JP2011227020A - Ground fault detecting system for distribution transformer secondary side - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground fault detecting system for the secondary side of a distribution transformer, which is capable of identifying an accidental portion when a ground fault accident occurs at the secondary side of the distribution transformer.SOLUTION: A ground fault detecting system for the secondary side of a distribution transformer comprises a ground-fault portion detecting device 10 that judges whether a ground-fault accident at the secondary side of a distribution transformer 1 is a power cable internal accident, an external accident in the distribution transformer side or a load side external accident on the basis of a zero-phase current transformer ZCT that is installed so that a secondary power cable 2 penetrates through the edge of a distribution transformer 1 side of the secondary power cable 2, a first instrument current transformer CT1 that is installed in a ground wire of a surge absorber SA, a secondary instrument current transformer CT2 that is installed in the ground wire of a metal sheath of the secondary power cable 2, a ZCT output current Ithat is input from the zero-phase current transformer ZCT, and a first CT output current Iand a second CT output current Ithat are respectively input from the first instrument current transformer CT1 and the secondary instrument current transformer CT2.

Description

  TECHNICAL FIELD The present invention relates to a distribution transformer secondary side ground fault detection system, and in particular, a distribution transformer suitable for specifying a ground fault accident location when a ground fault occurs on the secondary side of the distribution transformer. The present invention relates to a secondary side ground fault detection system.

Conventionally, when a ground fault has occurred on the secondary side of the distribution transformer 1 shown in FIG. 9 (6 kV bus side of the distribution transformer 1), for example, the ground fault sequence interrupting device (10G) 4 is The ground fault is detected based on the second GPT output voltage V _GPT2 (zero phase voltage V ₀ ) input from the second grounded instrument transformer GPT2 installed on the 6 kV bus, and the 6 kV bus is detected. The distribution circuit breakers CB1 and CB2 and the transformer primary circuit breaker CB installed on the distribution lines branched from the line are sequentially disconnected.

Alternatively, the ground fault overvoltage relay (64V) 3 is input from the first grounded-type instrument transformer GPT1 installed on the distribution line transformer 1 side (the side opposite to the 6 kV bus) of the transformer secondary circuit breaker CB0. This ground fault is detected based on the first GPT output voltage V _GPT1 (zero phase voltage V ₀ ) and the transformer primary circuit breaker CB is cut off.

  In the ground fault detection method disclosed in Patent Document 1 below, the secondary power is detected by detecting the current flowing in the ground wire of the metal shield (metal sheath) of the secondary power cable on the secondary side of the main transformer. The occurrence of a ground fault in the cable is determined.

Japanese Patent Laid-Open No. 2000-9786

  However, in the ground fault detection method using the ground fault sequence interrupting device 4, the ground fault accident location (ground fault occurrence location) can be specified for the ground fault occurring in the distribution line, but the distribution transformer When a ground fault has occurred between No. 1 and the transformer secondary circuit breaker CB0, the location of the ground fault cannot be specified, so the 22kV supply line is drawn from the tertiary of the distribution transformer 1 There was a problem that it took time to recover from the accident.

  The ground fault detection method using the ground fault overvoltage relay 3 can detect a ground fault occurring between the distribution transformer 1 and the transformer secondary circuit breaker CB0. Either a cable internal accident (accident that occurred in the secondary power cable 2 on the secondary side of the distribution transformer 1) or a load-side external accident (between the secondary power cable 2 and the transformer secondary circuit breaker CB0) Or the distribution transformer side external accident (accident that occurred on the distribution transformer 1 side rather than the secondary power cable 2).

  The ground fault detection method disclosed in the above-mentioned Patent Document 1 is for determining the occurrence of a ground fault in the secondary power cable 2, and a ground fault is detected on the secondary side of the distribution transformer 1. It is not specified whether there is a power cable internal accident, a load-side external accident, or a distribution transformer-side external accident.

  An object of the present invention is to provide a distribution transformer secondary-side ground fault detection system capable of specifying the location of a ground fault accident that has occurred on the secondary side of a distribution transformer.

The first distribution transformer secondary side ground fault detection system of the present invention is for distribution to specify a ground fault accident location when a ground fault occurs on the secondary side of the distribution transformer (1). A transformer secondary-side ground fault detection system, wherein a zero-phase current transformer (2) provided so that the secondary power cable passes through an end of the secondary power cable (2) on the distribution transformer side ZCT) and a first current transformer (CT1) attached to a ground line of a surge absorber (SA) or a charging current compensation capacitor provided between the distribution transformer and the secondary power cable. ), A second instrument current transformer (CT2) attached to the ground wire of the metal sheath of the secondary power cable, the ZCT output current (I _ZCT ) input from the zero-phase current _transformer, and the First and second CT outputs input from first and second instrument current transformers Based on the flow (I _CT1, I _CT2), the power cable internal fault when there is a ground fault in the secondary side of the distribution transformers, one of the distribution transformer side external fault and load-side external accident And a ground fault location detecting device (10) for determining whether or not.
Here, the ground fault location detecting device determines whether the first and second CT output current directions are the same and whether the ZCT output current direction is the external direction or the internal direction. It may be determined whether the distribution transformer side external accident or the load side external accident.
If the direction of the first CT output current and the direction of the second CT output current are opposite to each other, the ground fault location detecting device determines that a power cable internal fault has occurred, and the first CT output current And the direction of the second CT output current are the same direction and the direction of the ZCT output current is the external direction, it is determined that a load-side external accident has occurred, and the first CT output current If the direction and the direction of the second CT output current are the same direction, and the direction of the ZCT output current is the internal direction, it may be determined that the distribution transformer side external accident has occurred.
The ground fault location detection device has a zero-phase GPT output voltage (V _GPT1 ) input from a grounded instrument transformer (GPT1) installed on the opposite side of the distribution transformer from the secondary power cable. If it is equal to or higher than the voltage set value (V ₀₀ ), it may be determined that a ground fault has occurred, and the location of the ground fault may be specified.
The second distribution ground fault detection system of the present invention for distribution is used for specifying a ground fault accident location when there is a ground fault on the secondary side of the distribution transformer (1). A transformer secondary-side ground fault detection system between the distribution transformer and a secondary power cable (2) between a surge absorber (SA) or a charging current compensation capacitor on the distribution transformer side. A grounded-type instrument transformer (GPT1) installed, and a first zero-phase current transformer provided so that the secondary power cable penetrates the end of the secondary power cable on the distribution transformer side The secondary power cable penetrates the other end of the secondary power cable and the grounding wire of the metal sheath of the secondary power cable toward the distribution transformer. A second zero-phase current transformer (ZCT2) provided; Based on the first and second ZCT output current is input from the second zero-phase current transformer (I _ZCT1, I _ZCT2), power if there is a ground fault in the secondary side of the distribution transformer And a ground fault location detecting device (50) for determining whether the accident is a cable internal accident, a load-side external accident, or a distribution transformer-side external accident.
Here, the ground絡個plants detecting apparatus, the direction of the first ZCT output current I _ZCT1, based on the direction and magnitude of the second ZCT output current I _ZCT2, power cables internal fault, distribution transformers It may be determined whether the device side external accident or the load side external accident.
The ground fault location detecting device determines that the power cable has an internal fault when the direction of the first ZCT output current is an external direction and the magnitude of the second ZCT output current is zero, If the direction of the first ZCT output current is the external direction and the magnitude of the second ZCT output current is not zero but the direction is the external direction, it is determined that a load-side external accident has occurred. If the direction of the ZCT output current is the internal direction, it may be determined that the distribution transformer side external accident has occurred.
If the GPT output voltage (V _GPT1 ) input from the grounded-type instrument transformer is equal to or higher than the zero-phase voltage set value (V ₀₀ ), the ground fault location detecting device determines that a ground fault has occurred. Then, the location of the ground fault may be identified.

The distribution transformer secondary side ground fault detection system of the present invention has the following effects.
(1) Since the path of the fault current that flows when there is a ground fault on the secondary side of the distribution transformer, the secondary power cable is connected to the end of the secondary power cable on the distribution transformer side. A zero-phase current transformer is provided so as to penetrate, and the first instrument current transformer is attached to the ground line of the surge absorber or the charging current compensating capacitor, and the second current cable is attached to the ground line of the metal sheath of the secondary power cable. Install a current transformer and install a grounded instrument transformer between the distribution transformer and the surge absorber or charging current compensation capacitor by determining the direction of the current flowing through them. A first zero-phase current transformer is provided so that the secondary power cable penetrates the end of the secondary power cable on the distribution transformer side, and the secondary power cable penetrates the other end of the secondary power cable. And secondary Install a second zero-phase current transformer so that the grounding wire of the metal sheath of the power cable penetrates toward the distribution transformer, and determine the direction of the current flowing through them. Whether it is an external accident or an external accident on the distribution transformer side can be determined.
(2) Accident recovery can be shortened when a 22 kV supply line is drawn from the tertiary of the distribution transformer.

It is a figure which shows the structure of the distribution transformer secondary side ground fault detection system by 1st Example of this invention. It is a figure for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 27 shown in FIG.1 (b). It is a figure for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 27 shown in FIG.1 (b). It is a flowchart for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 27 shown in FIG.1 (b). It is a figure which shows the structure of the distribution transformer secondary side ground fault detection system by the 2nd Example of this invention. It is a figure for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 67 shown in FIG.5 (b). It is a figure for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 67 shown in FIG.5 (b). It is a flowchart for demonstrating the identification method of the ground fault accident location in the ground fault location specific | specification part 67 shown in FIG.5 (b). It is a figure for demonstrating the conventional ground fault detection method.

  For the above purpose, a ZCT output current input from a zero-phase current transformer provided so that the secondary power cable passes through the end of the secondary power cable on the distribution transformer side, and a distribution transformer; A first CT output current input from a first instrument current transformer attached to a ground wire of a surge absorber provided between the secondary power cable and a ground wire of a metal sheath of the secondary power cable Based on the second CT output current input from the second instrumental current transformer attached to the power transformer, if there is a ground fault on the secondary side of the distribution transformer, This was realized by judging whether it was a distribution-side external accident or a load-side external accident.

Hereinafter, an embodiment of a distribution transformer secondary side ground fault detection system of the present invention will be described with reference to the drawings.
As shown in FIG. 1 (a), the distribution transformer secondary side ground fault detection system according to the first embodiment of the present invention includes three secondary power cables 2 (red, white and blue phase 2). Zero-phase current transformer ZCT provided so that three secondary power cables 2 penetrate through the end of the distribution transformer 1 side of the secondary power cable), and the distribution transformer 1 and the three secondary power cables The first instrumental current transformer CT1 attached to the grounding wire of the surge absorber SA provided between the power cable 2 and the grounding wire of the metal sheath of the three secondary power cables 2 (secondary power cable) 2 is provided at the end of the transformer secondary circuit breaker CB0 side.) And a ground fault location detecting device 10 is provided.

Here, the ground fault location detecting device 10 includes a ZCT output current I _ZCT (zero phase current I ₀ ) input from the zero phase current _{transformer ZCT} and first and second instrument current transformers CT1 and CT2. From the first and second CT output currents I _CT1 and I _CT2 to be input, and from the first grounded instrument transformer GPT1 installed between the secondary power cable 2 and the transformer secondary circuit breaker CB0 Based on the input first GPT output voltage V _GPT1 (zero phase voltage V ₀ ), if there is a ground fault on the secondary side of the distribution transformer 1, an internal accident in the power cable, an external accident on the load side And to identify whether the accident is an external accident on the distribution transformer side.

  Therefore, as shown in FIG. 1B, the ground fault location detection device 10 includes an analog input unit 20, a set value memory 26, a ground fault location specifying unit 27, and a display control unit 28. The analog input unit 20, the settling value memory 26, the ground fault location specifying unit 27, and the display control unit 28 are connected through a bus.

  Here, the analog input unit 20 includes an input converter 21, a band pass filter 22 (hereinafter referred to as “BPF 22”), and a sampling hold circuit 23 (hereinafter referred to as “S / H circuit 23”). And a multiplexer circuit 24 (hereinafter referred to as “MPX circuit 24”) and an analog / digital converter 25 (hereinafter referred to as “A / D converter 25”).

The BPF 22 receives the first and second instrument current transformers CT1 and CT2, the zero-phase current transformer ZCT, and the first grounded instrument transformer GPT1 through the input converter 21. _Only the AC components (for example, commercial frequency 60 Hz) of the two CT output currents I _CT1 and I _CT2 , the ZCT output current I _{ZCT and} the first GPT output voltage V _GPT1 are extracted.
The S / H circuit 23 samples and holds the output signal of the BPF 22 at a predetermined sampling frequency (for example, 5760 Hz (electrical angle 3.75 ° in the case of a commercial frequency of 60 Hz)).
The MPX circuit 24 switches the output signal of the S / H circuit 23 and outputs it to the A / D converter 25.
The A / D converter 25 converts the AC first and second CT output currents I _CT1 and I _CT2 , the ZCT output current I _ZCT , and the first GPT output voltage V _GPT1 input from the MPX circuit 24. The digital first and second CT output currents I _CT1 and I _CT2 , the ZCT output current I _{ZCT and} the first GPT output voltage V _GPT1 (hereinafter, unless otherwise specified, “first and second CT output currents I _CT1 and _ICT2 ”,“ ZCT output current I _ZCT ”and“ first GPT output voltage V _GPT1 ”).

The settling value memory 26 is for storing a zero-phase voltage settling value V ₀₀ or the like input from the outside.

The ground fault location specifying unit 27 is based on the first and second CT output currents I _CT1 and I _CT2 , the ZCT output current I _{ZCT and} the first GPT output voltage V _GPT1 input from the A / D converter 25. The ground fault location is identified as follows.

(1) First and second CT output currents I _CT1 and I _{CT2 and} ZCT output current I _ZCT at the time of an accident inside the power cable
When a ground fault occurs inside the secondary power cable 2, as shown in the equivalent circuit of FIG. 2A, the fault point → the metal sheath of the secondary power cable 2 → the ground of the metal sheath of the secondary power cable 2 Wire (second instrument current transformer CT2) → Surge absorber SA grounding wire (first instrument current transformer CT1) → Secondary power cable 2 core wire (zero phase current transformer ZCT) → Fault point As the first fault current I ₁ flows along the path, the fault point → the metal sheath of the secondary power cable 2 → the ground capacitance C of the secondary power cable 2 → the core of the secondary power cable 2 → the path of the fault point A second fault current I ₂ flows.
As a result, the direction of the _first fault current I ₁ passing through the first instrument current transformer CT1 is opposite to the direction of the first fault current I ₁ passing through the second instrument current transformer CT2. Therefore, the direction of the first CT output current I _{CT1 and} the direction of the second CT output current I _CT2 input to the ground fault location specifying device 10 are opposite directions (the first and second CT output currents I _CT1 , I _CT2 phase difference is outside the range of ± 90 °) (see FIG. 3A).
Further, since the first fault current I ₁ passing through the zero-phase current transformer ZCT is directed from the distribution transformer 1 to the secondary power cable 2, the ZCT output current input to the ground fault location specifying device 10. The direction of I _ZCT is the external direction (the range of 0 ° to −180 ° when the phase of the ZCT output current I _{ZCT is based on} the phase of the first GPT output voltage V _GPT1 as shown in FIG. 3B). (Refer to FIG. 3A).

(2) First and second CT output currents I _CT1 and I _{CT2 and a} ZCT output current I _ZCT at the time of an external accident on the load side
When a ground fault occurs between the secondary power cable 2 and the transformer secondary circuit breaker CB0, as shown in the equivalent circuit of FIG. 2 (b), the fault point → the ground line of the surge absorber SA (first the first fault current I ₁ with flow in the path of the current transformer CT1) → 2 primary power cables 2 of the core wire (ZCT ZCT) → fault point, the fault point → 2 primary power cable 2 metal Sheath grounding wire (second instrument current transformer CT2) → Metal sheath of secondary power cable 2 → Ground capacitance C of secondary power cable 2 → Core wire of secondary power cable 2 → Path of accident point A second fault current I ₂ flows.
As a result, the direction of the _first fault current I ₁ passing through the first instrument current transformer CT1 and the direction of the second fault current I ₂ passing through the second instrument current transformer CT2 are the same. Therefore, the direction of the first CT output current I _{CT1 and} the direction of the second CT output current I _CT2 input to the ground fault location specifying device 10 are the same direction (first and second CT output currents I _CT1 , I _{CT2 has} a phase difference within a range of ± 90 ° (see FIG. 3A).
Further, since the first fault current I ₁ passing through the zero-phase current transformer ZCT is directed from the distribution transformer 1 to the secondary power cable 2, the ZCT output current input to the ground fault location specifying device 10. The direction of I _ZCT is the external direction (the range of 0 ° to −180 ° when the phase of the ZCT output current I _{ZCT is based on} the phase of the first GPT output voltage V _GPT1 as shown in FIG. 3B). (Refer to FIG. 3A).

(3) First and second CT output currents I _CT1 , I _{CT2 and} ZCT output current I _ZCT at the time of an external fault on the distribution transformer side
When a ground fault occurs between the distribution transformer and the secondary power cable 2, as shown in the equivalent circuit of FIG. 2 Current transformer CT2) → Metal sheath of secondary power cable 2 → Ground capacitance C of secondary power cable 2 → Core wire of secondary power cable 2 (zero-phase current transformer ZCT) → Fault point The first fault current I ₁ flows along the path, and the fault point → the ground line of the surge absorber SA (first current transformer CT1) → the core of the secondary power cable 2 → the second path in the path of the fault point fault current I ₂ flows.
As a result, the direction of the second fault current I ₂ passing through the first instrument current transformer CT1 and the direction of the first fault current I ₁ passing through the second instrument current transformer CT2 are the same. Therefore, the direction of the first CT output current I _{CT1 and} the direction of the second CT output current I _CT2 input to the ground fault location specifying device 10 are the same direction (first and second CT output currents I _CT1 , I _{CT2 has} a phase difference within a range of ± 90 ° (see FIG. 3A).
In addition, since the first fault current I ₁ passing through the zero-phase current transformer ZCT is directed from the secondary power cable 2 to the distribution transformer 1, the ZCT output current input to the ground fault location specifying device 10. The direction of I _ZCT is the internal direction (the phase of the ZCT output current I _ZCT falls within the range of 0 ° to 180 ° when the phase of the first GPT output voltage V _GPT1 is used as shown in FIG. 3C). Direction) (see FIG. 3A).

Therefore, when the first GPT output voltage V _GPT1 is equal to or higher than the zero-phase voltage set value V ₀₀ (step S11 in FIG. 4), the ground fault location specifying unit 27 determines that a ground fault has occurred, and In order to identify the location of the fault, the direction of the first CT output current I _CT1 is compared with the direction of the second CT output current I _CT2 (step S12).
As a result, if the direction of the first CT output current I _CT1 is opposite to the direction of the second CT output current I _CT2 , the ground fault location specifying unit 27 determines that the power cable has an internal accident (step S14). .
On the other hand, if the direction of the first CT output current I _{CT1 and} the direction of the second CT output current I _CT2 are the same direction, the ground fault location specifying unit 27 indicates that the direction of the ZCT output current I _ZCT is the internal direction. Or whether the direction is the outside (step S13).
As a result, if the direction of the ZCT output current I _ZCT is the external direction, the ground fault location specifying unit 27 determines that the load-side external accident has occurred (step S15).
On the other hand, if the direction of the ZCT output current I _ZCT is the internal direction, the ground fault location specifying unit 27 determines that the distribution transformer side external accident has occurred (step S16).
Thereby, the ground fault accident location can be specified.

  The display control unit 28 displays the ground fault location specified by the ground fault location specifying unit 27 on an external display device.

Next, a secondary transformer ground fault detection system for distribution according to a second embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 5 (a), the distribution transformer secondary-side ground fault detection system according to the present embodiment has three secondary power cables 2 (red, white and blue phase secondary power cables). The first zero-phase current transformer ZCT1 provided so that three secondary power cables 2 penetrate through the end of the distribution transformer 1 side, and the transformer secondary of the three secondary power cables 2 The three secondary power cables 2 pass through the end of the circuit breaker CB0 side, and the grounding wire of the metal sheath of the three secondary power cables 2 faces the distribution transformer 1 from the transformer secondary circuit breaker CB0. And a second zero-phase current transformer ZCT2 provided so as to penetrate therethrough and a ground fault location detecting device 50.
In the distribution transformer secondary side ground fault detection system according to the present embodiment, the first grounded instrument transformer GPT1 is installed between the distribution transformer 1 and the surge absorber SA.

Here, the land絡個plants detector 50, the first and second ZCT output current I _ZCT1, I _ZCT2 input from the first and second zero-phase current transformer ZCT1, ZCT2, first earth type Inside the power cable when there is a ground fault on the secondary side of the distribution transformer 1 based on the first GPT output voltage V _GPT1 (zero phase voltage V ₀ ) input from the instrument transformer GPT1 This is to determine whether the accident is an accident on the load side or an external accident on the distribution transformer side.

  Therefore, as shown in FIG. 5B, the ground fault location detection device 50 includes an analog input unit 60, a set value memory 66, a ground fault location specifying unit 67, and a display control unit 68. The analog input unit 60, the set value memory 66, the ground fault location specifying unit 67, and the display control unit 68 are connected via a bus.

  Here, the analog input unit 60 includes an input converter 61, a band pass filter 62 (hereinafter referred to as “BPF 62”), and a sampling hold circuit 63 (hereinafter referred to as “S / H circuit 63”). , A multiplexer circuit 64 (hereinafter referred to as “MPX circuit 64”) and an analog / digital converter 65 (hereinafter referred to as “A / D converter 65”).

The BPF 62 includes first and second ZCT output currents I _ZCT1 input from the first and second zero-phase current transformers ZCT1 and ZCT2 and the first grounded instrument transformer GPT1 via the input converter 61. , the AC component of the I _ZCT2 and first GPT output voltage V _GPT1 (e.g., commercial frequency 60Hz) to extract only.
The S / H circuit 63 samples and holds the output signal of the BPF 62 at a predetermined sampling frequency (for example, 5760 Hz (electrical angle 3.75 ° in the case of a commercial frequency of 60 Hz)).
The MPX circuit 64 switches the output signal of the S / H circuit 63 and outputs it to the A / D converter 65.
A / D converter 65, first and second digital AC components of the MPX circuit first and second analog input from 64 ZCT output current I _ZCT1, I _ZCT2 and first GPT output voltage V _GPT1 2 of ZCT output current I _ZCT1, I _ZCT2 and first GPT output voltage V _GPT1 (hereinafter, unless otherwise stated, the "first and second ZCT output current I _ZCT1, I _ZCT2" and "first GPT output This is converted to an AC component of voltage V _GPT1 ”

The settling value memory 66 is for storing a zero-phase voltage settling value V ₀₀ or the like input from the outside.

Earth絡個plant identification unit 67, based on the first and second ZCT output current I _ZCT1, I _ZCT2 and first GPT output voltage V _GPT1 inputted from the A / D converter 65, as follows Identify the ground fault location.

(1) Power cable internal fault when the first and second ZCT output current I _ZCT1, I _ZCT2
When a ground fault occurs inside the secondary power cable 2, as shown in the equivalent circuit of FIG. 6A, the fault point → the metal sheath of the secondary power cable 2 (second zero-phase current transformer ZCT2) → Metal sheath grounding wire of secondary power cable 2 (second zero-phase current transformer ZCT2) → Grounding wire of surge absorber SA → Core wire of secondary power cable 2 (first zero-phase current transformer ZCT1) → The first fault current I ₁ flows along the path of the fault point, and the fault point → the metal sheath of the secondary power cable 2 → the ground capacitance C of the secondary power cable 2 → the core of the secondary power cable 2 → the fault point The second fault current I ₂ flows through the path.
As a result, the direction of the first fault current I ₁ passing through the first zero-phase current transformer ZCT1 is directed from the distribution transformer 1 to the secondary power cable 2, and thus the ground fault location specifying device 50 The direction of the first ZCT output current I _ZCT1 input to the external direction is the external direction (the phase of the first GPT output voltage V _GPT1 is the reference as shown in FIG. _7C , where the phase of the first ZCT output current I _ZCT1 is In the direction from 0 ° to −180 °) (see FIG. 7A).
In addition, the first accident current I ₁ flowing through the metal sheath of the secondary power cable 2 passing through the second zero-phase current transformer ZCT ₂ and the first accident flowing through the ground wire of the metal sheath of the secondary power cable 2 since the same magnitude direction of the current I ₁ are canceled each other become opposite, second ZCT output current I _ZCT2 inputted to the ground絡個plant identification device 10 becomes zero (see FIG. 7 (a)).

(2) the load side external accident of the first and second ZCT output current I _ZCT1, I _ZCT2
When a ground fault occurs between the secondary power cable 2 and the transformer secondary circuit breaker CB0, as shown in the equivalent circuit of FIG. 6B, the fault point → the ground line of the surge absorber SA → the secondary power The core wire of the cable 2 (first zero-phase current transformer ZCT1) → the core wire of the secondary power cable 2 (second zero-phase current transformer ZCT2) → the first fault current I ₁ flows through the path of the fault point , Accident point → grounding wire of the metal sheath of the secondary power cable 2 (second zero-phase current transformer ZCT2) → metal sheath of the secondary power cable 2 (second zero-phase current transformer ZCT2) → secondary power The ground capacitance C of the cable 2 → the core of the secondary power cable 2 (second zero-phase current transformer ZCT2) → the second fault current I ₂ flows along the path of the fault point.
As a result, the direction of the first fault current I ₁ passing through the first zero-phase current transformer ZCT1 is directed from the distribution transformer 1 to the secondary power cable 2, and thus the ground fault location specifying device 50 The direction of the first ZCT output current I _ZCT1 input to the external direction is the external direction (the phase of the first GPT output voltage V _GPT1 is the reference as shown in FIG. _7C , where the phase of the first ZCT output current I _ZCT1 is In the direction from 0 ° to −180 °) (see FIG. 7A).
In addition, the second fault current I ₂ flowing through the metal sheath of the secondary power cable 2 penetrating the second zero-phase current transformer ZCT2 and the second fault current flowing through the ground wire of the metal sheath of the secondary power cable 2 Since the currents flowing through the core of the secondary power cable 2 are the sum of the first accident current I ₁ and the second accident current I ₂ , the magnitude is the same as I ₂ but the directions are reversed and cancel each other. , the direction of the second ZCT output current I _ZCT2 inputted to the ground絡個plant identification device 10 is an external direction (see FIG. 7 (a)).

(3) distribution transformer side external accident of the first and second ZCT output current I _ZCT1, I _ZCT2
When a ground fault occurs between the distribution transformer and the secondary power cable 2, as shown by the equivalent circuit in FIG. 2 zero-phase current transformer ZCT2) → secondary power cable 2 metal sheath (second zero-phase current transformer ZCT2) → secondary power cable 2 ground capacitance C → secondary power cable 2 core ( the first fault current I ₁ with flows in the path of the first zero-phase current transformer ZCT1) → fault point, the core wire → fault point of the grounding line → 2 primary power cables 2 of the fault point → surge absorber SA 2 Accident current I ₂ flows.
As a result, the direction of the first fault current I ₁ passing through the first zero-phase current transformer ZCT1 is directed from the secondary power cable 2 to the distribution transformer 1, so that the ground fault location specifying device 50 The direction of the first ZCT output current I _ZCT1 input to the internal direction is the internal direction (the phase of the first _ZPT output voltage V _{GPT1 is based on} the phase of the first ZCT output current I _ZCT1 as shown in FIG. 7B). In the direction of 0 ° to 180 °) (see FIG. 7A).
In addition, the first fault current I ₁ flowing through the metal sheath of the secondary power cable 2 passing through the second zero-phase current transformer ZCT2 and the first fault current flowing through the ground wire of the metal sheath of the secondary power cable 2 because cancel each other out becomes opposite have the same magnitude direction of the I _1, second ZCT output current I _ZCT2 inputted to the ground絡個plant identification device 10 becomes zero (see FIG. 7 (a)).

Therefore, when the first GPT output voltage V _GPT1 is equal to or higher than the zero-phase voltage set value V ₀₀ (step S21 in FIG. 8), the ground fault location identifying unit 67 determines that a ground fault has occurred, In order to specify the location of the fault, the direction of the first ZCT output current I _ZCT1 is examined (step S22).
As a result, _if the direction of the first ZCT output current I _ZCT1 is the internal direction, the ground fault location specifying unit 67 determines that the distribution transformer side external accident has occurred (step S26).
On the other hand, when the direction of the first ZCT output current I _ZCT1 is external direction, land絡個plant identification unit 67 examines the direction and magnitude of the second ZCT output current I _ZCT2 (step S23).
As a result, determines the magnitude of the second ZCT output current I _ZCT2 is If it is zero, the land絡個plant identification unit 67 and the power cable internal fault (step S24).
On the other hand, not with a size of zero second ZCT output current I _ZCT2, and, when the direction of the second ZCT output current I _ZCT2 is external direction, land絡個plant identification unit 67 and the load side external accident determining (Step S25).
Thereby, the ground fault accident location can be specified.

  The display control unit 68 displays the ground fault location specified by the ground fault location specifying unit 67 on an external display device.

  In the above, the case where the surge absorber SA is provided between the distribution transformer 1 and the secondary power cable 2 has been described as an example. However, when the surge absorber SA is not installed, a charging current compensation capacitor is used. What is necessary is just to install between the transformer 1 for power distribution, and the secondary power cable 2. FIG.

DESCRIPTION OF SYMBOLS 1 Distribution transformer 2 Secondary power cable 3 Ground fault overvoltage relay 4 Ground fault sequence interruption | blocking apparatus 10, 50 Ground fault location detection apparatus 20, 60 Analog input part 21, 61 Input converter 22, 62 Band pass filter (BPF)
23, 63 Sampling hold circuit (S / H circuit)
24, 64 Multiplexer circuit (MPX circuit)
25, 65 Analog / digital converter (A / D converter)
26, 66 Setting value memory 27, 67 Ground fault location specifying unit 28, 68 Display control unit SA Surge absorber GPT1, GPT2 First and second grounded instrument transformer CB Transformer primary circuit breaker CB0 Transformer secondary Breakers CB1, CB2 Distribution line breakers CT1, CT2 First and second instrument current transformers ZCT Zero-phase current transformers ZCT1, ZCT2 First and second zero-phase current transformers V _GPT1 , V _GPT2 First and second GPT output voltage V ₀ the zero-phase voltage V ₀₀ zero-phase voltage set value I _ZCT ZCT output current I _ZCT1, I _ZCT2 first and second ZCT output current I ₀ zero-phase current I _CT1, I _CT2 first And second CT output currents I ₁ , I ₂ first and second fault currents C to ground capacitances S11-16, S21-S26 steps

Claims (8)

A distribution transformer secondary side ground fault detection system for identifying a ground fault accident location when a ground fault occurs on the secondary side of the distribution transformer (1),
A zero-phase current transformer (ZCT) provided so that the secondary power cable passes through the end of the secondary power cable (2) on the side of the distribution transformer;
A first current transformer (CT1) attached to a ground line of a surge absorber (SA) or a charging current compensation capacitor provided between the distribution transformer and the secondary power cable;
A second instrumental current transformer (CT2) attached to the ground wire of the metal sheath of the secondary power cable;
The ZCT output current (I _ZCT ) input from the zero-phase current _transformer and the first and second CT output currents (I _CT1 , I _CT2 ) input from the first and second instrument current transformers Based on the above, when there is a ground fault on the secondary side of the distribution transformer, it is determined whether it is a power cable internal accident, a distribution transformer external accident, or a load external accident A ground fault location detection device (10);
A secondary-side ground fault detection system for a distribution transformer, comprising:   The ground fault location detecting device has a power cable internal fault and power distribution based on whether the directions of the first and second CT output currents are the same and whether the direction of the ZCT output current is an external direction or an internal direction. 2. The distribution transformer secondary-side ground fault detection system according to claim 1, wherein it is determined whether the transformer-side external accident or the load-side external accident. The ground fault location detecting device is
When the direction of the first CT output current and the direction of the second CT output current are opposite directions, it is determined that the power cable has an internal accident,
When the direction of the first CT output current and the direction of the second CT output current are the same direction, and the direction of the ZCT output current is an external direction, it is determined as a load-side external accident,
When the direction of the first CT output current and the direction of the second CT output current are the same direction, and the direction of the ZCT output current is the internal direction, it is determined that the distribution transformer side external accident has occurred. To
3. The distribution transformer secondary-side ground fault detection system according to claim 2, wherein: The ground fault location detection device has a zero-phase GPT output voltage (V _GPT1 ) input from a grounded instrument transformer (GPT1) installed on the opposite side of the distribution transformer from the secondary power cable. The distribution transformer according to any one of claims 1 to 3, wherein if it is equal to or higher than the voltage set value (V ₀₀ ), it is determined that a ground fault has occurred and the location of the ground fault is specified. Secondary side ground fault detection system. A distribution transformer secondary side ground fault detection system for identifying a ground fault accident location when a ground fault occurs on the secondary side of the distribution transformer (1),
A grounding-type instrument transformer (GPT1) installed between the distribution transformer and the surge absorber (SA) or the charging current compensation capacitor on the distribution transformer side of the secondary power cable (2); ,
A first zero-phase current transformer (ZCT1) provided so that the secondary power cable passes through an end of the secondary power cable on the side of the distribution transformer;
The second power cable is provided so that the secondary power cable penetrates to the other end of the secondary power cable and a grounding wire of a metal sheath of the secondary power cable penetrates toward the distribution transformer. Zero-phase current transformer (ZCT2),
Based on the first and second ZCT output current inputted from the first and second zero-phase current transformer (I _ZCT1, I _ZCT2), the ground fault on the secondary side of the distribution transformer A ground fault location detection device (50) for determining whether there is a power cable internal accident, a load-side external accident, or a distribution transformer-side external accident,
A secondary-side ground fault detection system for a distribution transformer, comprising: The ground絡個plants detecting apparatus, the direction of the first ZCT output current I _ZCT1, based on the direction and magnitude of the second ZCT output current I _ZCT2, power cables internal fault, distribution transformer side external 6. The distribution transformer secondary side ground fault detection system according to claim 5, wherein it is determined whether the accident is an accident or a load-side external accident. The ground fault location detecting device is
When the direction of the first ZCT output current is an external direction and the magnitude of the second ZCT output current is zero, it is determined that the power cable has an internal accident,
When the direction of the first ZCT output current is an external direction and the magnitude of the second ZCT output current is not zero but the direction is an external direction, it is determined that a load-side external accident is caused.
When the direction of the first ZCT output current is the internal direction, it is determined that the power distribution transformer side external accident has occurred.
The distribution transformer secondary-side ground fault detection system according to claim 6, wherein the distribution transformer secondary-side ground fault detection system is characterized. If the GPT output voltage (V _GPT1 ) input from the grounded-type instrument transformer is equal to or higher than the zero-phase voltage set value (V ₀₀ ), the ground fault location detecting device determines that a ground fault has occurred. The ground fault detection system according to any one of claims 5 to 7, wherein a ground fault accident location is identified.

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