Xylem IM167 R8 Aquavar CPC (Centrifugal Pump Control) - Manual (Page 10)

10
POWER DISTRIBUTION SYSTEMS
Resistance grounding and ground fault protection:
Connecting the Wye secondary neutral to ground through a resistor is an acceptable
method of grounding. Under a short circuit secondary condition, any of the output phases
to ground will not exceed the normal line to line voltage. This is within the rating of the MOV
input protection devices on the drive. The resistor is often used to detect ground current
by monitoring the associated voltage drop. Since high frequency ground current can flow
through this resistor, care should be taken to properly connect the drive motor leads using
the recommended cables and methods. In some cases, multiple drives on one transformer
can produce a cumulative ground current that can trigger the ground fault interrupt circuit.
Open Delta
(consult factory)
:
This type of configuration is common on 230 volt systems. From time to time it may be
encountered where only single phase power is available and three-phase power is required.
The technique uses two single phase transformers to derive a third phase. When used to
power a drive this configuration must be derated to about 70% of the single phase rating of
one transformer. This system provides poor regulation and it is possible that only the two line
connected phases will provide power. In this case the drive must be derated to 50% of its
rating. (Ex. A 20 HP 230 volt drive now becomes a 10 HP 230 volt drive.)
Single Phase Connection:
For small drive with a diode rectifier front end it is possible to run a three phase output with a
single phase input. Only part of the three phase input bridge is used. Ripple current becomes
120 Hz rather than 360. This places a greater demand on the DC filter components (capacitor
bank and DC choke). The result is that the drive must be derated to 50% current. Single phase
will not work with an SCR front end drive.