Terminology Pertaining To Electric Machinery

Index of Protection Code: A European definition describing motor enclosures. Common ones are IP55 - totally enclosed fan cooled, and IP23 - weather protected I. See charge in enclosure for the complete listing.

Inductance: The characteristic of coil or wire to cause the current to lag the voltage in time phase. The current reaches its peak after the voltage does.

Induction Motor: An alternating current motor in which the primary winding on one member (usually the stator) is connected to the power source. A secondary winding on the other member (usually the rotor) carries the induced current. There is no physical electrical connection to the secondary winding; its current is induced.

Inertia: A measure of a body’s resistance to changes in velocity, whether the body is at rest or moving at a constant speed. The velocity can be either lineal or rotational. The moment of inertia (WK²) is the product of the weight (W) of an object and the square of the radius of gyration (K²). The radius of gyration is a measure of how the mass of the object is distributed about the axis of rotation. WK² is usually expressed in units of lb. ft.².

Inertial Load: A load (flywheel, fan, etc.) which tends to cause the motor shaft to continue to rotate after the power has been removed (stored kinetic energy). If this continued rotation cannot be tolerated, some mechanical or electrical braking means must normally be applied.

Inline Thrust Motor: A specialized vertical solid shaft motor which can handle thrust values up to 2000 pounds (depending on the horsepower and speed) and the thrust can be either up or down thrust.

Instability: The state or property of a system where there is an output but no corresponding input.

Insulator: A material which tends to resist the flow of electric current (paper, glass, etc.).

Integral Horsepower Motor: In terms of HP, a motor built in a frame having a continuous rating of one horsepower or more. An integral horsepower motor is in the 1 to 500 horsepower range.

Interconnection Diagram: An interconnection diagram is a diagram which shows only the external connections between controllers and associated machinery and equipment.

Intermittent Duty: A motor that never reaches equilibrium temperature, but is permitted to cool down between operations. For example, a crane, hoist, or machine tool bar is often rated for 15 or 30 duty.

Interrupting Capacity: The interrupting capacity is the maximum value of current that a contact assembly is required to successfully interrupt at a specified voltage for a limited number of operations under specified conditions.

Inverter: A term commonly used for an AC adjustable frequency drive. An inverter is also a term used to describe a particular section of an AC drive. This section uses the DC voltage from a previous circuit stage (intermediate DC circuit) to produce an AC current or voltage having the desired frequency.

IR Compensation: A way to compensate for the voltage drop across resistance of the AC or DC motor circuit and the resultant reduction in speed. This compensation also provides a way to improve the speed regulation characteristics of the motor, especially at low speeds. Drives that use a tachometer generator for speed feedback do not require an IR compensation circuit because the tachometer will inherently compensate for the loss in speed.

Isolation Transformer: A transformer that electrically separates the drive from the AC power line. An isolation transformer provides the following functions:

In DC motor applications, it guards against inadvertent grounding of power plant lines through grounds in the DC motor armature circuit.
Enhances protection of semiconductors from line voltage transients.
Reduces disturbances from other solid state control equipment such as drives without isolation transformers, time clock systems and electronic counters.

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