SU721875A1 - Arrangement for maximum current protection of electric network - Google Patents

Description

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The invention relates to devices for overcurrent protection of power plants against short circuits and long-term overloads.

A device for maximum current protection is known, comprising a current sensor, a pulse shaper, binary pulse counters and an actuator JL}. However, the use of such devices is limited to low and medium voltage AC networks.

The closest to the invention to the technical essence is a device for overcurrent protection of the electrical network, containing a current traformator, logic elements AND a rectangular pulse shaper, a binary counter, a decoder and an actuator 23. However, this device does not depend on the time delay ..the region of its use is not ac networks, the speed does not exceed the half-period of industrial frequency.

The aim of the invention is to increase the speed and expansion of the functionality of the device by providing a time dependent performance characteristic. This is achieved by the fact that the proposed device additionally introduces an element, a delay, and a ring counter connected between the code of the rectangular pulse generator and the main input of the binary counter, the reset circuit of which is connected through the element to the output of the ring counter, and the output of the binary counter is connected to the input executive body.

On (the drawing is given a functional diagram of the described device.

The device contains a current sensor (DT) 1, controlled multivibrator (MIND), for example, Roeer's generator

2, the functions of the rectangular impulse fogger, the ring counter (CS) 3, the binary counter (DS) 4, the actuator (IO) 5 and the delay element (EZ) 6.

The device works as follows.

A constant (superior) voltage, proportional to the controlled current, from the DT 1 output is fed to the UM 2 input. Pulses from the UM output are fed to the KC 3 input, in which the unit starts to circulate, and the cycle speed is proportional to the number of input pulses, and At the end of each cycle of operation, the signal from the output of CS 3 is fed to the input of DS 4. At the same time, EZ 6 is started. If the monitored current is less than the protection setting current, the CS cycle time exceeds the EZ setting and the DS is reset.

If the monitored current exceeds the value of the protection operation setpoint, the frequency at the output of the MIND 2 increases, the corresponding cycle time of the CS is reduced. The time interval between the arrival of pulse signals at the input of DC 4 becomes less than the set value of EZ 6. EZ does not have time to work. DC 4 is filled up, as a result of which IO5 is triggered. The EZ is started when the signal from COP 3 arrives at its input. The arrival of the next signal brings the EZ 6 back to its initial state, and the time starts again.

If the current increase is short-lived and the DS 4 did not have time to completely fill, then as the monitored current drops below the setpoint under the action of EZ 6, the DS is reset. This eliminates the possibility of a false triggering of the device with currents lower than the current of the ICT, and current surges during short-term overloads, as well as during self-removal of the short circuit.

In order for the protection to function properly, the EZ 6 setting must satisfy the condition

k.so. E.S. to .. with. Wed

 K.Snom "c.tp. the cycle times in the ring meter, respectively, at rated current and controlled current and at protection tripping current. The time for filling the DS is determined by

Continuing the work of the COP cycles. Therefore, the greater the controlled current, the faster the DS is filled and the shorter the response time of the protection. This provides the inversely dependent delay of the protection response.

The speed of the device is not limited by the duration of the half-direction of the oscillations of the monitored current, but is determined by the chosen frequency of the MIND 2 (tens of kilohertz) and the time required for the counters to be CAN (very little in the microsecond range).

Claims (2)

1. Kazansky V.E., Morozov L.N. Technical implementation of the limited-time response of a discrete (measuring) relay with one affecting value. Lime universities, Electrical Engineering № 7, 1976, p. 780-786. 2.Bochkarev V.N. On increasing the speed and sensitivity of overcurrent protection. Information scientific and technical collection Electrotechnical Industry, series Low-pressure apparatuses, vol. 4, 197O, p. 28-29,