C-Face (Motor Mounting): This type of motor mounting is used to close couple pumps and similar applications where the mounting holes in the face are threaded to receive bolts from the pump. Normally, the C-Face is used where a pump or similar item is to be overhung on the motor. This type of mounting is a NEMA standard design and available with or without feet.
C-Flange: A type of mounting used to connect motors/gearmotors to driven equipment with dimensions defined by NEMA. This type of mounting is used to close couple pumps and similar applications where the mounting holes in the face are threaded to receive bolts from the driven equipment.
Capacitance: The value in microfarads of a capacitor or condenser.
Capacitor: A device which, when connected in an alternating current circuit, causes the current to lead the voltage in time phase. The peak of the current wave is reached ahead of the voltage wave. This is the result of the successive storage and discharge of electric energy.
Cascade Drive System: Two or more drives connected to a master speed setting potentiometer. The master speed setting potentiometer sets the speed of the master drive. Each of the slave drives has a potentiometer of trimming the speed reference from the master speed setting potentiometer.
CEMF: Abbreviation for counter electromotive force, which is the product of a motor armature rotating in a magnetic field. This generating action takes place whenever a motor is rotating. Under stable motoring conditions the generated voltage (CEMF) is equal to the voltage supplied to the motor minus small losses. However, the polarity of the CEMF is opposite to that of the power being supplied to the armature.
Center Distance: The measured distance from the center of a pinion to the center of its mating gear.
Centrifugal Cutout Switch: A centrifugally operated automatic mechanism used in conjunction with single phase induction motors. Centrifugal cutout switch will open or disconnect the starting winding when the rotor has reached a predetermined speed, and re-connect it when the motor speed falls below it. Without such a device, the starting winding would be susceptible to rapid overheating and subsequent burnout.
Closed Loop: Closed loop refers to a regulator circuit in which the actual value of the controlled variable (e.g., speed) is sensed and a signal proportional to this value (feedback signal) is compared with a signal proportional to the desired value (reference signal). The difference between these signals (error signal) causes the actual value to change in the direction that will reduce the difference in signals to zero.
Code Letter: A code letter is a letter which appears on the nameplate of alternating-current motors to show their locked-rotor KVA per horsepower.
Cogging: A term used to describe non-uniform angular velocity. It refers to rotation occurring in jerks or increments rather than smooth motion. When an armature coil enters the magnetic field produced by the field coils, it tends to speed up and slow down when leaving it. This effect becomes apparent at low speeds. The fewer the number of coils, the more noticeable it can be.
Commutation (DC Motors): Reversing the current in an armature coil when the coil (ends) move from one side of the brush to the other side of the same brush. This completes the connection between the armature winding and the external circuit.
Commutation (Inverter): The process by which forward current is interrupted or transferred from one switching device to the other. In most circuits where power is supplied from an AC source, turn-on control is adequate and turn-off occurs naturally when the AC cycle causes the polarity across a given device to reverse.
Commutator: A cylindrical device mounted on the armature shaft and consisting of a number of wedge-shaped copper segments arranged around the shaft (insulated from it and each other). The motor brushes ride on the periphery of the commutator and electrically connect and switch the armature coils to the power source.
Comparator: A device that compares one signal to another, usually the process signal compared to the set point or command signal.
Computerized Numerical Control (CNC): A numerical control system where a computer is used to perform some or all of the basic numerical control functions on a machine tool.
Conduit Box: Metal box on motor where motor leads terminate.
Constant Horsepower: A multi-speed wound motor where all the windings are of the same horsepower.
Constant Horsepower Range: In VFD applications, a range of motor operation where the motor speed is controlled by field weakening. In this range, motor torque decreases as speed increases. Since horsepower is speed times torque (divided by a constant), the value of horsepower developed by the motor in this range is constant.
Constant Torque: A multi-speed motor wound so that the horsepower varies directly as the speed.
Constant Torque Range: In VFD applications, a speed range in which the motor is capable of delivering a constant torque, subject to cooling limitations of the motor.
Constant Voltage Range (AC Drives): The range of motor operation where the drive’s output voltage is held constant as output frequency is varied. This speed range produces motor performance similar to a DC drive’s constant horsepower range.
Constant Volts Per Hertz (V/HZ): This relationship exists in AC drives where the output voltage is varied directly proportional to frequency. This type of operation is required to allow the motor to produce constant rated torque as speed is varied.
Control Circuit: The control circuit of a control apparatus or system is the circuit which carries the electric signals directing the performance of the controller, but does not carry the main circuit power.
Control Device: A control device is an individual device used to control functions.
Control Transformer: A control transformer is a voltage transformer utilized to supply voltage suitable for the operation of control devices.
Counter Electromotive Force: (CEMF) The induced voltage in motor armature, caused by conductors moving through or "cutting" field magnetic flux. This induced voltage opposes the armature current and tends to reduce it.
Conductor: Any material which tends to make the flow of electric current relatively easy (copper, aluminum, etc.).
Contactor: A two-state (On-Off) device for repeatedly establishing an interrupting an electric power circuit. Interruption is obtained by introducing a gap or a very large impedance.
Contactor Reversing: A method of reversing motor rotation by the use of two separate contactors, one of which produces rotation in one direction and the other produces rotation in the opposite direction. The contactors are electrically (and mechanically) interlocked so that both cannot be energized at the same time.
Continuous Duty: A motor that can continue to operate within the insulation temperature limits after it has reached normal operating temperature.
Continuous Rating: The maximum constant load that can be carried continuously without exceeding established temperature rise limitations under prescribed conditions of load and within the limitations of established standards.
Control Transformer: A control transformer is a voltage transformer utilized to supply voltage suitable for the operation of control devices.
Converter: The process of changing AC to DC and back to AC again. This is accomplished through the use of a diode rectifier or thyristor rectifier circuit. The term "converter" may also refer to the process such that is found in an adjustable frequency drive, consists of a rectifier, a DC intermediate circuit, an inverter and a control unit.
Copper Bar Rotor: Specialized rotor construction used on high inertia applications that require high slip or torques. Centrifugal cast end rings are fully brazed to each rotor bar. Rotor bars are swagged preventing inslot movement and tight bar constructions. Heavy finger plates tightly hold the rotor cove together controlling internal stress and maintaining dimension stability under all loads.
CORRO-DUTY ®: USEM special created motor for withstanding corrosive environments.
Coupling: A means for which the driven load is connected to the driver (motor). Couplings are divided into 2 halves with one placed on the motor shaft and the other on the driven equipment. The 2 halves are then bolted together.
Coupling Angle: The mechanical degree relationship between the rotor and the rotating electrical field in a motor. While present in both synchronous and non-synchronous A.C. motors, it is usually of concern in synchronous applications. At no load, the rotor poles line up exactly with the field poles and the coupling angle is considered to be zero. When a load is applied, the lines of force coupling the rotor with the stator field are stretched, causing the rotor to fall behind the field. The mechanical angle by which the rotor lags behind the field is called the coupling angle. The coupling angle will continue to increase with load until it reaches the "pull-out" point. The maximum angle which is possible prior to pull-out is dependent on motor type and rotor design.
Critical Speed: All rotating masses have a so-called critical speed (RPM) where abnormal vibrations occur. Induction motors (rotors), generally run well above this speed, but occasionally in redesigning -- the critical speed may occur at or near the operating speed -- and intolerable situation.
Crusher Duty: Specific-duty motor design including special rotor, larger shaft (if needed), increased locked rotor and breakdown torques, end turn bracing and lock washers, and minimized stress riser.
Current Limit: An electronic method of limiting the maximum current available to the motor. This is adjustable so that the motor's maximum current can be controlled. It can also be preset as a protective device to protect both the motor and controller from extended overloads.
Current Limit Acceleration: A system of control in which acceleration is so governed that the motor current does not exceed an adjustable maximum value.
Current Limiting Fuse: A fuse that, when it is melted by a current within its specified current limiting range, abruptly introduces a high impedance to reduce the current magnitude and duration.
Current Relay: A current relay functions at a predetermined value of current. It may be an overcurrent relay, an undercurrent relay or a combination of both.
Current Transformers: Option available on titan motors to maintain the same magnitude of current flowing in and out of each phase of the motor winding. A breakdown in the insulation system alters this balance resulting in measurable "difference" when the current flowing in and out of each circuit is compared for symmetry. Any dissimilarity within an individual circuit is knows as "differential current" which can be detected with current transformers that provide differential protection.
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