Motor Protection Relay Function - 9 Things You Must Know

Motor Protection Relay Function – 9 Things You Must Know

The motor protection relay can provide all-around protection for the motor. The most basic motor protection relay functions include overload protection, underload protection, overheat protector, phase loss protection, phase sequence protection, under voltage protection, overvoltage protection, leakage protection, short circuit protection, starting overtime protection, current protection, and so on. So, under what circumstances will these all come into play? And how does it work?

1. Motor protection relay function - overload protection

When the motor is under the fault of overload and runs above its rated current for a long time, it will cause the motor to overheat, reduce the insulation or even burn out. At this time, the integrated motor protector relay.will calculate the heat capacity of the motor according to the heating characteristics of the motor, and simulate the heating characteristics of the motor to protect the motor. This protection mode is called overload protection.

2. Motor protection relay function - underload protection

When the load carried by the motor is a pump load, no-load or under-load operation of the motor will cause harm. The underload protection function provided by the motor protection relay is that when the percentage of the average current of the three phases to the rated current is lower than the set value, the motor protector relay should act within the action (delay) set time or alarm within the alarm time. This motor protection relay function is mainly applied to the protection of pump equipment.

3. Motor protection relay function - overheat protection

When the three-phase power supply current is unstable due to environmental factors, and one phase is disconnected or abnormal, the motor protector relay will detect the lack of phase of the equipment, and then act to protect it. This protection behavior is phase loss protection.

4. Motor protection relay function - Phase loss protection

5. Motor protection relay function - Phase sequence protection

For a motor protector relay with a phase sequence protection function, when the voltage phase sequence on the power supply side is consistent with the original set sequence, the motor protection relay will not operate; when the motor protection relay detects that the phase sequence of the motor is connected incorrectly, the motor protector relay will react and act, so that the motor cannot start.

6. Motor protection relay function - under voltage protection

During the operation of the motor, the working voltage is too low to cause the motor speed to decrease, or even stop running. When the operating voltage of the motor drops to the set under voltage protection range, the motor protector relay will protect according to the set requirements, operate within the set time of action (delay), or alarm within the alarm time, so as to avoid confusion in important production processes and seriously affect production.

7. Motor protection relay function - overvoltage protection

If the working voltage is too low, it will cause failure, and if it is too high, it will cause damage to the insulation of the motor. When the operating voltage of the motor exceeds the set protection voltage, the Moto Protector relay will protect according to the set requirements, act within the action (delay) set time, or alarm within the alarm time to ensure the safety of the motor equipment.

8. Motor protection relay function - grounding and leakage protection

The grounding protection current signal is derived from the vector sum of the internal current transformers, and it is used to protect the short circuit protection of the phase wires to the motor’s metal outer box. Moreover, the motor protector relay can detect the fault current by adding leakage transformers, and it can be used for indirect ground protection equipment, so as to ensure the personal safety of operators and improve the safety of equipment use.

9. Motor protection relay function - start timeout protection

During the starting process of the motor, the motor protector relay has protection functions such as phase failure (three-phase unbalance) and grounding/leakage and other protection functions cannot play a protective role. All motor protection functions (according to the actual settings of the user) will be put into protection automatically only after the start-up is completed. The starting overtime protection means that when the starting time of the motor exceeds the starting time actually set by the user, and the current is greater than 1.1 times the rated current, the integrated motor protector relay will take protection work according to the set requirements and will issue a stop warning within the action (delay) set time so that the motor will stop running and the protection equipment will fail accordingly.