Standard_Drives_Guide

Industry White Papers Glossary– Drives Terminology

Regeneration : The characteristic of a motor to act as a generator when the rotor synchronous frequency is greater than the applied frequency. Regenerative Braking: The technique of slowing or stopping a drive by regeneration. Regenerative Control: A regenerative drive contains the inherent capability and/or power semiconductors to control the flow of power to and from the motor. Regulation: The ability of a control system to hold a 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: A. Load regulation (speed regulation) is the percentage of speed change with a defined change in load. Assuming all other parameters to be constant. B. Line regulation is the percentage of speed change with a given line voltage change, assuming all other parameters to be constant. Resolution: The smallest distinguishable increment into which a quantity can be divided (ex. position or shaft speed). It is also the degree to which nearly equal values of a quantity can be discrim- inated. For encoders, it is the number of unique electrically identified positions occurring in 360 degrees of input shaft rotation. SCR (Silicon Control Rectifier): A solid-state device that has an anode, a cathode, and gate which controls when it allows conduction. Service Factor: When used on a motor nameplate, a number that indicates how much above the nameplate rating a motor can be loaded without causing serious degradation (ex. A motor with 1.15 S.F. can produce 15% greater torque than one with 1.0 S.F.). When used in applying motors or gearmotors, it is a figure of merit which is used to adjust measured loads in an attempt to compensate for conditions which are difficult to measure or define. Set Speed: The desired operating speed. Shock Load: The load seen by a clutch, brake, or motor in a system which transmits high peak loads. This type of load is present in crushers, separators, grinders, conveyors, winches, and cranes. Slewing: An incremental motion of the motor shaft or machine table from one position to another at maximum speed without losing position control. Slip: The difference between rotating magnetic field speed (syn- chronous speed) and rotor speed of ac induction motors. Usually expressed as a percentage of synchronous speed. Speed Range: The speed minimum and maximum at which a motor must operate under constant or variable torque load con- ditions. A 10:1 speed range for a motor with top speed of 1800 rpm means the motor must operate as low as 180 rpm and still remain within regulation specifications. Controllers are capable of wider controllable speed ranges than motors because there is no thermal limitation, only electrical. Controllable speed range of a motor is limited by the ability to deliver 100% torque below base speed without additional cooling.

PLC (Programmable Logic Controller): Solid-state control logic for machines and processes where a sequence of operations can be changed easily with programming (software). Plugging: A type of motor braking provided by reversing either line voltage polarity or phase sequence so that the motor devel- ops a counter torque which exerts a retarding force to brake the motor. Position Transducer: An electronic device (ex. encoder or resolver) that measures actual position and converts this meas- urement into a feedback signal convenient for transmission. This signal may then be used as an input to a programmable con- troller which controls the parameters of the positioning system. Positive Feedback: A condition where the feedback is additive to the input signal. This generally results in an unstable system. Power: Work done per unit of time. Measured in horsepower or watts: 1 hp = 33,000 ft/lbs = 746 watts. Power Factor: A measurement of the time phase difference between the voltage and current in an ac circuit. It is represented by the cosine of the angle of this phase difference. Power factor is the ratio of real power (kW) to total kVA, or the ratio of actual power (W) to apparent power (VA). Displacement Power Factor - The displacement component of power factor. The ratio of the active power of the funda- mental wave, in watts, to the apparent power of the fundamental wave, in volt-amperes. Total Power Factor - The ratio of the total power input, in watts, to the total volt-ampere input to the converter. The power factor is determined at the ac line terminals of the converter. Distortion Factor - The ratio of the root-mean square of the harmonic content to the root-mean-square value of the fundamental quantity, expressed as a percent of the fundamental. Preset Speed: One or more fixed speeds at which the drive will operate. Pull-Up Torque: The torque required to accelerate the load from standstill to full speed (where breakdown torque occurs), expressed in percent of running torque. It is the torque required not only to overcome friction, windage, and product loading, but also to overcome the inertia of the machine. The torque required by a machine may not be constant after the machine has started to turn. This load type is characteristic of fans, centrifugal pumps, and certain machine tools. PWM (Pulse Width Modulated): A type of ac adjustable frequen- cy drive that accomplishes frequency and voltage control at the output section (inverter) of the drive. The drive’s output voltage is always a constant amplitude and by “chopping” (pulse width modulating) the average, voltage is controlled. Reactance: Any force that opposes changes in current or voltage. The inertia of electrons causes them to oppose sudden changes in current flow or voltage. Rectifier: A device that transforms alternating current to direct current.

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