Protective shutdown relay. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Protective shutdown relay. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Current Devices

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The article describes a protective shutdown relay that prevents the possibility of electric shock in case of accidental contact with live parts. It is intended for electrical networks with grounded neutral. The device does not require adjustment.

The considered residual current relay (RZO) is based on a well-known principle (see [1, 2, 3]). When an unbalance occurs in the load current, due to the leakage of the current of the phase wire to the "ground" and exceeding the threshold level of operation, a signal appears at the output of the sensor - a differential current transformer. It is amplified, stored and fed to the relay winding, which leads to load disconnection. The RZO is triggered when the leakage current exceeds 7 mA, and the load is disconnected within 60 ms (the response time is determined by the executive relay and can be reduced by using optoelectronic relays).

The main attention during the development was paid to improving noise immunity, eliminating false inclusions caused by load switching, reducing power consumption and eliminating any adjustment circuits.

Current unbalance sensor - transformer T1 (see diagram). With an inequality of currents flowing through the primary (network) windings (I and II), an EMF is induced in the secondary winding (III), which ultimately causes the relay K1 to turn on, disconnecting the load from the network.

Residual current relay

Unlike device [2], relay K1 is disabled in operating mode and turns on only when a leak occurs. This leads to a reduction in energy consumption and an increase in the service life of the device. To match the high-resistance secondary winding of the differential transformer with the amplifier DA2, a voltage follower was used on the operational amplifier DA1, which has a large input impedance. Such an inclusion made it possible to use the resonant properties of the oscillatory circuit formed by the secondary winding of the current transformer T1 and the capacitor C1 to increase the sensitivity of the device (removing the capacitor reduces the sensitivity by about 1,5 times). The unbalance variable voltage amplifies the DA2 operational amplifier, is detected by the C4VD2VD3C5 circuit and is fed to the emitter follower (VT1 transistor) that controls the VS1 trinistor.

To eliminate regulation in the bias circuits of operational amplifiers, they are powered by a bipolar voltage of + 9 V, in contrast to the device described in [2].

To reduce the mass, the RZO amplifier is fed directly from a 220 V network without a step-down transformer, which was used in the device [3].

The reduction in current consumption was achieved by using micropower operational amplifiers KR140UD1208.

The operation of the relay K1 is indicated by the LED HL1. To check the operability of the device, a circuit of the resistor R11 and the SB1 button is provided. Return to the initial state after switching on the relay is carried out by the "reset" button switch SB2. Unlike the device [3], at the initial inclusion of the RZO in the network or when the load is connected, the relay K1 does not work.

The current transformer is made on the ring magnetic circuit OL 25/40. The primary windings are wound with a double wire for power cords with a cross section of 2 (0,5 mm 2, the number of turns is 8. The secondary winding contains approximately 5000 turns of PEV-2 wire with a diameter of 0,09 mm. Capacitors C3-C5 - K73-17 and can be replaced on K73-11, K73-16 or similar ones with a rated voltage of at least 25 V; capacitor C2 - KM-6, K10-17, K10-23; capacitor C6 - K73-17, K73-11; capacitor C7 - any oxide All film capacitors must have a permissible deviation of capacitance from the nominal value of not more than 20% Relay K1 - RP21-002 110 V; it can be replaced by RPU-2-OM11020 with a voltage of 110 or 220 V, or by a small-sized unified relay of Western European production R2 or RUC for a voltage of 110 or 220 V. If a relay for 220 V is used, it is necessary to exclude the resistor R14. All resistors are MLT or similar with a permissible deviation of resistance from the nominal value of not more than 10%. Transistor VT1 - KT315 or KT503 with any letter index. Trinistor VS1 - KU201K, KU201L. Replace the VD1 zener diode with any symmetrical voltage of 5,6 ... 8,2 V, and VD5, VD6 - with any with a stabilization voltage of 9 ... 10 V. Diode VD7 - any with a permissible reverse voltage over 300 V. Pushbutton switches SB1 , SB2 - any for a voltage of at least 250 V and a current of more than 100 mA.

The load current for the relays RP21, RPU-2, R2 should not exceed 10 A. The RUC relay allows you to switch a current of 16 A at a voltage of 220 V. If you need to turn off a larger current, you can use a circuit breaker with an independent release, as is done in the residual current device "RCD" [4].

The operational amplifier DA1 and the resistor R1 can apparently be eliminated without a noticeable loss in the sensitivity of the device. In this case, the left (according to the diagram) output of the resistor R3 is connected to the right output C1. The speed of the device will increase slightly when a capacitor with a capacity of 1 ... 2,2 μF is connected to an operating voltage of 300 V between the cathode of the VD7 diode and the cathode of the trinistor VS1 (only when using a relay for a voltage of at least 220 V).

Literature

Vodyanitsky Yu. Protects the machine. - Model designer, 1994, No. 10, p. fourteen.
Pavlov V. Automatic load disconnector. - Radio, 1989, No. 11, p. 31.
Kuznetsov A. Protection device against electric shock. - Radio, 1997, No. 4, p. 47.
Residual current device type UZO 20, IZHTSH656111085TO. - Stavropol, 1997.

Author: F. Dubinin, St. Petersburg

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