48
Fig. 3-36 Installation requirement for relay, contactor and electromagnetic braking unit
3.3.5 Leakage current and countermeasures
The leakage current will pass the line capacitor and motor capacitor at the input and output ends of the drive.
Its magnitude depends on the distribution capacitor and carrier frequency. The leakage current includes the
ground leakage current and line-to-line leakage current.
Fig. 3-37 Leakage current path
Grounding leakage current
The leakage current will not only pass the drive system, but also pass other equipment through the
grounding wire, causing the mis-operation of the leakage circuit breaker, relay or other equipment. The higher
the drive carrier frequency, or the longer the motor cable is, the larger the leakage current will be.
Suppression measures:
·Reduce the carrier frequency, but the motor noise will increase.
·Shorten the motor cable.
·Adopt the leakage circuit breaker designed for the leakage current of higher harmonics/ surge in the drive
system and other system.
Line-to-line leakage current
The higher harmonics of the leakage current that passes the distribution capacitors between the output cables
of the drive may cause the mis-operation of the external thermal relay. Especially the drives with small
Drive
Motor
R
S
T
QF
RC-filter
Diode
24VDC
220V
AC
Varisto
Drive
220V
AC
Power
supply
Distributed capacitor
between lines
Distributed capacitor
between cable and earth
Distributed
capacitor
between
motor and earth
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