Frequency converters are widely used power control devices, and most people are familiar with them. However, various issues can arise in practical applications. One common problem is the frequency converter tripping as soon as it is powered on. What might be causing this? Oulu Electric’s technical specialists point out: It could be because you have installed a leakage protection device!

Whether in daily life or industrial production, leakage protection devices are commonly seen, and for good reason. They effectively protect against direct and indirect electric shock in low-voltage power systems and can also serve as phase-loss protection for three-phase motors.

It is a widely recognized principle in the industry that leakage protection devices should generally not be used in conjunction with frequency converters. However, some users still install leakage protection alongside frequency converters, resulting in immediate tripping upon startup and preventing the system from operating normally.

In many factories, leakage protection is often integrated into switches or even used as the main switch in workshop electrical installations. When frequency converters are employed in such setups, the leakage protection device tends to trip as soon as the converter is powered on, causing operational disruptions.

If a production facility uses frequency converters, it is advisable to either remove the leakage protection or replace it with a moulded case circuit breaker to avoid unnecessary tripping. Standard leakage protection devices with a sensitivity of 30 mA are not suitable for use with frequency converters, as the inherent leakage current of the converter can cause false tripping, rendering the device ineffective for personal safety protection.

If leakage protection must be installed due to specific requirements, it is essential to use a device with a leakage current rating of 100 mA or higher. This helps maintain insulation integrity in the circuit and prevents potential hazards such as electrical fires.

Oulu Electric independently develops and manufactures frequency converter products.

It is well known that the working principle of a leakage protector is based on zero-sequence current being zero. However, when a frequency converter is in operation, the zero-sequence current is not zero! The output side of the frequency converter generates a PWM wave, and the long motor cable exhibits capacitive coupling with the ground. This capacitive effect becomes more pronounced when shielded cables are used.

During frequency converter operation, the capacitance charges and discharges, causing current to flow to the ground and then back to the frequency converter through the grounding wire on the input side, forming a current loop. If a leakage protection device is installed, it will trip and interrupt system operation. Therefore, it is not advisable to use leakage protection in conjunction with frequency converters. To ensure safety, it is sufficient to properly ground the equipment.

After reading the above explanation, we believe you now understand why a frequency converter may trip immediately after power-on.

As a professional frequency converter manufacturer, Oulu Electric independently develops and produces a wide range of models. Feel free to contact us for consultation — our experts will provide you with professional product selection and support services.