1. The difference between the structure of current relay and voltage relay
The main thing is that the coils are different.
The coil of the current relay is connected in series with the load to reflect the load current, so it has a small number of coil turns and a thick wire, so that the voltage drop when passing through the current is very small and 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, and its coil turns are many and the wires are thin.
2. What is the difference between a current signal relay and a voltage signal relay? How to distinguish in application?
Current type signal relays; The voltage is low, the current is large, the wire is thick, the number of turns is small, the impedance is small, and the volume is small, which is generally used in series with electrical appliances.
Voltage type signal relays; The voltage is high, the current is small, the wire is thin, the number of turns is many, the impedance is large, and the volume is large, which is generally directly connected to the power supply at both ends through the switch.
Third, the characteristics and application occasions of voltage relays and current relays.
(1) Characteristics and applications of voltage relays:
Voltage relay is a commonly used electromagnetic relay, which is used for voltage maintenance and control of the power drive system.
The coil of the voltage relay is connected to the main circuit in parallel to sense the line voltage of the main circuit; The contacts are connected to the control circuit and are fulfillment elements.
According to the size of the pick-up voltage, the voltage relay can be divided into overvoltage relay and undervoltage relay.
The overvoltage relay (FV) is used for the overvoltage maintenance of the line, and its suction setting value is 1.05-1.2 times of the additional electricity of the maintained line. When the voltage of the line to be maintained is normal, the armature does not operate; When the voltage of the maintained circuit is higher than the additional value and reaches the setting value of the overvoltage relay, the armature is engaged, the contact mechanism acts, the control circuit loses power, and the controlled contactor breaks the maintained circuit in time.
The undervoltage relay (KV) is used for the undervoltage maintenance of the line, and its release setting value is 0.1-0.6 times of the additional voltage of the line. When the voltage of the maintained line is normal, the armature is firmly engaged; When the voltage of the maintained line drops to the setting value of the undervoltage relay, the armature is released, the contact mechanism is reset, and the contactor is controlled to break the maintained circuit in time. The zero-voltage relay is released when the circuit voltage is reduced to 5%-25%UN, and the zero-voltage maintenance is completed for the circuit. It is used for the loss of voltage maintenance of the line.
Complementary small technology: A center relay is essentially a voltage relay. It is characterized by a large number of contacts and an increase in current capacity, which plays a role in center expansion (number of contacts and current capacity).
(2) Characteristics and applications of current relays.
The current relay is a commonly used electromagnetic relay, which is used for the current maintenance and control of the electric drive system. Its coil is connected in series to the main circuit and is used to sense the line current of the main circuit; The contacts are connected to the control circuit and are fulfillment elements.
A current relay reflects a current signal. There are two commonly used current relays: undercurrent relay and overcurrent relay.
The undercurrent relay (KA) is used for the maintenance of the undercurrent of the circuit, the induced current is 30%-65% of the additional current of the coil, and the release current is 10%-20% of the additional current.
When the current of the maintained line is higher than the additional value, when the setting value of the overcurrent relay is reached, the armature is engaged, the contact mechanism acts, the control circuit loses power, and then the contactor is controlled to break the circuit in time. It plays the role of overcurrent maintenance for the circuit.
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