telephone influence factor
(TIF) A measure of the tendency of distortion on an AC power circuit to interfere with telephone systems and similar communications equipment. As the harmonic distortion on the line increases, this factor also increases.

three contactor bypass
A drive bypass that uses three contactors. One connects the output of the drive to the motor. A second connects the power line to the motor. This is used in conjunction with the motor overload to form the bypass motor starter. These two contactors are interlocked to ensure that the motor canít be connected to the driveís output and the power line at the same time. A third contactor connects the driveís input to the power line. This allows the drive to be disconnected from the power line for service. A four-position "Drive-Off-Bypass-Test" switch controls the operation of the contactors. This can be used with automatic or manual bypass.

thyristor
see SCR

torque
A turning force applied to a shaft that tends to cause rotation. It is normally measured in pound feet and is equal to the force applied times the effective radius through which it acts.

total harmonic distortion
A measure of the amount of distortion of a non-sinusoidal wave. It is calculated by adding the squares of the amplitudes of all of the harmonics above the fundamental frequency, dividing by the square of the amplitude of the fundamental frequency, and taking the square root. It is expressed as a percent. An undistorted wave would have a total harmonic distortion of 0%. Total harmonic distortion values greater than 100% are possible. Voltage and current total harmonic distortion values at any point in a circuit can be greatly different, so it is important to know whether voltage or current distortion is being considered.

transducer
A device that converts one energy form to another. Also a device that, when actuated by signals from a source, can supply signals to other systems.

transfer switch bypass

A simple drive bypass scheme using a three position manual switch. The switch either connects the drive to the motor (drive position), the line to the motor (bypass position) or disconnects both the drive and the line from the motor (off position). A motor starter must be supplied in the input line supplying the line terminals of the transfer switch.

transfer switch motor selection
This manual switch transfers the drive from one motor to another. This allows the drive to operate either one motor or the other at adjustable speed.

transformer
Electrical device designed to change the voltage in an alternating current circuit. A step-up transformer increases the voltage, a step-down transformer decreases the voltage. Because electromagnetic induction is used to transmit the energy from the input (primary) side of the transformer to the output (secondary) side of the transformer, the transformer can also provide a degree of isolation, protecting the load from noise on the line and protecting the line from noise produced by the load. An isolation transformer may have the same input and output voltage.

transient
see surge A momentary deviation in an electrical system.

transistor
A solid-state electronic component that can be used to control the flow of electric current. Transistors can be used in a variety of places in the power and control circuitry of adjustable frequency drives.

triplen harmonics
Multiples of the 3rd harmonic (3rd, 6th, 9th, 12th, etc.) that cancel out to zero in a balanced three phase system.