SU1691778A1 - Method of determining active insulation resistance and mains capacity with respect to ground of three-phase mains with isolated neutral - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure insulation resistance and capacitance of electrical networks with a voltage of 6-10 kV. The aim of the invention is to increase electrical safety and accuracy by connecting an additional resistor to the secondary winding of the transformer. The method consists in measuring the voltage of the insulation with transformers, the voltage of the phases relative to the earth, then to the secondary winding of the transformer. In parallel with one of the insulation control voltmeters, an additional resistor is connected in one of the phases meters of insulation control voltmeters in the other two phases establish the optimum voltage displacement, in one of these phases the voltage is measured and the resistance and the network capacity are determined according to in the description of the invention. 1 il. (L

Description

The invention relates to electrical measuring equipment and can be used to measure the insulation resistance and capacitance of asymmetric mine electrical networks with a voltage of 6-10 kV, as well as in quarries and other mining facilities.

The purpose of the invention is to increase electrical safety and accuracy by connecting an additional resistor to the secondary winding of the transformer.

The method consists in measuring the voltage of the insulation with transformers, the phase voltage to ground, then the secondary winding of the transformer parallel to one of the insulation control voltmeters is connected to an additional resistor in one of the phases, changing the value of the additional resistor to read meters of insulation control voltmeters in the other two phases establish the optimal displacement of the voltage of one of these phases, measure the voltage, the active resistance of the insulation and the network capacity dissolved by the formulas:

Och Ch)

N |

00

(a-a1) 2 + () 2. ) one

with

d1a -da1

ea

° HA (a-a1) 2+ (d-d1) 2 2 U & - (US + U§)

eif

+ if;

-1-2 (UA)) 2-KUJ) 2 .... a 6UF if1

d

UC-UB.

2V3 if

di- (uJ) 2- (uB) 2

02V3 Of

r.- total active resistance of the insulation relative to the earth of a three-phase network with an isolated neutral, kΩ;

 total capacity relative to the earth of a three-phase network with an isolated neutral, microfarad;

gd - connected resistor value (corresponds to the condition of 10% bias), kΩ;

a) - angular frequency of the network, with

if - nominal phase voltage, V;

UA, UB, Uc, UA, UB, Ucf - respectively, readings of voltmeters for monitoring the insulation of phases A, B, C before and after connecting the capacitor store to one of the phases, B.

The drawing shows a diagram of the measuring circuit of the device that implements the method.

The device contains a transformer 1 voltage with primary and secondary windings 2, 3, fuses A, voltmeters 5 of the insulation control, resistance box b, power transformer 7 and the equivalent circuit of network 8.

The first pins of the primary winding 2 are connected via fuses 4 to the corresponding network phases, the first pins of the secondary winding 3 are connected via a suitable voltmeter to an earthing switch, to which the second terminals of the primary and secondary windings 2,3 of the transformer 1 are also connected. resistance shop 6.

For this scheme, the total conductance of the network relative to the earth is determined by

t + tg- N -) (1)

R2. k rv1

where rv is the resistance of the voltmeter 5 insulation control;

K W 1 / - the transformation ratio of the measuring transformer 1;

lL.1 - resistance of the transformer 7;

0

five

0

five

0) capacitive component of the total conductance of the network relative to the earth.

The earth fault current of phase A is determined by

1u UAU. (2)

At the same time, if there is an additional well-known resistor in the secondary winding of phase A of the resistance magazine 6

  UA (), (3)

where UA is the voltage of phase A with the inclusion of additional resistance in the secondary winding.

From formulas (2) and (3) we get

UA 1

W ..- -

(four)

UA-UA

Therefore, the active and capacitive components of the total conductivity of the network can be determined respectively as the real and imaginary parts of the same complex (4), i.e.

1 - g ± Re (yA}

GA IA-UA

7 +

k2rv

(five)

wCr

±, t (CA)

1 gd Ni pg

(6)

Since the values of ГУ, К and LI are previously known (they are usually much greater than the insulation resistance and capacitance resistance, and therefore they can be ignored in the measurement conditions), we define the desired parameters in the form:

rA (a-a1) 2+ (d-d1) 23tK6M a1 (a-a1) + d1 (d-dT)

I - i

2. yugd

(Gaam

microfarad (8).

(a-a + td-d1) 2 21D - (U | + U§), G1

(andA) 2 - ((andUz +. 6 ifv

ui-ufj.

0 2V3 if

di - (utf- (uff

0 2V3 0F

are the phase voltage modulus coefficients obtained from the vector diagram of a three-phase network with an isolated neutral.

The method is implemented as follows.

The voltage is applied to the secondary winding of the power transformer 7. The readings of the insulation control voltmeters 5 are measured. Then between phase A of the secondary winding 5 of the transformer 1 voltage and

An additional resistor is introduced through the ground using the resistance box 6. Changing the value of the resistor, changing the resistance of the corresponding phase of the secondary winding 3, which leads to a voltage change in one of the other two phases of 10 or more percent, take voltmeter readings and determine the desired values.

Claims (1)

Claims The method of determining the active insulation resistance and network capacity relative to the earth of a three-phase network with insulated neutral, which is measured using insulation control voltmeters, having transformers, phase voltage relative to earth, then measured voltage when connected to one of the phases of the network of additional resistor and the results of two measurements determine the insulation resistance and capacitance, characterized in that, in order to improve electrical safety and accuracy, Connecting an additional resistor to the secondary winding of the transformer parallel to one of the insulation control voltmeters changes the value of the additional resistor, according to the measurements of the insulation control voltmeters of the other two phases, set the optimum voltage offset of one of these phases, and the insulation resistance and the network capacity by formulas r-rA (a-a1) 2+ (d-d1) 2. ga ca-a1) d1a- a1c 0 where a ShGD (a-a1) 2+ (d-d1) 2 2 1D - (C & Ug) eif + U (f ai-2 (uJtf- (u & f + Cuff 6 1) ff  and§ - and & d1 2V3 if (S) 2- (col) 2 2V3 Of yy is the total resistance of the insulation relative to the earth of a three-phase network with an isolated neutral, kΩ;  total capacity relative to the earth of a three-phase network with an isolated neutral, microfarad; Hz - connected resistor value, kΩ; and) - angular frequency network 11f - nominal phase voltage, V; UA, UB, Uc, UA, UB, Uc - respectively, readings of voltmeters to monitor the insulation of phases A, B, C before and after connecting the store of resistors to one of the phases, B. Tr7 her. one L -V -Jt Zhom Himself  D t D t. 0. t RuiS Bw Pack Sizs