Xylem IM167 R8 Aquavar CPC (Centrifugal Pump Control) - Manual (Page 11)

11
INTRODUCTION
Input Power and Line Transformer Requirements
The Aquavar CPC™ requires that the input line voltage and transformer power that meet
certain phase and balance requirements. If you or your installing electrical contractor is in
doubt of the requirements, the following provide guidelines for the Aquavar CPC. When
in doubt contact the local power utility or the factory.
Drive input isolation transformers are not generally required for the Aquavar CPC. The
Aquavar CPC utilizes as standard 3% line impedance, therefore unless additional filtering is
needed, an input line reactor is not required.
NOTE: 60 THROUGH 550 HP UNITS PROVIDE AN ACTUAL 3% IMPEDANCE LINE REACTOR
BUILT INTO THE DRIVE CABINET.
The internal power circuit of the drive is floating with respect to earth ground except for
transient protection (MOV’s and EMI capacitors) therefore earth ground potential reference is
established only by the user’s power line grounding configuration. The drive can operate with
many different power grounding schemes. The drive requires only that the steady state RMS
voltage from any input line to ground be always less than 110% of the nominal power line to
line voltage. The use of optional RFI/EMC filters may require that the voltage from any input
line to ground be less than 110% of the nominal power line to neutral voltage.
Drive input isolation or dry type transformers may be required for the following:
1. Step up or down: An input transformer may be required to step the local input power
line voltage up or down to the level of the drive input rating.
2. Ground Isolation: An input isolation transformer with a direct or a high impedance wye
neutral secondary ground connection may be required to establish a local power source
with a ground relationship different from the utility power source.
A. If ground isolation is required to prevent a ground fault in one section from shutting
down equipment in another section.
B. To bring local line voltages within the line to ground limits (110% balance) stated in
the opening paragraph.
C. Some ground fault protection schemes and peripheral components require a
grounded neutral power source.
D. A symmetrical wye neutral grounded power source along with proper ground wiring
techniques according to NEC (good ac grounding from motor to drive and from
drive to earth ground) provides the best means to control the ground currents that
the drive switching frequency and dv/dt rate insert into the motor frame and shaft.
3. Phase shifting delta-wye or “zig-zag” isolation transformers are used to feed 12 or 18
pulse drive inputs to provide harmonic mitigation.
If an isolation transformer is used for 6 pulse input, the best choice is ONE three phase,
six winding transformer. A delta primary is best for third harmonic cancellation. A
wye secondary avoids circulating current problems and provides the very desirable option
of grounding the secondary neutral for minimum voltage stress and ripple to ground. The
transformer should have a KVA rating at least 1.1 times the maximum connected HP. A K
Factor of 6 is sufficient if transformer impedance is greater than 2%. A K Factor of 5 is sufficient