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System Grounding
Continued
Line Impedance
Line Reactors
Load Reactors
MN723
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
Baldor controls are 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 control 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 control.
S
If the feeder or branch circuit that provides power to the control has power
factor correction capacitors that are switched on line and off line, the capacitors
must not be switched while the control is connected to the AC power line. If the
capacitors are switched on line while the control 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 control.
The Baldor control requires a minimum line impedance. If the impedance of the incoming
power does not meet the requirement for the control, 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.
Control Size
Line Impedance Required
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 +
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.
(V
L +
(I
Where:
L
Minimum inductance in Henries.
V
Input volts measured line to line.
L-L
0.03
Desired percentage of input impedance.
I
Input current rating of control.
377
Constant used with 60Hz power.
Use 314 if input power is 50Hz.
Line reactors may be used at the control output to the motor. When used this way, they
are called Load Reactors. Load reactors serve several functions that include:
S
Protect the control from a short circuit at the motor.
S
Limit the rate of rise of motor surge currents.
S
Slowing the rate of change of power the control delivers to the motor.
Load reactors should be installed as close to the control as possible. Selection should be
based on the motor nameplate FLA value.
A, B, C, D, E
3%
* Volts
(Volts
No Load Speed
(Volts
No Load Speed
0.03)
L*L
3
377)
B2, C2, D2, F, G
1%
)
Full Load Speed
100
)
Receiving & Installation 3-5
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Table of Contents
Troubleshooting
