JPH0152972B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in testing methods for artificial ground faults for power distribution lines. As is well known, in order to test the operation of distribution line ground fault protection relays and measure the distribution line-to-ground line constant,
This is done by combining a 6kV pole transformer and a water resistor. Figure 1 shows the operation test of a ground fault protection relay, where ZCT is a zero-phase current transformer installed on a distribution line,
DG is a ground fault direction relay (−V〓 _N and I〓 _g operate with the same polarity),
OVG is a ground fault overvoltage relay, V _N is a voltmeter for measuring neutral point to ground voltage, and PT is a voltage transformer.
2N and 3N are the primary, secondary, and tertiary windings, respectively, I _g
is an ammeter for measuring ground fault current, CT is a current transformer for I _g ,
is V〓 Phase meter for measuring the phase difference between _N and I _g , T _r is 6kV
Pole-mounted transformer, V _g is a voltmeter for measuring ground fault-to-ground voltage,
W and R are water resistors, RH is a high resistor for preventing ferro-resonance, ~ is a test personnel, EP is an artificial ground point, SW is a switch, and L is a conductor. In the above configuration, adjust the water resistors W and R.
Minimum ground fault current I〓 _g for each of OVG and DG to operate
Find the size of and read V _g . The sensitivity of OVG and DG at this time is expressed in terms of the number of ohms of the ground fault resistance R: R=V _g /I _g・n _p /n _c [Ω] [However, np: Transformation ratio of the test transformer nc: I The current transformation ratio of CT for _g is Further, FIG. 2 shows a method of determining the ground constant from the charging current. That is, three single-phase pole transformers P and Tr are connected to the star on the high voltage side and the open delta on the low voltage side, and voltage is applied from the low voltage side to apply zero-sequence voltage to the high voltage distribution line. Voltmeter V, ammeter A in the same figure,
Convert the reading of the wattmeter W to the high voltage side and obtain V ₀ and
If A ₀ and W ₀ , the complete one-wire ground fault current I _G in this distribution system is (However, VΔ is the line voltage). Therefore, the three-wire collective ground admittance 3Y ₀ of this system is 3Y ₀ = A ₀ /V ₀ [] If 3Y ₀ is decomposed into conductance 3g ₀ and susceptance 3b ₀ , 3g ₀ = 3Y ₀ W ₀ /V ₀・A ₀ [] 3b ₀ = 3√ ² ₀ − ² ₀ []. Note that there is an imbalance in each relative ground admittance,
If there is residual voltage, reverse the polarity of the test power supply, measure, and take the average value of the results. Further, in FIG. 2, the same parts as in FIG. 1 are given the same reference numerals. The conventional artificial ground fault testing device as described above has the following problems. (1) Since a pole-mounted transformer and water resistor are used, the test equipment is heavy and difficult to handle. (2) Since a pole-mounted transformer is used, there is a possibility of iron resonance, which includes the risk of abnormal voltage generation. (3) Since a water resistor is used, errors occur in the measured values due to temperature changes. Therefore, it is desired to develop a method to solve these problems. This invention was made based on the above-mentioned circumstances, and instead of using a pole transformer and a water resistor, the distribution line is grounded through a variable capacitance capacitor. By performing the artificial ground fault test by converting the equivalent value in the case of This is what we are trying to provide. An embodiment of the present invention will be described below with reference to the drawings. First, an overview of the invention will be explained. This invention artificially connects one line of a power distribution line to ground via a capacitor. Then, in order to ensure that the fault voltage (zero-sequence voltage) and fault current (ground fault current) that occur at this time are equal to those in the case of a resistor ground fault, the reactance of the capacitor corresponding to the required resistance value (number of ohms) is adjusted. It calculates the value (ohm number). Therefore, while creating a ground fault with a capacitor, we simulate an actual ground fault, that is, a resistance ground fault such as insulation breakdown or contact with a tree, and at this time, the distribution line ground fault protection relays OVG, OCG, DG, etc. It is possible to conduct an artificial ground fault test to comprehensively check whether or not it operates correctly. The conversion formula for the relationship between the ohm number of the resistor and the capacitor that makes the magnitude of the zero-sequence voltage equal in the case of a single line ground fault in the distribution line, and the relationship between the ohm number of the resistor and the capacitor that makes the magnitude of the ground fault current the same is as follows. This will be explained later. Next, a configuration for implementing the test method according to the present invention will be explained. In FIG. 3, a zero-phase current transformer ZCT provided in the distribution line is connected to one input end of a ground fault direction relay DG. The other input end of this DG is connected to terminals a and f provided on the tertiary winding 3N of the voltage transformer PT. Also, this DG
Connected to the other input terminal of the earth fault overvoltage relay OVG, a voltmeter V _N for measuring neutral point to ground voltage, and one input terminal of a phase meter. The other input terminal of this phase meter is connected to terminals b and c provided on the secondary winding of the voltage transformer PT, as well as a voltmeter VΔ for measuring line voltage.
connected to. This phase meter measures the phase difference between V〓Δ and _V〓N . On the other hand, X is a variable capacitor. This capacitor X is a series type or series-parallel type multistage tap variable capacitor as shown in FIGS. 4a and 4b, and the capacitance is varied by switching switches 41 and 42, respectively. As shown in FIG. 3, one end of this capacitor X is connected to one line of the distribution line at an artificial ground fault point EP via a switch SW and a conductor L, and the other end is grounded. An ammeter I _g for measuring ground fault current is provided at the other end of the capacitor X via a current transformer CT. In addition, ~ are test personnel. In the above configuration, an artificial ground fault is created using the capacitor X, and the neutral point-to-ground voltage V _N and phase difference at this time are measured. From this measured value, the ground constant of the distribution line is equivalently converted and determined, and the sensitivity of the ground fault directional relay DG and the ground fault overvoltage relay OVG is actually measured. Next, the measurement principle will be explained. (1) First, the one-wire ground fault relation equation in a general circuit will be explained. Here, we will consider a three-phase, three-wire, neutral point ungrounded power distribution system as shown in FIG. In Figure 5, each symbol is defined as follows.

【table】

[Table] 〓

Claims (1)

[Claims] 1. In the artificial ground fault test method for distribution lines, which tests the operation of distribution line ground fault protective relays and measures the distribution line-to-ground line constant by subjecting the distribution line to an artificial ground fault, the normal line voltage V of the distribution line without a ground fault is measured. The first step is to measure the magnitude and phase of 〓Δ and the residual zero-sequence voltage V〓NO, and after this first step, the distribution line is grounded with a capacitor of impedance Z〓g to measure the zero-sequence voltage. V〓N
After this second step, the measured line voltage V〓Δ,
Based on the residual zero-sequence voltage V〓NO and zero-sequence voltage V〓N,
3-wire collective ground admittance Y ₀₀ and its unbalanced portion
A third step of calculating Y〓′ ₀₀ , and after this third step, the resistance of the distribution line is adjusted based on the calculated three-wire collective ground admittance Y〓 ₀₀ and its unbalance Y〓′ ₀₀ . a fourth step of calculating a resistance value to obtain a zero-sequence voltage V〓N equal to the zero-sequence voltage V〓N obtained by the ground fault caused by the capacitor when a ground fault occurs through the capacitor; An artificial ground fault testing method for a distribution line, characterized in that a ground fault caused by the capacitor is equivalently converted into a ground fault caused by the resistor, and an operation test of the distribution line ground fault protection relay and a distribution line-to-ground line constant are measured. .