Power reception 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, the ground fault overcurrent relay may operate unnecessarily in response to the unbalanced current even though no actual ground fault has occurred.

[0003] Non-Patent Document 1 discloses a circuit for preventing unnecessary operation of the above ground fault overcurrent relay (also referred to as a "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 wire.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The countermeasure circuit according to Non - Patent Document 1 requires additional components such as a canceling ground wire or an auxiliary current transformer, which may lead to an increase in component costs. In addition, it is necessary to change the circuit configuration depending on the type of distribution line. As a result, various design man - hours become complicated and the cost may increase.

[0006] The present disclosure has been made to solve the above - mentioned problems, and its object is to provide a power receiving system and a ground - fault over - current relay for avoiding unnecessary operation of the ground - fault over - current relay while reducing component costs and design man - hours.

Means for Solving the Problems

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

[0008] A power receiving system according to another aspect of the present disclosure includes a circuit breaker, a grounding device, and a ground fault overcurrent relay. The circuit breaker is connected to a distribution line that receives power from a three-phase AC power source. The grounding device is connected between the distribution line and the ground. The ground fault overcurrent relay is configured to detect a ground fault overcurrent 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 a detection result of an unbalanced current in the distribution line. The second input receives a second signal that 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 detection of a ground fault overcurrent or a second value indicating non-detection of a ground fault overcurrent according to the first signal and the second signal. When the first signal indicates the presence of an unbalanced current and the second signal is not a signal related to the activation of the grounding device, the signal output circuit generates an output signal having the first value.

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

[0010] A ground fault overcurrent relay according to another aspect of the present disclosure is configured to detect a ground fault overcurrent in a distribution line that receives power from a three-phase AC power source. A circuit breaker is connected to the distribution line. A grounding device is connected between the distribution line and the ground. 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 a detection result of an unbalanced current in the distribution line. The second input receives a second signal that 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 detection of a ground fault overcurrent or a second value indicating non-detection of a ground fault overcurrent according to the first signal and the second signal. When the first signal indicates the presence of an unbalanced current and the second signal is not a signal related to the energization of the grounding device, the signal output circuit generates an output signal having the first value.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to avoid unnecessary operations of the ground fault overcurrent relay while reducing component costs and design man-hours.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and their descriptions will not be repeated. Each of the embodiments and their modifications may be combined with each other as appropriate.

[0014] [Embodiment 1] FIG. 1 is an overall configuration diagram of a power transmission and distribution system in Embodiment 1. Referring to FIG. 1, the power transmission and distribution system 1 includes a grid power source 10, power transformation equipment 20, and power receiving equipment 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 a first phase, a second phase, and a 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 to 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). When the measured value is greater than a predetermined value, the overcurrent flowing through the distribution line DL is detected. 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 ground fault overcurrent relay 51GR is configured to detect a ground fault overcurrent in the distribution line DL. The ground fault overcurrent relay 51GR generates an output signal OSg indicating the detection result of the ground fault overcurrent. When the ground fault overcurrent is detected, the output signal OSg has a value (in this example, "1") indicating the detection of the ground fault overcurrent. When the ground fault overcurrent is not detected, the output signal OSr has a value (in this example, "0") indicating the non-detection of the ground fault overcurrent. The ground 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 ground 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 the logical value of at least one 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 circuit breaker 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 shown, but in reality, the circuit breaker 52_2 includes three main contacts MC respectively connected to the first phase, second phase, and third phase 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 lighting and non-lighting of a lamp (not shown) indicating 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 of FIG. 1, a signal line SL1 extends from the auxiliary contact SC. The signal line SL1 is disposed between the auxiliary contact SC and the ground fault overcurrent relay 51GR.

[0024] Note that there may be a plurality of auxiliary contacts that interlock with the main contact MC of the circuit breaker 89R_2. For example, the contact 303 in FIG. 3 described later is an auxiliary contact that interlocks with the main contact MC and is electrically insulated from the auxiliary contact SC.

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

[0026] The voltage divider VD is provided on the distribution line DL and generates a signal indicating the presence or absence of the voltage of the distribution line DL. The interlock circuit 300 is provided to make the grounding device ES inoperable (unable to be operated) when the circuit breaker 89R_2 is in the closed state or when the signal indicating the presence or absence of the voltage of the distribution line DL indicates that there is voltage on the distribution line DL, in order to prevent the misoperation of the grounding device ES. When this signal indicates that there is no voltage on the distribution line DL, the grounding device ES can be switched on by user operation. The interlock circuit 300 is connected to the ES operation circuit 400. The configurations of the interlock circuit 300 and the ES operation circuit 400 will be described in detail later.

[0027] The breaker 52_2 is connected to feeders F1 to F3 and trips (cuts off the circuit) in response to a trip command TRI. The circuit breaker 89F1 and the breaker 52F1 are provided between the feeder F1 and the electrical load L1. The circuit breaker 89F2 and the breaker 52F2 are provided between the feeder F2 and the electrical load L2. The circuit breaker 89F3 and the breaker 52F3 are provided between the feeder F3 and the electrical load L3.

[0028] Figure 2 is a diagram showing in detail an example of the configuration of the current transformer CT, the overcurrent relay 51R, and the earth 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 conversion section CTa, a third-phase current conversion section CTc, and a zero-phase current conversion section ZCT. The first-phase current conversion section CTa converts the current flowing in the first phase of the distribution line DL into a smaller current. The third-phase current conversion section CTc converts the current flowing in the third phase of the distribution line DL into a smaller current. The zero-phase current conversion section ZCT is configured to detect the zero-phase current, which is the unbalanced current between the three phases of the distribution line DL.

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

[0031] The auxiliary current conversion sections ACTa, ACTc are respectively provided on the secondary sides of the first-phase current conversion section CTa and the third-phase current conversion section CTc. The auxiliary current conversion sections ACTa, ACTc respectively convert the current flowing on the secondary sides of the first-phase current conversion section CTa and the third-phase current conversion section CTc into smaller currents.

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

[0033] OR circuit CR takes the logical sum of the logical values of the signals generated by level detectors LDa and LDc and generates an output signal OSr based on the result of the logical sum. For example, when 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, when both of the 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 provided on the secondary side of the zero-phase current transformer ZCT and converts the current flowing through 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 conversion unit ACTz (the current on its secondary side), and generates a signal SG1 based on the measured value of this sensor. The signal SG1 indicates the detection result of the unbalanced current in the power distribution line DL, and specifically has a logical value of "1" or "0". The unbalanced current is the unbalanced component of the three-phase alternating current. When the magnitude of the converted unbalanced current is greater than the threshold value, the level detector 105 generates a signal SG1 having a logical value of "1". This signal SG1 indicates the presence of the unbalanced current (the three-phase alternating current is not in a balanced state). On the other hand, when the magnitude of the converted current is less than or equal to the threshold value, the level detector 105 generates a signal SG1 having a logical value of "0". This signal SG1 indicates the absence of the unbalanced current (the three-phase alternating current is in a balanced state). The signal SG1 corresponds to an example of the "first signal" of the present disclosure.

[0037] The NOT circuit 110 receives a signal SG02 transmitted through the signal line SL1 from the operation circuit of the circuit breaker 89R_2 and generates a signal SG2 as its inverted signal. The signal SG02 is output from the auxiliary contact SC of the circuit breaker 89R_2. The signal SG02 indicates the open / closed state of the circuit breaker 89R_2. Specifically, since the signal SG02 indicates the open / closed state of the auxiliary contact SC, it also indicates the open / closed state of the main contact MC. The signal SG02 has a logical value of "0" when the main contact MC is in the closed state, while having a logical value of "1" when the main contact MC is in the open state.

[0038] Similar to the signal SG02, the signal SG2 indicates the open / closed state of the circuit breaker 89R_2 (main contact MC). The signal SG2 has a logical value of "1" when the main contact MC is in the closed state, while having a logical value of "0" when the main contact MC is in the open state. The signal SG2 corresponds to an example of the "second signal" of the present disclosure.

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

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

[0041] Figure 3 is a diagram showing an example of the configuration of the voltage divider VD, the interlock circuit 300, and the ES operation circuit 400.

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

[0043] The coaxial cable CBL includes a power line pair connected to both ends of a resistor R and interfaces between the interlock circuit 300 and the voltage divider VD. The coaxial cable CBL has a stray capacitance C2. The grounded side of the power line pair of the resistor R is connected to the outer conductor side of the 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 exactly equal, the voltage across the terminals of the resistor R is zero. However, in reality, it is not always perfectly balanced, and the stray capacitances C1A, C1B, and C1C are not exactly equal. Therefore, when the distribution line DL is connected to the grid power supply 10, an AC voltage is detected at the detection point Pvd. Generally, since the discharge time constants of the stray capacitance C1 and the resistor R are much larger than around the commercial frequency, when the distribution line DL is connected to the grid power supply 10, the voltage of the distribution line DL appears across the terminals of the resistor R as the voltage division of the stray capacitances C1A, C1B, and C1C and the stray capacitance C2. Also, when the distribution line DL is not connected to the grid power supply 10, if a time much longer than the discharge time constants of the stray capacitance C1 and the resistor R has elapsed, no voltage is detected across the terminals of the resistor R. In this way, by detecting the voltage across the terminals of the resistor R, the power detection device 302 can determine whether the distribution line DL is connected to the grid power supply 10.

[0044] The interlock circuit 300 includes a power detection device 302 and a contact 303. The power detection device 302 includes a power detection circuit 305, a transistor 315, a relay 317, and an interlocking contact 320 of the relay 317. Also, the grounding device ES is electrically operated and closes the grounding device ES from the open state by driving a motor 415. One end of the contact 303 is connected to the driving power supply PS1 of the motor 415, 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 input operation switch 380. The other end of the input operation switch 380 is connected to the motor 415 via a contact 405 and is also connected to an ES operation auxiliary relay 390. That is, the contact 303, the interlocking contact 320, and the input operation switch 380 are connected in series to form the interlock circuit.

[0045] The voltage detection circuit 305 detects the voltage of the power distribution line DL by detecting the potential difference across both ends of the resistor R (the voltage caused by the parasitic 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 circuit 350.

[0046] The amplifier 335 receives the voltage (AC voltage) of the power line pair of the coaxial cable CBL as the output of the voltage divider VD and amplifies this voltage. The comparator 340 compares the amplified voltage with a threshold voltage. The comparator 340 generates its output signal based on the result of the comparison. For example, when the amplified voltage is equal to or greater than the threshold voltage, this output signal has a logical value of "1". On the other hand, when the amplified voltage is less than the threshold voltage, this output signal has a logical value of "0". Since the input signal of the comparator 340 is an AC voltage, the output signal of the comparator 340 is a pulse signal of the 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 above AC voltage. The output signal of the off-delay circuit 345 indicates the presence or absence of the voltage of the power distribution line DL, and specifically has a logical value of "1" or "0". This output signal has a logical value of "0" when indicating the absence of the voltage of the power distribution line DL, while having a logical value of "1" when indicating the presence of the voltage of the power distribution line DL. The off-delay circuit 345 is a retriggerable circuit.

[0048] The on-delay circuit 347 receives the output signal of the off-delay circuit 345 via the NOT circuit 350 and is configured to on-delay this input signal. "On-delay" corresponds to generating an output signal that rises after a reference time (delay time) from 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 the voltage on the power distribution line DL and has a logical value of "1" or "0", similar to the output signal of the off-delay circuit 345. The off-delay circuit 345 and the on-delay circuit 347 are retriggerable circuits. Therefore, the output of the off-delay circuit 345 has a continuous logical value of "1" when the grid power supply 10 is connected to the power distribution line DL, and has a continuous logical value of "0" when the grid power supply 10 is not connected to the power 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 the voltage on the power distribution line DL. Specifically, signal SG3 has a logical value of "1" when indicating the presence of the voltage on the power distribution line DL, while having a logical value of "0" when indicating the absence of the voltage on the power distribution line DL. Thus, 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 the present disclosure.

[0051] The transistor 315 is used, for example, in an open collector configuration. One end of the excitation coil of the relay 317 is connected to the power supply PS0 of the control circuit, and the other end is connected to the collector of the transistor 315. The transistor 315 is turned on and off according to whether the output signal of the on-delay circuit 347 has a logical value of "1" or "0" (the presence or absence of the voltage on the power distribution line DL). When there is no voltage on the power distribution line DL, since this output signal has a logical value of "1", the transistor 315 is in the on state (conductive state). As a result, the relay 317 is in the excited state. When there is voltage on the power distribution line DL, since the output signal of the on-delay circuit 347 has a logical value of "0", the transistor 315 is in the off state (non-conductive state). As a result, the relay 317 is in the non-excited state.

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

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

[0054] The off-delay circuit 330 is configured to receive the signal SG3 as an input signal through the on-delay circuit 325, perform off-delay, and transmit the signal SG4 to the ground fault overcurrent relay 51GR through the signal line SL2. The signal SG4 is generated according to the signal SG3 and indicates the presence or absence of the voltage of the distribution line DL. The signal SG4 is an example of the "fourth signal" of the present disclosure. "Performing off-delay" corresponds to generating an output signal that rises after a predetermined time (delay time) from the fall 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 generally changes the output from "0" to "1" without delay. 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 based on the time from the energization of the grounding device ES to the completion of the discharge of the residual charge of the distribution line DL through a preliminary evaluation test so that the anti-maloperation effect shown in FIG. 5 described later works when an unbalanced current occurs at the time of energization of the grounding device ES. 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 the "signal transmission circuit" (signal generation circuit) of the present disclosure. The function of the off-delay circuit 330 will be described in detail later.

[0055] The contact 303 is an auxiliary contact of the circuit breaker 89R_2 that is interlocked to be in the closed state when the circuit breaker 89R_2 (main contact MC) is in the open state and is interlocked to be in the open state when the circuit breaker 89R_2 is in the closed state.

[0056] The closing operation switch 380 is operated to open and close the grounding device ES (FIG. 1). The contact 385 is an interlocking contact of the ES operation auxiliary relay 390 that is turned on and off in conjunction with the ES operation auxiliary relay 390.

[0057] The contact 405 is a limit switch interlocked with the grounding device ES, which is closed when the grounding device ES is in the open state and is opened when the energization is completed.

[0058] When both the contact 303 and the interlocking contact 320 are in the closed state, when the closing operation switch 380 is closed, the motor 415 operates, and as a result, the grounding device ES closes. At the same time, the ES operation auxiliary relay 390 operates and the contact 385 is turned on. As a result, an input command ON_INS indicating that a command to turn on the grounding device ES has been issued is generated. The contact 405 opens when the grounding device ES is turned on, and the operation of the motor 415 stops, preventing the motor 415 from operating continuously.

[0059] On the other hand, when at least one of the contact 303 and the interlocking contact 320 is in the open state, the motor 415 does not operate even when the closing operation switch 380 is closed, and the ES operation auxiliary relay 390 remains in the non-excited state. As a result, the input command ON_INS is not generated. From the above, when the circuit breaker 89R_2 (main contact MC) is in the closed state or when there is voltage on the distribution line DL, it is impossible to turn on the grounding device ES even if the closing operation switch 380 is closed. In other words, the grounding device ES is set to be inoperable. Note that the circuit shown in FIG. 3 is a circuit for the closing operation of the grounding device ES, and the illustration of the circuit for the opening operation of the grounding device ES is omitted.

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

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

[0062] Also, one end of the contact 425 is connected to the power supply PS3, the other end is connected to the pull - down resistor Rd2, and the ES operation - in - progress signal OP_SG is output from the connection point between the contact 425 and the pull - down resistor Rd2. With such a configuration, the input command ON_INS has a logical value of "0" when the contact 385 is in the open state and a logical value of "1" when the contact 385 is in the closed state. The ES operation - in - progress signal OP_SG is generated so as to have a logical value of "0" when the contact 425 is in the open state and a logical value of "1" when the contact 425 is in the closed state.

[0063] The circuit breaker 89R_2, the grounding device ES, the ground - fault over - current relay 51GR, the signal line SL1, the voltage divider VD, the interlock circuit 300, and the ES operation circuit 400 form an example of the "power - receiving system" of the present disclosure.

[0064] Referring back to FIG. 1 for explanation. During the inspection of the power - receiving facility 30, the circuit breakers 52_1 (and the circuit breaker 89R_1) of the substation equipment 20 and the circuit breaker 89R_2 (and the circuit breaker 52_2) of the power - receiving facility 30 may be opened. The circuit breaker 52_1 is opened to prevent the inflow of current from the grid power supply 10. The circuit breaker 89R_2 is opened to prevent the inflow of discharge current from the feeders F1 to F3 during the operation of the grounding device ES.

[0065] When the grounding device ES is closed after the disconnector 52_1 and the circuit breaker 89R_2 are opened, the residual charge on the distribution line DL may be discharged, and current may flow from the distribution line DL to the ground through the grounding device ES. At that time, an unbalanced current may flow in the distribution line DL. As a result, although no ground fault actually occurs, the ground fault overcurrent relay 51GR may react to the unbalanced current and malfunction (operate erroneously). As a result, an output signal OSg indicating the detection of a ground fault overcurrent may be input to the data collection device 250, and an incorrect history may be recorded in the data collection device 250. Such a situation is not preferable.

[0066] Figure 4 is a diagram showing an example of a circuit configuration for preventing the malfunction of the ground fault overcurrent relay. Figure 4(A) represents an example of the circuit configuration when the distribution line is an overhead line. Figure 4(B) represents an example of the circuit configuration when the distribution line is an underground cable. Each of Figure 4(A) and Figure 4(B) is described as a comparative example.

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

[0068] Referring to FIG. 4(B), each of the overcurrent relay 51Rb and the earth-fault overcurrent relay 51GRb operates based on the measured value of the current converted by the current transformer CTb1. The earth-fault overcurrent relay 51GRb is also connected to the current transformer CTb2. The current transformer CTb2 is provided between the grounding device ESb and the ground. When the grounding device ESb is closed after the circuit breaker 52_1 and the disconnector 89Rb are opened, a current flows through the distribution line DLb (underground cable) due to the discharge of the residual charge of 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 toward the earth-fault overcurrent relay 51GRb. As a result, since these currents cancel each other out, the earth-fault overcurrent relay 51GRb does not operate in response to the current in the distribution line DLb. Therefore, unnecessary operation of the earth-fault overcurrent relay 51GRb is avoided.

[0069] As described above, in the comparative example, since components such as the canceling earth wire CEL or the current transformer CT2b are required, there is a possibility of increasing the component cost. In addition, it is necessary to change the circuit configuration depending on the type of the distribution line (whether the distribution line is an overhead line or an underground cable). As a result, various design man-hours become complicated and the cost may increase.

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

[0071] With such a configuration, even when the residual charge in the distribution line DL is discharged as described above and an unbalanced current in the distribution line DL is detected (when the signal SG1 has a logical value of "1"), since the circuit breaker 89R_2 is in the open state and the logical value of the signal SG2 is "0", an output signal OSG indicating the non-detection of a ground fault overcurrent is generated. In other words, when the circuit breaker 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 (does not operate). Therefore, it is possible to avoid a situation where the ground fault overcurrent relay 51GR operates unnecessarily when the grounding device ES2 is turned on. Furthermore, unlike the comparative example (FIG. 4), the above configuration does not require components such as a canceling earth wire CEL or a current transformer CT2a. Therefore, the component cost can be reduced. In addition, the circuit configuration of the ground fault overcurrent relay 51GR is applicable regardless of whether the distribution line DL is an overhead line or an underground wire (not affected by the type of the 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 a signal SG2 as a signal related to the open / closed state of the main contact MC, which is transmitted via the NOT circuit 110 through the signal line SL1 from the auxiliary contact SC of the circuit breaker 89R_2. When the logical value of the signal SG2 is "1", it is an example of "when the second signal is a signal related to the closed state of the circuit breaker" in the present disclosure.

[0073] The signal SG02 is output from the auxiliary contact SC of the circuit breaker 89R_2. In the above description, the signal SG02 from the auxiliary contact SC has a logical value of "0" when the main contact MC of the circuit breaker 89R_2 is in the closed state and a logical value of "1" when the main contact MC is in the open state. However, if the signal SG02 from the auxiliary contact SC has a logical value of "1" when the main contact MC of the circuit breaker 89R_2 is in the closed state and a logical value of "0" when the main contact MC is in the open state, the NOT circuit 110 can be omitted.

[0074] In order to prevent the above-mentioned unnecessary operation of the ground fault overcurrent relay 51GR, it is theoretically possible for the ground fault overcurrent relay 51GR to receive a signal indicating the open / closed state of the circuit breaker 52_1 of the substation equipment 20 from the circuit breaker 52_1 and lock the ground fault overcurrent relay 51GR based on this signal. However, the substation equipment 20 is within the management area A1 and is far away from the power receiving equipment 30 within the management 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 is necessary to arrange a long-distance signal line connecting the circuit breaker 52_1 to the ground fault overcurrent relay 51GR. This is unrealistic.

[0075] In the first embodiment, the ground fault overcurrent relay 51GR receives the signal SG2 transmitted through the signal line SL1. Since both the circuit breaker 89R_2 (auxiliary contact SC) and the ground fault overcurrent relay 51GR are within the power receiving equipment 30, they are not so far apart. Therefore, it is practical to arrange the signal line SL1 connecting the auxiliary contact SC to the ground fault overcurrent relay 51GR.

[0076] As described above, according to the first embodiment, when the circuit breaker 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, it is possible to avoid the above-mentioned unnecessary operation of the ground fault overcurrent relay 51GR while reducing component costs and design man-hours.

[0077] [Modification Example of the First Embodiment] Due to some reason (for example, due to a defect in the auxiliary contact of the circuit breaker 89R_2), a situation may be assumed where, although the main contact MC is actually in the closed state, the signal SG2 (or signal SG02) indicates the open state of the main contact MC. In such a case, the situation where the ground fault overcurrent detection function is unintentionally locked and the actual ground fault is missed is not preferable. The ground fault overcurrent relay according to this modification example has a configuration for dealing with such problems.

[0078] FIG. 5 is a diagram showing the configuration of the ground fault overcurrent relay according to this modification example. Referring to FIG. 5, the ground fault overcurrent relay 51GR1 of this modification example further includes an OR circuit 112, and the second input 114 of the AND circuit 115 is configured to input the output of the OR circuit 112. 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. The output of the OR circuit 112 is different from that of the ground fault overcurrent relay 51GR (FIG. 2) of the first embodiment in that it is the logical sum 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.

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

[0080] The OR circuit 112 performs a logical OR operation on 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 in the voltage detector 302, and generates a signal SG5 based on the result of the logical OR operation. The NOT circuit 110 generates the inverted signal of the signal SG02 as the signal SG2. In this modification, the signal SG5 corresponds to an example of the "second signal" in the present disclosure, is related to the open / closed state of the circuit breaker 89R_2, and its logical value can change depending on the open / closed state (details will be described later).

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

[0082] When the output of the on-delay circuit 325 changes from the first state indicating the presence of the voltage on the power distribution line DL to the second state indicating the absence of the voltage on the power distribution line DL (i.e., when indicating the disappearance of this voltage, more specifically, when the logical value of the signal SG3 changes from "1" (the first state) to "0" (the second state) and the output of the on-delay circuit 325 changes from the logical value of "1" to "0"), the off-delay circuit 330 delays the change (fall) of the signal SG4 for a predetermined time and transmits it as the signal SG4 to the ground fault overcurrent relay 51GR1. For example, when the logical value of the signal SG3 changes from "1" to "0", the off-delay circuit 330 generates a signal obtained by delaying the change of the signal SG3 for a predetermined time as the signal SG4. The predetermined time of the delay of this off-delay circuit 330 is longer than the operating time of the protection relay at the time of three-phase ground fault, and is, for example, 1 second. When the signal received by the off-delay circuit 330 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 (when the level of this signal has not changed from "1" to "0"), or when it has changed from the second state to the first state, the input signal is directly transmitted to the ground fault overcurrent relay 51GR1. For example, when the logical value of the signal SG3 remains "1", since the output signal of the on-delay circuit 325 also remains 1, the off-delay circuit 330 generates a signal corresponding to the signal SG3 (for example, a signal having the same logical value "1" as the signal SG3) as the signal SG4.

[0083] In this modification, the signal SG5 has a logical value of "1" when the signal SG2 has a logical value of "1" (the main contact MC of the circuit breaker 89R_2 is in the closed state) or when the signal SG4 from the off-delay circuit 330 has a logical value of "1". Otherwise (for example, when both the signal SG2 and the signal SG4 are "0"), the signal SG5 has a logical value of "0".

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

[0085] When the signal SG4 from the off-delay circuit 330 indicates the presence of voltage on the power distribution line DL (when the logical value of the signal SG4 is "1"), the signal SG5 has a logical value of "1" regardless of the signal SG2 (SG02). In this case, the logical value of the output signal OSg reflects the logical value of the signal SG1 as it is. Therefore, when the signal SG1 indicates the presence of unbalanced current on the power distribution line DL (when the signal SG1 has a logical value of "1"), the AND circuit 115 generates an output signal OSg with a logical value of "1" regardless of the signal SG2. The AND circuit 115 generates an output signal OSg with a logical value of "1" only when both of the signals SG1 and SG5 have a logical value of "1". Otherwise (for example, when the signal SG1 has a logical value of "1" and the signal 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, the voltage disappears on all phases of the power distribution line DL. As a result, no current flows through the resistor R of the voltage divider VD (Figure 3), and the voltage of the voltage divider VD disappears. Consequently, the signal SG3 changes from the state indicating the presence of voltage on the power distribution line DL ("1" logical value) to the state indicating no voltage ("0" logical value), indicating the disappearance of the voltage on the power distribution line DL.

[0087] If the voltage detector 302 does not include the off-delay circuit 330, when a three-phase ground fault occurs, the logical value of the signal SG3 input to the OR circuit may immediately change from "1" to "0". 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 its malfunction, the signal SG2 has a logical value of "0". As a result, the output signal OSg has a logical value of "0", and the ground fault overcurrent relay 51GR cannot detect the ground fault overcurrent in the distribution line DL.

[0088] In this modification, the signal SG3 (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 when the signal SG2 indicating the open state of the circuit breaker 89R_2 has a logical value of "0" due to the malfunction of the circuit breaker 89R_2 and a three-phase ground fault occurs, the signal SG4 indicating the disappearance of the voltage in the distribution line DL is delayed by a predetermined time and input from the off-delay circuit 330 to the OR circuit 112. In other words, even during a three-phase ground fault, until a predetermined time elapses, the signal SG4 indicating the presence of voltage (having a logical value of "1") continues to be input from the off-delay circuit 330 to the OR circuit 112. During a three-phase ground fault, an unbalanced current may flow in the distribution line DL. In this case, the signal SG1 has a logical value of "1", indicating the presence of an unbalanced current in the distribution line DL. Therefore, in this modification, the output signal OSg indicating the detection of the ground fault overcurrent (having a logical value of "1") can continue to be generated regardless of the opening of the circuit breaker 89R_2 until a predetermined time elapses even after the three-phase ground fault. In other words, the lock of the ground fault overcurrent detection function caused by the opening of the circuit breaker 89R_2 can be temporarily disabled until a predetermined time elapses. As a result, even when a three-phase ground fault occurs when the signal SG2 indicating the open state of the circuit breaker 89R_2 is unintentionally generated, the ground fault overcurrent can be appropriately detected.

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

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

[0091] As described above, according to this modification example, it is possible to avoid a situation in which a three-phase ground fault is not detected due to the locking of the ground fault overcurrent detection function when a three-phase ground fault actually occurs.

[0092] [Embodiment 2] In Embodiment 1 and its modification, the ground fault overcurrent detection function of the ground fault overcurrent relay is locked based on a signal related to the open / closed state of the circuit breaker 89R_2 (for example, signal SG2 or signal SG5). In contrast, the ground fault overcurrent detection function may be locked based on a signal related to the open / closed (insertion) state of the grounding device ES (for example, a signal indicating the state).

[0093] FIG. 6 is a diagram showing the configuration of the ground fault overcurrent relay according to Embodiment 2. Referring to FIG. 6, in this Embodiment 2, the ground fault overcurrent relay 51GR2 includes a NOT circuit 111 instead of the NOT circuit 110, and the NOT circuit 111 is connected to a signal line SL3 to which a 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 this regard, it is different from the above-described ground fault overcurrent relays 51GR, 51GR1 (FIGS. 2 and 5). For other points, unless otherwise specified, the ground fault overcurrent relay 51GR2 has basically the same configuration as the ground fault overcurrent relays 51GR, 51GR1. Therefore, detailed description will not be repeated.

[0094] The signal line SL3 is disposed between the ES operation circuit 400 and the NOT circuit 111. The signal SG2x is a signal output from the ES operation circuit 400 and indicating the insertion of the grounding device ES. The signal SG2x is generated when the grounding device ES is inserted. The signal SG2x is not generated when the grounding device ES is not inserted. In this example, the signal SG2x is the ES operation signal OP_SG (FIG. 3), but it may be the insertion command ON_INS. The logical value of the signal SG2x is "0" when the grounding device ES is open, and becomes "1" due to the generation of the ES operation signal OP_SG or the insertion command ON_INS immediately before the grounding device ES is inserted.

[0095] The NOT circuit 111 receives the signal SG2x from the ES operation circuit 400 through the signal line SL3 and generates a signal SG2z as its inverted signal. The signal SG2z is an example of the "second signal" of the present disclosure.

[0096] The signal SG2z is a signal related to the on / off state (energized state) of the grounding device ES. Specifically, when the grounding device ES is in the energized state, or when the energization is started (when the ES operation signal OP_SG or the energization command ON_INS is generated), the signal SG2z has a logical value of "0". When the signal SG2z has a logical value of "0", it is a signal related to the energization of the grounding device ES. When the grounding device ES is not in the energized state and the energization has not started (when neither the ES operation signal OP_SG nor the energization command ON_INS is generated), the signal SG2z has a logical value of "1". The signal SG2z is an example of the "second signal" of the present disclosure. The second input 114 of the AND circuit 115 is configured to receive the signal SG2z. When the signal SG2z has a logical value of "1", it is not a signal related to the energization of the grounding device ES. When the logical value of the signal SG2z is "1", it is an example of "when the second signal is not a signal related to the energization of the grounding device" of the present disclosure.

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

[0098] With such a configuration, even when the residual charge of the distribution line DL is discharged due to the opening of the circuit breaker 89R_2 and the energization of the grounding device ES, and an unbalanced current in the distribution line DL is detected (when the signal SG1 has a logical value of "1"), an output signal OSg indicating non-detection of the ground fault overcurrent is generated. In other words, when the grounding device ES is in the energized state immediately before being energized, the logical value of the output signal OSG becomes "0", so that the ground fault overcurrent detection function of the ground fault overcurrent relay 51GR2 is locked. Therefore, it is possible to avoid a situation where the ground fault overcurrent relay 51GR2 operates unnecessarily in response to the aforementioned unbalanced current. Furthermore, also in the second embodiment, components such as the canceling earth wire CEL or the current transformer CT2a are not required. Thus, the component cost can be reduced. In addition, the circuit configuration of the ground fault overcurrent relay 51GR2 is applicable regardless of whether the distribution line DL is an overhead line or an underground cable (not affected by the type of distribution line). Thus, the design can be simplified and the design man-hours can be reduced.

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

[0100] [Modification Example of the Second Embodiment] It is preferable that the length of time for which the ground fault overcurrent relay is locked is the minimum necessary. If the lock of the ground fault overcurrent relay continues for a long time after the grounding device ES is energized and the inspection of the power receiving facility 30 is completed, the ground fault overcurrent relay may fail to detect an actual ground fault. Such a situation is not preferable. The ground fault overcurrent relay according to this modification example has a configuration for dealing with such a problem.

[0101] FIG. 7 is a diagram showing the configuration of the ground fault overcurrent relay according to this modification. Referring to FIG. 7, the ground fault overcurrent relay 51GR2a is different from the ground fault overcurrent relay 51GR2 (FIG. 6) of the second embodiment 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, detailed description 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 an input and generates the signal SG2y as an 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 generated or at the start of turning on). Specifically, when the logical value of the signal SG2x changes from "0" to "1", the one-shot circuit 117 generates a signal SG2y having a logical value of "1" for a certain period of time, and then generates a signal SG2y having a logical value of "0". The certain period of time is appropriately determined by a prior evaluation test based on the time from the turn-on of the grounding device ES to the completion of the discharge of the residual charge on the distribution line DL. The certain period of time is, in this example, more than several seconds and less than 1 minute.

[0104] The NOT circuit 111 generates the inverted signal of the signal SG2y as the signal SG2z. The signal SG2z has a logical value of "0" while the signal SG2y is generated as a one-shot pulse (having a logical value of "1"). After the elapse of the above-mentioned fixed time, since the pulse is no longer generated, the signal SG2z has a logical value of "1". Thus, the level (signal value) of the signal SG2z changes only for a fixed time from the time when the input command ON_INS is output or from the start time of the energization operation of the grounding device ES when the grounding device ES is energized. The fixed 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 circuit 115 generates an output signal OSg having a logical value of "0" while the level of the signal SG2z is changing (while the one-shot pulse is being generated), and then generates the output signal OSg according to the signal SG1 (generates the same output signal OSg as the signal SG1).

[0106] With such a configuration, only the output signal OSg indicating non-detection of the ground fault overcurrent is generated (the ground fault overcurrent detection function is locked) from the start time of the energization operation until the time when a fixed time has elapsed from the start time of the energization operation just before the main contact of the grounding device ES actually contacts and the residual charge in the distribution line DL etc. discharges, and the lock is released after the elapse of the fixed time. Thereby, the length of the time during which the ground fault overcurrent detection function is locked can be minimized. Therefore, it is possible to avoid the unnecessary operation of the ground fault overcurrent relay 51GR2a until the fixed time has elapsed, and to reactivate the ground fault overcurrent detection function after the elapse of the fixed time (for example, the ground fault overcurrent can be appropriately detected after the inspection of the power receiving facility 30 is completed).

[0107] [Other Modification Examples] The current transformer CT includes the zero-phase current transformation section ZCT (Figure 2), but it may not include the zero-phase current transformation section ZCT.

[0108] FIG. 8 is a diagram for explaining the configuration of the current transformer CT in this modification. Referring to FIG. 8, the current transformer CT includes a second-phase current conversion unit CTb instead of the zero-phase current conversion unit ZCT. The overcurrent relay 51R further includes an auxiliary current conversion unit ACTb and a level detector LDb. The OR circuit CR generates an output signal OSr based on the logical sum result of the level detectors LDa to LDc. The auxiliary current conversion unit ACTz is configured to be able to detect the currents at the neutral points of the first-phase current conversion unit CTa, the second-phase current conversion unit CTb, and the third-phase current conversion unit CTc. Also in this case, the level detector 105 is configured to be able to detect the 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 FIG. 3, the on-delay circuit 325 and the off-delay circuit 330 have been described as being within the power detector 302, but the on-delay circuit 325 and the off-delay circuit 330 may be provided not within the power detector 302 but within the ground fault overcurrent relay 51GR1.

[0110] It should be considered that all aspects of the embodiments disclosed this time are illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0111] 1 Power transmission and distribution system, 10 Grid power source, 20 Substation equipment, 30 Power receiving equipment, 51GR, 51GR1, 51GR2, 51GR2a, 51GRa, 51GRb Ground fault overcurrent relays, 51R, 51Ra, 51Rb Overcurrent relays, 52, 52F1, 52F2, 52F3 Circuit breakers, 89F2, 89F3, 89F1, 89R, 89Ra, 89Rb Disconnecting switches, DL, DLa, DLb Distribution lines, ES, ES2, Esa, Esb Grounding devices.

Claims

1. A circuit breaker connected to a distribution line that receives power from a three-phase AC power source, A grounding device connected between the distribution line and the ground, A ground fault overcurrent relay configured to detect a ground fault overcurrent in the distribution line, and The ground fault overcurrent relay A first input that receives a first signal indicating a detection result of an unbalanced current in the distribution line, A second input that receives a second signal that is a signal related to the open / closed state of the circuit breaker, A signal output circuit that generates an output signal having a first value indicating detection of the ground fault overcurrent or a second value indicating 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 circuit breaker, the signal output circuit generates the output signal having the first value.

2. A voltage divider provided in the 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, A signal transmission circuit that receives the third signal and transmits it to the signal output circuit, and The signal transmission circuit 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, delays the change of the third signal for a predetermined time and transmits the third signal to the signal output circuit, When the third signal from the voltage detection circuit has not changed from the first state to the second state, transmits the third signal to the signal output circuit, The signal output circuit When the second signal indicates the closed state of the circuit breaker, or when the third signal from the signal transmission circuit indicates the presence of voltage and the first signal indicates the presence of the unbalanced current, Generates the output signal having the first value, the power receiving system according to claim 1.

3. A circuit breaker connected to a distribution line that receives power from a three-phase AC power source, A grounding device connected between the distribution line and the ground, A ground fault overcurrent relay configured to detect a ground fault overcurrent in the distribution line, and The ground fault overcurrent relay A first input that receives a first signal indicating a detection result of an unbalanced current in the distribution line, A second input that receives a second signal that is a signal related to the open / closed state of the grounding device, A signal output circuit configured to generate an output signal having a first value indicating detection of the ground fault overcurrent or a second value indicating non-detection of the ground fault overcurrent according to the first signal and the second signal, A power receiving system in which, when the first signal indicates the presence of the unbalanced current and the second signal is not a signal related to the connection of the grounding device, the signal output circuit generates the output signal having the first value. **Claim 4** The second signal is an output of a signal generation circuit that generates a signal whose level changes for a certain period of time from the time when a connection command for the grounding device is output or from the start time of the connection operation of the grounding device, 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. **Claim 5** A ground fault overcurrent relay configured to detect a ground fault overcurrent in a distribution line that receives power from a three-phase AC power source, wherein a circuit breaker is connected to the distribution line, and a grounding device is connected between the distribution line and the ground, A first input for receiving a first signal indicating a detection result of an unbalanced current in the distribution line, A second input for receiving a second signal that is a signal related to the open / closed state of the circuit breaker, A signal output circuit configured to generate an output signal having a first value indicating detection of the ground fault overcurrent or a second value indicating non-detection of the ground fault overcurrent according to the first signal and the second signal, A ground fault overcurrent relay in which, 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 circuit breaker, the signal output circuit generates the output signal having the first value. **Claim 6** A ground fault overcurrent relay configured to detect a ground fault overcurrent in a distribution line that receives power from a three-phase AC power source, wherein a circuit breaker is connected to the distribution line, and a grounding device is connected between the distribution line and the ground, A first input for receiving a first signal indicating a detection result of an unbalanced current in the distribution line, A second input for receiving a second signal that is a signal related to the open / closed state of the grounding device, A signal output circuit configured to generate an output signal having a first value indicating detection of the ground fault overcurrent or a second value indicating non-detection of the ground fault overcurrent according to the first signal and the second signal, When the first signal indicates the presence of the unbalanced current and the second signal is not a signal related to the connection of the grounding device, the signal output circuit generates the output signal having the first value, a ground fault overcurrent relay.

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