Xylem IM244R04 SPD Plus Variable Speed Pump Control - Manual (Page 14)

14
WARNING
Hazardous
voltage
WARNING
Hazardous
voltage
SECTION 6: POWER SUPPLY AND WIRING
(CONTINUED)
INPUT POWER AND LINE TRANSFORMER
REQUIREMENTS
NOTE
Installation and maintenance MUST be performed
by properly trained and qualified personnel.
Always follow the National Electrical Code (NEC) or
Canadian Electric Code (CEC), as well as all state,
local and provincial codes when wiring the system.
The type of transformer and the connection
configuration feeding a drive plays an important
role in its performance and safety. The following is
a brief description of some of the more common
configurations and a discussion of their virtues and
shortcomings. Always ask what type of power system
the site has before sizing the drive.
DELTA/WYE WITH GROUNDED WYE NEUTRAL:
This configuration is one of if not the most common.
It provides rebalancing of unbalanced voltage with
a 30 degree phase shift. Depending on the output
connections from the drive to motor, the grounded
neutral may be a path for common mode current
caused by the drive output.
DELTA/DELTA WITH GROUNDED LEG
Another common configuration providing voltage
rebalancing with no phase shift between input and
output. Again, depending on the output connections
from the drive to motor, the grounded neutral may be
a path for common mode current caused by the drive
output.
WARNING
If the secondary of the transformer is
a delta with a grounded leg (corner
grounded delta) or floating network,
the line to ground EMC filter components and line
to ground MOV protection must be disconnected or
damage to the controller can result. Remove screws
EM1 and EM3 for frame sizes R4/N4 or F1 and F2
for frame sizes R5/N5 and R6/N6 to disable line to
ground EMC filter and MOV protection. Refer to
Figures 1, 2 and 3 for screw locations.
UNGROUNDED SECONDARY
Grounding of the transformer secondary is essential
to the safety of personnel as well as the safe operation
of the drive. Leaving the secondary floating can
permit dangerously high voltages between the
chassis of the drive and the internal power structure
components. In many cases this voltage could exceed
the rating of the input MOV protection devices of
the drive causing a catastrophic failure. In all cases,
the input power to the drive should be referenced to
ground. If the transformer can not be grounded, then
an isolation transformer must be installed with the
secondary of the transformer grounded.
WARNING
If the secondary of the transformer is
a delta with a grounded leg (corner
grounded delta) or floating network,
the line to ground EMC filter components and line
to ground MOV protection must be disconnected or
damage to the controller can result. Remove screws
EM1 and EM3 for frame sizes R4/N4 or F1 and F2
for frame sizes R5/N5 and R6/N6 to disable line to
ground EMC filter and MOV protection. Refer to
Figures 1, 2 and 3 for screw locations.
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.