Technical specifications
12.2 General specifications
Inverter chassis units
Operating Instructions, 07/2016, A5E00331449A
559
Using an isolating transformer to reduce transient overvoltages according to IEC 61800-5-1
This drops overvoltage category III to overvoltage category II, thereby reducing the
requirements for insulation capacity of the air. Additional voltage derating (reduction of the
input voltage) is not required if the following framework conditions are observed:
● The isolating transformer must be fed from a low-voltage or medium-voltage network and
must not be power directly from a high-voltage supply system.
● The isolating transformer may be connected to one or more converter units.
● The cables between the isolating transformer and the converter unit(s) must be routed in
such a manner as to rule out direct lightening strike, i.e. overland lines must not be used.
● The following types of system are permissible:
– TN systems with grounded star point (no grounded outer conductor).
– IT systems (operation with a ground fault must be restricted to the shorted possible
time).
Current derating as a function of the pulse frequency
When the pulse frequency is increased, the derating factor of the output current must be
taken into account. This derating factor must be applied to the currents specified in the
technical data.
Table 12- 4 Derating factor of the output current as a function of the pulse frequency for devices with a rated pulse fre-
quency of 2 kHz
Derating factor at the pulse frequency
Supply voltage 3-phase 380 VAC ... 480 VAC
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