Use of Frequency Converters
Used together with the frequency converter are:
- output chokes, also known as motor chokes;
- input (or network) chokes.
Motor Chokes
Motor chokes play an important role in frequency conversion systems. They are used at the output of the frequency converter to perform several important functions:
- Effective suppression of high-frequency harmonics. High-frequency harmonics can cause active heating of the electric motor, which can reach 6-10% at low pulse width modulation (PWM) frequencies.
- Limiting the short-circuit current amplitude. Motor chokes reduce the short-circuit current strength, providing significant protection for the electric motor.
- Reduction of electrical voltages. This prevents insulation breakdown on wires, which can occur due to wear of insulating properties during operation.
- Protection against overcurrents. Motor chokes compensate for capacitive currents in long motor cables, helping to avoid tripping of overcurrent protection.
- Delay in the operation of electronic protection circuits. This allows the emergency short-circuit currents to rise more slowly, reducing heat generation from the active converter.
- Protection of the input circuit of the frequency converter. Motor chokes help to reduce the negative impact caused by voltage spikes from powerful electrical appliances.
- Barrier to voltage surges in the electrical network. In case of converter failure, the damage will be minimal thanks to the motor choke, as the input circuit breaker will have enough time to disconnect the power supply.