Installation 2-3
MN1221
System Grounding Continued
Ungrounded Distribution System
With an ungrounded power distribution system it is possible to have a continuous current
path to ground through the MOV devices. To avoid equipment damage, an Isolation
transformer with a grounded secondary is recommended. This provides three phase AC
power that is symmetrical with respect to ground.
Input Power Conditioning
The BPS is designed for direct connection to standard three phase lines that are
electrically symmetrical with respect to ground. Certain power line conditions must be
avoided. An AC line reactor or an isolation transformer may be required for some power
conditions.
S
If the feeder or branch circuit that provides power to the BPS has permanently
connected power factor correction capacitors, an input AC line reactor or an
isolation transformer must be connected between the power factor correction
capacitors and the BPS.
S
If the feeder or branch circuit that provides power to the BPS has power factor
correction capacitors that are switched on line and off line, the capacitors must
not be switched while the BPS is connected to the AC power line. If the
capacitors are switched on line while the BPS is still connected to the AC power
line, additional protection is required. TVSS (Transient Voltage Surge
Suppressor) of the proper rating must be installed between the AC line reactor
or an isolation transformer and the AC input to the BPS.
Line Impedance
The BPS requires a minimum 3% line impedance. If the impedance of the incoming
power does not meet the requirement for the BPS, a 3 phase line reactor can be used to
provide the needed impedance in most cases. Line reactors are optional and are
available from Baldor.
The input impedance of the power lines can be determined as follows:
Measure the line to line voltage at no load and at full rated load.
Use these measured values to calculate impedance as follows:
%Impedance
+
(Volts
No Load Speed
*
Volts
Full Load Speed
)
(Volts
No Load Speed
)
100
Line Reactors
Three phase line reactors are available from Baldor. The line reactor to order is based on
the full load current of the motor (FLA). If providing your own line reactor, use the
following formula to calculate the minimum inductance required.
L
+
(V
L
*
L
0.03)
(I
3
Ǹ
377)
Where:
L
Minimum inductance in Henries.
V
L-L
Input volts measured line to line.
0.03
Desired percentage of input impedance.
I
Input current rating of BPS.
377
Constant used with 60Hz power.
Use 314 if input power is 50Hz.
