Effect Of Surge Voltages; Countermeasures Against Surge Voltages - Fuji Electric FRENIC-HVAC User Manual

Figure B.2 Measured Example of Wiring Length and Peak Value of Motor Terminal Voltage
B.2

Effect of surge voltages

The surge voltages originating in LC resonance of wiring may be applied to the motor
terminals and depending on their magnitude sometimes cause damage to the motor
insulation.
When the motor is driven with a 200 V class inverter, the dielectric strength of the
insulation is no problem since the peak value at the motor terminal voltage increases
twice due to the surge voltages (the DC voltage is only about 300 V).
But in case of a 400 V class inverter, the DC voltage is approximately 600 V and
depending on the wiring length, the surge voltages may greatly increase and sometimes
result in damage to the insulation.
B.3

Countermeasures against surge voltages

When driving a motor with a 400 V class inverter, the following are countermeasures
against damage to the motor insulation by the surge voltages.
[ 1 ] Using a surge suppressor unit, SSU
The surge suppressor unit (SSU) is a newly structured unit using circuits based on the
impedance-matching theory of a transmission line. Just connecting the SSU to the
surge suppressor cable of the existing equipment can greatly reduce the surge voltage
that results in a motor dielectric breakdown.
For 50 m of wiring length: SSU 50TA-NS For 100 m of wiring length: SSU 100TA-NS
A-14