SU769676A1 - Method of automatic compensation for leakage capacitive current - Google Patents

Description

one

This invention relates to methods for compensating for capacitive leakage current, and is mainly intended to improve the compensation efficiency of the capacitive component of leakage currents in 5 electrical networks with an isolated transformer neutral.

There is a method of autocompensation, in which the network capacity is measured with the help of an operational source current, a U signal proportional to the measured capacitance is converted into a bias current of the compensating throttle, and its inductive conductivity is adjusted by the indicated current to resonance with the network capacity 1.15

However, this method of autocompensation and tuning of the inductive conductivity of a droplet takes into account induction in its magnetically conducting circuit and on it, which, depending on the type and magnitude of the leakage, varies from zero to the phase voltage of the network. In this connection, the required control current for adjusting the inductive and conductivity of throttles to resonance with the network capacity, with different leakage resistances, varies over a wide limit. This leads to the fact that this tuning method ensures acceptable accuracy of compensation in a narrow range of changes in active leakages in the network. thirty

For a wide range of changes in the active conductivities of network insulation, for example, in cable electric networks of coal, mining and chemical industries, the accuracy of compensation of capacitive leakage currents by this method is not high enough.

There is also known an autocompensation method in which the automatic control system is closed to the auxiliary throttle. The automatic control system adjusts the specified choke to resonate with the network capacity at the operating frequency with a current that is introduced into the control circuit of the compensation throttle, adjusting the latter to resonance with the network capacity at the operating network frequency. 2

This method is characterized by the same drawback, since the closed-loop automatic control system does not cover the compensating choke, and its state is not monitored. Disregarding the voltage on the compensating choke and the induction in its magnetic core leads to significant errors when adjusting the compensating circuit, since the required control current for its fine tuning with different types and magnitude of the active leakage varies depending on the state of the compensating thrusts over a wide range. In connection with this, the development of automatic control current control with regard to changing only the magnitude of the capacitive network does not provide sufficient accuracy to compensate for the capacitive leakage current.

There is also known a method of autocompensation 3, which consists in measuring the network capacity and the equivalent inductance of a compensating throttle using an operational source current superimposed on the working network and the winding of the specified throttle processing a mismatch signal by changing the inductance of the compensating circuit.

Such an autocompensation method does not have the indicated disadvantages, since in addition to measuring the capacitance, it compensates for the state of the compensating throttle.

Its disadvantage is as follows. The condition for tuning into resonance with the network capacitance at the industrial frequency inductance w /, etc. of the working windings of the compensating throttle is to adjust the inductance LIIS of the measuring windings of the throttles to resonance with the network capacitance at the frequency of the operative source, i.e.

but -iL -j-. This ratio

/ 0)

of

It is provided by selecting the appropriate number of turns between the working and measuring windings and the frequency of the operational source. At the same time, in order to adjust the computational circuit, the current of the operational source is imposed on the network capacity and on the working and measuring windings of the choke. In this connection, the control current of the tuning sensor — the phase-sensitive detector is determined not only by the network capacitance and inductance of the measuring windings of the choke, but also by the inductance of its working windings. In addition, the electrical connection between the measuring and working windings of the throttles necessitates the inclusion in the circuit of the measuring windings of additional droplets with an air gap and an attachment filter, an inductance measurement circuit to ground to eliminate the effect of the bias voltage of the industrial frequency neutral on the automatic control system. The scatter of the parameters of the inductance measuring circuit, especially the change in the parameters of chokes with an air gap in the manufacture (stamping, heat treatment of magnetic circuits) and in use (voltage fluctuations in the network, aging, mechanical effects), leads to the fact that to maintain the specified ratio between the inductances of workers and measuring windings is difficult. As a result, even a small detuning of inductance in the circuit of the measuring windings leads to significant errors in the setting of the compensating throttle. The purpose of the invention is to improve the accuracy of compensation of capacitive leakage current. This is achieved by the fact that, according to the method of automatic compensation of capacitive leakage current, consisting in measuring the network capacity and inductance of the throttle compensation circuit by superposing the operating current of the first non-industrial frequency, measuring the electrical parameter characterizing the state of the compensated network, comparing it with the reference value and deflection signal shaping to change the inductance of the compensating circuit, additionally superimpose the operating current of the second epromyshlennoy frequency, and as an electrical parameter characterizing the state compensated network using said difference frequency currents.

The drawing shows a block diagram of the connections of functional units for implementing the proposed method for automatically compensating for capacitive leakage current.

The source I operating voltage of the operating frequency with the help of frequency converters, respectively multiplier 2 and divider 3 frequencies, is converted into signals the same number of times increased

and lower relative to the frequency of the operative source. The currents i and h, proportional to these signals, through the input elements 4 and 5 of the comparison device 6 are superimposed on a circuit consisting of

connecting filter 7, tank 8 network, and a compensating choke 9.

The error signal of the currents i and b, formed in the comparison device 6, is fed to the relay element 10, which works out the error by changing the inductance of the compensating throttle 9 by biasing the magnetization current of the control windings 11.

The condition for tuning in the resonance of the inductive conductivity of the compensating choke and equivalent capacitive conductivity at the operating frequency of the network is the equality of the currents 1 and b. With the same amplitude of the frequency converters formed by the frequency converters, the currents 1 and / g will be respectively determined by the sum of the conductivity of the ecBivalence of capacitance 8 and the inductance L of the drosellers

parallel circuit, i.e., the conductivity of the circuit for the current / 1 is determined by psoHnuiL

dl, where n - n

frequency generation. Consequently, if

L L, Tolshs + - n i L

From where

eleven

3 l

shs / g -

u) L p

Consequently, when the currents i and / 2 are equal, the condition of resonance at the operating frequency of equivalent capacitance and inductance of the compensating throttle is observed. At the same time, the presence of active conductivities of the network insulation, as well as the magnitude of the neutral bias voltage, depending on the type and magnitude of the leakage in the network, do not affect the accuracy of the compensation circuit, since the automatic control system processes the difference between the currents, the absolute increments of which due to the specified reasons are the same.

As a result, devices that implement the proposed method of autocompensation are greatly simplified, since there are no measuring windings and special functional units to eliminate the effect of the bias neutral voltage of the operating frequency on the operation of the automatic control system. In this case, the accuracy of compensation increases, since the setting condition is a stable parameter — the difference of the currents proportional to the signals by the same number of times the boosted and reduced frequency relative to the operating frequency at which the compensation circuit is tuned.

According to the proposed autocompensation method, the relative instability of the transformed frequency of the operational source when multiplying or dividing the frequency remains unchanged.

If it takes the value co + Aso, then the output frequency of the multiplier will be lsh- | + To), and the divider co / «+ D / n. Consequently ,

Before)

/ gDi pdsh

That is, the absolute shifts of the input frequency are transformed in the same way as the frequencies themselves, so the relative instabilities are unchanged.

Thus, this method of automatically compensating for capacitive leakage current adjusts the compensation circuit at the operating frequency, since it takes into account the state of the compensating

throttle depending on the size and type of leakage. In this case, without additional functional units, the influence of the presence of the active conductivities of the insulation in the network and the neutral bias voltage on the operation of the automatic control system is excluded.

The proposed method makes it possible to extend the zone of automatic compensation of capacitive currents, since the depth of automatic control is determined not by the limit of the possible measurement of capacitance, but by the parameters of the compensating throttle, by the range of its inductance control.

Claims (3)

1. Author's certificate of JSC 493857, cl. H 02J 3/18, 1976. 2. USSR author's certificate N ° 235162, cl. H 02 H 9/02, 1965. 3. USSR author's certificate To 390620, cl. H 02 H 3/16, 1971.