JP5972097B2 - High voltage insulation monitoring device and high voltage insulation monitoring method - Google Patents

Description

  The present invention relates to a high voltage insulation monitoring device and a high voltage insulation monitoring method, and, for example, relates to a high voltage insulation monitoring device and a high voltage insulation monitoring method for detecting a decrease in insulation of a high voltage distribution line.

  In high-voltage power receiving equipment, it is common to provide a ground fault protection by installing a switch (section switch) at a power receiving point from the distribution system and combining the switch with a ground fault relay. Normally, a ground fault relay of a high-voltage power receiving facility performs a shut-off operation by a switch when a ground fault occurs that exceeds the set values of zero-phase voltage and zero-phase current set from the viewpoint of protection coordination with the distribution system. Do. Moreover, when performing a breaking operation, the ground fault relay obtains a load current value for protecting the rated breaking capacity of the switch from a current transformer (CT) inside the switch.

  As a method for detecting the above-mentioned ground fault, a zero phase voltage and a zero phase current are obtained by a zero phase voltage detector (ZPD) and a zero phase current transformer (ZCT) in a switch, and the obtained zero phase is obtained. A method of detecting a ground fault using a voltage and a zero-phase current is used (see, for example, Patent Document 1). In addition, the insulation resistance value at the time of the ground fault becomes 0 to several tens kΩ, and the ground fault relay detects a zero-phase current of about 100 mA for the detection of the ground fault.

JP-A-6-284559

  However, instead of detecting the ground fault as described above, it is necessary to detect a high resistance of several MΩ, that is, to detect a zero-phase current of several mA, in order to detect a decrease in insulation before the occurrence of the ground fault. An error due to the load current occurs in the zero-phase current, which hinders detection of a zero-phase current of several mA flowing at a high resistance of several MΩ. Therefore, an error in the zero-phase current due to the load current becomes a problem in detecting the insulation drop before the occurrence of the ground fault, and it is difficult to detect the insulation drop with high accuracy. For example, in the 6 MΩ insulation drop detection, it is necessary to detect a zero-phase current equivalent to 1 mA. However, the load current has a large effect on the zero-phase current equivalent to 1 mA, which is an obstacle to highly accurate insulation drop detection. Yes.

  The cause of the output error of the zero-phase current transformer due to the load current (zero-phase current error) is that the shape of the zero-phase current transformer in the switch is not a perfect circle, and each three-phase line is a zero-phase current transformer. This is because variation occurs in the influence of the magnetic field lines on the core of the vessel. In addition, because of the difference in the positional relationship between the main line and the zero-phase current transformer for each individual switch and the machining state, the output error of the zero-phase current transformer becomes a specific size for each individual switch. .

  The present invention has been made in view of the above, and an object of the present invention is to provide a high voltage insulation monitoring device and a high voltage insulation monitoring method capable of performing highly accurate insulation deterioration detection.

  A high voltage insulation monitoring device according to the present invention is a high voltage insulation monitoring device that detects a decrease in insulation of a high voltage distribution line, a zero phase current transformer that detects a zero phase current of the high voltage distribution line, and each phase of the high voltage distribution line Using the current transformer that detects the load current of the current, the load current of each phase detected by the current transformer, and the characteristics of the zero-phase current transformer, the error of the zero-phase current due to the effect of the load current of each phase is suppressed A correction unit for correcting the zero-phase current detected by the zero-phase current transformer.

  In the high voltage insulation monitoring apparatus according to the present invention described above, it is desirable that the correction unit uses an equation that defines an error of the zero phase current due to the influence of the load current of each phase.

  Further, in the high voltage insulation monitoring device according to the present invention described above, the characteristics of the zero-phase current transformer are that the three-phase load is connected to the load side of the switch equipped with the zero-phase current transformer and the current transformer, and the switch The three-phase balanced voltage is applied from the power supply side, the balance of the three-phase load is changed in a state where the composition of the load current of each phase becomes zero, and the load current of each phase detected by the current transformer and the zero-phase change It is desirable that the characteristic is obtained by obtaining a relationship with the zero-phase current detected by the flow device and applying the relationship to the above equation.

  In the above-described high voltage insulation monitoring apparatus according to the present invention, the correction unit applies the load current of each phase detected by the current transformer and the characteristics of the zero-phase current transformer to the above equation, and loads the load of each phase. It is desirable to obtain an estimated value of the error of the zero phase current due to the influence of the current and subtract the estimated value from the zero phase current detected by the zero phase current transformer.

  A high voltage insulation monitoring method according to the present invention is a high voltage insulation monitoring method for detecting a decrease in insulation of a high voltage distribution line, the step of detecting a zero phase current of the high voltage distribution line with a zero phase current transformer, The zero-phase current due to the influence of the load current of each phase using the step of detecting the load current of each phase with the current transformer, the load current of each phase detected by the current transformer and the characteristics of the zero-phase current transformer And correcting the zero-phase current detected by the zero-phase current transformer so as to suppress the above error.

  In the above-described high voltage insulation monitoring method according to the present invention, it is desirable to use an equation that defines the error of the zero phase current due to the influence of the load current of each phase in the correcting step.

  In the high voltage insulation monitoring method according to the present invention described above, the zero-phase current transformer is characterized by connecting a three-phase load to a load side of a switch equipped with the zero-phase current transformer and the current transformer. The three-phase balanced voltage is applied from the power supply side, the balance of the three-phase load is changed in a state where the composition of the load current of each phase becomes zero, and the load current of each phase detected by the current transformer and the zero-phase change It is desirable that the characteristic is obtained by obtaining a relationship with the zero-phase current detected by the flow device and applying the relationship to the above equation.

  In the high voltage insulation monitoring method according to the present invention described above, in the correcting step, the load current of each phase detected by the current transformer and the characteristics of the zero phase current transformer are applied to the above equation, and It is desirable to obtain an estimated value of the error of the zero phase current due to the influence of the load current and subtract the estimated value from the zero phase current detected by the zero phase current transformer.

  According to the high voltage insulation monitoring apparatus or the high voltage insulation monitoring method according to the present invention, the load current of each phase detected by the current transformer and the characteristics of the zero phase current transformer are used, and zero due to the influence of the load current of each phase is used. The zero-phase current detected by the zero-phase current transformer is corrected so as to suppress the phase current error. As a result, the influence of the load current of each phase on the zero-phase current used for insulation reduction detection can be mitigated, so that highly accurate insulation reduction detection can be performed.

  In addition, when using an equation that defines the error of the zero-phase current due to the influence of the load current of each phase, it becomes possible to easily and accurately obtain the error of the zero-phase current due to the influence of the load current of each phase. As a result, the influence of the load current of each phase on the zero-phase current used for insulation drop detection can be reliably mitigated.

  In addition, the characteristics of the zero-phase current transformer is that the three-phase load is connected to the load side of the switch equipped with the zero-phase current transformer and the current transformer, and the three-phase balanced voltage is applied from the power source side of the switch, The relationship between the load current of each phase detected by the current transformer and the zero-phase current detected by the zero-phase current transformer by changing the balance of the three-phase load with the composition of the load current of each phase being zero If the relationship is obtained by applying the relationship to the above equation, the exact zero-phase current transformer characteristic can be used. The influence of the load current of each phase on can be more reliably mitigated.

  In addition, the load current of each phase detected by the current transformer and the characteristics of the zero-phase current transformer are applied to the above equation, and an estimated value of the error of the zero-phase current due to the effect of the load current of each phase is obtained. When the estimated value is subtracted from the zero-phase current detected by the zero-phase current transformer, the zero-phase current can be accurately corrected. The influence of the load current can be mitigated more reliably.

It is a block diagram which shows schematic structure of the high voltage | pressure insulation monitoring apparatus which concerns on embodiment of this invention. It is explanatory drawing for demonstrating the circuit which measures the output of the zero phase current transformer (ZCT) which concerns on embodiment of this invention. It is a graph which shows the relationship between the load current in the three-phase equilibrium state which concerns on embodiment of this invention, a ZCT output level, and a ZCT output phase. It is a schematic diagram which shows the vector change of ZCT output accompanying the change of the load current of each phase which concerns on embodiment of this invention. It is explanatory drawing for demonstrating the characteristic of the switch concerning embodiment of this invention. It is explanatory drawing for demonstrating the characteristic of the zero phase current transformer which concerns on embodiment of this invention. It is a graph which shows the relationship between the load current in the three-phase equilibrium state which concerns on embodiment of this invention, and the ZCT output level before and behind correction | amendment.

  An embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a high voltage insulation monitoring apparatus 1 according to this embodiment includes a switch (partition switch) 2 provided on a high voltage distribution line L1 of a distribution system that supplies electricity from a substation to a customer. A ground fault relay 3 that performs a breaking operation by the switch 2 in response to the occurrence of a ground fault accident, and a display unit 4 that notifies the occurrence of the ground fault accident and the like are provided.

  The switch 2 includes a zero-phase voltage detector (ZPD) 2a that detects a zero-phase voltage of the high-voltage distribution line L1, a zero-phase current transformer (ZCT) 2b that detects a zero-phase current of the high-voltage distribution line L1, and a high voltage And a current transformer (CT) 2c for detecting each of the three-phase load currents of the distribution line L1. The switch 2 is provided at a power receiving point from a power distribution system in the high voltage power receiving facility. As the zero-phase voltage detection device 2a, for example, a capacitor-type zero-phase voltage detection device that detects the zero-phase voltage by combining the ground voltages of the respective phases can be used.

  In the ground fault relay 3, the zero phase voltage detected by the zero phase voltage detection device 2a and the zero phase current detected by the zero phase current transformer 2b are set from the viewpoint of protection coordination with the distribution system. It is determined whether or not voltage and zero-phase current settling values are exceeded. When it is determined that the zero-phase voltage and the zero-phase current have exceeded the set values, it is determined that a ground fault has occurred, and the breaking operation by the switch 2 is performed. Thereby, the high voltage distribution line L1 is interrupted by the switch 2.

  The ground fault relay 3 has a correction unit 3a that corrects the zero phase current detected by the zero phase current transformer 2b, and a ground fault occurs using the zero phase current corrected by the correction unit 3a. Detect insulation drop of several MΩ before. The correction unit 3a is configured by hardware such as an electric circuit, but is not limited thereto. For example, the correction unit 3a may be configured by software such as a program or a combination of both. May be.

  The display unit 4 performs a display for notifying that a ground fault has occurred and a display for notifying that an insulation decrease of several MΩ before the occurrence of the ground fault has occurred. As the display unit 4, for example, a magnetic reversal display or the like can be used. In addition, a display lamp such as an LED lamp, an LED display, or the like can be used. In addition, when using an indicator lamp, an LED display, etc., power supplies, such as a solar cell and a rechargeable battery, are provided, and electric power is supplied to the display part 4 from the power supply.

  Next, the correction process by the correction unit 3a will be described in detail. First, the influence of the load current on the output of the zero-phase current transformer 2b (hereinafter simply referred to as ZCT output) will be described, and then the actual correction procedure will be described.

First, in order to investigate the influence of the load current on the ZCT output, the ZCT output (zero phase current) is measured. As shown in FIG. 2, a load (R _UV , R _VW , R _WU ) is connected to the load side of the switch 2, and a three-phase balanced voltage (V _U , V _V , V _W ) is applied from the power source side. . The applied voltage is varied and the ZCT output is measured. In addition, although (triangle | delta) load is used as load, it is not restricted to this, For example, Y load can also be used.

In this measurement, an ideal ZCT output I _ZCT is expressed by the following equation (1) by each load current I _U , I _V , I _W.
I _ZCT = I _U + I _V + I _W = 0 (1)
Therefore, when the ZCT output is generated (I _ZCT ≠ 0), the cause is the influence of the load current.

According to the measurement results described above, as shown in FIG. 3, the ZCT output (graph A1) increases in proportion to the load current, and the ZCT output phase (graph B1) becomes substantially constant. In FIG. 3, R _UV = 0.30Ω, R _VW = 0.30Ω, and R _WU = 0.30Ω. At this time, the change in the vector of the ZCT output accompanying the change in each load current is, for example, as shown in FIG.

  Here, as shown in FIG. 3, the ZCT output level due to the influence of the load current is about 2 mA even when the load current is 25 A. Normally, the ground fault relay 3 detects a zero fault current of 100 mA or more that flows with a ground fault resistance of 10 kΩ or less to determine a ground fault, so a load current of about 2 mA affects the detection of a normal ground fault. There is almost nothing.

  However, when it is necessary to detect an accurate zero-phase current when the insulation resistance is reduced by several MΩ, it is necessary to detect a zero-phase current of about 1 mA as a ZCT output due to the insulation reduction. The effect on output is a major obstacle to detection. Therefore, it is necessary to remove or alleviate the influence of the load current in order to detect the insulation degradation with high accuracy.

  In the measurement described above, the zero-phase current is theoretically not as shown in the equation (1), and therefore the cause of the load current affecting the ZCT output is due to the ZCT characteristics. For this reason, in order to correct the ZCT output, it is necessary to acquire each load current from the current transformer 2c and grasp the ZCT characteristics. In order to obtain only the zero-phase current value from the ZCT output including the influence of the load current, the influence of the load current on the zero-phase current using the load current value and the ZCT characteristic (characteristic of the zero-phase current transformer 2b). Will be corrected.

The ZCT output I _UVW generated by the influence of each load current has ZCT characteristic vectors α _U , α _V , α _W representing the influences of the load current vectors I _U , I _V , I _{W on} the ZCT output I _UVW . Used and represented by the following equation (2).
I _UVW = α _U · I _U + α _V · I _V + α _W · I _W (2)

This equation (2) is an equation that defines the error of the zero-phase current due to the influence of each load current. At this time, if the combination of the load currents is zero, I _UVW is equal to the ZCT output. Therefore, here, in order to simplify the calculation, the ZCT characteristic is obtained from each load current and I _{UVW in} a combined state at zero.

When the measurement is performed in a state where the balance of the load currents is maintained (three-phase resistance values are equal), the influence of each load current included in I _UVW is separated even if the load current is varied. It is not possible. Therefore, the load currents are synthesized and the balance between the load currents is changed while maintaining zero, and the current waveform and the ZCT output waveform of each phase are measured, and the ZCT characteristic vectors α _U , α _V , α _W Find the value of.

Thereafter, an estimated value I _UVW of the zero-phase current error is obtained from the equation (2) using the obtained values of the ZCT characteristic vectors α _U , α _V , and α _W , and finally, the ZCT output to be corrected is expressed as I _ZCT is obtained, and the corrected ZCT output I ₀ is obtained using the following equation (3).
I ₀ = I _ZCT -I _UVW (3)

Here, as an example, FIG. 5 shows data used to calculate the ZCT characteristic vectors α _U , α _V , and α _W. The data shown in FIG. 5 is a measurement result with a three-phase balanced load. At this time, the measurement circuit shown in FIG. 2 is used, and the balance of the three-phase load is changed, and measurement is performed in three patterns. In the measurement circuit shown in FIG. 2, since the current flowing to the load side always returns to the power supply side, current imbalance does not occur and does not appear in the ZCT output.

Such data shown in FIG. 5 is substituted into the above-described equation (2) to obtain three polynomials. These polynomials are solved, and ZCT characteristic vectors α _U , α _V and α _W for each load current are obtained as shown in FIG. These ZCT characteristic vectors α _U , α _V and α _W are used at the time of correction.

That is, in the correction, each load current and the ZCT characteristic at that time are used for an arbitrary ZCT output, and an estimated value I _UVW of the zero-phase current error is obtained from the equation (2). Further, Equation (3) is used, and the estimated value I _UVW of the zero-phase current error is subtracted from the ZCT output I _ZCT to obtain a corrected ZCT output I ₀ .

According to this correction, the corrected ZCT output (waveform A2) is stable at about 0.2 mA regardless of the value of the load current, as shown in FIG. 7, compared to the ZCT output (waveform A1) before correction. ing. 0.2 mA corresponds to a zero-phase current flowing at a ground fault resistance of 20 MΩ. As described above, the corrected ZCT output is closer to 0.0 mA than the uncorrected ZCT output, which indicates that the influence of the load current is reduced by the correction. In FIG. 7, R _UV = 0.30Ω, R _VW = 0.30Ω, and R _WU = 0.30Ω.

  Such correction processing is performed by the correction unit 3a. At this time, the load current (each load current) of each phase detected by the current transformer 2c and the characteristics (ZCT characteristics) of the zero-phase current transformer 2b are used, and the zero-phase current due to the influence of the load current of each phase is used. The zero-phase current detected by the zero-phase current transformer 2b is corrected so as to suppress the error. As a result, the ZCT output affected by the load current can be corrected to a level at which high-precision insulation reduction detection is possible, and the detection accuracy at the time of insulation reduction of several MΩ can be improved.

  In particular, since it is possible to detect an insulation drop of several MΩ from the output (ZCT output) of the zero-phase current transformer 2b, the detection limit has hitherto been several tens of mA due to the influence of noise components due to the load current of each phase. However, the detection of about 1 mA can be realized by correcting the zero-phase current by the vector calculation of the correction unit 3a. In addition, since it is possible to detect an insulation decrease of several MΩ before the occurrence of the ground fault accident, the display unit 4 can notify that the insulation decrease of several MΩ before the occurrence of the ground fault accident has occurred. For this reason, the worker who performs the restoration work or the like can visually recognize the occurrence of the insulation drop of several MΩ before the occurrence of the ground fault, and can use the information for the work.

  In addition, when a device for separately monitoring insulation deterioration is provided, it is necessary to add a new sensor, and the cost for that is generated, but in this embodiment, the zero-phase current transformer 2b is used. Therefore, since it is not necessary to provide a new sensor, cost reduction can be realized. Furthermore, when measuring the insulation resistance value to find out the insulation drop of several MΩ before the occurrence of the ground fault without using a separate device, it is necessary to check in a power failure state, which is troublesome. However, in this embodiment, since the display unit 4 notifies the insulation drop of several MΩ before the occurrence of the ground fault accident, the operator can easily know the insulation drop of several MΩ before the occurrence of the ground fault accident. Thus, the above-described trouble can be saved.

  As described above, according to this embodiment, the load current of each phase detected by the current transformer 2c and the characteristics of the zero-phase current transformer 2b are used. The zero phase current detected by the zero phase current transformer 2b is corrected so as to suppress the error. As a result, the influence of the load current of each phase on the zero-phase current used for insulation reduction detection can be mitigated, so that highly accurate insulation reduction detection can be performed.

  Also, by using the equation that defines the error of the zero-phase current due to the influence of the load current of each phase, that is, the above-described equation (2), the error of the zero-phase current due to the influence of the load current of each phase can be easily accurate. Since it can be obtained well, the influence of the load current of each phase on the zero-phase current used for detection of the insulation drop can be surely mitigated.

  Furthermore, the characteristic of the zero-phase current transformer 2b is that a three-phase load is connected to the load side of the switch 2 including the zero-phase current transformer 2b and the current transformer 2c, and the three-phase balanced from the power source side of the switch 2 When the voltage is applied, the load current of each phase detected by the current transformer 2c is changed by changing the balance of the three-phase load in a state where the composition of the load current of each phase becomes zero, and the current detected by the current transformer 2b. Since it is the characteristic obtained by calculating | requiring the relationship with a zero phase electric current and applying the relationship to above-mentioned Formula (2), it becomes possible to use the characteristic of the exact zero phase current transformer 2b. Thus, the influence of the load current of each phase on the zero-phase current used for detecting the insulation drop can be reliably mitigated.

  Further, the load current of each phase detected by the current transformer 2c and the characteristics of the zero-phase current transformer 2b are applied to the above equation (2), and the error of the zero-phase current due to the influence of the load current of each phase is estimated. Since the value is obtained and the estimated value is subtracted from the zero-phase current detected by the zero-phase current transformer 2b, the zero-phase current can be accurately corrected. The influence of the load current of each phase on the current can be reliably mitigated.

  In the above-described embodiment, the correction unit 3a is provided in the ground fault relay 3. However, the present invention is not limited to this. For example, the correction unit 3a may be provided in the switch 3. In this case, the correction unit 3 a in the switch 3 outputs the corrected zero-phase current to the ground fault relay 3.

  Finally, the above-described embodiments are illustrative, and the scope of the invention is not limited thereto. The above-described embodiment can be variously modified. For example, some components may be deleted from all the components shown in the above-described embodiment, and further, components according to different embodiments may be appropriately combined. Also good.

1 High Voltage Insulation Monitoring Device 2 Switch 2a Zero Phase Voltage Detection Device 2b Zero Phase Current Transformer 2c Current Transformer 3 Ground Fault Relay 3a Correction Unit 4 Display Unit L1 High Voltage Distribution Line

Claims (4)

A high voltage insulation monitoring device that detects a decrease in insulation of a high voltage distribution line,
A zero-phase current transformer for detecting a zero-phase current of the high-voltage distribution line;
A current transformer for detecting a load current of each phase of the high-voltage distribution line;
Using the load current of each phase detected by the current transformer and the characteristics of the zero phase current transformer, the zero phase change is suppressed so as to suppress the error of the zero phase current due to the influence of the load current of each phase. A correction unit for correcting the zero-phase current detected by the flow device ,
The correction unit uses an equation that defines an error of the zero-phase current due to the influence of the load current of each phase,
The characteristic of the zero-phase current transformer is that a three-phase load is connected to the load side of the switch equipped with the zero-phase current transformer and the current transformer, and a three-phase balanced voltage is applied from the power source side of the switch. The load current of each phase detected by the current transformer and the zero-phase current transformer detected by changing the balance of the three-phase load in a state where the composition of the load current of each phase becomes zero A high-voltage insulation monitoring device characterized by obtaining a relationship with the zero-phase current and applying the relationship to the equation . The correction unit applies the load current of each phase detected by the current transformer and the characteristics of the zero phase current transformer to the equation, and the error of the zero phase current due to the influence of the load current of each phase. 2. The high voltage insulation monitoring apparatus according to claim 1 , wherein an estimated value is obtained and the estimated value is subtracted from the zero phase current detected by the zero phase current transformer. A high voltage insulation monitoring method for detecting a decrease in insulation of a high voltage distribution line,
Detecting a zero-phase current of the high-voltage distribution line by a zero-phase current transformer;
Detecting a load current of each phase of the high-voltage distribution line with a current transformer;
Using the load current of each phase detected by the current transformer and the characteristics of the zero phase current transformer, the zero phase change is suppressed so as to suppress the error of the zero phase current due to the influence of the load current of each phase. Correcting the zero-phase current detected by a flow device ,
In the correcting step, an equation defining an error of the zero-phase current due to the influence of the load current of each phase is used,
The characteristic of the zero-phase current transformer is that a three-phase load is connected to the load side of the switch equipped with the zero-phase current transformer and the current transformer, and a three-phase balanced voltage is applied from the power source side of the switch. The load current of each phase detected by the current transformer and the zero-phase current transformer detected by changing the balance of the three-phase load in a state where the composition of the load current of each phase becomes zero A high voltage insulation monitoring method characterized by obtaining a relationship with the zero phase current and applying the relationship to the equation . In the correcting step, the load current of each phase detected by the current transformer and the characteristics of the zero-phase current transformer are applied to the equation, and the zero-phase current due to the influence of the load current of each phase is applied. 4. The high voltage insulation monitoring method according to claim 3 , wherein an estimated value of the error is obtained and the estimated value is subtracted from the zero phase current detected by the zero phase current transformer.

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