A–6

Bibliography

Appendix A

Thermal Switch An electromechanical safety device that opens to stop current flow when the temperature at the device reaches a specific temperature threshold. Thermal switches are sometimes installed in the motor in order to protect the windings from heat damage. The inverter can use thermal switch signals to trip (shut down) if the motor overheats. See also trip.

Thermistor

Three-phase Power

A type of temperature sensor that changes its resistance according to its temperature. The sensing range of thermistors and their ruggedness make them ideal for motor overheating detection. Hitachi inverters have built-in thermistor input circuits, which can detect an overheated motor and shut OFF (trip) the inverter output.

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. Therefore, 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

A measure of rotational force. The units of measurement are the product 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 transis-

 

tors 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

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 specifications 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