Mitsubishi Electronics FR-F700 Why Can the Inverter Save Energy?, Damper control discharge side

Why Can the Inverter Save Energy?

The load torque of a motor-driven machine generally changes depending on speed. On the other hand, motor output is proportional to the product of load torque and speed as indicated in the following formula, and therefore, necessary motor output varies with speed.

Motor output P = T × N/(9550 × η) [kW]

T : Motor shaft-equivalent load torque [N·m]

N : Motor speed [r/min]

η: Machine efficiency

When this motor is operated by the inverter, the inverter output provides the frequency f appropriate to the motor speed, and the then output voltage V is determined by a "V/f = constant" pattern in the case of a constant-torque load.

For example, when the motor is operated at middle speed, f, i.e. output voltage V, decreases, and therefore, the inverter output power V × I reduces if the output current I is constant.

Proportionately, the inverter input current decreases and the power consumption reduces. Namely, when the motor output reduces, the input power of the inverter also decreases as a matter of course.

The fundamental principle of energy saving by the inverter is to eliminate wasted power consumption by minimizing loss caused by the other devices and minimizing the motor output as compared to the other system (for example, commercial power supply operation or secondary resistance control of wound-rotor motor). A maximum energy saving effect is produced on a fan, pump or like by the variable-torque load characteristic that reduces load torque as speed decreases.

Motor speed control enables substantial energy-saving operation as compared to commercial power supply operation.

		Features
Peripheral Devices		Why energy		savings?
	Standard		Specifications
Outline		Dimension		Drawings
Terminal Connection	Diagram		Terminal Specification		Explanation
	Operation		Panel

Damper control (discharge side)

	100
(%)	80
Consumption	60
		Amount of
		energy saved
	40
Power
				Inverter control
	20
	0	40	60	80	100

For example, when a 15kW motor is operated at 60% air volume and the power charge is 17 yen/kW·h, the power charge as much as below can be saved in a year.

(1)Damper control

15kW×0.9×17 yen×24h×365days 2.01 million yen (2)Inverter control

15kW×0.3×17 yen×24h×365days 0.67 million yen

(1)- (2) = energy-saving effect Approx. 1.34 million yen

Parameter		List
Explanations	of		Parameters
Protective		Functions
	Options

Air volume (%)

Damper control

15kW
2,010,000	15kW
	Save
	1,340,000
Inverter	a year
energy-saving
control
15kW
670,000

Warranty Compatibility Motor Instructions

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