Terminology Pertaining To Electric Machinery

Radial Magnetic Pull: The magnetic force on the rotor resulting from its radial (air gap) displacement from magnetic center.

Random Wound Coils: Also called mush wound coils -- where the turns are wound without definite placement, or, at random.

Reactance: The opposition to the flow of current made by an induction coil or a capacitor.

Reactance (Inductive): The characteristic of a coil, when connected to alternating current, which causes the current to lag the voltage in time phase. The current wave reaches its peak later than the voltage wave reaches its peak.

Rectification: Designates the process by which electric energy is transferred from an alternating current (AC) to a direct current (DC) circuit.

Rectifier: An electronic circuit which converts alternating current into direct current.

Reed Critical Frequency: Rotational elements generate natural resonance frequencies which is a function of shaft stiffness, mounting, and environment conditions (i.e., vibration from equipment nearby). Vertical motors are affected more by this condition because of mounting at one end with the other end free to move. Under normal operating conditions with the motor operating at rated speed, the resonant frequencies is not a concern. However, inverter applications changes the base speed which affects the motor harmonics and will give an unstable resonance or vibration condition. To correct for potential operation in a critical speed zone, pump manufacturers can make their discharge heads either stiff or loose.

Regeneration: The characteristic of a motor to act as a generator when the CEMF is larger than the drive's applied voltage (DC drives) or when the rotor's synchronous frequency is greater than the applied frequency (AC drives).

Regeneration Braking: The technique of slowing or stopping a drive by regeneration.

Regeneration Control: A regeneration drive contains the inherent capability and/or power semi-conductors to control the flow of power to the motor and from the motor back to the power supply.

Regulation: The ability of a control system to hold speed once it has been set. Regulation is given in percentages of either base speed or set speed. Regulation is rated upon two separate sets of conditions:

Speed Regulation - is the percentage of speed change with a defined change in load, assuming all other parameters to be constant.

Line Regulation - is the percentage of speed change with a given line voltage change, assuming all other parameters to be constant.

Relay: An electrically controlled device that causes electrical contacts to change status. Open contacts will close and closed contacts will open when rated voltage is applied to the coil of the relay.

Reluctance: The characteristic of a magnetic material which resists the flow of magnetic lines of force through it.

Remote Control: Remote Control is a control function which provides for initiation or change of a control function from a remote point.

Reset: To reset is to restore a mechanism, storage or device to a prescribed state.

Resistance: The degree of obstacle presented by a material to the flow of electric current is known as resistance and is measured in ohms.

Resilient Mounting: A suspension system or cushioned mounting designed to reduce the transmission of normal motor noise and vibration to the mounting surface.

Resolution: The smallest distinguishable increment into which a quantity can be divided (e.g., position or shaft speed). It is also the degree to which nearly equal values of a quantity can be discriminated. For encoders, it is the number of unique electrically identified positions occurring in 360 degrees of input shaft rotation.

Response Time: The time required, following the initiation of a specified stimulus to a system, for an output going in the direction of necessary corrective action to first reach a specified value.

Reversing: Changing the direction of rotation of the motor armature or rotor. A DC motor is reversed by changing the polarity of the field or the armature, but not both. An AC motor is reversed by reversing the connections of one leg on the three phase power line or by reversing the leads on a single phase power line.

Reverse Torque: A torque created by harmonics in a three phase motor and often resulting in a motor running at a reduced speed. Normally the forces of the revolving field all rotate in the same direction but an improperly designed motor can cause counter rotating harmonic fields that exceed the strength of the forward field at some specific speed. This speed may be zero RPM or some speed below the rated value. This phenomenon is quite common in re-designs of motors to 10 poles or more.

Reversing: Changing the direction of rotation of the motor armature or rotor. A DC motor is reversed by changing the polarity of the field or the armature, but not both. An AC motor is reversed by reversing the connections of one leg on the three phase power line, or by reversing the leads on a single phase power line.

Rotor: The rotating member of an induction motor with a shaft. Current is normally induced in the rotor which reacts with the magnetic field produced by the stator to produce torque and rotation.

Running Torque: Also called stable torque, or equilibrium torque. A term loosely used meaning available torque at full (rated) speed, as opposed to starting torque.

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