A-18
Figure C.2 Measured Example of Wiring Length and Peak Value of Motor Terminal Voltage
C.2 Effect of surge voltages
The surge voltages originating in LC resonance of wiring may be applied to the motor input 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.
C.3 Countermeasures against surge voltages
The following methods are countermeasures against damage to the motor insulation by the surge
voltages and using a motor driven with a 400 V class inverter.
[ 1 ] Using a surge suppressor unit, SSU (Patent pending)
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
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