SU501445A1 - Method of protection of the generator from single-phase short circuits - Google Patents

Description

one

The invention relates to the field of relay protection, in particular to the protection of a generator against single-phase earth faults.

A known method of protecting the generator from single-phase short circuits is based on comparing the levels of the components of the non-industrial frequency of the stator winding phase currents.

The purpose of the invention is to increase the sensitivity and speed of protection.

This is achieved by isolating the components of the non-industrial frequency difference between the currents of the beginning and end of the stator winding.

FIG. 1-5 shows the implementation of the proposed method, where 1 is the stator winding of the generator; 2 - phase current transformers; 3 - input resistance of the measuring organ of the protection phase.

If there is no ground fault, the differential current flowing through the measuring unit Protection of each phase is fundamentally equal to the capacitive current to the ground of the corresponding phase. Almost the difference current can have a greater value due to the non-identity of current transformers of one phase. The component of the fundamental frequency of the unbalance current is irrelevant, since for further comparison only the components of the nonindustrial frequency are separated from the differential current. The protection threshold is selected by the trim from the maximum level difference.

components of the non-industrial frequency of unbalance currents of the three phases in different modes of operation of the generator, therefore, in the absence of a ground fault, the protection is

in the lock state.

With a stable metal circuit to earth, one of the terminals of the stator winding (Fig. 3) receives the highest harmonic components of the currents due to the total capacitances of the intact phases of the network (Figs. 2, 3) through the two Intact phases of this winding. These components fold into the damaged phase and flow through it to the closure point. Under these conditions, the level of higher harmonics of the difference current of the damaged phase is many times higher than approximately equal, close to zero, levels of the difference currents of the intact phases. The protection is triggered; in this case, the sensitivity coefficient Ki is more than one.

When the closure point moves inward into the stator winding (Fig. 4), the components of the higher harmonics of the currents of the intact phases decrease, and the currents of the damaged phase grow.

The level of the higher harmonics of the components of the differential current of the damaged phase is determined by the sum of the components of both the damaged and intact phases, and the corresponding levels of the intact phases remain close to zero. Protection works.

In the case of short circuits without transient resistance, the insensitive zone of protection, | Vypolinoi io the proposed method is the part of the stator winding, which is close to

1HG

neutral, defined as-, where L - kK .Z

sensitivity effect at metal circuit at the output of the stator winding (Fig. 3).

With an external stable single-phase short circuit to earth (Fig. 5), two harmonics of the generator stator winding are intact, the higher harmonics of currents occur due to the total capacitances of the intact network phases, and the current in the damaged phase is equal to their sum (Fig. 1 n 5). In this case, the levels of higher harmonics of the difference currents of all phases are close to zero. The protection is in the blocking state. The possible higher value of the unbalance level of the differential current of the damaged phase in this mode is one of the conditions by which the specified threshold is triggered. The protection is triggered by comparing the levels of the unsaturated frequency components of the differential currents of the three phases between themselves. Comparison of the indicated levels of differential TOiKOB with each other makes it possible to choose the threshold of protection operation according to the ratio of the levels under the worst conditions, and e according to the maximum absolute value of the differential current level of one of the phases, which allows the protection to be more sensitive, respectively .

The operation of the protection but the ratio of the levels of the components of the non-industrial frequency differential currents ensures its selective operation with high sensitivity and in the conditions of the transition process of the ground circuit.

Claims (1)

Invention Formula The method of protecting the generator from single-phase short circuits, based on the equalization of the components of the nonindustrial frequency currents of the phases of the stator winding, characterized in that, in order to increase sensitivity and speed, the differences of the currents of the beginning and end of the stator windings are selected to increase the sensitivity and speed. rw t. lit , 2 st: j -, (PUi .J .