related to a closed state of the disconnector.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a power receiving system and a ground fault overcurrent relay.

Background Art

[0002] Equipment of power consumers such as factories (consumer equipment) is generally provided with a circuit breaker, a grounding device, and a ground fault overcurrent relay. The circuit breaker is connected to a distribution line. The grounding device is connected between the distribution line and the ground. The distribution line is connected to a circuit breaker of equipment of an electric power company (for example, substation equipment). The ground fault overcurrent relay is configured to detect a ground fault overcurrent based on an unbalanced current in the distribution line. During inspection of the consumer equipment, after the above circuit breaker and the breaker are opened, the grounding device of the consumer equipment may be switched on (closed). In this case, the residual charge of the distribution line may be discharged, and a current may flow from the distribution line through the grounding device to the ground. At that time, an unbalanced current may flow in the distribution line. As a result, although no actual ground fault has occurred, the ground fault overcurrent relay may operate unnecessarily in response to the unbalanced current.

[0003] Non-Patent Document 1 discloses a circuit for preventing unnecessary operation of the above ground fault overcurrent relay (also referred to as "ground fault protection relay"). According to this circuit, a canceling ground wire is added to the circuit before countermeasures when the distribution line is an overhead line, or an auxiliary current transformer (CT) is added when the distribution line is an underground cable.

Prior Art Documents

Non-Patent Documents

[0004] <00000,​​​"Regarding Equipment Design for Grid Connection," pp. V14-V15, Tokyo Electric Power Grid Co., Ltd., [online], April 1, 2020, [Retrieved August 2, 2023], Internet<URL: https: / / www.tepco.co.jp / pg / consignment / rule-tr-dis / pdf / setuse2-j.pdf> [Overview of the project] [Problems that the invention aims to solve]

[0005] The countermeasure circuit described in Non-Patent Document 1 requires additional components such as a cancellation earth wire or auxiliary current transformer, which could lead to increased component costs. In addition, the circuit configuration must be modified depending on the type of power distribution line. As a result, various design man-hours become more complex, potentially increasing costs.

[0006] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a power receiving system and a ground fault overcurrent relay that reduce component costs and design man-hours while avoiding unnecessary operation of the ground fault overcurrent relay. [Means for solving the problem]

[0007] A power receiving system according to a certain aspect of this disclosure comprises a disconnector, a grounding device, and a ground fault overcurrent relay. The disconnector is connected to a distribution line receiving power from a three-phase AC power source. The grounding device is connected between the distribution line and the earth. The ground fault overcurrent relay is configured to detect ground fault overcurrents in the distribution line. The ground fault overcurrent relay includes a first input, a second input, and a signal output circuit. The first input receives a first signal indicating the detection result of an unbalanced current in the distribution line. The second input receives a second signal, which is a signal related to the open / closed state of the disconnector. The signal output circuit generates an output signal having a first value indicating the detection of a ground fault overcurrent, or a second value indicating the non-detection of a ground fault overcurrent, according to the first and second signals. If the first signal indicates the presence of an unbalanced current and the second signal is a signal related to the closed state of the disconnector, the signal output circuit generates an output signal having a first value.

[0008] A power receiving system according to other aspects of this disclosure comprises a disconnector, a grounding device, and a ground fault overcurrent relay. The disconnector is connected to a distribution line receiving power from a three-phase AC power source. The grounding device is connected between the distribution line and the earth. The ground fault overcurrent relay is configured to detect ground fault overcurrents in the distribution line. The ground fault overcurrent relay includes a first input, a second input, and a signal output circuit. The first input receives a first signal indicating the result of detecting an unbalanced current in the distribution line. The second input receives a second signal, which is a signal related to the open / closed state of the grounding device. The signal output circuit generates an output signal having a first value indicating the detection of a ground fault overcurrent, or a second value indicating the non-detection of a ground fault overcurrent, according to the first and second signals. If the first signal indicates the presence of an unbalanced current and the second signal is not a signal related to the closing of the grounding device, the signal output circuit generates an output signal having the first value.

[0009] A ground fault overcurrent relay according to a certain aspect of the present disclosure is configured to detect a ground fault overcurrent in a distribution line receiving power from a three-phase AC power source. A disconnector is connected to the distribution line. A grounding device is connected between the distribution line and the ground. The ground fault overcurrent relay comprises a first input, a second input, and a signal output circuit. The first input receives a first signal indicating the detection result of an unbalanced current in the distribution line. The second input receives a second signal, which is a signal related to the open / closed state of the disconnector. The signal output circuit generates an output signal having a first value indicating the detection of a ground fault overcurrent, or a second value indicating the non-detection of a ground fault overcurrent, according to the first and second signals. If the first signal indicates the presence of an unbalanced current and the second signal is a signal related to the closed state of the disconnector, the signal output circuit generates an output signal having the first value.

[0010] A ground fault overcurrent relay according to other aspects of this disclosure is configured to detect a ground fault overcurrent in a distribution line receiving power from a three-phase AC power source. A disconnector is connected to the distribution line. A grounding device is connected between the distribution line and the ground. The ground fault overcurrent relay comprises a first input, a second input, and a signal output circuit. The first input receives a first signal indicating the detection result of an unbalanced current in the distribution line. The second input receives a second signal, which is a signal related to the open / closed state of the grounding device. The signal output circuit is configured to generate an output signal having a first value indicating the detection of a ground fault overcurrent, or a second value indicating the non-detection of a ground fault overcurrent, according to the first and second signals. If the first signal indicates the presence of an unbalanced current and the second signal is not a signal related to the closing of the grounding device, the signal output circuit generates an output signal having the first value. [Effects of the Invention]

[0011] According to this disclosure, it is possible to reduce component costs and design man-hours while avoiding unnecessary operation of ground fault overcurrent relays. [Brief explanation of the drawing]

[0012] [Figure 1] This is an overall configuration diagram of the power transmission and distribution system in Embodiment 1. [Figure 2] This diagram shows in detail an example of the configuration of a current transformer, overcurrent relay, and ground fault overcurrent relay. [Figure 3] This diagram shows an example of the configuration of a voltage divider, interlock circuit, and ES control circuit. [Figure 4] This figure shows an example of a circuit configuration to prevent unwanted operation of a ground fault overcurrent relay. [Figure 5] This diagram shows the configuration of a ground fault overcurrent relay according to a modified example of Embodiment 1. [Figure 6] This diagram shows the configuration of a ground fault overcurrent relay according to Embodiment 2. [Figure 7] This diagram shows the configuration of a ground fault overcurrent relay according to a modified example of Embodiment 2. [Figure 8] This diagram illustrates the configuration of the current transformer in other variations. [Modes for carrying out the invention]

[0013] Embodiments of this disclosure will be described in detail below with reference to the drawings. The same or corresponding parts in the drawings will be denoted by the same reference numerals and their descriptions will not be repeated. Each embodiment and its modifications may be combined with one another as appropriate.

[0014] [Embodiment 1] Figure 1 is an overall diagram of the power transmission and distribution system in Embodiment 1. Referring to Figure 1, the power transmission and distribution system 1 comprises a grid power source 10, a substation 20, and a power receiving facility 30.

[0015] The grid power supply 10 is a three-phase AC power supply and is connected to the transmission line TL. The substation equipment 20 is installed within the management area A1 of the power company and is, for example, a transformer (not shown). The substation equipment 20 steps down the power of the transmission line TL and supplies the stepped-down power to the distribution line DL. The distribution line DL has three phases consisting of the first phase, the second phase, and the third phase, and receives power from the grid power supply 10 through the substation equipment 20. The substation equipment 20 includes a circuit breaker 89R_1 and a disconnector 52_1. The circuit breaker 89R_1 is operated to open the circuit when no load current is flowing in the circuit. The disconnector 52_1 is provided to cut off the circuit when an overcurrent is flowing in the circuit.

[0016] The power receiving equipment 30 is customer equipment provided in the customer's management area A2, which is a factory in this example. The power receiving equipment 30 includes a current transformer CT, an overcurrent relay 51R, a ground fault overcurrent relay 51GR, a signal line SL1, an OR circuit 200, and a data collection device 250. The power receiving equipment 30 further includes circuit breakers 89R_2, 89F1~89F3, a grounding device ES, a voltage divider VD, an interlock circuit 300, and an ES operation circuit 400. The power receiving equipment 30 further includes disconnectors 52_2, 52F1~52F3, feeders F1~F3, and electrical loads L1~L3.

[0017] A voltage divider VD is connected to the distribution line DL, a grounding device ES is connected via the current transformer CT, and is connected to the load-side feeders F1~F3 via the circuit breaker 89R_2 and the disconnector 52_2. Circuit breakers 89F1~89F3, disconnectors 52F1~52F3, and electrical loads L1~L3 are respectively connected to the feeders F1~F3.

[0018] The current transformer CT reacts to the magnetic field formed by the current flowing in the distribution line DL (primary side) and converts this current into a current of a smaller magnitude (secondary side). The secondary side of the current transformer CT is connected to each of the overcurrent relay 51R and the ground fault overcurrent relay 51GR.

[0019] The overcurrent relay 51R is configured to detect an overcurrent flowing through the distribution line DL. Specifically, the overcurrent relay 51R includes a sensor (not shown) that measures the current converted by the current transformer CT (the current on its secondary side), and detects an overcurrent flowing through the distribution line DL when the measured value is greater than a predetermined value. The overcurrent relay 51R generates an output signal OSr indicating the detection result of the overcurrent. When the measured value is greater than the predetermined value, the output signal OSr has a first logical value indicating the detection of the overcurrent. When the measured value is less than or equal to the predetermined value, the output signal OSr has a second logical value indicating the non-detection of the overcurrent. In the following description, let "1" (logical H level) be the first logical value and "0" (logical L level) be the second logical value.

[0020] The earth fault overcurrent relay 51GR is configured to detect an earth fault overcurrent in the distribution line DL. The earth fault overcurrent relay 51GR generates an output signal OSg indicating the detection result of the earth fault overcurrent. When an earth fault overcurrent is detected, the output signal OSg has a value (in this example, "1") indicating the detection of the earth fault overcurrent. When no earth fault overcurrent is detected, the output signal OSr has a value (in this example, "0") indicating the non-detection of the earth fault overcurrent. The earth fault overcurrent relay 51GR is connected through the output of the auxiliary contact SC of the circuit breaker 89R_2 and the signal line SL1 (described later). The configurations of the current transformer CT, the overcurrent relay 51R, and the earth fault overcurrent relay 51GR will be described in detail later.

[0021] The OR circuit 200 takes the logical sum of the output signals OSr and OSg and generates a trip command TRI based on the result of the logical sum. Specifically, when at least one of the logical values of the output signals OSr and OSg is 1, the OR circuit 200 generates a trip command TRI. The trip command TRI is generated to trip the circuit breaker 52_2 (described later) of the power receiving facility 30. The data collection device 250 collects the logical values of the output signals OSr and OSg and records the history of the collected values.

[0022] The disconnector 89R_2 includes a main contact MC and an auxiliary contact SC. The main contact MC is connected to the distribution line DL. The main contact MC is opened and closed to open the circuit when no load current is flowing through the distribution line DL. In this example only one main contact MC is illustrated, but in reality the circuit breaker 52_2 includes three main contact MCs, each connected to the first, second, and third phases of the distribution line DL.

[0023] The auxiliary contact SC switches in conjunction with the main contact MC. Therefore, the open / closed state of the auxiliary contact SC reflects the open / closed state of the main contact MC. The auxiliary contact SC is provided, for example, to switch the illumination and de-illumination of a lamp (not shown) that indicates the open / closed state of the main contact MC. This lamp is provided to inform the user of the open / closed state of the main contact MC. In the embodiment shown in Figure 1, a signal line SL1 extends from the auxiliary contact SC. The signal line SL1 is arranged between the auxiliary contact SC and the ground fault overcurrent relay 51GR.

[0024] Furthermore, there may be multiple auxiliary contacts that are linked to the main contact MC of the disconnector 89R_2. For example, contact 303 in Figure 3, which will be described later, is an auxiliary contact that is linked to the main contact MC and is electrically isolated from the auxiliary contact SC.

[0025] The grounding device ES is located downstream of the current transformer CT and is connected between the distribution line DL and the ground. It is switched on (closed) when the power receiving equipment 30 is inspected.

[0026] The voltage divider VD is installed on the distribution line DL and generates a signal indicating the presence or absence of voltage on the distribution line DL. The interlock circuit 300 is installed to prevent accidental activation of the grounding device ES. It prevents activation (operation) of the grounding device ES when the disconnector 89R_2 is closed or when the signal indicating the presence or absence of voltage on the distribution line DL indicates that there is voltage on the distribution line DL. When this signal indicates that there is no voltage on the distribution line DL, the grounding device ES can be activated by user operation. The interlock circuit 300 is connected to the ES operation circuit 400. The configuration of the interlock circuit 300 and the ES operation circuit 400 will be explained in detail later.

[0027] Circuit breaker 52_2 is connected to feeders F1 to F3 and trips (interrupts the circuit) in response to the trip command TRI. Disconnector 89F1 and circuit breaker 52F1 are installed between feeder F1 and electrical load L1. Disconnector 89F2 and circuit breaker 52F2 are installed between feeder F2 and electrical load L2. Disconnector 89F3 and circuit breaker 52F3 are installed between feeder F3 and electrical load L3.

[0028] Figure 2 is a detailed diagram illustrating an example configuration of a current transformer CT, an overcurrent relay 51R, and a ground fault overcurrent relay 51GR. Figure 2 shows an example in which the current transformer CT is composed of a two-phase current transformer and a zero-phase current transformer.

[0029] Referring to Figure 2, the current transformer CT includes a first-phase current transformer CTa, a third-phase current transformer CTc, and a zero-sequence current transformer ZCT. The first-phase current transformer CTa converts the current flowing through the first phase of the distribution line DL into a smaller current. The third-phase current transformer CTc converts the current flowing through the third phase of the distribution line DL into a smaller current. The zero-sequence current transformer ZCT is configured to detect the zero-sequence current, which is the unbalanced current between the three phases of the distribution line DL.

[0030] The overcurrent relay 51R includes auxiliary current transformers ACTa and ACTc, level detectors LDa and LDc, and an OR circuit CR.

[0031] The auxiliary current transformers ACTa and ACTc are located on the secondary side of the first phase current transformer CTa and the third phase current transformer CTc, respectively. The auxiliary current transformers ACTa and ACTc convert the current flowing on the secondary side of the first phase current transformer CTa and the third phase current transformer CTc into a smaller current.

[0032] The level detectors LDa and LDc each generate a signal with a logical value of "1" when the magnitude of the current converted by the auxiliary current transformers ACTa and ACTc is greater than a predetermined value. The level detectors LDa and LDc each generate a signal with a logical value of "0" when the magnitude of the current converted by the auxiliary current transformers ACTa and ACTc is less than or equal to a predetermined value.

[0033] The OR circuit CR takes the logical OR of the logical values ​​of the signals generated by the level detectors LDa and LDc, and generates the output signal OSr based on the result of the logical OR. For example, if at least one of the logical values ​​of the signals generated by these detectors is "1", the output signal OSr has a logical value of "1". On the other hand, if both logical values ​​of the signals generated by these detectors are "0", the output signal OSr has a logical value of "0".

[0034] The ground fault overcurrent relay 51GR includes an auxiliary current transformer ACTz, a level detector 105, a NOT circuit 110, and an AND circuit 115.

[0035] The auxiliary current transformer ACTz is located on the secondary side of the zero-sequence current transformer ZCT, and converts the current flowing on this secondary side into a smaller current.

[0036] The level detector 105 includes a sensor (not shown) that measures the current after conversion by the auxiliary current transformer ACTz (the current on its secondary side), and generates a signal SG1 based on the measurement value of this sensor. The signal SG1 indicates the detection result of an unbalanced current in the distribution line DL, and specifically has a logical value of "1" or "0". An unbalanced current is the unbalanced component of the three-phase alternating current. When the magnitude of the unbalanced current after conversion is greater than a threshold, the level detector 105 generates a signal SG1 with a logical value of "1". This signal SG1 indicates the presence of an unbalanced current (the three-phase alternating current is not in a balanced state). On the other hand, when the magnitude of the current after conversion is less than or equal to the threshold, the level detector 105 generates a signal SG1 with a logical value of "0". This signal SG1 indicates the absence of an unbalanced current (the three-phase alternating current is in a balanced state). Signal SG1 corresponds to an example of the "first signal" of this disclosure.

[0037] The NOT circuit 110 receives signal SG02 transmitted via signal line SL1 from the operating circuit of disconnector 89R_2, and generates signal SG2 as its inverted signal. Signal SG02 is output from the auxiliary contact SC of disconnector 89R_2. Signal SG02 indicates the open / closed state of disconnector 89R_2. More specifically, since signal SG02 indicates the open / closed state of auxiliary contact SC, it also indicates the open / closed state of main contact MC. Signal SG02 has a logical value of "0" when main contact MC is closed, and a logical value of "1" when main contact MC is open.

[0038] Signal SG2, like signal SG02, indicates the open / closed state of the disconnector 89R_2 (main contact MC). Signal SG2 has a logical value of "1" when the main contact MC is closed, and a logical value of "0" when the main contact MC is open. Signal SG2 corresponds to an example of the "second signal" in this disclosure.

[0039] The AND gate 115 includes a first input 113 and a second input 114. The first input 113 is configured to receive signal SG1. The second input 114 is configured to receive signal SG2.

[0040] The AND circuit 115 takes the logical AND of signals SG1 and SG2 and generates an output signal OSg according to the result of the logical AND. The output signal OSg indicates the detection result of ground fault overcurrent in the distribution line DL, and specifically has a logical value of "1" or "0". If the output signal OSg has a logical value of "1", it indicates the detection of ground fault overcurrent. On the other hand, if the output signal OSg has a logical value of "0", it indicates the non-detection of ground fault overcurrent. The AND circuit 115 generates the output signal OSg according to signals SG1 and SG2. For example, if both logical values ​​of signals SG1 and SG2 are "1", the AND circuit 115 generates an output signal OSg with a logical value of "1". On the other hand, if at least one of the logical values ​​of signals SG1 and SG2 is "0", the AND circuit 115 generates an output signal OSg with a logical value of "0". The AND circuit 115 corresponds to an example of a "signal output circuit" in this disclosure.

[0041] Figure 3 shows an example of the configuration of the voltage divider VD, the interlock circuit 300, and the ES control circuit 400.

[0042] Referring to Figure 3, the voltage divider VD is installed on the distribution line DL and has stray capacitances C1A, C1B, and C1C for each of the three phase lines of the distribution line DL and the detection point Pvd. The voltage divider VD includes a resistor R. The resistor R is the resistance between the detection point Pvd and the ground point, and the detection point Pvd side of the resistor R is connected to the core wire side of the coaxial cable described later and connected to the power line pair.

[0043] The coaxial cable CBL includes a power line pair connected to both ends of resistor R and interfaces between the interlock circuit 300 and the voltage divider VD. The coaxial cable CBL has a stray capacitance C2. The ground side of the power line pair of resistor R is connected to the outer conductor side of coaxial cable CBL. When the distribution line DL is connected to the grid power supply 10, if the grid power supply 10 is in an ideal three-phase balanced state and the stray capacitances C1A, C1B, and C1C are perfectly equal, the terminal voltage of resistor R will be zero. However, in reality, it is not always perfectly balanced, and the stray capacitances C1A, C1B, and C1C are not perfectly equal. Therefore, when the distribution line DL is connected to the grid power supply 10, an AC voltage will be detected at detection point Pvd. Generally, the discharge time constant of the stray capacitance C1 and the resistor R is sufficiently large compared to the surrounding commercial frequency. Therefore, when the distribution line DL is connected to the grid power supply 10, the voltage of the distribution line DL will appear between the terminals of the resistor R as a voltage divider between the stray capacitances C1A, C1B, C1C and the stray capacitance C2. Also, when the distribution line DL is not connected to the grid power supply 10, the voltage between the terminals of the resistor R will no longer be detectable after a time sufficiently longer than the discharge time constant of the stray capacitance C1 and the resistor R has elapsed. In this way, the voltage detection device 302 can detect the voltage between the terminals of the resistor R and determine whether or not the distribution line DL is connected to the grid power supply 10.

[0044] The interlock circuit 300 includes a voltage detection device 302 and a contact 303. The voltage detection device 302 includes a voltage detection circuit 305, a transistor 315, a relay 317, and an interlocking contact 320 for the relay 317. The grounding device ES is electrically operated and is closed by driving a motor 415. One end of the contact 303 is connected to the power supply PS1 for driving the motor 415, and the other end is connected to one end of the interlocking contact 320, and one end of the interlocking contact 320 is connected to one end of the closing operation switch 380. The other end of the closing operation switch 380 is connected to the motor 415 via the contact 405 and is also connected to the ES operation auxiliary relay 390. In other words, the interlock circuit is formed by connecting the contact 303, the interlocking contact 320 and the closing operation switch 380 in series.

[0045] The voltage detection circuit 305 detects the voltage of the power distribution line DL by detecting the potential difference across the resistor R (voltage due to stray capacitance C2). The voltage detection circuit 305 includes an amplifier 335, a comparator 340, an off-delay circuit 345, an on-delay circuit 347, and a NOT gate 350.

[0046] Amplifier 335 receives the voltage (AC voltage) from the power line pair of the coaxial cable CBL as the output of voltage divider VD and amplifies this voltage. Comparator 340 compares the amplified voltage with a threshold voltage. Comparator 340 generates its output signal based on the result of the comparison. For example, if the amplified voltage is greater than or equal to the threshold voltage, the output signal has a logical value of "1". On the other hand, if the amplified voltage is less than the threshold voltage, the output signal has a logical value of "0". Since the input signal to comparator 340 is an AC voltage, the output signal of comparator 340 is a pulse signal at commercial frequency.

[0047] The off-delay circuit 345 converts the pulse signal from the comparator 340 into a continuous signal and generates this continuous signal as an output signal. The delay time of the off-delay circuit 345 is longer than the period of the AC voltage mentioned above. The output signal of the off-delay circuit 345 indicates the presence or absence of voltage in the distribution line DL, and specifically has a logical value of "1" or "0". This output signal has a logical value of "0" when it indicates that there is no voltage in the distribution line DL, and a logical value of "1" when it indicates that there is voltage in the distribution line DL. The off-delay circuit 345 is a retriggerable circuit.

[0048] The on-delay circuit 347 is configured to receive the output signal of the off-delay circuit 345 via the NOT circuit 350 and to delay this input signal. "Delaying" means generating an output signal that rises a reference time (delay time) after the rising edge of the input signal. As long as the input signal does not rise, the on-delay circuit 347 generates the same output signal as the input signal. This output signal indicates the presence or absence of voltage in the distribution line DL and, like the output signal of the off-delay circuit 345, has a logical value of "1" or "0". The off-delay circuit 345 and the on-delay circuit 347 are retriggerable circuits. Therefore, the output of the off-delay circuit 345 continuously has a logical value of "1" when the grid power supply 10 is connected to the distribution line DL, and continuously has a logical value of "0" when the grid power supply 10 is not connected to the distribution line DL.

[0049] The NOT circuit 350 receives the output signal of the off-delay circuit 345 as an input signal and transmits the inverted signal of this input signal to the control electrode (e.g., base) of the transistor 315 via the on-delay circuit 347.

[0050] The output signal of the off-delay circuit 345 is also referred to as signal SG3. Signal SG3 indicates the presence or absence of voltage in the power distribution line DL. Specifically, signal SG3 has a logical value of "1" when it indicates the presence of voltage in the power distribution line DL, and a logical value of "0" when it indicates the absence of voltage in the power distribution line DL. In this way, the voltage detection circuit 305 generates signal SG3 according to the output of the voltage divider VD. Signal SG3 is an example of the "third signal" of this disclosure.

[0051] Transistor 315 is used, for example, in an open collector configuration. One end of the excitation coil of relay 317 is connected to the power supply PS0 of the control circuit, and the other end is connected to the collector of transistor 315. Transistor 315 is turned on or off depending on whether the output signal of the on-delay circuit 347 has a logic value of "1" or "0" (whether or not there is voltage on the power distribution line DL). If there is no voltage on the power distribution line DL, this output signal has a logic value of "1", so transistor 315 is in the on state (conducting state). As a result, relay 317 is in the excited state. If there is voltage on the power distribution line DL, the output signal of the on-delay circuit 347 has a logic value of "0", so transistor 315 is in the off state (not conducting state). As a result, relay 317 is in the de-excited state.

[0052] The interlocking contact 320 of relay 317 is switched on and off according to the state of relay 317. Specifically, when relay 317 is energized (when there is no voltage on the power distribution line DL), the interlocking contact 320 of relay 317 is in the closed state. On the other hand, when relay 317 is de-energized (when there is voltage on the power distribution line DL), the interlocking contact 320 of relay 317 is in the open state.

[0053] The on-delay circuit 325 is configured to receive signal SG3 as an input signal and perform an on-delay. "On-delay" means generating an output signal that rises a predetermined time (delay time) after the rising edge of the input signal. That is, when the input signal changes from "0" to "1", the on-delay circuit 325 changes from "0" to "1" after the predetermined delay time. When the input signal changes from "1" to "0", the on-delay circuit 325 changes its output from "1" to "0" without delay in principle. As long as the input signal does not change, the on-delay circuit 325 generates an output signal that is the same as the input signal.

[0054] The off-delay circuit 330 is configured to receive signal SG3 as an input signal through the on-delay circuit 325, perform an off-delay, and transmit signal SG4 to the ground fault overcurrent relay 51GR through the signal line SL2. Signal SG4 is generated according to signal SG3 and indicates the presence or absence of voltage in the distribution line DL. Signal SG4 is an example of the "fourth signal" of this disclosure. "Off-delaying" corresponds to generating an output signal that falls after a predetermined time (delay time) from the falling edge of the input signal. That is, when the input signal changes from "1" to "0", the off-delay circuit 330 changes from "1" to "0" after a predetermined delay time. When the input signal changes from "0" to "1", the off-delay circuit 330 changes the output from "0" to "1" without delay in principle. As long as the input signal does not change, the off-delay circuit 345 generates the same output signal as the input signal. The delay time of the on-delay circuit 325 is determined appropriately by prior evaluation tests based on the time from when the grounding device ES is turned on until the discharge of residual charge in the distribution line DL is completed, so that the unwanted operation prevention effect shown in Figure 5 described later is activated when an unbalanced current is generated when the grounding device ES is turned on, and the delay time is longer than the time until the discharge is completed. In this example, the delay time is longer than 0 seconds and shorter than 1 second. The on-delay circuit 325 and the off-delay circuit 330 correspond to an example of a "signal transmission circuit" (signal generation circuit) in this disclosure. The function of the off-delay circuit 330 will be described in detail later.

[0055] Contact 303 is an auxiliary contact for disconnector 89R_2, which closes in conjunction with disconnector 89R_2 (main contact MC) when disconnector 89R_2 is open, and opens in conjunction with disconnector 89R_2 when disconnector 89R_2 is closed.

[0056] The on / off switch 380 is operated to open and close the grounding device ES (Figure 1). Contact 385 is the interlocking contact of the ES operation assist relay 390, which is turned on and off in conjunction with the ES operation assist relay 390.

[0057] Contact 405 is a limit switch that is linked to the grounding device ES. It is closed when the grounding device ES is open and opens when the closing is complete.

[0058] When both contact 303 and interlocking contact 320 are closed, the motor 415 operates when the closing operation switch 380 is closed, and as a result the grounding device ES closes. At the same time, the ES operation auxiliary relay 390 operates and contact 385 is turned on. As a result, a closing command ON_INS is generated, indicating that a command to close the grounding device ES has been issued. Contact 405 opens when the grounding device ES is closed, stopping the operation of the motor 415 and preventing continuous operation of the motor 415.

[0059] On the other hand, if at least one of contact 303 and interlocking contact 320 is open, the motor 415 will not operate even if the closing operation switch 380 is closed, and the ES operation auxiliary relay 390 will remain de-energized. As a result, the closing command ON_INS will not be generated. Therefore, if the disconnector 89R_2 (main contact MC) is closed, or if there is voltage on the distribution line DL, it is impossible to close the grounding device ES even if the closing operation switch 380 is closed. In other words, the grounding device ES cannot be closed. Note that the circuit shown in Figure 3 is the circuit for closing the grounding device ES, and the circuit for opening the grounding device ES is not shown.

[0060] Contact 425 is an auxiliary contact linked to the grounding device ES, and is turned on when the closing operation of the grounding device ES begins, during the closing operation, when the closing operation is completed, when the opening operation begins, or during the opening operation. On the other hand, contact 425 is turned off when the opening operation of the grounding device ES is completed. Contact 425 is, for example, a microswitch, which is turned on and off based on the position of the operating rod (not shown) for operating the grounding device ES. While contact 425 is on, the ES operation signal OP_SG is generated (ES operation signal OP_SG is "1"). When the grounding device ES is completely open (when the opening operation is completed), contact 425 is off, so the ES operation signal OP_SG is not generated (ES operation signal OP_SG is "0"). The ES operation signal OP_SG is a signal indicating that an operation is being performed on the grounding device ES.

[0061] Furthermore, one end of contact 385 is connected to the power supply PS2, and the other end is connected to the pull-down resistor Rd1, and the ON_INS command is output from the connection point between contact 385 and the pull-down resistor Rd1.

[0062] Furthermore, one end of contact 425 is connected to the power supply PS3, and the other end is connected to the pull-down resistor Rd2, and the ES operation signal OP_SG is output from the connection point between contact 425 and the pull-down resistor Rd2. With this configuration, the ON_INS command becomes a logical value of "0" when contact 385 is open, and a logical value of "1" when contact 385 is closed. The ES operation signal OP_SG is generated to become a logical value of "0" when contact 425 is open, and a logical value of "1" when contact 425 is closed.

[0063] The disconnector 89R_2, grounding device ES, ground fault overcurrent relay 51GR, signal line SL1, voltage divider VD, interlock circuit 300, and ES operating circuit 400 form an example of the “power receiving system” of this disclosure.

[0064] Refer to Figure 1 again for further explanation. During inspection of the power receiving equipment 30, the circuit breaker 52_1 (and disconnector 89R_1) of the substation 20 and the disconnector 89R_2 (and circuit breaker 52_2) of the power receiving equipment 30 may be opened. Circuit breaker 52_1 is opened to prevent current from flowing in from the grid power supply 10. Disconnector 89R_2 is opened to prevent discharge current from flowing in from feeders F1 to F3 when the grounding device ES is operated.

[0065] If the grounding device ES is closed after the circuit breaker 52_1 and disconnector 89R_2 are opened, residual charge in the distribution line DL may discharge, causing current to flow from the distribution line DL through the grounding device ES to the ground. At that time, an unbalanced current may flow in the distribution line DL. As a result, the ground fault overcurrent relay 51GR may react to the unbalanced current and malfunction, even though no ground fault has actually occurred. Consequently, an output signal OSg indicating the detection of a ground fault overcurrent may be input to the data acquisition device 250, and an incorrect history may be recorded in the data acquisition device 250. Such a situation is undesirable.

[0066] Figure 4 shows an example of a circuit configuration to prevent unwanted operation of a ground fault overcurrent relay. Figure 4(A) shows an example of a circuit configuration when the distribution line is an overhead line. Figure 4(B) shows an example of a circuit configuration when the distribution line is an underground cable. Figures 4(A) and 4(B) are explained as comparative examples.

[0067] Referring to Figure 4(A), each of the overcurrent relay 51Ra and the ground fault overcurrent relay 51GRa is connected to a current transformer CTar. Each of these operates based on the measured current transformed by the current transformer CTar. A cancellation earth wire CEL is provided near the distribution line DLa (overhead line). After the circuit breaker 52_1 and disconnector 89Ra are opened and the grounding device ESa is closed, current flows in both the distribution line DLa (overhead line) and the cancellation earth wire CEL due to the discharge of residual charge in the distribution line DLa (overhead line). At this time, the current flowing in the distribution line DLa and the current flowing in the cancellation earth wire CEL are the same in magnitude but opposite in direction. As a result, the magnetic fields formed by these currents cancel each other out. Consequently, the overcurrent relay 51Ra and the ground fault overcurrent relay 51GRa do not react to the current in the distribution line DLa and do not operate. Therefore, unnecessary operation of the ground fault overcurrent relay 51GRa is avoided.

[0068] Referring to Figure 4(B), each of the overcurrent relay 51Rb and the ground fault overcurrent relay 51GRb operates based on the measured current converted by the current transformer CTb1. The ground fault overcurrent relay 51GRb is also connected to the current transformer CTb2. The current transformer CTb2 is installed between the grounding device ESb and the ground. When the grounding device ESb is closed after the circuit breaker 52_1 and disconnector 89Rb have opened, current flows through the distribution line DLb (underground wire) due to the discharge of residual charge in the distribution line DLb. At this time, both the current converted by the current transformer CTb1 and the current converted by the current transformer CTb2 flow towards the ground fault overcurrent relay 51GRb. As a result, these currents cancel each other out, and the ground fault overcurrent relay 51GRb does not react to the current in the distribution line DLb and does not operate. Therefore, unnecessary operation of the ground fault overcurrent relay 51GRb is avoided.

[0069] Thus, the comparative example requires components such as a cancellation earth wire CEL or a current transformer CT2b, which could lead to increased component costs. In addition, the circuit configuration needs to be changed depending on the type of distribution line (whether it is an overhead or underground line). As a result, various design man-hours become more complex, potentially increasing costs.

[0070] Referring again to Figure 2, the ground fault overcurrent relay 51GR according to Embodiment 1 has a configuration that reduces component costs and design man-hours while avoiding unnecessary operation. Specifically, the AND circuit 115 of the ground fault overcurrent relay 51GR generates an output signal OSG indicating detection of ground fault overcurrent (having a logical value of "1") only when signal SG1 indicates the presence of unbalanced current in the distribution line DL (having a logical value of "1") and signal SG2 is related to the closed state of the disconnector 89R_2 (in this example, indicating the closed state (in other words, having a logical value of "1")), and generates an output signal OSG indicating non-detection of ground fault overcurrent (having a logical value of "0") otherwise. For example, when signal SG1 indicates the presence of unbalanced current in the distribution line DL (having a logical value of "1") and signal SG2 indicates the open state of the disconnector 89R_2 (having a logical value of "0"), the AND circuit 115 generates an output signal OSG indicating non-detection of ground fault overcurrent (having a logical value of "0").

[0071] With this configuration, even if the residual charge in the distribution line DL is discharged and an unbalanced current is detected in the distribution line DL (when signal SG1 has a logical value of "1"), the disconnector 89R_2 is in the open state and the logical value of signal SG2 is "0", so an output signal OSG indicating no detection of ground fault overcurrent is generated. In other words, when the disconnector 89R_2 is open, the logical value of the output signal OSG becomes 0, so the ground fault overcurrent detection function of the ground fault overcurrent relay 51GR is locked (deactivated). Therefore, it is possible to avoid the ground fault overcurrent relay 51GR operating unnecessarily when the grounding device ES2 is turned on. Furthermore, unlike the comparative example (Figure 4), the above configuration does not require components such as a cancellation earth wire CEL or a current transformer CT2a. Thus, component costs can be reduced. In addition, the circuit configuration of the ground fault overcurrent relay 51GR is applicable whether the distribution line DL is an overhead line or an underground line (it is not affected by the type of distribution line DL). Therefore, the design can be simplified and the design man-hours can be reduced.

[0072] The second input 114 of the AND circuit 115 receives signal SG2 as a signal related to the open / closed state of the main contact MC, transmitted from the auxiliary contact SC of the disconnector 89R_2 via the signal line SL1 through the NOT circuit 110. When the logical value of signal SG2 is "1", this is an example of "the case in which the second signal is a signal related to the closed state of the disconnector" as described in this disclosure.

[0073] The signal SG02 is output from the auxiliary contact SC of the disconnector 89R_2. In the previous explanation, it was stated that the signal SG02 from the auxiliary contact SC has a logical value of "0" when the main contact MC of the disconnector 89R_2 is closed, and a logical value of "1" when the main contact MC is open. However, if we assume that the signal SG02 from the auxiliary contact SC has a logical value of "1" when the main contact MC of the disconnector 89R_2 is closed, and a logical value of "0" when the main contact MC is open, then the NOT circuit 110 can be omitted.

[0074] In order to prevent the aforementioned unnecessary operation of the ground fault overcurrent relay 51GR, it is theoretically possible for the ground fault overcurrent relay 51GR to receive a signal from the circuit breaker 52_1 indicating the open / closed state of the circuit breaker 52_1 of the substation equipment 20, and to lock the ground fault overcurrent relay 51GR based on this signal. However, the substation equipment 20 is located within controlled area A1 and far from the power receiving equipment 30, which is located within controlled area A2. Therefore, in order to lock the ground fault overcurrent relay 51GR using the signal from the circuit breaker 52_1 as described above, it would be necessary to install a long-distance signal line connecting the circuit breaker 52_1 to the ground fault overcurrent relay 51GR. This is impractical.

[0075] In Embodiment 1, the ground fault overcurrent relay 51GR receives the signal SG2 transmitted through the signal line SL1. The disconnector 89R_2 (auxiliary contact SC) and the ground fault overcurrent relay 51GR are both located within the power receiving equipment 30 and are therefore not far apart. Thus, it is practical to install the signal line SL1 connecting the auxiliary contact SC to the ground fault overcurrent relay 51GR.

[0076] As described above, according to this embodiment 1, when the disconnector 89R_2 (main contact MC) is open, the ground fault overcurrent detection function of the ground fault overcurrent relay 51GR is locked. As a result, the aforementioned unnecessary operation of the ground fault overcurrent relay 51GR can be avoided while reducing component costs and design man-hours.

[0077] [Modified example of Embodiment 1] For some reason (for example, due to a malfunction of the auxiliary contacts of the disconnector 89R_2), it is conceivable that the signal SG2 (or signal SG02) may indicate that the main contact MC is open, even though the main contact MC is actually closed. In such a case, it is undesirable for the ground fault overcurrent detection function to be unintentionally locked, resulting in a failure to detect an actual ground fault. The ground fault overcurrent relay according to this modification has a configuration to address such problems.

[0078] Figure 5 is a diagram showing the configuration of a ground fault overcurrent relay according to this modified example. Referring to Figure 5, the ground fault overcurrent relay 51GR1 of this modified example further includes an OR circuit 112, the second input 114 of the AND circuit 115 is configured to take the output of the OR circuit 112 as its input, the signal SG3 which is the output of the voltage detection circuit 305 is input to the off-delay circuit 330 via the on-delay circuit 325, and the output of the OR circuit 112 is the logical OR of the signal SG2 which is the output of the NOT circuit 110 and the signal SG4 which is the output of the off-delay circuit 330, which is different from the ground fault overcurrent relay 51GR of Embodiment 1 (Figure 2).

[0079] Regarding other points, unless otherwise specified, the ground fault overcurrent relay 51GR1 has essentially the same configuration as the ground fault overcurrent relay 51GR. Therefore, a detailed explanation will not be repeated.

[0080] The OR circuit 112 takes the logical OR of signal SG2, which is the output of the NOT circuit 110, and signal SG4, which is the output of the off-delay circuit 330 in the voltage detection device 302, and generates signal SG5 based on the result of the logical OR. The NOT circuit 110 generates the inverted signal of signal SG02 as signal SG2. In this modified example, signal SG5 corresponds to an example of the "second signal" of this disclosure and is related to the open / closed state of the disconnector 89R_2, and its logical value may change depending on the open / closed state (details will be described later).

[0081] Within the voltage detection circuit 305 (Figure 3), signal SG3 is delayed via the on-delay circuit 325, and then further delayed by the off-delay circuit 330 to generate signal SG4.

[0082] The off-delay circuit 330, when the output of the on-delay circuit 325 changes from a first state indicating the presence of voltage on the distribution line DL to a second state indicating the absence of voltage on the distribution line DL (i.e., when this voltage disappears, more specifically, when the logical value of signal SG3 changes from "1" (first state) to "0" (second state) and the logical value of the output of the on-delay circuit 325 changes from "1" to "0"), delays the change (falling edge) of signal SG4 by a predetermined time and transmits it to the ground fault overcurrent relay 51GR1 as signal SG4. For example, when the logical value of signal SG3 changes from "1" to "0", the off-delay circuit 330 generates a signal as signal SG4 that is a predetermined delay of the change of signal SG3. The predetermined delay time of this off-delay circuit 330 is longer than the operating time of the protective relay when a three-phase ground fault occurs, for example, 1 second. The off-delay circuit 330 transmits the input signal to the ground fault overcurrent relay 51GR1 as is if the signal received from the voltage detection circuit 305 (voltage detection device 302) through the on-delay circuit 325 has not changed from the first state to the second state (i.e., the level of this signal has not changed from "1" to "0"), or if it has changed from the second state to the first state. For example, if the logical value of signal SG3 remains "1", the output signal of the on-delay circuit 325 also remains 1, so the off-delay circuit 330 generates a signal equivalent to signal SG3 (for example, a signal with the same logical value "1" as signal SG3) as signal SG4.

[0083] In this modified example, signal SG5 has a logic value of "1" if signal SG2 has a logic value of "1" (main contact MC of disconnector 89R_2 is closed) or if signal SG4 from off-delay circuit 330 has a logic value of "1". Otherwise (for example, if both signals SG2 and SG4 are "0"), signal SG5 has a logic value of "0".

[0084] If the signal SG4 from the off-delay circuit 330 indicates no voltage on the distribution line DL (i.e., the logical value of signal SG3 is "0"), the logical value of signal SG5, based on the logical OR of signals SG2 and SG4, directly reflects the logical value of signal SG2. In this case, the AND circuit 115 generates the output signal OSg according to signal SG1 and signal SG5, which is equal to signal SG2.

[0085] When the signal SG4 from the off-delay circuit 330 indicates the presence of voltage in the distribution line DL (when the logical value of signal SG4 is "1"), signal SG5 has a logical value of "1" independently of signal SG2 (SG02). In this case, the logical value of the output signal OSg directly reflects the logical value of signal SG1. Therefore, when signal SG1 indicates the presence of unbalanced current in the distribution line DL (when signal SG1 has a logical value of "1"), the AND circuit 115 generates an output signal OSg with a logical value of "1" independently of signal SG2. The AND circuit 115 generates an output signal OSg with a logical value of "1" only when both signals SG1 and SG5 have a logical value of "1". Otherwise (for example, when signal SG1 has a logical value of "1" and SG5 has a logical value of "0"), the AND circuit 115 generates an output signal OSg with a logical value of "0".

[0086] When a three-phase ground fault occurs, voltage is lost in all phases of the distribution line DL. As a result, no current flows through the resistor R of the voltage divider VD (Figure 3), and the voltage across the voltage divider VD disappears. Consequently, the signal SG3 changes from a state indicating voltage is present in the distribution line DL (logical value of "1") to a state indicating no voltage (logical value of "0"), indicating the loss of voltage in the distribution line DL.

[0087] If the voltage detection device 302 does not include the off-delay circuit 330, the logical value of the signal SG3 input to the OR circuit may immediately change from "1" to "0" during a three-phase ground fault. In this case, if the signal SG2 indicating the open state of the main contact MC (having a logical value of "0") is generated due to this malfunction, then the signal SG2 will have a logical value of "0". As a result, the output signal OSg will have a logical value of "0", and the ground fault overcurrent relay 51GR will not be able to detect the ground fault overcurrent in the distribution line DL.

[0088] In this modified example, signal SG3 (more specifically, the output signal of the on-delay circuit 325 that receives this signal) is off-delayed by the off-delay circuit 330. Therefore, even if signal SG2, which indicates the open state of disconnector 89R_2, has a logical value of "0" due to a malfunction of disconnector 89R_2, and a three-phase ground fault occurs, signal SG4, which indicates the loss of voltage in the distribution line DL, is input from the off-delay circuit 330 to the OR circuit 112 after a predetermined delay. In other words, even in the event of a three-phase ground fault, signal SG4 (which has a logical value of "1") indicating the presence of voltage continues to be input from the off-delay circuit 330 to the OR circuit 112 until a predetermined time has elapsed. In the event of a three-phase ground fault, there is a possibility that an unbalanced current will flow in the distribution line DL, in which case signal SG1 will have a logical value of "1", indicating the presence of an unbalanced current in the distribution line DL. Therefore, in this modified version, the output signal OSg (having a logical value of "1") indicating the detection of ground fault overcurrent can continue to be generated regardless of the opening of the disconnector 89R_2 until a predetermined time has elapsed, even after a three-phase ground fault. In other words, the lock of the ground fault overcurrent detection function caused by the opening of the disconnector 89R_2 can be temporarily disabled until a predetermined time has elapsed. As a result, even when a three-phase ground fault occurs while the signal SG2 indicating the open state of the disconnector 89R_2 is unintentionally generated, the ground fault overcurrent can be properly detected.

[0089] When circuit breaker 52_1 and disconnector 89R_2 are opened, the voltage in distribution line DL disappears, causing the logical value of signal SG3 to change from "1" to "0". As a result, after a predetermined delay time, both signals SG2 and SG4 become "0", and the logical value of signal SG5 becomes "0". Therefore, even if the grounding device ES is then closed and an unbalanced current flows in distribution line DL, causing the logical value of signal SG1 to become "1", the output signal OSg will have a logical value of "0". Consequently, unnecessary operation of the ground fault overcurrent relay 51GR1 is prevented.

[0090] The grounding device ES is basically switched on by manual operation, and this manual operation is performed after a certain amount of time has elapsed since the disconnector 89R_2 was opened. If the delay time of the off-delay circuit 330 is long, the signal SG4 from the off-delay circuit 330 will have a logical value of "1" for a long time, and if the logical value of signal SG3 is "1" when the grounding device ES is operated, the ground fault overcurrent relay 51GR1 may operate unnecessarily depending on the logical value of signal SG1. However, since the above delay time is less than 1 second, even if the timing of the change in the logical value of signal SG4 from the off-delay circuit 330 from "1" to "0" is delayed by the said delay time, in most cases the logical value of signal SG4 has already changed to "0" when the grounding device ES is operated. As a result, when the grounding device ES is operated after the disconnector 89R_2 has been opened, both signals SG2 and SG4 (SG3) are 0, and signal SG5, which is the output of the OR circuit 112, basically has a logical value of "0". Therefore, the ground fault overcurrent relay 51GR1 is locked. Thus, the possibility that the off-delay circuit 330 causes unwanted operation of the ground fault overcurrent relay 51GR1 can be practically ignored.

[0091] As described above, this modification makes it possible to avoid situations where a three-phase ground fault fails to be detected due to a lock-up of the ground fault overcurrent detection function when a three-phase ground fault actually occurs.

[0092] [Embodiment 2] In Embodiment 1 and its modified versions, the ground fault overcurrent detection function of the ground fault overcurrent relay is locked based on a signal (e.g., signal SG2 or signal SG5) related to the open / closed state of the disconnector 89R_2. Alternatively, the ground fault overcurrent detection function may be locked based on a signal (e.g., a signal indicating that state) related to the open / closed state of the grounding device ES.

[0093] Figure 6 is a diagram showing the configuration of a ground fault overcurrent relay according to Embodiment 2. Referring to Figure 6, Embodiment 2 differs from the aforementioned ground fault overcurrent relays 51GR and 51GR1 (Figures 2 and 5) in that the ground fault overcurrent relay 51GR2 includes a NOT circuit 111 instead of a NOT circuit 110, the NOT circuit 111 is connected to the signal line SL3 through which the signal SG2x related to the open / closed state of the grounding device ES is transmitted, and the NOT circuit 111 is connected to the second input 114 of the AND circuit 115. In other respects, unless otherwise specified, the ground fault overcurrent relay 51GR2 has basically the same configuration as the ground fault overcurrent relays 51GR and 51GR1. Therefore, a detailed explanation will not be repeated.

[0094] The signal line SL3 is located between the ES operation circuit 400 and the NOT circuit 111. The signal SG2x is output from the ES operation circuit 400 and indicates that the grounding device ES is turned on. The signal SG2x is generated when the grounding device ES is turned on. The signal SG2x is not generated when the grounding device ES is not turned on. In this example, the signal SG2x is the ES operation signal OP_SG (Figure 3), but it may also be the turn-on command ON_INS. The logical value of the signal SG2x is "0" when the grounding device ES is open, and becomes "1" immediately before the grounding device ES is turned on due to the generation of the ES operation signal OP_SG or the turn-on command ON_INS.

[0095] The NOT circuit 111 receives the signal SG2x from the ES operation circuit 400 via the signal line SL3 and generates the signal SG2z as its inverted signal. Signal SG2z is an example of the “second signal” of this disclosure.

[0096] Signal SG2z is a signal related to the open / closed state (closed state) of the grounding device ES. Specifically, when the grounding device ES is in the closed state, or when closing has been initiated (when the ES operation signal OP_SG or closing command ON_INS is generated), signal SG2z has a logical value of "0". When signal SG2z has a logical value of "0", it is a signal related to closing the grounding device ES. When the grounding device ES is not in the closed state and closing has not been initiated (when neither the ES operation signal OP_SG nor the closing command ON_INS is generated), signal SG2z has a logical value of "1". Signal SG2z is an example of the "second signal" in this disclosure. The second input 114 of the AND circuit 115 is configured to receive signal SG2z. When signal SG2z has a logical value of "1", it is not a signal related to closing the grounding device ES. When the logical value of signal SG2z is "1", it is an example of the "case in which the second signal is not a signal related to closing the grounding device" in this disclosure.

[0097] The AND circuit 115 is configured to generate an output signal OSg according to signals SG1 and SG2z. For example, if signal SG1 indicates the presence of an unbalanced current (signal SG1 has a logical value of "1") and signal SG2z is related to the closing of the grounding device ES (signal SG2z has a logical value of "0"), the AND circuit 115 generates an output signal OSg with a logical value of "0". Only if signal SG1 indicates the presence of an unbalanced current and signal SG2z is not related to the closing of the grounding device ES (in other words, if signal SG2z has a logical value of "1"), the AND circuit 115 generates an output signal OSg with a logical value of "1".

[0098] With this configuration, even if the residual charge in the distribution line DL is discharged due to the opening of the disconnector 89R_2 and the closing of the grounding device ES, and an unbalanced current is detected in the distribution line DL (when signal SG1 has a logical value of "1"), an output signal OSg indicating no detection of ground fault overcurrent is generated. In other words, if the grounding device ES is in the closed state from just before it is closed, the logical value of the output signal OSG becomes "0", and the ground fault overcurrent detection function of the ground fault overcurrent relay 51GR2 is locked. Therefore, it is possible to avoid the ground fault overcurrent relay 51GR2 making unnecessary operation in response to the aforementioned unbalanced current. Furthermore, in the second embodiment, components such as the cancellation earth wire CEL or the current transformer CT2a are not required. Thus, component costs can be reduced. In addition, the circuit configuration of the ground fault overcurrent relay 51GR2 is applicable whether the distribution line DL is an overhead line or an underground line (it is not affected by the type of distribution line). Thus, the design can be simplified and design man-hours can be reduced.

[0099] Thus, according to Embodiment 2, the ground fault overcurrent relay 51GR2 is locked based on signal SG2z instead of signal SG2 (Figure 2). As a result, similar to Embodiment 1, it is possible to avoid unnecessary operation of the ground fault overcurrent relay 51GR2 while reducing component costs and design man-hours.

[0100] [Modified version of Embodiment 2] The duration for which the ground fault overcurrent relay is locked is preferably kept to the minimum necessary. If the ground fault overcurrent relay remains locked for a long period of time after the grounding device ES has been switched on and the inspection of the power receiving equipment 30 has been completed, the ground fault overcurrent relay may fail to detect an actual ground fault. Such a situation is undesirable. The ground fault overcurrent relay according to this modification is configured to address such a problem.

[0101] Figure 7 shows the configuration of a ground fault overcurrent relay according to this modification. Referring to Figure 7, the ground fault overcurrent relay 51GR2a differs from the ground fault overcurrent relay 51GR2 of Embodiment 2 (Figure 6) in that it further includes a one-shot circuit 117. In other respects, unless otherwise specified, the ground fault overcurrent relay 51GR2a has basically the same configuration as the ground fault overcurrent relay 51GR2. Therefore, a detailed explanation will not be repeated.

[0102] The one-shot circuit 117 is connected between the signal line SL3 and the NOT circuit 111. The one-shot circuit 117 receives the signal SG2x transmitted through the signal line SL3 as input and generates the signal SG2y as output. The signal SG2y, which is the output of the one-shot circuit 117, is input to the NOT circuit 111, and the signal SG2z, which is the output of the NOT circuit 111, is input to the second input 114 of the AND circuit 115.

[0103] The one-shot circuit 117 generates a one-shot pulse when the signal SG2x rises (when the ON_INS command for turning on the grounding device ES is issued or when turning on begins). Specifically, when the logical value of signal SG2x changes from "0" to "1", the one-shot circuit 117 generates a signal SG2y with a logical value of "1" for a certain period of time, and then generates a signal SG2y with a logical value of "0". The certain period of time is determined appropriately by prior evaluation tests based on the time from turning on the grounding device ES to the completion of the discharge of residual charge in the distribution line DL. In this example, the certain period of time is several seconds or more and less than one minute.

[0104] The NOT circuit 111 generates the inverted signal of signal SG2y as signal SG2z. Signal SG2z has a logical value of "0" while signal SG2y is being generated as a one-shot pulse (having a logical value of "1"). After the above-mentioned period of time has elapsed, since the pulse is no longer generated, signal SG2z has a logical value of "1". In this way, the level (signal value) of signal SG2z changes for a certain period of time from the time the ON_INS command is output or the start of the ON operation of the grounding device ES when it is turned on. This period of time is predetermined based on the specifications of the one-shot circuit 117. The NOT circuit 111 and the one-shot circuit 117 are also referred to as the "signal generation circuit 118".

[0105] The AND gate 115 generates an output signal OSg with a logic value of "0" while the level of signal SG2z is changing (while a one-shot pulse is being generated), and then generates an output signal OSg according to signal SG1 (generating the same output signal OSg as signal SG1).

[0106] With this configuration, from the moment the main contacts of the grounding device ES actually make contact and just before residual charge in the distribution line DL etc. is discharged until a certain period of time has elapsed, only the output signal OSg indicating no detection of ground fault overcurrent is generated (the ground fault overcurrent detection function is locked), and the lock is released after the elapsed period of time. This makes it possible to minimize the length of time that the ground fault overcurrent detection function is locked. Therefore, unnecessary operation of the ground fault overcurrent relay 51GR2a can be avoided until a certain period of time has elapsed, and the ground fault overcurrent detection function can be reactivated after the elapsed period of time (for example, ground fault overcurrent can be appropriately detected after the inspection of the power receiving equipment 30 is completed).

[0107] [Other variations] The current transformer CT is assumed to include a zero-phase current transformer ZCT (Figure 2), but it does not necessarily have to include a zero-phase current transformer ZCT.

[0108] Figure 8 is a diagram illustrating the configuration of the current transformer CT in this modified example. Referring to Figure 8, the current transformer CT includes a second-phase current transformer CTb instead of a zero-phase current transformer ZCT. The overcurrent relay 51R further includes an auxiliary current transformer ACTb and a level detector LDb. The OR circuit CR generates an output signal OSr based on the result of the logical OR of level detectors LDa to LDc. The auxiliary current transformer ACTz is configured to detect the neutral point current of the first-phase current transformer CTa, the second-phase current transformer CTb, and the third-phase current transformer CTc. In this case as well, the level detector 105 is configured to detect unbalanced current in the distribution line DL and generates a signal SG1 according to the presence or absence of this current.

[0109] Referring again to Figure 3, the on-delay circuit 325 and the off-delay circuit 330 were described as being located within the voltage detection device 302. However, the on-delay circuit 325 and the off-delay circuit 330 may be located within the ground fault overcurrent relay 51GR1 instead of within the voltage detection device 302.

[0110] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0111] 1 Power transmission and distribution system, 10 Grid power source, 20 Substation equipment, 30 Power receiving equipment, 51GR,51GR1,51GR2,51GR2a,51GRa,51GRb Earth fault overcurrent relay, 51R,51Ra,51Rb Overcurrent relay, 52,52F1,52F2,52F3 Circuit breakers, 89F2, 89F3, 89F1, 89R, 89Ra, 89Rb disconnectors, DL, DLa, DLb distribution lines, ES, ES2, ESa, ESb grounding devices.

Claims

1. A disconnector connected to a power distribution line that receives power from a three-phase AC power source, A grounding device connected between the aforementioned power distribution line and the ground, The system includes a ground fault overcurrent relay configured to detect ground fault overcurrents in the aforementioned power distribution line, The aforementioned ground fault overcurrent relay is, A first input that receives a first signal indicating the detection result of an unbalanced current in the distribution line, A second input that receives a second signal which is a signal related to the open / closed state of the disconnector, The system includes a signal output circuit that generates an output signal having a first value indicating the detection of the ground fault overcurrent, or a second value indicating the non-detection of the ground fault overcurrent, according to the first signal and the second signal. A power receiving system wherein, when the first signal indicates the presence of the unbalanced current and the second signal is a signal related to the closed state of the disconnector, the signal output circuit generates the output signal having the first value.

2. A voltage divider installed in the aforementioned power distribution line, A voltage detection circuit that generates a third signal indicating the presence or absence of voltage in the distribution line according to the output of the voltage divider, The system further comprises a signal transmission circuit that receives the third signal and transmits it to the signal output circuit, The aforementioned signal transmission circuit is When the third signal from the voltage detection circuit changes from a first state indicating the presence of voltage to a second state indicating the absence of voltage, the change in the third signal is delayed by a predetermined time and the third signal is transmitted to the signal output circuit. If the third signal from the voltage detection circuit has not changed from the first state to the second state, the third signal is transmitted to the signal output circuit. The aforementioned signal output circuit is When the second signal indicates the closed state of the disconnector, or when the third signal from the signal transmission circuit indicates the presence of the voltage, and the first signal indicates the presence of the unbalanced current, The power receiving system according to claim 1, which generates the output signal having the first value.

3. A disconnector connected to a power distribution line that receives power from a three-phase AC power source, A grounding device connected between the aforementioned power distribution line and the ground, The system includes a ground fault overcurrent relay configured to detect ground fault overcurrents in the aforementioned power distribution line, The aforementioned ground fault overcurrent relay is, A first input that receives a first signal indicating the detection result of an unbalanced current in the distribution line, A second input that receives a second signal which is a signal related to the open / closed state of the grounding device, The system includes a signal output circuit configured to generate an output signal having a first value indicating the detection of the ground fault overcurrent, or a second value indicating the non-detection of the ground fault overcurrent, according to the first signal and the second signal. A power receiving system wherein, when the first signal indicates the presence of the unbalanced current and the second signal is not a signal related to the closing of the grounding device, the signal output circuit generates the output signal having the first value.

4. The second signal is the output of a signal generation circuit that generates a signal whose level changes for a certain period of time from the time the grounding device is turned on or from the time the grounding device is turned on. The power receiving system according to claim 3, wherein the signal output circuit generates the output signal having the second value while the level of the second signal is changing.

5. A ground fault overcurrent relay configured to detect ground fault overcurrent in a power distribution line receiving power from a three-phase AC power source, wherein a disconnector is connected to the power distribution line, and a grounding device is connected between the power distribution line and the ground. A first input that receives a first signal indicating the detection result of an unbalanced current in the distribution line, A second input that receives a second signal which is a signal related to the open / closed state of the disconnector, The system includes a signal output circuit that generates an output signal having a first value indicating the detection of the ground fault overcurrent, or a second value indicating the non-detection of the ground fault overcurrent, according to the first signal and the second signal. A ground fault overcurrent relay, wherein the signal output circuit generates the output signal having the first value when the first signal indicates the presence of the unbalanced current and the second signal is a signal related to the closed state of the disconnector.

6. A ground fault overcurrent relay configured to detect ground fault overcurrent in a power distribution line receiving power from a three-phase AC power source, wherein a disconnector is connected to the power distribution line, and a grounding device is connected between the power distribution line and the ground. A first input that receives a first signal indicating the detection result of an unbalanced current in the distribution line, A second input that receives a second signal which is a signal related to the open / closed state of the grounding device, The system includes a signal output circuit configured to generate an output signal having a first value indicating the detection of the ground fault overcurrent, or a second value indicating the non-detection of the ground fault overcurrent, according to the first signal and the second signal. A ground fault overcurrent relay wherein, when the first signal indicates the presence of the unbalanced current and the second signal is not a signal related to the closing of the grounding device, the signal output circuit generates the output signal having the first value.

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