SU1436171A1 - Load protection device - Google Patents

Abstract

The invention relates to electrical engineering. The aim of the invention is to increase the reliability of protection and expand the functionality by introducing automatic re-activation in case of short-term accidents and shutdown in case of emergency situations lasting longer than a predetermined time. When a current overload occurs, the current increases, the flow through the current sensor 5, the relay 6 is activated. As a result, the transformer 2 and the load I are disconnected from the network. After the selected time has elapsed, the monostable multivibrator of the unit 8 returns to the initial steady state, which leads to the opening of the switch 12. At the same time, the transformer 2 and the load J are again connected to the network. If, after switching on the actuator 15, an overcurrent occurs again, the device goes into self-oscillating mode. In this case, the pulses from the output of the delay unit B charge memory (L

Description

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: a capacitor 20. As soon as 1 voltage on the capacitor 20 is transformed; the voltage is on the divider 17, the operational amplifier 16 is actuated and executing: the amplifier 15 disconnects the load 1 from the mains. f-ly, 1 silt,

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I The invention relates to electrical engineering and can be used to protect loads and feeding transformers against overloads and short circuits.

I The goal of the enhancement is to increase the reliability of protection and expansion, 1 functionality by I Introduce automatic re; switching on during short-term accidents and shutdowns in case of emergency situations lasting longer than a predetermined time.

; The drawing shows the principle-I-scheme of the device.

A device for protecting a load connected to the mains via transformer 2 contains a rectifier 3 whose protection input is connected in series with the primary windings of transformer 2, and the output is connected to a switching protection unit 4, made in the form of a current sensor 5, shunted by a coil of a relay 6, the closing contact of which is connected between the output of the power source 7 and the input of the delay unit 8, the output of which through the first separation diode 9 is connected to the input of the blocking node 10, and through the second separation diode 11 to the control present entry key 12 to which via a third divider 13 is connected as diode output node 10 locking. The key 12 is connected to the output of the power supply 7 through the coil 14 of the actuating element 15, the closing contacts of which are connected in series with the primary windings of the transformer 2.

Blocking node 10 can be made at the operational amplifier 16, the inverting input of which is connected to the midpoint of the voltage divider 17, and the direct to the connection point of the input resistor 18, the feedback diode 19

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sensor 20, another winding of which is connected to the positive output of the power source 7.

Block 8 delay can be made in the form of a monostable standby multivibrator on an operational amplifier.

The device works as follows.

When the power source 7 is turned on, the key 12 is opened through the coil 14 of the actuating element. 15 current flows, causing the contacts of element 15 to close and supply power to transformer 2 and load 1. In normal operation, the voltage drop across sensor 5 of the current of switching protection unit 4 is not enough to trigger relay 6, therefore the signal at the input of block B is delayed missing.

When a current overload occurs in the primary windings of transformer 2 for any reason, the current flowing through the current sensor 5 increases, the relay 6 is activated and the signal from the current sensor 5 is triggered by the standby monostable multivibrator of block 8. Output signal of the logic zero of the multivibrator of unit 8 through a diode 11 locks the key -12, as a result of which the coil 14 of the element 15 is de-energized and its contacts open, i.e. transformer 2 and load

1 disconnected from the network. After the selected time has elapsed, the monostable multivibrator of the block B returns to its initial steady state, which leads to the opening of the key 12 and the switching on of the control element 15. At the same time, the transformer

2 and load 1 are re-connected to the network. If there is no current overload, the circuit remains in this state until the next operation of block 4. If after switching on the operating element 14 of the element 15 again an overcurrent occurs, for example, a fault or a short circuit in the load, the device will switch to self-oscillatory mode. The on time is determined by the response time of block 4 and the response time of the actuator 15. The off time is determined only by the selected value of the return time of the multivibrator of block 8 to steady state. The pulses from the output of the multivibrator unit 8 is fed to the input of the node 10. blocking. When the device operates in the self-oscillating mode, the pulses from the output of the delay unit 8 charge the memory capacitor 20. As soon as the voltage on the storage capacitor 20 exceeds the voltage set on the voltage divider 17, the operational amplifier 16 will operate and block in this state. The output signal of the logical zero of the operational amplifier 16 through the diode 13 will close the key 12, and the executive element 15 will disconnect the load: terminal: 1 from the mains. The device can be brought out of this steady state only by disconnecting and re-turning on the power source 7. In this case, the operation of the node 10 occurs only in the case of the sequential operation of the block 4 for a short period of time. In case of random current overloads, which, as a rule, do not follow one another, the operation of node 10 does not occur, as the storage capacitor 20 due to self-discharge and the presence of input current of the operational amplifier 16 has time to discharge during rare operation of the unit 4.

Thus, due to the introduction of an automatic restoration of a normal mode of operation in the event of the disappearance of a malfunction with the help of test inclusions and automatic shutdown

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Claims (2)

Conclusions in an emergency situation that lasted more than a predetermined time, the reliability increases and the functionality of the device expands. The invented formula is also 1. A device for protecting a load connected to a network through a transformer containing a rectifier of protection, the input of which is intended to be connected in series with the primary windings of the transformer and the output connected to a switching protection unit, characterized in that, in order to increase reliability and expansion of functionality, it is supplied with a source. power supply, actuator, delay unit, interlock unit, matching unit, key and three separation diodes, - and the switching protection unit is designed as a current sensor, shunted by a relay coil, the closing contact of which is connected between the power source and the input of the delay unit, the output of which is through the first dividing diode is connected to the input of the blocking node and through the second dividing diode to the control input of the key, to which the output of the blocking node is also connected via the third dividing diode and, the switch is connected to the output of the power source through the coil of the actuating element, the closing contacts of which are intended to be connected in series with the primary windings of the transformer. 2. The device according to claim., Lt is the fact that the blocking node is made on an operational amplifier, the inverting input of which is connected to the midpoint of the voltage divider, and the direct one to the point soy: the length of the input resistor, the anode of the diode - feedback and capacitor plates, the other of which is connected to the positive terminal of the power source.