A–8

Bibliography

Appendix A

Three-phase power

An AC power source with three Hot connections that have phase

 

offsets of 120 degrees is a 3-phase power source. Usually, Neutral

 

and Earth Ground wires accompany the three Hot connections.

 

Loads may be configured in a delta or Y configuration. A Y-

 

connected load such as an AC induction motor will be a balanced

 

load; the currents in all the Hot connections are the same. There-

 

fore, the Neutral connection is theoretically zero. This is why

 

inverters that generate 3-phase power for motors do not generally

 

have a Neutral connection to the motor. However, the Earth Ground

 

connection is important for safety reasons, and is provided.

Torque

The rotational force exerted by a motor shaft. The units of measure-

 

ment consist of the distance (radius from shaft center axis) and

 

force (weight) applied at that distance. Units are usually given as

 

pound-feet, ounce-inches, or Newton-meters.

Transistor

A solid state, three-terminal device that provides amplification of

 

signals and can be used for switching and control. While transistors

 

have a linear operating range, inverters use them as high-powered

 

switches. Recent developments in power semiconductors have

 

produced transistors capable of handling high voltages and currents,

 

all with high reliability. The saturation voltage has been decreasing,

 

resulting in less heat dissipation. Hitachi inverters use state-of-the-

 

art semiconductors to provide high performance and reliability in a

 

compact package. See also IGBT and Saturation Voltage.

Trip Event

An event that causes the inverter to stop operation is called a “trip”

 

event (as in tripping a circuit breaker). The inverter keeps a history

 

log of trip events. They also require an action to clear.

Watt Loss

A measure of the internal power loss of a component, the difference

 

between the power it consumes and what its output delivers. An

 

inverter’s watt loss is the input power minus the power delivered to

 

the motor. The watt loss is typically highest when an inverter is

 

delivering its maximum output. Therefore, watt loss is usually

 

specified for a particular output level. Inverter watt loss specifica-

 

tions are important when designing enclosures.

Bibliography

 

 

 

 

 

Title

 

Author and Publisher

 

 

 

 

Variable Speed Drive Fundamentals, 2nd Ed.

Phipps, Clarence A.

 

 

The Fairmont Press, Inc. / Prentice-Hall, Inc. 1997

 

 

ISBN 0-13-636390-3

 

 

Electronic Variable Speed Drives

Brumbach, Michael E.

 

 

Delmar Publishers 1997

 

 

ISBN 0-8273-6937-9

 

 

Hitachi Inverter Technical Guide Book

Published by Hitachi, Ltd. Japan 1995

 

 

Publication SIG-E002