How to test the setting current of a thermal relay

1."Measure the resistance of the contacts"Use the resistance level of the universal meter to measure the resistance of the normally closed contact and the moving point, and its resistance value should be 0; The resistance between the normally open contact and the moving point is infinite. From this, it is possible to distinguish which is a normally closed contact and which is normally open.

2."Measure the coil resistance"The resistance of the relay coil can be measured with the universal meter R 10 to determine whether there is an open circuit in the coil.

3."Measurement of pick-up voltage and pick-up electricity"An adjustable regulated power supply and an ammeter are found, a set of voltages are input to the relay, and an ammeter is connected to the power supply circuit for monitoring. Slowly increase the power supply voltage, and when you hear the relay sucking sound, make a note of the sucking voltage and pick-up current.

To be accurate, you can try several times to find the average.

4."Measure the release voltage and release current"It is also the same as the above connection test, when the relay is engaged, and then gradually reduce the power supply voltage, when you hear the relay release sound again, write down the voltage and current at this time, you can also try several times to obtain the average release voltage and release current. Under normal circumstances, the release voltage of the relay is about 10 50 of the pick-up voltage, if the release voltage is too small (less than the pick-up voltage of 1 10), it can not be used normally, which will pose a threat to the stability of the circuit, and the work is unreliable.

When testing the setting current of a thermal relay, the thermal elements of each phase can be connected in series, and for the thermal elements with phase break protection, the thermal elements can be connected in series in separate phases. In the test, a stabilized current power supply or a stabilized voltage power supply should be used to ensure the stability of the test current.

The working principle of the thermal relay is to generate heat by the current flowing into the heating element, so that the bimetal sheet with different expansion coefficients is deformed, when the deformation reaches a certain distance, the connecting rod action is promoted, the control circuit is disconnected, so that the contactor loses power, the main circuit is disconnected, and the overload protection of the motor is realized. As an overload protection component of the motor, the relay has been widely used in production due to its small size, simple structure and low cost.

The range of the setting current of a thermal relay is determined by its own characteristics. It describes the inverse proportionality of the square of the operating time of the thermal relay to the current under a certain current condition.

When the thermal relay is used to protect the motor of long-term duty system or intermittent long-term duty system, it is generally selected according to the rated current of the motor. For example, the setting value of a thermal relay can be equal to the rated current of a motor at a time, or the median setting current of a thermal relay can be equal to the rated current of the motor and then adjusted.

1. The setting current of the thermal relay is adjusted to the times of the rated current of the motor. The thermal element of a thermal relay has a thermal inertia, and the action of the thermal relay contacts takes a while under the action of an overload current. This is the protective nature of thermal relays.

Therefore, reasonable overload is allowed in the operation of the motor.

2. Based on the protection characteristics, the setting current of the thermal element is usually set to be equal to the rated current of the motor. However, if the motor is dragging an impact load, or the starting time is long, or the dragged equipment is not allowed to stop, it can be adjusted to times the rated current of the motor.

3. The working principle of the thermal relay is that the thermal relay should be connected in series in the main circuit first, and the normally closed contact is connected in series in the control circuit, when the motor is overloaded, the current flowing through the resistance wire exceeds the setting current of the thermal relay, the resistance wire is heated, and the bimetal sheet is heated and expanded.

4. Due to the different thermal coefficients, the bimetal sheet will bend to drive the transmission mechanism to act, the normally closed point will be disconnected, the control loop will be de-energized, and the contactor coil will lose power and the contactor will cut off the power supply of the motor. To achieve protection, the main circuit has no electricity, the resistance wire is not heating, the bimetal sheet is cooled and reset, the normally closed contact is closed, and the motor can be started again.

1. Adjustment of thermal relay: There is a knob to adjust the setting current on the thermal relay, and the pointer can be turned to the required current position with a flathead screwdriver, which is generally the rated current value of the load.

2. The setting current of the thermal relay: the current at which the load works for a long time at the rated current and the thermal relay does not operate.

34.The rated current and the setting current of the thermal relay are not the same thing, so we must pay attention to it.

The setting current refers to the maximum current that passes through the heating element for a long time without causing the thermal relay to operate, and describes that the action time of the thermal relay under a certain current condition is proportional to the square of the current.

It is the operating current of the thermal relay.

The current setting value of the thermal relay is selected according to the rated current of the motor on the motor nameplate.

Because the thermal relay is used for overload protection, the protection characteristics of the thermal relay are in line with the thermal overload characteristics of the motor.

If you choose according to the rated current of the motor, 2 times, you can also choose.

It should be set according to the 1.5 of the rated current of the motor.