A variety of definitions of terms that are used in the motor industry are given below.
Copyright © 2007 Francis J. Martino

Star-Delta Motor Starters are for reduced voltage starting. Star-Delta is also known as Wye-Delta.

There are two types available:

Open Transition operation.
The wye contactor is opened, the motor is disconnected from the power so that the motor loses speed, the delta
contactor is closed, the motor draws an inrush current as it returns to full speed. The advantage of open
transition is lower cost of the starter.

Closed Transition operation.
The contactors change from wye to delta and momentarily maintain power to the motor through a resistor bank. The motor
does not lose speed and no inrush current will flow during the transition. The advantage is less mechanical stress
on the motor, pump and pump systems.

Enclosure types that are available:
NEMA 1 and UL Type 1 are for use in a clean environment.
NEMA 12 and UL Type 12 have a gasket for protection against severe dust and oil.
NEMA 3R and UL Type 3R are for use in the rain.
NEMA 4 and UL Type 4 will protect against pressurized water from any direction.
NEMA 4X and UL Type 4X will protect against pressurized water from any direction and are corrosion resistant.

Chassis is intended for mounting in a customer supplied enclosure. With smaller controls, a NEMA 1
enclosure may often be supplied and the customer must then remove the cover to use the control for panel mounting.

Programming of Variable Frequency Drives:

PID Control will cause the controller output speed to follow an input signal at an inversely proportional
manner. Thus, a 0 to 10 VDC signal will cause the motor speed to increase from minimum to maximum as the voltage
signal changes from 10 to 0. A 4 to 20 mA signal will cause the motor speed to increase from minimum to maximum
as the current signal changes from 20 to 4 mA.

The "P" allows the proportional gain to be programmed. The change in output speed will be proportional to the
magnitude of the input signal.

"I" allows the value of integral gain to be programmed. The change in output speed will be proportional to the
integral of the magnitude of the input signal. The integral is therefore an average value over a period of time.

"D" allows a differential gain to be programmed. The change in output speed will be proportional to the
rate of change of the magnitude of the input signal.

Due to the difficulty of programming the differential in many applications and due to the limited advantage
of having a differential gain, many manufacturers are manufacturing their drives with PI control
and not PID.

V/Hz is the ratio of Volts to Hertz that is generated by the variable frequency drive. The standard configuration
is to have a constant V/Hz ratio as the output frequency increases from 0 to the base frequency of either
50 or 60 Hz. When operating above the base frequency of 50 or 60 Hz, the output will normally have a varying
V/Hz ratio, with the volts remaining constant as the frequency increases. The torque capability of the motor
will then drop off at a rate inversely proportional to the square of the frequency. In the range above base
frequency the motor will then exhibit a constant horsepower capability rather than a constant torque.

The base frequency is normally the frequency at which the motor is rated, thus, a two-pole motor is rated at
3600 RPM at 60 Hz, or 3000 RPM at 50 Hz.


Vector, Flux Vector or Field Orientated describes a drive that will operate similarly to the V/Hz control except
that the V/Hz ratio output of the drive will be determined by the position of the motor shaft as calculated by the drive.
Thus, the V/Hz ratio will not be constant and will be altered as the drive attempts to maintain the desired motor
speed when the motor experiences an increasing or decreasing speed that is due to load changes. A vector drive
will allow better control at low speed and higher efficiency at all speeds.

Variable Torque Load: fan, blower, centrifugal pump. The torque requirement diminishes with the cube of the speed.

Constant Torque Load: positive displacement pump (a pump that uses pistons) and most other machinery. The torque
requirement remains constant as speed varies.

Constant Horsepower or Constant kW load: a drill press. The torque requirement increases with the square of the
reduction in speed.

Amperage Interrupting Capacity (AIC) in RMS symmetrical amperes: The amperage which the device will safely pass
and/or interrupt under a fault or short-circuit condition. If the interrupting capacity is exceeded, the device
will burn or fragment.