Relays
Relays and contactors are constructed and operated in much the same way.
The main difference is that the main contact of the contactor can pass a large current; the volume of the relay and the contact capacity are small, the number of contacts is large, and only a small current can be passed. Therefore, relays are generally used in control circuits.
1. Current and voltage relays
Current relays: can be used for overload or overload protection.
Voltage relays: mainly used as undervoltage and voltage loss protection.
2. Intermediate relays
are commonly used to transmit signals and control multiple circuits simultaneously, and can also be used directly to control small-capacity motors or other electrical actuators.
The intermediate relay has a small contact capacity and a large number of contacts for controlling the wiring.
3. Time relay
is a relay that operates after a period of delay from the time the input signal is received (the coil is energized or de-energized). Suitable for timing control
(1) DC electromagnetic time relay
Working principle: When the armature is not sucked, the magnetic circuit air gap is large, the coil inductance is small, the excitation current is established quickly after energization, the armature is pulled in, and the relay contact changes state immediately. When the coil is de-energized, the magnetic flux in the core will be attenuated. The change of the magnetic flux will generate an induced electromotive force in the copper sleeve, and generate an induced current to prevent the magnetic flux from attenuating. When the magnetic flux drops to a certain extent, the armature can be released. The contact changes state. Therefore, when the relay is engaged, it is a momentary action, and when it is released, it is delayed, so it is called a power-off delay.
(2) Air time delay relay
a) Power-on delay relay
(2) Air time relay
Thermal relay
for overload protection of the motor
Working principle The
heating element is connected to the main circuit of the motor. If it is overloaded for a long time, the bimetal is heated. Due to the large expansion coefficient of the lower metal sheet, the upper flange is bent upward, the lever is pulled back by the spring, and the normally closed contact is broken.
Relays and contactors are constructed and operated in much the same way.
The main difference is that the main contact of the contactor can pass a large current; the volume of the relay and the contact capacity are small, the number of contacts is large, and only a small current can be passed. Therefore, relays are generally used in control circuits.
1. Current and voltage relays
Current relays: can be used for overload or overload protection.
Voltage relays: mainly used as undervoltage and voltage loss protection.
2. Intermediate relays
are commonly used to transmit signals and control multiple circuits simultaneously, and can also be used directly to control small-capacity motors or other electrical actuators.
The intermediate relay has a small contact capacity and a large number of contacts for controlling the wiring.
3. Time relay
is a relay that operates after a period of delay from the time the input signal is received (the coil is energized or de-energized). Suitable for timing control
(1) DC electromagnetic time relay
Working principle: When the armature is not sucked, the magnetic circuit air gap is large, the coil inductance is small, the excitation current is established quickly after energization, the armature is pulled in, and the relay contact changes state immediately. When the coil is de-energized, the magnetic flux in the core will be attenuated. The change of the magnetic flux will generate an induced electromotive force in the copper sleeve, and generate an induced current to prevent the magnetic flux from attenuating. When the magnetic flux drops to a certain extent, the armature can be released. The contact changes state. Therefore, when the relay is engaged, it is a momentary action, and when it is released, it is delayed, so it is called a power-off delay.
(2) Air time delay relay
a) Power-on delay relay
(2) Air time relay
Thermal relay
for overload protection of the motor
Working principle The
heating element is connected to the main circuit of the motor. If it is overloaded for a long time, the bimetal is heated. Due to the large expansion coefficient of the lower metal sheet, the upper flange is bent upward, the lever is pulled back by the spring, and the normally closed contact is broken.
