SU1277279A1 - Device for current protection of three-phase circuits with dependent time lag - Google Patents

Abstract

The invention relates to the field of relay protection and can be used to protect motors against overload and short circuit. The purpose of the invention is to increase reliability by eliminating the influence of the frequency instability and form of the supply voltage in the protected circuit on the operation of the protection device. The goal is achieved by introducing into the device a max-selector 4, a fundamental frequency filter 5, a fourth threshold pulse shaper 9, a reference voltage generator 10. At the same time, the definition of the degree of overload in a controlled network occurs only after the appearance of pulses at the outputs of the corresponding threshold pulse shapers, t . eliminates the effect of the instability of the frequency of the supply voltage in it. The use of the filter of the main frequency 5 allows to eliminate the influence of instability and shapes (L of the supply voltage in the controlled circuit on the operation of the device. From 1 il. 11 19 iNd .1} / 15 17 tons of

Description

The invention relates to relay protection and can be used to protect electric motors against overload and short circuits. The purpose of the invention is to increase reliability by eliminating the effect of frequency instability. R: and the shape of the supply voltage in the protected circuit on the operation of the protection device. The drawing shows a structural diagram of the device proposed, k. A device for current protection of three-phase circuits with a dependent time consists of sensors 1, 2, 3 currents, which are connected to the threshold formers of 6–9 pulses through max-selector 4 and filter 5 of the main frequency. The other inputs of the threshold formers 6–9 are connected to the four outputs of the generator 10 reference voltages. The outputs thresholds of the pulse shapers are connected to the temporary memory unit 11, to which the generator 12 of the reference frequency is also connected. Three outputs of the i1-time memory are connected to a delay device 13, three outputs of which are connected to the element OR 14, to the fourth input of which the fourth output of the time memory 11 is connected. The output of the element OR 14 is connected to the input of the element 15, to the second input of which the blocking element 16 is connected. To the inputs of the device 13 of the delay blocking element 16 a generator 12 of the reference frequency is connected. The second output of the locking element 16 is connected to the delay device 13. The output element And 15 through the Executive body i 7 is connected to the switching body 18, one output of which is connected to the blocking element 16, and three others - to the sensors 1, 2.3 current. The device works as follows. The switching unit 18 is turned on when the Start command is received from the executive unit 17. In this case, from the sensors 1, 2, 3 of the current to the max detector 4, periodic analog signals are received, the amplitude of which is directly proportional to the amount of current in the protected circuit. At the output of the Max-selector 4, there is a periodic analog signal from the phase with the highest current value at a given time. The fundamental frequency filter 5 passes from the max-selector 4 to the inputs of the threshold drivers 6-9 only the sinusoidal component of the analog signal and thus eliminates the influence of the instability of the shape of the mains supply voltage on the operation of the device. At the same time, constant threshold voltages U. come from the generator 10 of the reference voltages to the second inputs of the threshold formers 6–9 pulses, where tl U, where i is the number of the threshold pulse formator. As the current B of the controlled circuit increases, the amplitude of the sinusoidal signal at the inputs of the threshold pulse shapers increases. When uo. the corresponding threshold pulse shaper forms at its output a pulse that enters the temporary memory 11. At its outputs corresponding to the i-th threshold pulse shaper, to eliminate device failures from random current surges in the monitored circuit, the temporary memory forms according to a certain criterion. (. for example, in terms of the frequency of occurrence of pulses at any of its inputs) signals either to turn on (or reset) B a device 13 for delaying the dwell for extracting the switching body 18, or (in e short zamzhani a consumer of electrical energy) to switch off the circuit-komg 1utiruyuschego body without entirely Coy delay. In addition, to ensure the operation of the block of temporary memory 11 according to the indicated criterion, it stores for some time a sign that at the output of the i-ro threshold pulse shaper a pulse is generated. Switching off the switching body 18 occurs as follows. When a signal OR 14 arrives at any input, switching signal 18 is turned off at this input and arrives at the input of AND 15, which in turn issues a signal to the actuator 17, which forms a command to turn off the switching unit 18. To eliminate false positives for the duration of the starting period, a blocking element 16 is needed, which

Claims (1)

Invention Formula A device for current protection of three-phase circuits with a dependent service VNIderIvNIIPI Order 6753/51 Circulation 612 Subscription Branch PSh1 patent, Uzhgorod, ul. Project, 4 o five 0 five Time, containing three current sensors, switching to the corresponding phases of the protected three-phase circuit through the switching body, three threshold formers, pulses, time memory block, reference frequency generator, SHSh element, And element, blocking element, the first output of which is connected to the first input element And, the executive body, about the fact that, with tse-. To improve the reliability by eliminating the influence of frequency instability and the form of the supply voltage in the circuit to be protected, a max selector whose inputs are connected to the outputs of current sensors, a fundamental frequency filter connected by its input to the output of the max selector, the fourth threshold pulse shaper, the reference generator voltage, the outputs of which are connected to the first inputs of the threshold pulse formers, the delay element, the first three inputs of which are connected to the first three outputs b At the same time, the first four inputs of the temporary memory unit are connected to the outputs of the 0th threshold pulse shaper, the output of the fundamental frequency filter is connected to the second inputs of the threshold pulse shaper, the first input of the blocking element is connected to the output of the reference frequency generator, with the fifth input of the unit temporary memory and the fourth input of the delay element, the second input of the blocking element is connected to the output of the switching body, the second output of the blocking element is connected to the fifth input of the element aderzhki outputs delay element connected to the first three input member Hilti, - a fourth input element connected GSHI fourth output temporary memory unit whith 1SHI output element connected to a second input of the AND, AND output member; connected to the input of the executive body, and the output of the executive body is connected to the input of the switching body. five 0 five