Commonly used electromagnetic relays include current re […]
Commonly used electromagnetic relays include current relays, voltage relays, intermediate relays and time relays. The intermediate relay is actually a kind of voltage relay, but it has a large number of contacts with large capacity, which plays the role of intermediate amplification. Commonly used electromagnetic relays include current relays, voltage relays and intermediate relays. The appearance of a typical relay. The structure of an electromagnetic relay is similar to a contactor. It is composed of a static iron core, a moving iron core (armature), a coil, a release spring, and contacts. Only the contacts of the relay are not divided into main contacts and auxiliary contacts. The contact capacity of the relay is small, and there is no arc extinguishing device.
1. The contact action of electromagnetic voltage relay is related to the voltage of the coil's operating voltage. The relay is called voltage relay. The voltage relay plays the role of voltage protection and control in the electric drive control system. The coil of the voltage relay is a voltage coil, which is connected in parallel with the load, and its coil turns are many and the wire is thin. According to the type of coil current, voltage relays can be divided into AC voltage relays and DC voltage relays. According to the size of pull-in voltage, it can be divided into overvoltage relay and undervoltage relay.
(1) Overvoltage relay The overvoltage relay plays the role of overvoltage protection in the circuit. When the coil of the overvoltage relay is at the rated voltage, the armature does not cause a pull-in action. Only when the voltage of the coil is higher than its rated voltage does the armature generate a pull-in action, so it is called an overvoltage relay. When the armature of the overvoltage relay is engaged, the normally closed contact is often used to disconnect the power supply of the electrical appliance to be protected. Since DC circuits generally do not produce over-voltage phenomena with large fluctuations, there is no DC over-voltage relay in the product. The adjustment range of the pull-in voltage of the AC overvoltage relay is U X = (1.05 ～ 1.2) U N where: U X represents the pull-in voltage; UN represents the rated voltage.
(2) Undervoltage relay Undervoltage relay plays the role of undervoltage protection in the circuit. When the electrical equipment in the circuit works normally at the rated voltage, the armature of the undervoltage relay is in the pull-in state; if the voltage in the circuit decreases to the release voltage of the coil, the armature changes from the pull-in state to the released state. Undervoltage relays often use their normally open contacts to disconnect power supplies that need to be protected. Generally, the setting range of the pull-in voltage and release voltage of the DC undervoltage relay are UX = (0.3 ～ 0.5) UN and UF = (0.07 ～ 0.2) UN; the setting range of the pull-in voltage and release voltage of the AC undervoltage relay UX = (0.6 ～ 0.85) UN and UF = (0.1 ～ 0.35) UN respectively. In the above formulas, U X represents the pull-in voltage; U N represents the rated voltage; U F represents the release voltage.
(3) Selection of voltage relay and setting of operating voltage When selecting a voltage relay, it is necessary to pay attention to the type of coil and the voltage level should be consistent with the control circuit; in addition, according to the role in the control circuit (overvoltage protection or undervoltage Voltage protection) for selection. For setting the operating voltage of the voltage relay, a voltmeter is connected in parallel to both ends of the coil, and the voltage applied to the coil is adjusted with a sliding wire resistance. If you want to set the pull-in voltage, adjust the voltage to the required pull-in value, then disconnect the power supply (do not change the resistance of the slide wire), adjust the reaction spring, turn the power supply once every time, until the power supply is closed, the armature Just close in. If you want to set the release voltage, mainly change the thickness of the non-magnetic gasket (if there is no fixed requirement for the pull-in voltage, the reaction spring can also be adjusted). At this time, the relay should be closed first, and then the resistance of the slide wire should be changed, and the voltage of the coil should be reduced until the voltage reaches the required value, and then the thickness of the non-magnetic conductive gasket should be adjusted (the coil voltage should be disconnected for each adjustment) Until the armature opens at the required release voltage. Electromagnetic current relay contact action or not depends on the current in the coil. The relay is called a current relay. The current relay plays the role of current protection and control in the electric drive control system. The coil of the current relay is a current coil, which is connected in series with the load, the number of coil turns is small and the wire is thick. According to the type of coil current, current relay can be divided into AC current relay and DC current relay. According to the size of pull-in current, it can be divided into over-current relay and under-current relay.