There are many types of relays. According to the input quantity, they can be divided into voltage relays, current relays, time relays, speed relays, pressure relays, etc. According to the working principle, they can be divided into electromagnetic relays, inductive relays, electric relays, electronic relays, etc. According to the purpose, it can be divided into control relays, protection relays, etc., according to the input change form can be divided into with or without relays and measuring relays.
The presence or absence of a relay acts according to the presence or absence of the input value. The relay does not act when there is no input value, and the relay acts when there is an input value, such as intermediate relays, general relays, and time relays.
The measuring relay acts according to the change of the input quantity. The input quantity always exists during work. The relay will only operate when the input quantity reaches a certain value, such as current relay, voltage relay, thermal relay, speed relay, pressure relay, Liquid level relay, etc.
Most of the relays used in the control circuit are electromagnetic relays. Electromagnetic relay has simple structure, low price, convenient use and maintenance, small contact capacity (generally below SA), large number of contacts and no distinction between main and auxiliary, no arc extinguishing device, small size, rapid and accurate action, and control Sensitive, reliable, etc., are widely used in low-voltage control systems. Commonly used electromagnetic relays include current relays, voltage relays, intermediate relays, and various small general-purpose relays.
The structure and working principle of an electromagnetic relay are similar to that of a contactor, and it is mainly composed of an electromagnetic mechanism and contacts. There are two types of electromagnetic relays: DC and AC. Apply voltage or current to both ends of the coil to generate electromagnetic force. When the electromagnetic force is greater than the spring reaction force, the armature is sucked to make the normally open and normally closed contact act; when the voltage or current of the coil drops or disappears, the armature is released and the contact is Reset.
Thermal relays are mainly used for overload protection of electrical equipment (mainly motors). Thermal relay is an electrical appliance that uses the principle of current thermal effect. It has inverse time action characteristics similar to the allowable overload characteristics of the motor. It is mainly used in conjunction with contactors to protect three-phase asynchronous motors from overload and phase failure. In actual operation, asynchronous motors often encounter overcurrent (overload and phase failure) caused by electrical or mechanical reasons. If the overcurrent is not serious, the duration is short, and the winding does not exceed the allowable temperature rise, this overcurrent is allowed; if the overcurrent is serious and the duration is long, it will accelerate the aging of the motor insulation and even burn the motor. Therefore, in A motor protection device should be installed in the motor circuit. There are many types of commonly used motor protection devices, and the most commonly used and most common is the bimetallic thermal relay. The bimetal thermal relays are all three-phase, and there are two types with phase protection and without phase protection.
The time relay is used for time control in the control circuit. There are many types. According to its operating principle, it can be divided into electromagnetic type, air damping type, electric type and electronic type. According to the delay mode, it can be divided into power-on delay type and power-off delay type. The air damping time relay uses the principle of air damping to obtain the time delay. It is composed of three parts: an electromagnetic mechanism, a time delay mechanism and a contact system. The electromagnetic mechanism is a direct-acting double E-type iron core, the contact system uses an I-X5 micro switch, and the delay mechanism uses an airbag damper.