RU1772859C - Ac circuit overload and open-circuit fault protection pickup - Google Patents

Abstract

Usage: in devices for protecting electrical circuits of alternating current from overloads and breaks. SUMMARY OF THE INVENTION: in a sensor for protecting an AC electric circuit against overload and open circuit containing a current transformer, the overload and open circuit control units are connected to the output of the secondary current transformer by input terminals, the open circuit control unit is made on a resistor, transistor, capacitor and threshold element, which allows to simplify the sensor and increase its reliability. 1 ill.

Description

The invention relates to electrical engineering and is intended for use in relay protection devices.

The purpose of the invention is to simplify and increase reliability.

The drawing shows a diagram of the sensor.

The sensor for protecting the AC electric circuit from overload and breakage contains a current transformer 1 with terminals 2, 3 for connecting its primary circuit (winding) 4 to the protected electric circuit, overload control unit 5, input 6 of which is connected to the output of the secondary circuit (winding) 7 current transformer 1, and output 8 serves as an overload signal output, and an open circuit control unit 9 connected to the output of the secondary circuit 7 with input terminals 10, 11, a current transformer 1 parallel to input 6 of the overload control unit 5, which has terminals 12, 13 for connecting power supply point 14.

In the sensor, the open circuit control unit 9 is made on a resistor 15, transistor 16, capacitor 17 and threshold element 18, and the resistor 15 and the control transition of transistor 16 are connected in series between the input terminals 10 and 11 of the open circuit control unit 9, the first terminal 12 for connecting the source 14 of the operational power supply is connected to the collector, and the second to the emitter of the transistor .16, between the terminals 12, 13 a capacitor 17 is connected to connect the power supply 14, the first output of the threshold element 18 is connected to the second output which is the output signal 19 open.

Between the emitter and the base of the transistor 16, a diode 20 can be turned on counter-parallel to the emitter-base transition of the transistor. The first terminal 12 for connecting the operational piggly source 14 may be connected to the collector of the transistor 16

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through series-connected resistors 21, 22.

The sensor operates as follows: When the controlled current flows from the beginning to the end of the primary winding 4, a secondary current flows from the beginning of the secondary winding 7, which induces a voltage across resistor 15 (the polarity of all voltages is indicated in the drawing), proportional to the magnitude of the controlled current. Secondary current opens transistor 16.

An overload or short circuit signal (short circuit) in the controlled circuit appears at the output 8 of the overload control unit 5 when the sum of the voltages at the resistor 15 and the input of the transistor 16 exceeds the unlocking voltage of the reference element in the overload control unit 5.

The magnitude of the monitored current at which an overload signal appears is determined by the transformation ratio of the windings 4, 7 of the transformer 1, the magnitude of the resistor 15 and the stabilization voltage of the support element in the overload control unit 5.

In real circuits, the voltage of the input circuit (BE) of the transistor 16 can be neglected.

When the current of the monitored circuit is zero, the transistor 16 closes, and the capacitor 17 is charged through the limiting resistor 21. As soon as the voltage on the capacitor 17 exceeds the stabilization voltage of the threshold element 18. at the output 19 of the open-circuit control unit 9, the monitored open signal chains.

If there is a current in the controlled circuit that exceeds the magnetization current (open circuit current) of the primary winding 4, the transistor 16 will open during the half-cycle of this current, and at this time, the capacitor 17 will discharge through an additional resistor 22 to the output circuit of the transistor 16.

In another half-period, the transistor 16 will be closed, and the reduced current of the secondary winding 3 will flow through an additional diode 20.

Capacitor 17 will charge across resistor 21 from supply voltage 14.

Parameters of resistors 21, 22 and capacitance

of the capacitor 17 are selected such that, in the presence of a current in the primary winding 4, the voltage of the capacitor 17 is always less than the stabilization voltage of the threshold element 18, which provides an open signal only when the current of the controlled circuit is practically equal to O,

The sensor has a time delay in the output of both overload, short-circuit and open circuit signals, moreover, the delay for the overload signal is equal to the half-cycle of the controlled alternating current, and for the open circuit signal the delay is determined by the parameters of the capacitor charge circuit

17.

Claims (1)

SUMMARY OF THE INVENTION A sensor for protecting an alternating current electrical circuit against overload and open circuit, comprising a current transformer with leads to include its primary circuit in an electric circuit, an overload control unit, the input of which is connected to the output of the secondary circuit of the current transformer, and the output serves as the output of the Overload signal, and the unit open circuit, connected to the output of the secondary circuit of the current transformer by input terminals parallel to the input of the overload control unit, having outputs for connecting an operational power source, characterized in that that, in order to simplify and improve reliability, the circuit break control unit is made on a resistor, transistor, capacitor and threshold element, and the resistor and the control transition of the transistor is connected in series between the input terminals of the open-circuit control unit, the first terminal for connecting the operational power supply is connected to the collector, and the second to an emitter of a transistor, between the terminals for connecting the operational power supply, a capacitor is connected, to one terminal of which a first output of a threshold element is connected, a second terminal of which serves as an output signal Open. 2t 5f  rev. Pete