JPS61266967A - Automatic monitoring device for ground constant of power distribution system - Google Patents

Abstract

PURPOSE:To measure the ground constant of a high voltage power distribution system automatically at any time without requiring locking a protective relay nor altering its settings by applying extremely small electromotive force which is put in optional phase to the neutral point of the high voltage power distribution system intermittently at intervals of short time. CONSTITUTION:A voltage phase controller EG under the control of controllers CONT1 and CONT2 generates the extremely small electromotive force for measurement which can be put in optional phase and applies it to the neutral point of the system intermittently through an overvoltage suppressing device Di, a switch So, and a grounding transformer GT. An A/D converter 1 inputs a neutral line current to a computer unit CPU, an A/D converter 2 connected to a grounding transformer GPT inputs a zero-phase voltage, and an A/D converter 3 inputs an interline voltage. Then, the CPU computes three-line batch ground admittance and unbalanced ground admittance and displays them on OUTs 1-4.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to automatic measurement of ground constants in power distribution systems in electric utilities, distribution substations, and power distribution systems of private electrical equipment in general industries.

[Conventional technology]

Figure 2 shows the voltage and current distribution when a one-line ground fault occurs in a power distribution system where the neutral point is not grounded. In the figure, each symbol is defined as follows.

Ea, Eb, Ec...... Symmetrical three-phase electromotive force Ya, Yb, Yc...-... Each relative ground admittance Va, Vb, Vc...・・・
・Each relative earth voltage Vn −−・−・・−・Neutral point N
voltage to ground (in this case Vn is equal to the zero-sequence voltage in the symmetric coordinate method).

Ia, Ib, Ic......Each phase current (ignore load current).

ig ......1 wire ground fault current LH--
−−−1. Ground constant to determine ground fault impedance ■oo
(three-wire collective ground atmittance) and ■oo (unbalanced ground admittance) are expressed by the following equations (1) and (2).

■oo = Ya + Yb + Yc = ■oo/
θ Town... (1) 8'oo = 'S'a + Yb
l −120'+ Yc/120°=YIoo/θI・
...(2) Fig. 3 shows an outline of a device conventionally used for measuring ■oo and 仝'oo. In the figure, PT is a voltage transformer, IN, 2
N and 3N are the primary winding, secondary winding, and tertiary winding, respectively. A resistor or capacitor is used for artificial ground fault impedance. O and 0 are instruments that measure zero-sequence voltage and phase, respectively, and O is an instrument that measures line voltage. Now, measure the constant residual zero-sequence voltage Vno and line voltage 9t on the power distribution bus, and set E = VL / 1 line. Next, at an arbitrary ground fault impedance Zg, the reference phase (a
An artificial ground fault is caused by the switch Sg (phase), and the zero and Y2O2 generated at that time are determined by the following equations (3) and (4).

The conventional power distribution system ground constant measuring device calculates ■oo and Y2O2 by applying the above equations (3) and (4). equipment).

[Problem that the invention seeks to solve]

In the conventional power distribution system ground constant measuring device as described above,
There is a problem in that it is necessary to lock the protective relay or change the setting during the measurement, and therefore a supervisor must be present at the measurement location during the measurement. The reason for this is shown below. In FIG. 3, the zero-sequence voltage Vn generated when the reference phase (a-phase) is grounded at zg is expressed by equation (5).

Dedication=-E←1+beg-Y'oo) / (1+λg
−■oo )・・・・・・・・・・・・(5) In equation (5), too and Y'oo are unknown quantities to be determined by measurement, so Vn must be accurately determined in advance before measurement. cannot be predicted. Further, the adjustable range of the impedance is also limited by the size, weight, economic efficiency, etc. of the impedance body. Therefore, regardless of the size of the system, it is impossible to suppress 9n generated by an artificial ground fault to the unset value of the relay. It is necessary to lock the relay so that the set value of the fault protection relay may not be exceeded, and to have personnel available to manually shut off the system immediately if a ground fault occurs in the system during measurement.

The present invention has been made to solve such problems, and an object of the present invention is to obtain an automatic power distribution system ground constant monitoring device that can automatically measure the ground constant.

[Means for solving problems]

The power distribution system ground constant automatic monitoring device according to the present invention is equipped with a function that can intermittently apply a minute electromotive force with an arbitrary phase to the neutral point of a high-voltage power distribution system. This method measures the ground constant of the system without requiring locking or setting changes.

FIG. 4 shows a circuit in which the ground fault impedance shown in FIG. 2 is removed and a measuring electromotive force EO, which is minute and can have an arbitrary phase, is added to the neutral point N. In the figure, So is the measurement power supply switch, and In is the neutral line current when SO is closed. stomach'! When So is closed, Vn = +Yc (Vn+
BZl 20°) =■oo Eo+Y'ooE -(6
) Also, when you open SO, father n = Vno, and In = ■
oo Vno + Y'oo E = 0
``'・''''(7) Y'oo = -(Vno / E) ■oo
--(8) (6) and (8)), ■oo = I'n / (Eo -V no)
−(9) is obtained. That is, E, Vno
When measuring and In, from equations (9) and (8), ■ o
o and Y2O2 are determined. Here, Eo can take any value and is a small value that does not require locking the protective relay.

[Effect]

In this invention, by adding an electromotive force to the neutral point of the high-voltage distribution system that is sufficiently small that it does not require locking or changing the setting of the protective relay and that can take any phase, the ground constant of the distribution system is constantly maintained. It can be measured automatically.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.
D-1, A/D-2, and A/D-3 are analog/digital converters, respectively. 0UT-1, 0UT-2, 0UT-3 and 0UT-4 are output devices respectively.
, C0NT-1 and C0NT-2 and C0NT-3 and C0N
T-4 is a control device. E G f'iE
18g is the switch for GT, Sn is the current breaker for the neutral point, So is the switch for supplying kO, GPT
is a grounding transformer. A/D-1 is In, A/D-2
inputs Vn (that is, Vno and zero), and A/D-3 inputs *t into the CPU (computer unit), respectively. ■oo and θ, Y'00 and θ', which are the outputs of the CPU, are 0, respectively.
Displayed on UT-1, 0UT-2, 0UT-3, and 0UT-4. In, Vn and Inui #) ■oo and 8'oo C
) calculation is processed by the CPU based on equations (8) and (9). C0NT-1 is the magnitude of Eo generated in EG,
C0NT-2 controls the phase of EO, C0NT-3 controls the opening/closing of So, and C0NT4 controls the opening/closing of an. D
i is the overvoltage suppressor l), Eo is the normal ground voltage 2
This is to prevent large EO from being applied to the grid by setting the voltage so that it does not exceed the voltage range, and to protect this measuring device from high voltage from the GT even if there is a one-wire ground fault in the grid. . The SO shall be open at all times to keep the neutral point of the system ungrounded, and shall be intermittently closed for a short period of time required for measurement. As mentioned above, Vn (i.e. Vno, !:E
By sending o) and In to the CPU, the constant system ■o
It is possible to automatically measure and monitor the values of o and Y'00.

Next, we will show test results showing that the automatic distribution system ground constant monitoring device can measure ground constants with high accuracy. The test was conducted in a 6KV experimental power distribution system with a generally standard ground constant, using a high-voltage power capacitor with a known capacity to set each relative ground admittance to the ground constant determined by automatic monitoring of the ground constant of the distribution system. A comparison of the true ground constant was made.

The test conditions are as shown in Table 1, where the single-wire ground fault current is approximately 10A and the unbalance ratio (Y'oo/■oo)
For the A system with 1.94% and the B system with 3.80%, we selected combinations in which the phase of Eo is positive and reversed, respectively.

In other words, the A system has the following plate capacitances: Ca = 2.5μF Cb = 2.6μF Cc = 2.67μF Three power high-voltage capacitors are connected to the 6KV bus, and a voltage is applied to each phase capacitor. By measuring the current and phase, the ground admittance of each phase was calculated in advance and the following values were obtained.

Ya = 808188.5°μs Yb = 831788.5°μs Yc = 863788.6°μs Therefore, according to equations (1) and (2), ■oo = 2502/88.5°μsY'oo = 4
8.5/-125.3[mu]s, that is, the 3-wire collective ground charging current of the 6600V A system is 9.54A. Note that the value of ■oo above includes Yn (=67
ZO°μs) is also included. For the B system, the name plate capacitances are as follows: Ca = 2.5 μF Cb = 2.77 μF Cc = 2.83 μF Three power high voltage capacitors are connected to the 6KV bus, and the ground admittance of each phase is calculated in advance. The following values were obtained.

Ya = 808Z88.5°μs Yb = 890Z88.6°μs Yc = 921788.5°μs Therefore, according to equations (1) and (2) .7°μs or 660
The 3-wire bulk ground charging current of the 0V B system is 9.98A. The above values of ■oo and Y'oo are taken as the true values of the ground constants of the A system and B system, respectively, and the error with respect to the measured value and true value of the ground constant obtained by this distribution system ground constant automatic monitoring device is calculated as the second value. The results are summarized in Tables 5 to 5.

Table 2 shows the results of Test A1 defined in Table 1, Table 3 shows the results of Test A2, Table 4 shows the results of Test &3, and Table 5 shows the results of Test &3.
The table shows the results of test 44 respectively.

Table 1 Test Case List Measurements 41004 to A1006 shown in Table 2 and Measurements A3008-43012 shown in Table 4 are E.

Since the phases of and Vno are equal, In stops flowing and ■
The measurement error of oo and Y2O2 increases. On the other hand, measurements 162002 to A2005 shown in Table 3 and measurements &4002 to A4009 shown in Table 51 are Eo and n.

Since the phases of are opposite to each other, the measurement error of The information is summarized in Table 6.

Table 6 Measurement error J■oo %: ■oo (Error in Q magnitude (%) δθ
': Error angle δY'oo of the phase of ■oo:
Error in the magnitude of Y'oo (ch) δθ'': Error angle in the phase of Y'OO Table 6 shows that it is possible to measure the ground constant with high accuracy by this automatic power distribution system ground constant monitoring device. Ta.

〔Effect of the invention〕

As explained above, in this invention, the ground constant can be measured when the zero-sequence voltage applied to the system is less than the residual zero-sequence voltage of the normal system, so it is possible to lock the earth fault protection relay or deal with an accident in the system during measurement. This has the effect that automatic measurement and monitoring of ground constants can be realized without having to deploy personnel to do so.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing the voltage and current distribution when a one-line ground fault is caused by ground fault impedance Zg, and Fig. 3 is a circuit diagram showing a conventional artificial FIG. 4 is a circuit diagram showing a means for measuring the ground constant due to a ground fault, and is a voltage-current distribution diagram for explaining the present invention in detail. In FIG. 1, A/D is an analog/digital converter, C0NT is a control device, OUT is an output device, and CPU is a computer unit. Fig. 1 gtP7iz Fig. 2 1a Va Fig. 3

Claims (1)

[Claims] By intermittently applying a small electromotive force with an arbitrary phase to the neutral point of the high-voltage power distribution system, the three-wire collective ground admittance (■oo), which is the ground constant of the power distribution system, and the unbalanced ground admittance are determined. An automatic power distribution system ground constant monitoring device characterized by automatically measuring (■'oo) at all times.