SU1394317A1 - Device for differential protection of electric plants - Google Patents

Abstract

This invention relates to electrical engineering, in particular, to relay protection. The purpose of the invention is to increase the sensitivity of protection in case of overloaded current transformers and inrush current magnetization of power transformers. With external damage and the surge current of the magnetizing power transformer, the differential current curve differs sharply from the sinusoidal function, and there is no signal at the output of the comparison unit 4. In this case, the executive body of the differential protection remains shunded by key element 6, and the protection does not work. In case of internal damage up to the moment of current transformers, the curve of the differential current does not differ from the sinusoidal function, there is a signal at the output of the comparison unit 4 and the protection executive body is shunted by the key element 6. 2 Il. with (L

Description

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This invention relates to relay protection and can be used as a differential protection for busbars, synchronous generators, power transformers and motors.

The purpose of the invention is to increase the sensitivity of protection in case of overloaded current transformers and inrush current magnetization of power transformers.

FIG. 1 is a block diagram of the device according to FIG. 2- time diagrams of the relay operation with internal (a) and external (b) short-circuits x

The diagram of the operation of the relay when the magnetizing current of a power transformer is injected is similar to the diagram for external damage.

The device contains a relay with a fast oning transformer 1, an intermediate current transformer with two secondary windings 2 connected in series, a block forming NIN 3 averages, a comparison block 4, a pulse expander 5, a semiconductor switch 6.,

The comparison unit 4 is supplied with signals proportional to the instantaneous and average values of the differential current. In this case, if the differential current is described by a sinusoidal function, then the equality

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where 1 is the amplitude value of the current, (- is the mean modulo value

current.

The transmission coefficients for the instantaneous and average value paths are chosen so that the signal at the output of comparison unit 4 appears only when the differential current is either sinusoidal or the sum of sinusoid and exponent. Thus, the signal at the output of the comparator unit 4 can appear only in case of internal damage until the current measuring transformers are saturated. With external damage and the surge current of the magnetization of the power transformer, the differential current curve differs sharply from the sinusoidal function and there is no signal at the output of the comparator unit. As an average value block, an NR integrating chain can be used. Semiconductor control

With a wrench 6, which is co-thyristor in the diagonal of the rectifier, it is produced from a pulse expander 5, which is a semiconductor DC amplifier with a return delay.

When the device operates with internal damage, the differential current is described by the expression

t / t

i (ujt4-e () - sin (E J.

At the output of the comparator 4, a signal appears, the duration of which increases to the period of the industrial frequency with the help of an expander of 5 pulses. The signal from the latter opens the semiconductor key 6. In this case, the execution is de-tuned. The body of the differential relay. Sensitivity is hardly increased and it works. The expander of 5 pulses ensures quick and reliable operation of the relay when the measuring current transformers are present.

In case of external damage and the surge of the magnetizing current of the power transformer, the differential current is non-sinusoidal, the output of the comparator unit 4 does not appear, the differential relay has a low sensitivity and does not operate.

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35 Forms of invention

A device for differential protection of electrical installations containing a differential relay with a fast-absorbing current transformer, on whose magnetic circuit there are working short-circuited and secondary windings with leads for connection to a controlled circuit, series-connected comparator, pulse expander, semiconductor switch, whose output is connected in parallel to the reacting an organ and an average value formation unit, characterized in that, in order to increase the sensitivity of the protection during transmission expeirmen- transformers current and inrush additionally introduced intermediate current transformer with a primary winding with terminals for connection to the controlled circuit and two secondary windings, the first of which is connected to the first and

 3139A3174

the second inputs of the comparison unit, and the value, the output of which is connected to the second secondary winding, is connected to the first and third input of the comparison unit to the input of the middle forming unit.

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Claims (1)

The claims where - the amplitude value of the current; - the average modulus of the current value. The transmission coefficients along the paths 40 of the instantaneous and average values are selected so that the signal at the output of the comparison unit 4 appears only when the differential current is either sinusoidal or 45 is the sum of the sinusoid and exponent. Thus, the signal at the output of the comparison unit 4 can appear only with internal damage until the measuring transformers of the current are saturated. With external damage and inrush of the magnetizing current of the power transformer, the differential current curve sharply differs from the sinusoidal function and there is no signal at the output of the comparison unit. As an average value block, an integrating RO integer can be used. Semiconductor control A device for differential protection of electrical installations, containing a differential relay with a fast-saturable current transformer, on the magnetic circuit of which there are working, short-circuited and secondary windings with leads for connection to a controlled circuit, series-connected comparison unit, pulse expander, semiconductor switch, the output of which is connected in parallel with the reacting organ , and an average value generating unit, characterized in that, in order to increase the sensitivity protection in case of overloaded current transformers and inrush currents of magnetization, an intermediate current transformer with one primary winding with leads for connecting to a controlled circuit and two secondary windings, the first of which is connected to the first and second inputs of the comparison unit, and the second secondary winding, is additionally introduced connected to the input of the average value generating unit, the output of which is connected to the first and third input of the comparison unit. FIG. 2