Hitachi SJ300 Series Switching, Commercial, Power Source

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SJ300 Inverter

CommercialPower SourceSwitching

The commercial power source switching function is useful in systems with excessive starting torque requirements. This feature permits the motor to be started “across the line,” sometimes called a bypass configuration. After the motor is running, the inverter takes over to control the speed. This feature can eliminate the need to oversize the inverter, reducing cost. However, additional hardware such as magnetic contactors will be required to realize this function. For example, a system may require 55KW to start, but only 15KW to run at constant speed. There- fore, a 15KW rated inverter would be sufficient when using the commercial power source switching.

The following block diagram shows an inverter system with bypass capability. When starting the motor directly across the line, relay contacts Mg2 are closed, and Mg1 and Mg3 are open. This is the bypass configuration, since the inverter is isolated from the power source and motor. Then Mg1 contacts close about 0.5 to 1 second after that, supplying power to the inverter.

			Mg2
Power source, 3-phase								Thermal
	MCCB	GFI
							Mg3	switch
			Mg1
L1				R	SJ300	U
L2				S		V			Motor
L3				T		W
				R0
				T0		AL1
				FW
				[RV]		AL0
				[CS]		AL2
				CM1
				H
				O
				L

Switching to inverter control occurs after the motor is running at full speed. First, Mg2 relay contacts open. Then about 0.5 to 1 seconds later, relay Mg3 contacts close, connecting the inverter to the motor. The following timing diagram shows the event sequence:

Mg1
	Mg2/Mg3 delay time 0.5 to 1 sec.
Mg2
Mg3

FW

Set to 0.5 to 1 sec. typical

Operations Monitoring and

[CS]

Inverter

B003 (Retry wait time

output

before motor restart)

Frequency matching

Normal operation