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Glossary Of Electro-Mechanical Terms

  • ALTERNATOR - A synchronous machine used to convert mechanical power into alternating current electric power.
  • AMBIENT TEMPERATURE - The temperature of the surrounding cooling medium. Commonly known as mom temperature when the air is the cooling medium in contact with the equipment.
  • AMPERES - Measure of current flow in electrical circuit.
  • BASE LINE - A vibration reading taken when a machine is in good operating condition that is used as a reference for monitoring and analysis.
  • BREAKDOWN TORQUE - The maximum torque that an ac motor will develop with rated voltage applied at rated frequency without an abrupt drop in speed. Also termed pull-out torque or maximum torque.
  • BEARINGS - Supports, guides, and reduces the friction of motion between fixed and moving machine parts.Sleeve: Preferred where low noise is important as on fan and blower motors.Ball: Used where high shaft load capacity is required or where periodic lubrication is impractical.
  • CODE LETTER - A letter which appears on the nameplates of ac motors to show their locked-rotor kilovolt amperes per horsepower at rated voltage and frequency.
  • CONSTANT HORSEPOWER MOTOR - A term used to describe a multi-speed motor in which the rated horsepower is the same for all operating speeds. When applied to a solid state drive unit, it refers to the ability to deliver constant horsepower over a predetermined speed range.
  • CONSTANT TORQUE MOTOR - A multi-speed motor for which the rated horse power varies in direct ratio to the synchronous speeds. The output torque is essentially the same at all speeds.
  • DELTA CONNECTION - A three-phase winding connection in which the phases are connected in series to form a closed circuit-
  • DESIGN - NEMA design letters A, B, C. D, and E define certain starting and running characteristics of polyphase squirrel care induction motors. These characteristics include locked-rotor torque, locked-rotor current, pull-up torque, breakdown torque, slip at rated load, and the ability to withstand full-voltage starting.
  • DIRECT CURRENT - Type of power supply available from batteries, generators or a rectified source used for special-purpose applications.
  • DUTY - A continuous or short-time rating of a machine. Continuous-duty machines reach an equilibrium temperature within the temperature limits of the insulation system. Machines which do not, or can not, reach an equilibrium temperature have a short-time or intermittent-duty rating. Short-time ratings are usually one hour or less for motors.
  • EFFICIENCY - The ratio between useful work performed and the energy expended in producing it. It is the ratio of output power divided by the input power.
  • ENCLOSURE - Housing of the motor.
  • FOOT-POUND - The amount of work, in the English system, required to raise a one pound weight a distance of one foot.
  • FRAME - The NEMA standardized motor mountings and shaft dimensions.
  • FREQUENCY - The number of cycles in a time period (usually one second). Alternating current frequency is expressed in cycles per second, termed Hertz (H z).
  • FULL LOAD AMPERES - Line current (amperage) drawn by a motor when opening at rated load and voltage on motor nameplate.
  • FULL-LOAD CURRENT - The current required for any electrical machine to produce its rated output or perform its rated function.
  • FULL-LOAD SPEED - The speed at which any rotating machine produces its rated output.
  • FULL-LOAD TORQUE - The torque required to produce rated power at full-load speed.
  • HARMONIC - A multiple of the fundamental electrical frequency. Harmonics are present whenever the electrical power waveforms (voltage and current) are not pure sine waves.
  • HERTZ (HZ) - The preferred terminology for cycles per second (frequency).
  • HORSEPOWER - A unit for measuring the power of motors or the rate of doing work. One horsepower equals 33,000 foot-pounds of work per minute (550ft-lbs per second) or 746 watts.IEC - International Electrotechnical Commission,IEEE - Institute of Electrical and Electronics Engineers
  • INSULATION - Non-conducting materials separating the our current-carrying parts of an electric machine from each other or from adjacent conducting material at a different potential.
  • INSULATION CLASS - A letter or number that designates the temperature rating of an insulation material or system with respect to thermal endurance.
  • KILOWATT - A unit of electrical power. Also, the output rating of motors manufactured and used off the North American continent.
  • LOCKED-ROTOR CURRENT - Steady-state current taken from the line with the rotor of a motor at standstill and at rated voltage and frequency.
  • LOCKED-ROTOR TORQUE - The minimum torque that a motor will develop at standstill for all angular positions of the rotor, with rated voltage applied at rated frequency.
  • MEGOHMMETER - An instrument for measuring insulation resistance.
  • MOTOR - A rotating machine that converts electrical power (either alternating current or direct current) into mechanical power.NEC - National Electrical Code. A code developed for the proper use of electricity used for regulating building codes and safety. NEMA - National Electrical Manufacturers Association. An organization that establishes voluntary industry standards relating to motors.
  • NEWTON-METER - Unit of torque, in the metric system, that is a force of one newton, applied at a radius of one meter and in a direction perpendicular to the radius arm.
  • PART-WINDING STARTING - A part-winding start polyphase motor is one arranged for starling by first energizing part of its primary winding and, subsequently. energizing the remainder of the primary winding. The leads are normally numbered 1,2,3 (starting) and 7,8,9 (remaining).
  • POLES - The magnetic poles set up inside an electric machine by the placement and connection of the windings.
  • POUND-FOOT - Unit of torque, in the English system, that is a force of one pound, applied at a radius of one foot, and in a direction perpendicular to the radius arm.
  • POWER FACTOR - The ratio of watts to volt-amperes of an ac electric circuit.
  • RATED TEMPERATURE RISE - The permissible rise in temperature above ambient for an electric machine operating under load.
  • RESISTANCE TEMPERATURE DETECTOR (RTD) - A device used for temperature sensing consisting of a wire coil or deposited film of pure metal for which the change in resistance is a known function of temperature. The most common type is nickel, with other types being copper, platinum, and nickel-iron.
  • ROTOR SERVICE FACTOR - The rotating element of any motor or generator. A multiplier which, when applied to rated power, Indicates a permissible power loading that may be carried under the conditions specified for the service factor.
  • SLIP - The difference between synchronous and operating speeds, compared to synchronous speed, expressed as a percentage. Also the difference between synchronous and operating speeds, expressed in rpm.
  • STARTING TORQUE - The torque produced by a motor at rest when power is applied. For an ac machine, this is the locked-rotor torque.
  • STATOR - The stationary part of a rotating electric machine. Commonly used to describe the stationary part of an ac machine that contains the power windings.
  • SYNCHRONOUS SPEED - The speed of the rotating machine element of an ac motor that matches the speed of the rotating magnetic field created by the armature winding.Synchronous speed = (Frequency x 120) / (Number of Poles)
  • TEMPERATURE RISE The amount by which a motor, operating under rated conditions is hotter than its surrounding ambient temperature.
  • THERMISTOR - A resistive device used for temperature sensing that is composed of metal oxides formed Into a bead and encapsulated in epoxy or glass. A typical thermistor has a positive temperature coefficient, that is. resistance increases dramatically arid non-linearly with temperature. Though less common, there are negative temperature coefficient thermistors.
  • TORQUE - The rotating force produced by a motor. The units of torque may be expressed as pound-foot, pound-inch (English system), or newton meter (metric system).
  • TRENDING - Analysis of the change in measured data over at least three data measurement intervals.
  • UL - Underwriters Laboratories, Inc. An independent testing organization that sets safety standards for motors and other electrical equipment.
  • VARIABLE- TORQUE MOTOR - A multi-speed motor in which the rated horse power varies as the square of the synchronous speeds.
  • VOLTAGE - The rate at which energy is drawn from a source that produces a flow of electricity in a circuit; expressed in volts
  • WATTS - A unit of electrical power equal to current times voltage
  • WYE CONNECTION - A three-phase winding connection formed by joining one end of each phase to make a "Y" point. The other ends of each phase are connected to the line. Also termed a star connection.
  • WYE-DELTA STARTING - Wye-delta is a connection which is used to re duce the inrush current and torque of a polyphase motor, A wye (star) start, delta run motor is one arranged for starting by connecting to the line with the winding initially connected wye (star). The winding is then reconnected to run in delta after a predetermined time. The lead numbers for a single run voltage are normally 1,2,3,4,5 and 6.