Section 2: Installation of the frequency converter
2. Installation of the frequency converter
2.1. Safety rules
Protective earthing
connections
The protection against indirect contact consists in the automatic shutdown of
the power supply voltage by special short-circuit (or differential-current) pro-
tection or voltage limitation to a level not exceeding the permissible values in
case of an insulation failure.
Due to the operation of the intermediate circuit, a ground fault at the fre-
quency converter output cannot be detected by short-circuit protection. Al-
though the protection against interpolar and ground faults at the frequency
converter output is provided, it is based on IGBT transistors blocking which
does not meet the requirements of electric shock protection. For these reas-
ons, to ensure the safety of personnel, local protective connections must be
made accordingly.
The frequency converter provides terminals, appropriately marked and protec-
ted against corrosion, for connecting protective conductors.
Protections
The frequency converter is equipped with protections: against electrical motor
overload, thermal motor (I
2
t limit), under- or over voltage in the converter inter-
mediate circuit, short-circuit at the converter output (it only protects the con-
verter!).
The usage of differential-current protection to prevent electric shock can ap-
pear unfavourable since it can trigger due to temporary or constant leakage
current of the power drive system, operating under normal conditions. If a dif-
ferential-current device is used, due to the different nature of the differential
current, only circuit breakers of a B type are permitted.
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TWERD Power Electronics