Part Winding Starting: Originally and still defined by NEMA as a motor that has one half its windings energized first, then the other half is paralleled with the first half for full on. Now used as the name for tow thirds start and double delta starting.
Partial Motor: A motor sold with rotor and stator only -- NO end bells -- and no containing frame. Also called a "shell type" motor.
Permeability: Is the measurement of the ease with which a material can be magnetized and how much better than air it is as a path for magnetic fields (permeability of 1).
Phase: Phase is a term, which indicates the space relationships of windings, and changing values of the recurring cycles of A.C. voltages and currents. Due to the positioning (or the phase relationship) of the windings, the various voltages and currents will not be similar in all aspects at any given instant. Each winding will lead or lag another, in position. Each voltage will lead or lag another voltage, in time. Each current will lead or lag another current, in time.
Phase Control: The process of varying the point within the cycle at which forward conduction is permitted to begin.
Pickup Voltage or Current: The pickup voltage or current of a magnetically operated device is the voltage or current at which the device operates.
Piggyback Mounting: A mounting configuration where the motor is mounted to the top of the gearbox and then the motor shaft is connected to the gearbox input shaft by belts.
Plain Bearing: A term used for a non-ball or roller bearing, i.e., a sleeve bearing.
Plate Bearing: A specialized vertical motor bearing which has practically unlimited life factor if the thrust capacity is properly selected, lubricated, cooled and not overloaded. Vibration, cavitation and heat can severely affect the life of this type bearing. Construction of this bearing calls for a solid plate runner and segmental pivoted shoes with the runner riding on a film of oil between it and the bearing shoes. Operation at higher loads than designed for, or higher temperatures, may break down the film of oil and destroy the bearing.
Plugging: Plugging refers to a type of motor braking provided by reversing either voltage polarity or phase sequence so that the motor develops a counter-torque which exerts a retarding force to brake the motor.
Plug Reversal: Reconnecting a motor’s windings to reverse its direction of rotation while running. Although it is an effective dynamic braking means in many applications, plugging is more severe than other methods and should be used with caution.
Polarities: Terms, (Positive, Negative: North and South) which indicate the direction of current and flux flow in electrical and magnetic circuits at any given instant.
Polarization Index: A term used to indicate the insulation value to ground of a winding. Actually the index determines the moisture content of a winding.
Pole: A definite group of coils connected in series that will show a uniform polarity with DC current applied. This can also be only one coil. This also applies to AC current rotating equipment.
Position Transducer: An electronic device (e.g., encoder or resolver) that measures actual position and converts this measurement into a feedback signal convenient for transmission. This signal may then be used as an input to programmable controller which controls the parameters of the positioning system.
Positive Feedback: Positive Feedback is a condition where the feedback is additive to the input signal.
Potentiometer: A three terminal rheostat, or a resistor with one or more adjustable sliding contacts, that function as an adjustable voltage divider.
Power: Work done per unit of time. Measured in horsepower or watts (1 HP = 33,000 ft. lb./min. = 746 watts).
Power Factor: A measurement of the time phase difference between the voltage and current in an A.C. circuit. It is represented by the cosine of the angle of this phase difference. For an angle of 0 degrees, the power factor is 100% and the volt/amperes of the circuit are equal to the watts.
Power Factor Correction Capacitor: A device used to raise the power factor on motors to avoid penalties from utilities for low power factors. This is because induction electrical equipment takes more power from the electrical supply system than is necessary to produce the work required. A properly sized capacitor will offset most of the lagging current of a motor and raise its power factor to about 95%.
Preset Speed: Preset speed refers to one or more fixed speeds at which the drive will operate.
Printed Circuit Board: A board for mounting of separately manufactured components which has the connections made by printed circuitry.
Prony Brake: A simple mechanical device, normally a wooden piece with an adjustable leather strap used to test torque output. The prony brake-loads the motor and a spring scale attached to it gives a relatively accurate measurement of torque.
Pull-Out Torque: The pull-out torque of a synchronous motor is the maximum sustained torque which the motor will develop at synchronous speed with rated voltage applied at rated frequency and with normal excitation.
Pull Up Torque: The minimum torque developed during the period of acceleration from locked-rotor to the speed at which breakdown torque occurs. It is usually expressed as a percentage of full-load torque.
Pulse: A pulse is a signal of relatively short duration.
Pulse Width Modulating Inverter (PWM): A type of AC adjustable frequency drive that accomplishes frequency and voltage control at the output section (inverter) of the drive. The drive’s DC bus voltage is always a constant amplitude and by "chopping" (pulse width modulating), the average voltage is controlled.
Push-Button: A push-button is a switch of relatively short duration
PWM: A type of AC adjustable frequency drive that accomplishes frequency and voltage control at the output section (inverter) of the drive. The drive's DC bus voltage is always a constant amplitude and by "chopping" (pulse width modulating), the average voltage is controlled.
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