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Goals and Symptoms
will it be possible to use ATV68 at 500V AC for the network with isolated neutral (75 and 90kW)?
Facts and Changes
usage of ATV68 with isolated neutral
Causes and Fixes
When the power supply is an IT one, for the protection against the indirect contact, it's the magnetic protection of the circuit-breaker which operate.
Regarding the ATV58 connected to an IT power supply, the included filters can operate till a 480V+/-10% power supply for the 380V/500V PRODUCTS and till 240V+/-10% for the 3 phases 200V/240V PRODUCTS.
1) IT supply and insulation fault (first fault) on the network upstream of the drive.
There isn't any risk for the drive if the fault doesn't cause any imbalance between phases.
In loading if the absorbed line currents imbalance is high (>30%):
- The fuses of strong phases can see a permanent current superior to the nominal one and end by melting.
- The too strong undulation of the rectified voltage can make the DC bus capacitors aging prematurely and overload the rectifier bridge.
2) IT supply and insulation fault (first fault) downstream of the drive (cable or motor).
In case of insulation to the earth fault, the static capacities of the network will see the dv/dt which are due to the switching of the motor voltage.
The resultant leakage current can considerably overload the capacitors, the diodes, the IGBT, the inductances, the motor filters, and other systems supplied by the same network and can cause their premature aging or their damage.
That's why it is essential to use the VW3A68190 earth fault kit in IT supply.
Tripping time of this protection are recommended according to the network type in order to avoid the premature aging of the drive elements:
weak static capacity : 10mn
strong static capacity : 2mn
drive supplied by individual transformer : 60mn
What influence on the rectifier bridge, the DC bus, and on the
uninterrupted power supply ?
Overheat and probably thermal tripping of the drive.
3) IT supply and insulation fault (first fault) downstream of the drive then apparition of an insulation fault (second fault) upstream of the drive.
In case of a double fault in an installation a strong short-circuit current takes place.
The ATV68 is equipped with a current sensor on each motor phase, what allows to trip in insulation fault in case of very high leakage voltage before there would be damages.