Baldor 15H manual System Grounding Ungrounded Distribution System, Input Power Conditioning

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

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.

SIf 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.

SIf 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.

Line Impedance	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	A, B, C, D, E	B2, C2, D2, F, G, G2, G+, H
	Line Impedance Required	3%	1%

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 +	(VoltsNo Load Speed	* VoltsFull Load Speed)	100
		(VoltsNo Load Speed)
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 +	(VL*L		0.03)
		(I ￿	3	377)
Where: L	Minimum inductance in Henries.
VL-L	Input volts measured line to line.

0.03Desired percentage of input impedance.

IInput current rating of control.

377 Constant used with 60Hz power. Use 314 if input power is 50Hz.

Load Reactors	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.

MN715 Receiving & Installation 3-5