SU1390685A1 - Device for protecting a d.c. circuit against overloads and short-circuits - Google Patents

Abstract

The invention relates to relay protection and automation and can be used to protect direct current circuits. The aim of the invention is to increase reliability. This is achieved by performing a tripping element in the form of a relay 9, the switching contacts 10 and 12 of which connect the load 11 to a power source. This eliminates the loss of voltage on the disconnecting element. 1 il.

Description

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The invention relates to relay protection and automation and can be used for the protection of direct current circuits, as well as various equipment, according to the conditions of operation of which the automatic switching on of the cause of the overload that caused the equipment to shut down is required.

The purpose of the invention is to increase the reliability by eliminating the voltage drop across the disconnecting element.

The drawing shows the structure of the proposed device.

: Current sensor 1 is included in one of the busbars. Output of the first source

The reference voltage is connected to one of the inputs of the first comparison circuit 3, the second input of which is connected

to current sensor 1. Output of the first circuit

3 comparisons connected via element

4 delays to the control electrode of the first key 5. The second source 6 of the reference voltage is connected to one of the inputs of the second comparison circuit 7 whose output is connected to the control electrode of the second key 8. Relay

9 through keys 5 and 8 is connected to a power source. The switching contact 10 of the relay is connected to the load t1. The closing contact 12 is connected via the current sensor 1 to the power rail. One of the inputs of the second circuit 7 compared with the disconnecting contact 13 and | through a resistor 14 with a load of 11, and | through the zener diode 15 - with the bus bus. In addition, a limiting resistor 16 is connected in parallel with pins 10 and 12.

The device works as follows.

When the supply voltage is applied to the terminals and - and when comparing the load 11 is larger than the nominal, the keys 5 and 8 are open. In this case, the relay 9 is activated, its contacts 10 and 12 are closed, and the resistance of the load 11 is connected to the power source (the keys 5 and 8 are open, because the voltage on the current sensor 1 is less than the reference voltage from source 2, and the voltage on the load 11 more reference voltage at source 6).

In the event of an overload, the voltage drop on the sensor 1 exceeds the reference voltage from source 2, and at the output of the comparison circuit 3, a signal appears that closes the key: 5. Relay 9

five

about

five

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turning and breaking the load supply circuit (pins 10 and 12 are opened and pins 10 and 13 are closed).

The load 11 through the limiting resistor 16 is supplied with a control current, which is 10-100 times less than the nominal. In case of overload, the load resistance is less than the nominal and the voltage on it is less than the reference voltage from source 6, as a result, the output of the comparison circuit 7 produces a signal closing the key 8, and the relay continues to be de-energized, although after breaking the load circuit, the key 5 opens . The delay element 4 holds the key 5 for some time in the closed state after the opening of the load circuit in order for the key 8 to close. In this state, the circuit is before the overload is removed.

After elimination of the overload, the voltage on the load supplied by the control current becomes greater than the reference voltage. The output of the lock switch 8 disappears at the output of the comparison circuit 7. The latter opens, the relay 9 is connected to the power source and is activated. Pins 10 and 12 close and connect the load to the power supply. The voltage on the load after actuation of the relay 9 is greater than when it is energized by the control current - and the key 8 continues to remain open. Zener diode 15 protects the comparison circuit 7 from the arrival at its input of a high voltage equal to the voltage of the power source when the load is connected to the power source.

Thus, the invention eliminates the voltage losses on the switching element, since the load is connected via the relay contacts, which increases the reliability of the device.

Claims (1)

Invention Formula The device dp of the direct current circuit from overloads and short circuits, containing a current sensor, the first output of which is connected to the first input of the first comparison circuit, the output connected via the delay element to the control input of the first switch, the second comparison circuit of the output which is connected to the control the input of the second key, the disconnecting element, the first output of which is connected to the first output of the current sensor, characterized in that, in order to increase reliability, the first and second sources of reference are additionally introduced into it Parameters connected by the outputs to the inputs of the first and second comparison circuits, the limiting resistor, the Zener diode, in this case, the tripping element is implemented as a relay, the output of the switching contact for two positions is connected to the terminal for connecting the first load output, the output of the first position of the switching contact is VL It is the first output of the tripping element. the output of the second position of the switching contact is connected to the first input of the second comparison circuit and to the cathode of the Zener diode, one end of the relay winding is connected via the first switch to the first output of the current sensor, the second end of the winding is connected via a second switch to the anode of the zener diode, which has a terminal for connecting to the source minus power supply and the second load terminal, parallel to the switching contact of the relay, the limiting resistor is turned on, and the second output of the current sensor has a terminal for connecting to the positive power source.