SU693501A1 - Device for short-circuiting protection of ac equipment - Google Patents

Description

The invention relates to relay protection and can be used to provide protection for the maximum current of an AC electrical installation. The devices are known to be fast-acting sewn up, reacting to an increase in current and containing functional and logic elements 11 and 2. The closest in technical essence to the invention is devices containing a block of formation of an electric quantity, two phase-rotating elements, the outputs of which are connected to the comparator and the executive body. Such devices have the possibility of false triggering under conditions of saturation of measuring current transformers of CTs during an intensive transient process in the primary circuit. The aim of the invention is to increase the reliability of high-speed overcurrent protection devices by eliminating incorrect actions in saturation of measuring current transformers in transient modes: short-circuit. This is achieved by the fact that in a known device containing a current sensor, the output of which is connected to the input of the first phase-turning element, the second phase-turning element, the outputs of which are connected to the comparator and the comparator's input through the respective quadrants and the common adder the first input of the newly introduced logic element I, the second output of which is connected to the output of the newly introduced circuit consisting of two square pulse drivers and a subconnect ennogo their outputs to an adder via a second absolute value formers, and the input of the rectangular pulses cQQfetstvedach connected to the outputs of said current detector and the first phase rotation

element, and to the output of the postfire, the input of the second phaeo-rotating element is connected.

FIG. 1 psjazano the invention; in fig. Figure 2 shows diagrams explaining the operation of individual components and the device as a whole in the transient mode of short locking with saturation of current transformers, which are current sensors. The numbers of this type correspond to the outputs of the blocks with the same numbers.

The protection device contains a current sensor 1, phase shifting elements 2 and 3, each of which performs an advance phase shift of the input signal by an angle close to / 2, quadrants 4 and 5, first adder 6, comparator 7 with adjustable threshold, logic element And 8 with two inputs, an executive optan 9, shapers 1O and 11 rectangular pulses, a second adder 12, designed to form different polarity pulses in the intervals of coincidence of the corresponding polarity of pulses at its inputs, and a shaper 13 absolute signs This translates bipolar pulses from the output of adder 12 into unipolar.

The scheme works as follows.

The monitored signal from the output of current sensor 1 is fed to phase rotation element 2, connected in series with analogous element 3, in each of which a leading phase shift is made by an angle close to 7Г / 2.

The signal from the output of element 3 goes through quad 4 to the first input of adder 6, and the second from the output of element 2 via quad 5. On a quad 5, a signal is generated that is proportional to the amplitude of the periodic component of the monitored current. If the signal generated on the quad 5 does not exceed the trigger setpoint of the comparator 7, then at the first input of the element 8 there will be a logical zero and the response of the actuator will not occur in any state of the second input of the switching element.

When the signal on the quad 5 exceeds the setpoint of the operation of the comparator 7 at the first input of the element 8, the logical signal is given.

In this case, the executive body 9 will work only if there is a logical unit and at the second input of the And 8 element.

The signal at the second input of the element And 8 is formed by an additional circuit consisting of elements 1 O - 13 in the following sequence. In the presence of

current shapers 10 and 11 produce rectangular pulses of both polarities. In the second adder 12, the signals from the 1O and 11 sum formers are set and sent to the shaper.

13 absolute values, from the output of which in the form of unipolar pulses arrive at the second input of the element And 8.

The drawing also shows the formation of a signal in transient conditions.

at the second input of element 8, At the moment

saturation of the current transformer, which is a current sensor, a pulsed voltage jump occurs at the output of the phase rotation element 2, which actually performs current differentiation. However, at the moment we perceived, the current and its derivatives have different signs, therefore, after the summation of the opposite-polarity pulses at the output of the adder, 12

A logical zero is generated, which, acting through the absolute value generator 13 on the second input of the AND 8 element, blocks the operation of the device.

Claims (1)

Thus, if the amplitude of the periodic component of the current does not exceed the setting of comparator 7, and the transformer is saturated, the device is triggered. When the amplitude of the variable component of the short-circuit current is exceeded. the settings of the comparator, the device is triggered without slowing down due to the fact that during the time before the test, the current and its derivative have the same sign, i.e. the signs of the signals from elements 1 and 2 coincide, providing a logical unit — at the second input of the element AND 8. Claims which, through appropriate quadrants and a common adder, are connected to a comparator, and an executive unit, characterized in that, in order to increase operational reliability by eliminating incorrect actions when current transformers are saturated in transient short-circuit modes, the first input of the newly introduced logic element I is connected between the input of the executive body and the input of the comparator, the second output of which is connected to the output of the newly introduced circuit consisting of two square drivers of pulse squares and connected to their outputs through the second adder of the absolute value generator, and the inputs of the rectangular pulse shapers are connected respectively to the outputs Yu. mentioned a current sensor and the first phase-twist element, and the output of the second element of the second element is connected to the output of the second. Sources of information taken into account in the examination 1. USSR author's certificate Ji 462229, cl. Ht6l H 83/00. 1975 ... ii. USSR Author's Certificate 229661, H O1 H 83/22, 1965.