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How to distinguish between voltage relay and current relay?

How to distinguish between voltage relay and current relay?


First, the structural difference between the current relay and the voltage relay:


The current relay and the voltage relay are mainly different coils:


The coil of the current relay is connected in series with the load to reflect the load current, so its coil turns are small and the wire is thick, so the voltage drop when passing the current is small, and it will not affect the current of the load circuit. The coil of the voltage relay is connected in parallel with the load to reflect the load voltage. The coil has a large number of coil turns and a thin wire.


Second, the performance characteristics of the current relay and the voltage relay are different:


Current type signal relay


Low voltage, high current, thick wire warp, few turns, small impedance, small volume, generally used in series with electrical appliances


Voltage type signal relay:


High voltage, small current, thin wires, many turns, large impedance, large volume, usually directly connected to the two ends of the power supply through a switch;


Third, the characteristics of voltage relays and current relays are different from the applications:


1. Characteristics and applications of voltage relays:


(1) The voltage relay is a commonly used electromagnetic relay. The voltage relay is used for voltage protection and control of the electric drag system;


(2) The coil of the voltage relay is connected to the main circuit in parallel, and the line voltage of the main circuit is sensed;


(3) The contact is connected to the control circuit, which is the actuator;


(4) According to the pull-in voltage, voltage relays can be divided into over-voltage relays and under-voltage relays;


(5) Over-voltage relay (FV) is used for over-voltage protection of the line, and its pull-in setting value is 1.05 to 1.2 times of the rated power of the protected line. When the voltage of the protected line is normal, the armature does not operate;


(6) When the voltage of the protected line is higher than the rated value and reaches the setting value of the over-voltage relay, the armature pulls in, the contact mechanism operates, the control circuit loses power, and the control contactor breaks the protected circuit in time;


(7) Under voltage relay (KV) is used for under voltage protection of the line, and its release setting value is 0.1 to 0.6 times of the rated voltage of the line. When the voltage of the protected line is normal, the armature is reliably pulled in;


(8) When the voltage of the protected line drops to the release setting value of the under-voltage relay, the armature is released, the contact mechanism is reset, and the contactor is controlled to timely break the protected circuit;


(9) The zero-voltage relay is released when the circuit voltage drops to 5% to 25% UN to achieve zero-voltage protection for the circuit;


(10) Used for voltage loss protection of the line.


Supplementary skills:


The intermediate relay is essentially a voltage relay. It is characterized by a large number of contacts, and the current capacity can be increased to play the role of intermediate amplification (number of contacts and current capacity).


2. Characteristics and applications of current relays:


(1) The current relay is a commonly used electromagnetic relay. The current relay is used for the current protection and control of the electric drag system. The coil is connected to the main circuit in series to sense the line current of the main circuit;


(2) The contact is connected to the control circuit, which is the actuator;


(3) The current relay reflects the current signal. Commonly used current relays are under current relays and over current relays;


(4) The undercurrent relay (KA) is used to protect the circuit from undercurrent. The attraction current is 30% to 65% of the rated current of the coil and the release current is 10% to 20% of the rated current. Therefore, when the circuit is working normally, the armature is The pull-in is only when the current drops to a certain setting value, the relay is released, the control circuit is de-energized, thereby controlling the contactor to open the circuit in time;


(5) The overcurrent relay (FA) does not operate during normal operation of the circuit. The setting range is usually 1.1 to 4 times the rated current. When the current of the protected line is higher than the rated value and the setting value of the overcurrent relay is reached, the armature attracts When the contact mechanism is turned on, the control circuit loses power, thereby controlling the contactor to open the circuit in time. Overcurrent protection for the circuit;