JP2020039190A - High voltage insulation monitoring device and high voltage insulation monitoring method - Google Patents

Abstract

To provide a high voltage insulation monitoring device and a high voltage insulation monitoring method, which are capable of correcting an error of a zero-phase current even in a switch comprising only a current transformer of two phases, and capable of highly precisely detecting insulation deterioration.SOLUTION: A representative configuration of a high voltage insulation monitoring device 10 is connected to a switch comprising a zero-phase current transformer 24 for detecting zero-phase current and a current transformer 26 for detecting load current of at least two phases in three phases, and detects insulation deterioration of a high-voltage distribution line. The high voltage insulation monitoring device 10 comprises a correction section 36 for correcting the zero-pase current so that an error of the zero-phase current due to influence of load current is suppressed by using characteristics of the current transformer 26 and the zero-phase current transformer 24. The correction section 36 corrects the error of the zero-phase current from the load current obtained from the two-phase current transformer 26 by assuming that the zero-phase current is so small as to be ignored with respect to the phase current.SELECTED DRAWING: Figure 1

Description

  The present invention 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 install a switch (separate switch) at a power receiving point from a power distribution system and perform ground fault protection by combining the switch and a ground fault relay. The ground fault relay performs a breaking operation by the switch when a ground fault that exceeds the set values of the zero-phase voltage and the zero-phase current occurs. In addition, 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 of detecting a ground fault, a method using a zero-phase voltage extracted from a zero-phase voltage detection device (ZPD) in a switch or a zero-phase current extracted from a zero-phase current transformer (ZCT) is used. (For example, see Patent Document 1). In addition, the insulation resistance value at the time of a ground fault is 0 to several tens kΩ, and a zero-phase current of about 100 mA is detected.

  On the other hand, when the cause of the ground fault is one that gradually deteriorates due to equipment contamination, there is a time when the insulation resistance slightly decreases before the accident. To detect this, it is necessary to detect a high resistance of about several MΩ, that is, to detect a zero-phase current of several mA. However, the zero-phase current is ideally zero, but when the load current increases, an error of about several mA occurs in the zero-phase current transformer (ZCT). Therefore, it is impossible to detect the zero-phase current of several mA. difficult. In view of this, the applicant has proposed a technique in Japanese Patent No. 5972097 (Patent Document 2) for correcting an error in the zero-phase current due to the influence of the load current of each phase. As a result, it is possible to perform highly accurate insulation deterioration detection.

JP-A-6-284559 Japanese Patent No. 5972097

  However, in the technique of Patent Document 2, when calculating the characteristics (correction coefficient of the equation) of the zero-phase current transformer, the balance of the three-phase load is changed in a state where the combination of the load currents of the respective phases becomes zero, and The relationship between the phase load current and the zero-phase current is determined. That is, the technique of Patent Document 2 requires three phases of load current (CT output). On the other hand, since two phases out of three phases become overcurrent at the time of a short circuit fault, overcurrent detection (detection of a short circuit fault or a ground fault fault) can be realized with a load current of at least two phases. For this reason, in the current market, there is provided a switch having a built-in two current transformers (CT) in two phases to reduce the cost.

  Therefore, an object of the present invention is to provide a high-voltage insulation monitoring device and a high-voltage insulation monitoring device capable of correcting a zero-phase current error and performing highly accurate insulation deterioration detection even in a switch having only two-phase current transformers. It is to provide an insulation monitoring method.

  In order to solve the above-described problems, a typical configuration of a high-voltage insulation monitoring device according to the present invention includes a zero-phase current transformer for detecting a zero-phase current and a transformer for detecting at least two-phase load current among three phases. A high-voltage insulation monitoring device connected to a switch equipped with a current transformer to detect a decrease in insulation of a high-voltage distribution line. A compensator for compensating the zero-phase current so as to suppress the error of the phase current is provided, and the compensator is obtained from the two-phase current transformer, assuming that the zero-phase current is negligibly small with respect to the phase current. It is characterized in that the error of the zero-phase current is corrected from the load current.

  According to the device having the above configuration, the influence of the load current of the zero-phase current can be canceled by using the load current of any two-phase current transformer in the three phases. Accordingly, a high-voltage insulation monitoring device capable of correcting a zero-phase current error and performing highly accurate insulation deterioration detection even for a switch having only two-phase current transformers for cost reduction. can do.

  A typical configuration of the high-voltage insulation monitoring method according to the present invention is a switching apparatus including a zero-phase current transformer for detecting a zero-phase current and a current transformer for detecting at least two-phase load current among three phases. And a zero-phase current transformer to detect the zero-phase current in the high-voltage distribution line, the current transformer to detect at least two-phase load current in the high-voltage distribution line, and connect the current transformer and the zero-phase current transformer. Using the characteristics, the zero-phase current is corrected so as to suppress the error of the zero-phase current due to the effect of the load current, and then, based on the corrected zero-phase current, a high-voltage insulation monitoring method that detects a decrease in high-resistance insulation is used. The error of the zero-phase current is corrected based on the load current obtained from the two-phase current transformer, assuming that the zero-phase current is negligibly small with respect to the phase current.

  According to the method having the above configuration, the effect of the zero-phase current due to the load current can be canceled by using the output (load current) of an arbitrary two-phase current transformer among the three phases. Therefore, to provide a high-voltage insulation monitoring method capable of correcting a zero-phase current error and performing highly accurate insulation deterioration detection even for a switch having only two-phase current transformers for cost reduction. can do. In addition, the components corresponding to the technical concept in the above-described high-voltage insulation monitoring device and the description thereof are also applicable to the high-voltage insulation monitoring method.

  According to the high-voltage insulation monitoring device or the high-voltage insulation monitoring method according to the present invention, even if the switch has only two-phase current transformers, the error of the zero-phase current is corrected and the insulation deterioration detection is performed with high accuracy. It is possible to provide a high-voltage insulation monitoring device and a high-voltage insulation monitoring method capable of performing the following.

It is a block diagram showing a schematic structure of a high voltage insulation monitoring device. FIG. 3 is a diagram illustrating a configuration of a test circuit. It is a figure which compares the experimental result of error elimination processing. It is a figure which compares the experimental result of estimation of V phase current.

[First Embodiment]
A first embodiment of a high-voltage insulation monitoring device and a high-voltage insulation monitoring method according to the present invention will be described. FIG. 1 is a block diagram showing a schematic configuration of the high-voltage insulation monitoring device. The high-voltage insulation monitoring device 10 includes a switch 20 (a sectional switch) provided on a U-phase, V-phase, or W-phase high-voltage distribution line of a distribution system that supplies electricity from a substation to a demand destination, and a ground fault accident. A ground fault relay 30 that performs a breaking operation by the switch 20 in response to the occurrence, and a display unit 50 that notifies occurrence of a ground fault or the like.

  The switch 20 includes a zero-phase voltage detector 22 (ZPD) that detects a zero-phase voltage of the high-voltage distribution line, a zero-phase current transformer 24 (ZCT) that detects a zero-phase current of the high-voltage distribution line, and a high-voltage distribution line. And a current transformer 26 (CT) for detecting the load current of each phase.

In the following description, the zero-phase current _IZCT detected by the zero-phase current _transformer 24 is referred to as a ZCT output. The load current detected by the current transformer 26 is called a CT output.

  In the present embodiment, the current transformer 26 has two current transformers 26U and 26W attached to only two-phase lines U and W phases of the three-phase lines U, V and W phases. The switch 20 is provided at a power receiving point from the power distribution system in the high-voltage power receiving equipment. As the zero-phase voltage detector 22, for example, a capacitor-type zero-phase voltage detector that combines the ground voltages of the respective phases and detects the zero-phase voltage can be used.

  The ground fault relay 30 has a zero-phase voltage detected by the zero-phase voltage detection device 22 and a zero-phase current detected by the zero-phase current transformer 24, the zero-phase current of which is set from the viewpoint of protection coordination with the distribution system. It is determined whether the set values of the voltage and the zero-phase current 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. Then, the ground fault relay 30 determines the phase of the zero-phase voltage-zero-phase current to determine whether the power-supply-side ground fault or the load-side ground fault occurs. Perform the shut-off operation. As a result, the high-voltage distribution line is cut off by the switch 20.

The ground fault relay 30 has a correction unit 36. The correction unit 36 corrects the ZCT output using characteristics of the current transformer 26 and the zero-phase current transformer 24 so as to suppress an error in the ZCT output due to the load current, as described later. In particular, in the present embodiment, the correction unit 36 estimates the remaining one-phase load current _{IV based} on the load currents I _U and I _W obtained from the two-phase current transformers 26U and 26W, and obtains the estimation by estimation. The error that the load current for three phases gives to the zero-phase current is obtained.

  The display unit 50 provides a display for notifying that a ground fault has occurred, and a display for notifying that insulation loss of several MΩ has occurred before the occurrence of the ground fault. As the display section 50, for example, a magnetic reversal display or the like can be used, and in addition, a display lamp such as an LED lamp or an LED display can be used. When an indicator light, an LED display, or the like is used, for example, a power supply such as a solar battery or a rechargeable battery is provided, and power is supplied to the display unit 50 from the power supply.

  Next, a correction process performed by the correction unit 36 will be described. First, error removal using three-phase CT outputs will be described, and then error removal using two-phase CT outputs will be described.

The ZCT output of the zero-phase current transformer 24 is expressed by the following equation (1) from the zero-phase current component actually flowing through the system and the error component due to the ZCT individual difference.

In the case of a three-phase equilibrium state, I _ZCT = 0 originally. Therefore, when a zero-phase current is generated in the three-phase equilibrium state (I _ZCT ≠ 0), the cause is the influence of the load current.

From the results of the studies by the inventors so far, the error component due to the individual difference of the ZCT is defined as the equation (2) from the CT output of each phase. However, the individual difference characteristic value is a coefficient representing the effect of each phase load current on the ZCT output in consideration of the variation in the characteristics of the current transformer for each phase, and is a constant unique to each switch.

From equation (1) (2), if the current transformer 26 to a three-phase switch 20 is built, zero-phase current component I ₀ flowing through the system, as from CT output and ZCT output equation (3) Desired.

  Next, error removal using the CT outputs for two phases will be described. When the current transformer 26 is built in only two phases of the switch 20, the zero-phase current cannot be obtained from Expression (3). Therefore, a correction coefficient for canceling the effect of the load current is derived from the ZCT output using the two-phase CT outputs built in the switch.

If the current transformer 26 of each phase has ideal characteristics, and the high-voltage converted value of the CT output completely matches the corresponding phase current, the zero-phase current flowing through the system and the load current of each phase are expressed by Equation (4). ) Holds.

Here, the zero-phase current generated due to insulation lowering of 1 [MΩ] or more, which is the object of insulation lowering detection, is about several [mA], and the number of phase currents [A] in general high-voltage consumers. Small enough to be ignored. Therefore, by setting the zero-phase current to 0 [mA], an unknown phase current estimated value can be obtained from Expression (4). For example, the V-phase current of the switch 20 in which the current transformer 26 is incorporated only in the UW two-phase is approximated as Expression (5).

From the equations (3) and (5), when the current transformer 26 is built in only the UW two-phase of the switch 20, the zero-phase current flowing through the system is expressed by the equation (6) from the CT output and the ZCT output for the two phases. Is required. Equation (6) is obtained by erasing the _{I U} in the formula (3) from equation (5).
Using this equation (6), two phases of the CT output _I U, it is possible to determine the zero-phase current _{I o} flowing through the system from _{I W} and ZCT output _{I ZCT.}

FIG. 2 is a diagram illustrating the configuration of the test circuit. A three-phase balanced voltage source 60 and a three-phase load resistor 62 are connected to the switch 20. Current transformers 26U and 26W are provided in the UW two-phase, and no current transformer is provided in the V-phase. For ground current path is not a test configuration of FIG. 2, the zero-phase current I _o is not flow through the switch, the zero-phase current I _o irrespective of the power supply and load resistance conditions is not generated. Therefore, only the output due to the effect of the load current appears in the ZCT output _IZCT .

First, errors of the current transformers 26U and 26W built in the switch 20 are corrected. A three-phase AC voltage is output from the three-phase balanced voltage source 60 so that a specified current flows through the current transformers 26U and 26W, and the high-voltage conversion values of the outputs of the current transformers 26U and 26W actually change the current transformers 26U and 26W. The high voltage conversion gain and offset value are set so as to match the flowing current. The high voltage converted values Iu, Iw of the outputs of the current transformers 26U, 26W are represented by the following equations.

In the equation (6), α ′ _U = α _U −α _V and α ′ _W = α _W −α _V are replaced. Since it can be assumed that the zero-phase current _Io is negligibly small, it is assumed that I ′ ₀ = 0. Then, equation (6) can be expressed as the following equation (8).

In two patterns having different ratios of the load resistance of each phase, a three-phase AC voltage is output from the three-phase balanced voltage source 60, and a high-voltage conversion value of the CT output and the ZCT output obtained at that time is obtained.
Using the acquired high-pressure converted value, the system of equations (9) derived from the equation (8) is solved to obtain a correction coefficient.

By substituting the correction coefficients α ′ _U and α ′ _W obtained as described above into Expression (6), it is possible to correct _IZCT , which is the ZCT output, and cancel the effect of the load current. That is, the “zero-phase current I ′ ₀ calculated from the CT outputs for the two phases” on the left side of the equation (6) can be regarded as the zero-phase current component I ₀ flowing through the system.

Next, the error amount of the method of the present invention will be examined. The accuracy of the error elimination using the two-phase CT output is compared with the case of using the three-phase CT output because one phase of the phase current used for obtaining the zero-phase current is an estimated value. It is thought that it decreases. From equations (3) and (5), the zero-phase current component flowing through the system can be expressed as in equation (10).

From the equation (10), the error amount when the zero-phase current is calculated using the UW two-phase CT outputs with respect to the case where the zero-phase current is calculated using the three-phase CT outputs is expressed by the equation (11). expressed.

  From the equation (11), the error amount of the processing result using the two-phase CT output with respect to the case where the three-phase CT output is used is determined by the individual difference characteristic value (constant) of the phase having no built-in CT and each It is the product of the combined values of the phase CT outputs.

  FIG. 3 is a diagram comparing experimental results of the error removal processing. 3A shows the result of the error removal processing using the CT outputs for three phases, FIG. 3B shows the result of the error removal processing using the CT outputs for two phases, and FIG. And the difference between the two-phase error removal processing results. Referring to FIGS. 3A to 3C, it can be seen that the result of the error removal processing using the CT outputs for two phases is almost the same as the case using the CT outputs for three phases.

  FIG. 4 is a diagram comparing the experimental results of the estimation of the V-phase current. 4A shows the measured value of the V-phase current, FIG. 4B shows the estimated value of the V-phase current, and FIG. 4C shows the difference (vector difference) between the measured value and the estimated value of the V-phase current. When the V-phase current is about 6.8 to 9.0 [A], the difference is 0.01 to 0.08 [A], which is a level of 1/100 or less. This indicates that the estimation in the present invention has high accuracy.

  As described above, the correction unit 36 can correct the ZCT output affected by the load current to a level that enables highly accurate detection of insulation deterioration. In particular, in the present invention, the correction unit 36 can cancel the effect of the load current on the ZCT output by using the CT output of any two-phase current transformer among the three phases. Accordingly, a high-voltage insulation monitoring device and a high-voltage insulation device capable of correcting an error in ZCT output and performing highly accurate insulation reduction detection even for a switch having only two-phase current transformers for cost reduction. A monitoring method can be provided.

  Finally, the above-described embodiments are examples, and the scope of the invention is not limited thereto. In the above-described embodiment, the description has been made that the current transformer of the V phase is not provided. However, the phase in which the current transformer is insufficient may be the U phase or the W phase. In addition, the above-described embodiments can be variously modified. For example, some components may be deleted from all the components shown in the above-described embodiments, and components according to different embodiments may be appropriately combined. May be.

  INDUSTRIAL APPLICABILITY The present invention can be used as 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.

DESCRIPTION OF SYMBOLS 10 ... High voltage insulation monitoring device, 20 ... Switch, 22 ... Zero phase voltage detection device, 24 ... Zero phase current transformer, 26 ... Current transformer, 30 ... Ground fault relay, 36 ... Correction part, 50 ... Display part, 60: three-phase balanced voltage source, 62: three-phase load resistance

Claims (2)

High-voltage insulation for detecting a decrease in insulation of a high-voltage distribution line by connecting to a switch having a zero-phase current transformer for detecting a zero-phase current and a current transformer for detecting at least two-phase load current among three phases. A monitoring device,
Using a characteristic of the current transformer and the zero-phase current transformer, a correction unit that corrects the zero-phase current so as to suppress the error of the zero-phase current due to the influence of the load current,
The correction unit,
A high-voltage insulation monitoring device, wherein a zero-phase current error is corrected based on a load current obtained from a two-phase current transformer, assuming that the zero-phase current is negligibly small with respect to the phase current. Connected to a switch comprising a zero-phase current transformer for detecting a zero-phase current and a current transformer for detecting at least two-phase load current among three phases,
The zero-phase current transformer detects a zero-phase current in the high-voltage distribution line,
The current transformer detects at least two-phase load current of the high-voltage distribution line,
Using the characteristics of the current transformer and the zero-phase current transformer, the zero-phase current is corrected so as to suppress the error of the zero-phase current due to the effect of the load current, and then the high-level current is corrected based on the corrected zero-phase current. A high-voltage insulation monitoring method for detecting insulation lowering of resistance,
A high-voltage insulation monitoring method comprising correcting a zero-phase current error from a load current obtained from a two-phase current transformer, assuming that the zero-phase current is negligibly small with respect to the phase current.