SU1086497A1 - Device for differential protecting of power transformer - Google Patents

Abstract

A DEVICE FOR DIFFERENTIAL PROTECTION OF THE POWER TRANSFORMER, containing current sensors installed in parallel branches of the transformer windings and connected to different inputs of the first summing unit, the output of which is connected with a reacting authority, different in that, in order to increase the sensitivity, A second summing unit, included for the sum of the currents of the parallel winding branches, a tuning unit made in the form of a proportional amplifier, and a comparison unit, with the output of the first sum The world unit is connected to the first input of the comparison unit, the second input of which is connected to the output of the setting block i, the input of which is connected to the output of the second summing block (L ka, and the output of the comparison unit is connected to the reacting authority. 00 Oi 4 QO vl

Description

The invention relates to electrical engineering, in particular to relay protection of transformers, and can be used to protect against internal short circuits of power transformers having a winding with an input in the middle.

A device for differential protection of a transformer is known, comprising current sensors mounted on the winding inputs, a comparison unit and a responsive organ fl}.

This device is characterized by low sensitivity and lack of speed due to the need to detune from magnetizing current surges.

Closest to the invention is a device for the differential protection of an electrical masque, comprising current sensors installed in the parallel branches of the winding of an electric machine, a comparator unit and a responsive member. The device has a higher sensitivity, since it does not require a detuning from the total current that occurs when the transformer is turned on under voltage, due to the equilibrium of these currents in parallel branches x of the winding Czj.

This device is characterized by a lack of sensitivity due to the need for detuning from the unbalance of currents in parallel branches x of the winding, caused by the different heights of the windings.

The purpose of the invention is to increase the sensitivity.

The goal is achieved by the fact that a device for differential power transformer, containing current sensors, installed in parallel branches of the transformer winding and connected to different polar inputs of the first cyan of its unit, the output of which is functionally connected to the reacting authority, is additionally introduced a second summation a unit included in the sum of the currents of the parallel winding branches, a tuner made in the form of a proportional amplifier, and a comparator unit, with the output of the first summing unit It is connected to the first input of the comparator unit, the second input of which is connected to the output of the tuner, whose input is connected to the output of the second summing unit, and the output of the comparator unit is connected to the reacting authority. FIG. -2 shows the functional diagrams of the proposed device

5 to protect one phase of the power transformer j in FIG. 3 - the same, to protect the three-phase power 1} of the transformer.

The device contains current sensors

0 1 and 2, installed in parallel branches x windings and made in the input of transformers with primary and secondary windings, the first summing unit 3 connected to the secondary

5 windings of sensors 1 and 2, the second

the summations of block 4, the block of comparison 5, the tuner 6, the response body 7. The second summing block 4 is included for the sum of the currents of the parallel branches of the transformer winding. In the diagrams in FIG. 2 and 3 instead, a current sensor 8 is used, connected to the phase output of the winding and equivalent to the second

5 summing block.

The outputs of current sensors 1 and 2 are connected to opposite-polar inputs of the first summing unit 3, in which the signals of these sensors subtract 0s and are converted into a signal proportional to the difference of the currents of the winding branches.

The tuning unit 6 is connected to the output of the second summing unit 4, in which the signals of the current sensors

add up (see Fig. t), or to the output of the phase current sensor 8 (see Fig. 2). Block 6 is a linear link with adjustable transmission coefficient in terms of magnitude and sign, and can be implemented as a proportional scale amplifier connected to the intermediate transformer via a reversing switch with its input. The signal at the output of block 6 is proportional to the magnitude of the current unbalance of parallel winding branches, due to the uneven height.

The circulating unbalance current in the single phase circuit jJ in FIG. 1 and FIG. 2, due to the different height of the transformer windings, is projected to phase current:

five (),

where K is a coefficient proportional to the relative difference in the height of the winding branches; the sign () or (-) is determined by the sign of elevation; LF - phase winding current; L, 1 -current in parallel branches x winding. The circulating unbalance current of the zero-sequence in the three-phase circuit of FIG. 3 :,. p (b) Y) -Y (4k-1z. V where, B, C is the phase index. If in all phases of the transformer the relative difference in the height of the winding branches is the same, i.e. .tK then. Ie we got the same ratio and for a single-phase circuit. Comparative unit 5 compensates for unbalance current and consists, for example, of operating and braking organs connected respectively to the output of blocks 3 and 6. The device operates as follows. With load current, external short circuit and surge nama; gnivaniya signals at the output of current sensors 1 and 2 differ from each other only and the amount of unbalance caused by different height of transformer winding branches. At the output of tuner 6 is proportional to the unbalance current, caused by different intensities of transformer windings. Thus, two identical signals are supplied to comparator 5 and the reacting organ does not work. the organ also does not work, since the unbalance current due to the asymmetry of the magnetic system is very small. When a short circuit occurs in the transformer winding, the equality of signals from current sensors 1 and 2 in the first Summit unit 3 breaks, the signal from the output of block 3 becomes larger than the signal from the output of tuner 6, which causes the appearance of the signal at the output of the comparator block 5 7; The proposed device is intended for installation on powerful block transformers of large power plants. Providing a higher sensitivity in comparison with the known protection devices, it allows to limit the amount of transformer destruction during internal short circuits and to reduce the time of the emergency just power unit. The device, in addition to its primary purpose, relay protection of a transformer, can be used to diagnose the deformation of the transformer windings after external short circuits. P

Claims (1)

DEVICE FOR DIFFERENTIAL PROTECTION OF POWER TRANSFORMER, containing current sensors installed in parallel branches of the winding transformer ki and connected to bipolar inputs of the first summing block, the output of which is connected to the reacting organ, characterized in that, in order to increase sensitivity, a second summing block is added, included in the sum of the currents of the parallel branches of the winding, the tuner made in the form of a proportional amplifier , and a comparison unit, while the output of the first summing unit is connected to the first input of the comparison unit, the second input of which is connected to the output of the tuner, the input of which is connected to Exit second summing unit, and the output of the comparator is connected to a reactant body. SU ..... 1086497 7 -