What are the protection functions of the frequency converter?

A frequency converter is a power control device that controls an AC motor by changing the frequency of the motor’s operating power supply for the purpose of energy saving and speed regulation.

Frequency converter have a variety of protection functions that protect the frequency converteritself and the motor connected to it from damage. The following are some of the main protection functions of the frequency converter:

Under-voltage protection: when the power supply voltage of the frequency converter is lower than the specified value (usually less than 10% of the rated voltage), the frequency converter will stop the output in order to prevent the malfunction of the control circuit and the main circuit components from working abnormally.

Over-voltage protection: when the voltage of DC circuit exceeds the specified value under the circumstances of high power supply voltage, rapid motor deceleration, etc., in order to prevent the main circuit components from being damaged due to over-voltage, the frequency converter will stop output.

Overcurrent protection: When the motor is started directly or the output side of the frequency converter is short-circuited between phases and grounded and other faults occur, the output current of the frequency converter will increase sharply in an instant.

In order to protect the main circuit components from being damaged, the inverter will shut down the main circuit components and stop output. The overcurrent protection is usually set at about 200% of the rated output current.

Instantaneous overcurrent protection: In the event of short circuit in the rectifier, inverter or load side of the frequency converter, if the current flowing through the rectifier and inverter switching devices reaches an abnormal value (exceeding the permissible value), the instantaneous overcurrent protection will be operated to stop the frequency converter operation.

Overload protection: When the output current of the inverter exceeds the set value and the current duration reaches above the set time limit value, in order to prevent the inverter switching device from being damaged, the overload protection will act to stop the inverter operation.

The overload protection has the characteristic of inverse time limit and is usually realized by using thermal relay or electronic thermal protection.

Ground overcurrent protection: When the load of the frequency control system is grounded, the ground overcurrent protection is set to protect the inverter. However, in order to ensure personal safety, it is also necessary to install leakage circuit breakers.

Overload protection: By setting the upper limit of load current, when the load is too heavy, the frequency converter will carry out alarm or shutdown protection to prevent the motor from being damaged due to overload.

Missing phase protection: The frequency converter monitors the current and voltage in the input power supply and automatically cuts off the power supply when some phases of the power supply are found to be missing, avoiding the danger of equipment destruction and personnel electric shock.

Stall protection: For synchronous motor, the stall protection is generally directly for the stall state. For asynchronous motor, the stall in the acceleration process may be manifested as overcurrent, and the frequency converter realizes the protection function through overcurrent and overload protection.

Stall in the deceleration process can be avoided by setting safe deceleration time in the commissioning process.

Over-frequency protection: frequency converter has frequency limitation function, so that the output frequency can only be within the specified range, thus realizing the over-frequency protection function.

Short-circuit protection: by monitoring the current and voltage in the circuit, the frequency converter will cut off the power supply immediately once short-circuit fault is found, so as to protect the safety of equipment and personnel.

Grounding protection: the frequency converter is equipped with a special grounding protection circuit, when one or two phases are grounded, the frequency converter will alarm and may protect the motor by stopping the machine.