Relay selection should know - how to select relay
In the daily production work, the relay has a very important role. Relay in electrical control circuit, used for amplification of minitype relay contact capacity, to drive a large load. As with the contacts of the relay to connect or disconnect the contactor coil. General relay is more open and close contacts of relay, through appropriate connection method can also achieve some special function, such as logical operation. Common relay the main thermal overload relay ( JR series relay, time relay ) ( JS series relay ( JZ ) and an intermediate relay series relay ). Then discuss some attention points of relay type.
To use the relay, correct selection is very important, we must first of the controlled object properties, characteristics and use requires a thorough understanding of, and a careful consideration. The selection principle of relay, usage, technical parameters, structure features, specifications to master and analysis. On the basis of the project should be based on the actual situation and specific conditions, to correctly select relay. Can refer to the following:
1 pairs of contact understanding
The relay coil is not energized when in open state of a dynamic and static contact, known as" normally open contact", conversely, is called " normally closed contact". A movable contact and a static contact normally closed and another static contact normally open, he called them" changeover contact". In the same relay, may have a pair or several pairs of normally open contact or normally closed contact ( both also is simultaneously ), also has a group or array changeover contact.
2 motor insulation level and structure
Because the motor insulation level is different, the permissible temperature rises and the ability to withstand overload are also different. Under the same conditions, the insulation level higher, stronger overload capacity. Even if the insulating material is the same, but the motor structure is different, in the selection of relay should also be differences. For example, enclosed type motor heat dissipation than open motor differential, the overload capacity than open motor is low, the relay setting current should be chosen as the motor rated current of 60 to 80%.
The 3 electric motor starting current and starting time
Motor starting current is generally rated current of 5 ~ 7 times. For less frequent start, continuous operation of the motor, the startup time is not more than 6S, according to the motor rated current selection relay.
4 if the thermal relay for motor open-phase protection, should be considered for earthing method
In particular, when adopting the heat death of electrical appliances, for Y shaped connecting method of motor, when a phase line, the rest is not broken phase winding current and flows through a heat relay current increases in proportion to the same. Common three-phase thermal relay, as long as the setting current regulation is reasonable, can Y shape connection of motor phase failure protection. For delta shaped connection motor, its are broken through, not broken phase winding current flowing through the current increase in the proportion of thermal relay is different. That is to say, through the thermal relay current cannot reflect the phase winding overload current, therefore, the general thermal relay, even the three-phase, nor a conformal connection method of three-phase asynchronous motor open-phase running to provide full protection. At this time, should choose JR20 or T series with these types of differential phase break protection mechanism of the thermal relay.
The above information by the country electric switch factory collection, www.jiandq.com 15957745520