Relay selection principle

Select the relay, the main consideration should be the power supply contacts, rated voltage and rated current, rated voltage or rated current coil, contact combination mode and quantity, operation time and release time etc.. Here are some commonly used relay selection principles.

1 Selection of electromagnetic relay

(1) the current relay can be divided into two types: overcurrent relay and under current relay.

Over current relay selection of T parameters is rated current and operating current, the rated current should be greater than or equal to the rated current of the motor is protected, operating current should be based on the work of the motor according to the starting current of 1.1 ~ 1.3 times of setting. General winding rotor asynchronous motor starting current according to 2.5 times the rated current, the cage asynchronous motor starting current according to 5-7 times rated current. When the overcurrent relay is selected, there should be some room for adjustment.

Under current relay is usually used in DC motor and electric breakdown of the weak magnetic protection. The selection of main parameters is rated current and discharge current, the rated current should be greater than or equal to the rated excitation current release current setting value should be less than the minimum excitation current may occur within the normal operating range of excitation circuit, can be 0.85 times of the minimum excitation current. When selecting the current release of the current relay, there should be some room for adjustment.

(2) according to the function of the voltage relay in the control circuit, the voltage relay is divided into two types: over voltage relay and under voltage (zero voltage) relay.

The main parameters of the relay selection is the rated voltage and the operating voltage, and its operating voltage can be adjusted by 1.1 to 1.5 times the rated voltage of the system. The undervoltage relay used as electromagnetic relay or contactor as the selection of small, as long as meet the general requirements, no special requirements on the release voltage.

2 selection of thermal relay

The thermal relay is mainly used for overload protection of the motor. It is usually considered in terms of the type of the motor, the working environment, the starting condition and the nature of the load.

(1) thermal relay structure when the motor windings for y coupling, thermal relay can choose a two-phase structure, if the grid voltage imbalance, poor working environment, thermal relay can choose the three-phase structure; when the motor winding is a connection, you should choose the three-phase structure thermal relay with phase interruption protection device.

(2) thermal relay for motor rated current long-term normal operation, the heat element of the heat relay rated current is 0.95 - 1.o5 times the motor rated current; motor overload capacity for the poor, the heat element of the heat relay for motor rated current rated current of 0.6 ~ 0.8 times.

For the motor to start, to ensure that the thermal relay does not produce false action in the motor starting process, if the motor starting current is 6 times of the rated current, and the starting time is not more than 6S, it can be selected according to the rated current of the motor thermal relay.

For repetitive short time working system, it is necessary to determine the allowable operating frequency of the thermal relay, which can be selected according to the starting parameters (starting time, starting current, etc.).

3 time relay selection relay manufacturers

There are many types of time relay, which should be considered from the following aspects:

(1) the current type and voltage type electromagnetic damping and air damping type time relay, current and voltage level of the coil should be the same with the control circuit; motor type and transistor type time relay, current type and voltage level power supply and control circuit of the same.

(2) a delay mode is selected according to the requirements of the control circuit.

(3) contact type and quantity according to the requirements of the control circuit to select the contact type (time delay or delay off) and quantity.

(4) the time delay precision electromagnetic damping time relay is suitable for the occasions where the precision is not high, and the motor type or the electronic time relay is suitable for occasions with high requirement of the delay precision.

(5) operating frequency should not be too high operating frequency, otherwise it will affect the electrical life, and even lead to the delay of the movement disorders.

4 intermediate relay selection

When selecting the intermediate relay, it is necessary to pay attention to the type of coil current and voltage level should be consistent with the control circuit, at the same time, the number of contacts, types and capacity must be selected according to the needs of the control circuit. If the number of contacts of an intermediate relay is not enough, the two intermediate relays can be used in parallel to increase the number of contacts.