A–7

L100 Inverter

Single-phase power

An AC power source consisting of Hot and Neutral wires. An Earth

 

Ground connection usually accompanies them. In theory, the

 

voltage potential on Neutral stays at or near Earth Ground, while

 

Hot varies sinusoidally above and below Neutral. This power source

 

is named Single Phase to differentiate it from three-phase power

 

sources. Some Hitachi inverters can accept single phase input

 

power, but they all output three-phase power to the motor. See also

 

Three-phase.

Slip

The difference between the theoretical speed of a motor at no load

 

(determined by its inverter output waveforms) and the actual speed.

 

Some slip is essential in order to develop torque to the load, but too

 

much will cause excessive heat in the motor windings and/or cause

 

the motor to stall.

Squirrel Cage

A “nick-name” for the appearance of the rotor frame assembly for

 

an AC induction motor.

Stator

The windings in a motor that are stationary and coupled to the

 

power input of the motor. See also Rotor.

Tachometer

1. A signal generator usually attached to the motor shaft for the

 

purpose of providing feedback to the speed controlling device of the

 

motor. 2. A speed-monitoring test meter that may optically sense

 

shaft rotation speed and display it on a readout.

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

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.

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.

A Appendix