Motors and Drives Demystified -- Terms and Definitions (A-L)

A-L

AC Contactor Designed for the specific purpose of establish or interrupting an AC power circuit. A contactor is a high power, electromagnetic switch. It is constructed of a low voltage "control circuit" (for example, 24VDC) and a "power circuit," where the high voltage is being controlled (for example - 460VAC, 3-Phase). A contactor is essentially a high power relay.

AC Drive An electronic device that converts a fixed frequency and voltage source to an adjustable frequency and AC voltage source. It controls the speed, torque, horsepower, and direction of an AC motor.

A/D Converter A device that converts an analog signal (continuous values of voltage or current, e.g., sinewave) to a digital number.

Adjustable Speed Varying the speed of a motor, either manually or automatically. The desired operating speed (set speed) is relatively constant regardless of load.

Adjustable Speed Drive (Electrical) An adjustable-speed drive consists of the motor, drive controller, and operator's controls (either manual or automatic).

Analog Input (AI) An analog input is an input for the user-supplied DC signal. The signal may be a speed reference or a process feedback. This signal can be from manual speed pot DC voltage (0 to 10 VDC) DC current (0 to 20 mA DC). For many drives, the abbreviation is AI.

Analog Input Module An I/O module that converts an analog signal from an analog measuring device that may be processed by the processor.

Analog Output Module An I/O module that converts a digital signal from the processor into an analog output signal for use by a user analog device.

Analog-to-Digital Converter (A/D) A hardware device that senses an analog signal and converts it to a representation in digital form.

ASCII Acronym for American Standards Code for Information Interchange. Basically, it is a 7-bit code with an optional parity bit used to represent alpha numeric, punctuation marks, and control code characters.

Bandwidth The frequency range of a system input over which the system will respond satisfactorily to a command.

Base Speed The point where the motor will develop rated horsepower (HP) at rated load and voltage. With DC drives it is commonly the point where full armature voltage is applied with full rated field excitation. With AC systems, it is commonly the point where 60 Hz and rated voltage is applied to the induction motor.

Baud A unit of signaling speed equal to the number of discrete conditions or signal events per second.

BCD (Binary Coded Decimal) A numbering system that is used to express individual decimal digits (i.e., 0 through 9) in a four-bit binary rotation.

Bearing (Ball) A ball-shaped component that is used to reduce friction and wear while supporting rotating elements. For a motor, this type of bearing provides a relatively rigid support for the output shaft.

Bearing (Roller) A special bearing system with cylindrical rollers capable of handling belted load applications that are too large for standard ball bearings.

Binary Digit (Bit) In the binary system, a bit can represent either 0 or 1; to a computer a bit will indicate an off or on signal. Bits are the units of information that, when combined in certain configurations, will signal to the computer what it is to do. Bits are organized into larger units called words for access by computer instructions. Computers are often categorized by word size in bits, that is, the maximum word size that can be processed as a unit during an instruction cycle (e.g., 16-bit or 32-bit computers). The number of bits in a word is an indication of the processing power of the system, especially for calculations or for high-precision data.

Bit Rate The speed at which bits are transmitted, usually expressed in bits per second (sometimes referred to as baud rate).

Block A group of electronic words transmitted as a one unit.

Braking Provides a means of stopping an AC or DC motor and can be accomplished in several ways:

Braking (Dynamic AC Drives). AC motors do not have separate field excitation. Dynamic braking is accomplished by continuing to excite the motor from the drive. This causes a regenerative current to flow back to the drive's DC bus. In Drive terminology, the DC bus is an actual circuit that dissipates the power returned. The brake resistor is usually switched by a transistor or other power switch controlled by the drive.

Braking (Dynamic DC Drives). The motor slows by applying a resistive load across the armature leads after disconnection from the DC supply. This must be done while the motor field is energized. The motor then acts as a generator until the energy of the rotating armature is dissipated. This is not a holding brake.

Braking (Regenerative). This is essentially electronic braking. The generated power is returned to the line through the power converter. It may also be dissipated as losses in the converter (within its limitations).

Braking (Mechanical). This is a positive-action friction device. In a normal configuration the brake is set when power is removed. This can be used as a holding brake. (Note: A separately-mounted brake is one that is located on some part of the mechanical drive train other than the motor.) Breakaway Torque The torque required to start a machine from a stopped position. It is always greater than the torque needed to maintain motion.

Bridge Rectifier A full-wave rectifier that conducts current in only one direction of the input current. AC applied to the input results in approximate DC at the output. A diode bridge rectifier is a non-controlled full-wave rectifier that produces a constant DC voltage. An SCR bridge rectifier is a full-wave rectifier with an output that can be controlled by switching on the gate-control element.

Burn-In The process of operating a unit (e.g., drive) at elevated temperatures. This operation, performed before the unit's use in an application, tends to stabilize the unit's characteristics and detects early failures.

Byte This is equal to eight consecutive bits.

"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.

CEMF Counter electromotive force 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. The polarity of the CEMF is opposite to that of the power being supplied to the armature.

Cable Termination Filters--Filters installed at the motor, designed to match the terminating impedance at the motor to the characteristic impedance of the power cable between the drive and motors.

CE Marking CE marking is a label attached by the manufacturer to a product certifying that the product complies with certain European directives (e.g., EMC) and safety standards.

Closed Loop A regulator circuit in which the actual value of the controlled variable (e.g., speed) is sensed. 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.

Cogging A motor condition where the shaft does not rotate smoothly but "steps" or "jerks" from one position to another. Cogging is most evident at low motor speeds and can cause objectionable vibrations in the driven machine.

Common DC Bus--A drive system where several inverters are connected to a common DC bus. The advantages are space reduction, reduced cabling costs (only one incoming section is used), and in some instances, energy saving. For example, in a sugar mill, a battery of centrifuges can be driven by a common DC bus Bus system such that energy generated from a decelerating machine may be utilized, via the DC bus, by an accelerating machine.

----AC Drive Common DC Bus Configuration

Commutation (Inverter) This is a process where forward current is interrupted or transferred from one switching device to the other. In most AC circuits, turn-on-control is adequate and turn-off occurs naturally when the AC cycle causes the polarity across a given device to reverse.

Complementary Metal-Oxide Semiconductor (CMOS) An integrated circuit logic family characterized by very low power dissipation and moderate circuit density per chip, at moderate speed of operation.

Comparator A device that compares one signal to another, usually the process signal compared with the set point or command signal.

Concentric Windings--Motor windings that are wound so that each turn of the coil is next to the previous turn, and the coil is built up in successive layers. This ensures that each turn of the coil is in contact with immediately preceding and successive turns.

Constant Horsepower Load A load characterized by torque relative to the inverse of speed, abbreviated CHP. This type of load occurs above base speed. Horsepower stays constant because torque decreases as speed increases. The load requires low torque at high speeds. Some typical applications would be drilling, shaping, milling, and turning metal. In AC applications, the CHP range is sometimes referred to as the constant voltage range.

Constant Horsepower Range A motor-operation range where 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 Load A load characterized by torque proportional to a constant at any speed.

Torque stays constant because horsepower increases as speed increases up to base speed. The load requires the same amount of torque from zero to base speed. Some typical applications would be hoists, conveyors, and printing presses.

Constant Torque Range A speed range in which the motor is capable of delivering a constant torque, subject to cooling limitations of the motor.

Constant Voltage Range This term is related to AC drives. It is 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) The relationship that exists in AC drives where the output voltage is varied in direct proportion to frequency. This type of operation is required to allow the motor to produce constant-rated torque as speed is varied.

Continuous Duty A motor that can continue to operate within the insulation-temperature limits after it has reached normal operating temperature.

Control Logic Section Low voltage and current circuits that tell the power conversion sub-section devices when to switch on or off.

Converter The process of changing AC to DC. This is accomplished through use of a diode rectifier or thyristor rectifier circuit. The term converter may also refer to the process of changing AC to DC to AC (e.g., in an adjustable-frequency drive). A frequency converter, such as that found in an adjustable frequency drive, consists of a rectifier, a DC intermediate circuit (DC bus), an inverter, and a control unit.

A variable-frequency drive uses a three-phase diode bridge to convert the applied AC line voltage to rectified DC. The DC bus Bus consists of the DC potential source (internal rectifier bridge or external source), DC link inductor (connecting the DC bus Bus capacitors to the DC potential source), and DC bus Bus capacitors that, together with the DC link inductor, provide filtration of the DC source potential and provide some buffering between the DC source and the power inverter section. The DC bus Bus voltage is 1.35 × supply voltage (V in).

Critical Frequency The frequency at which continuous operation will cause mechanical vibration of the machine being controlled.

Current Limiting An electronic method of limiting the maximum current available to the motor. This is adjustable so that the motor's maximum current can be con trolled. It can also be preset as a protective device to protect both the motor and control from extended overloads.

Current Regulation This is the drive's ability to control the amount of current output. If the motor current exceeds the current limit setting, the drive output will stop.

The output frequency will decrease until the motor current is reduced below the current limit level. The drive will then accelerate at the rate determined by the acceleration time.

Cycle One complete cycle is the variation of an AC signal from zero to a maxi mum and back to zero in a positive direction and then in a negative direction.

"D" Flange (Motor Mounting) This type of motor mounting is used when the motor is to be built as a part of the machine. The mounting holes of the flange are not threaded. The bolts protrude through the flange from the motor side. Normally "D" flange motors are supplied without feet since the motor is mounted directly to the driven machine.

D/A Converter--A device that converts a digital number into an analog voltage or current level (continuous values of voltage or current, e.g., sinewave).

Damping The reduction in amplitude of an oscillation in the system.

DC Braking This is sometimes referred to as DC injection braking. This process provides quicker stopping times compared with a standard ramp-to-stop. The drive applies a DC voltage to the stator windings, quickly dissipating any energy within the drive system.

DC Bus Circuitry that filters the DC voltage entering the power output subsection from the rectifier.

DC Contactor A contactor specifically designed to establish or interrupt a direct-current power circuit.

DC Line Reactor Sometimes called a DC link inductor, this component adds impedance to the DC bus. Because of this, the inductor slows the rate of rise of current spikes, smoothing the effects of DC ripple on the bus Bus voltage output.

The results are improvement in the displacement power factor and lower harmonic distortion sent back to the AC line.

Dead Band The range of values through which a system input can be changed without causing a corresponding change in system output.

Default A default is a preprogrammed value for a parameter. During start-up of an AC drive, all application macro parameter values appearing on the keypad display are default settings. These default settings may be changed during the process of customizing your drive for your particular application.

Definite-Purpose Motor A definite-purpose motor is any motor design, listed, and offered in standard ratings with standard operating characteristics from a mechanical construction for use under service conditions other than usual, or for use on a particular type of application.

Definite-Purpose Inverter-Fed Motor--Motors that are specifically designed for use with adjustable-frequency drives, also called inverter duty motors. NEMA MG1-1993, Part 31 defines performance requirements for definite-purpose inverter-fed motors.

Deviation Difference between an instantaneous value of a controlled variable and the desired value of the controlled variable corresponding to the set point.

Also called error.

di/dt The rate of change in current versus the rate of change in time. Line reactors and isolation transformers can be used to provide the impedance necessary to reduce the effects of unlimited current on phase-controlled rectifiers (SCRs).

Digital Communications Transfer of information by means of a sequence of signals called bits (for binary digits), each of which can have one of two different values. The signals may, for example, take the form of two different voltage levels on a wire or the presence or absence of light in a fiber-optic light guide. It can be made arbitrarily insensitive to external disturbances by means of error control procedures.

Digital Input (DI) The digital inputs (DI) receive bi-stable (two-state on-off) control signals from the outside world. An example would be a two-position start-stop selector switch. Digital inputs are on some AC drive keypad displays.

Digital Signal Processor (DSP) A digital signal processor is a fast-acting component for mathematical calculations. It operates at 40 MHz and is able to multiply two numbers (8,000,000) in the time it takes for light to travel 20 m.

Diode--A device that allows current to flow in one direction but does not allow current t flow in the reverse direction.

Direct Torque Control (DTC™) Direct torque control is a term used for vector control without feedback, similar to a sensor-less flux vector AC drive. It is an optimized AC drive control principle where inverter switching directly controls the motor variables (e.g., flux and torque). The measured motor current and voltage are inputs to an adaptive motor model, which produces an exact value of flux and torque every 25 µs. Motor torque and flux two-level comparators compare the actual values produced by torque and flux reference controllers. Depending on the outputs from the two-level controllers, the optimum pulse selector directly determines the optimum inverter switch

positions. The inverter switch positions again determine the motor voltage and current, which in turn influence the motor torque and flux, and the control loop is closed.

Drift Deviation from the initial set speed with no load change over a specific time period. Normally the drive must be operated for a specific warm-up time at a specified ambient temperature before drift specifications apply.

Drift is normally caused by random changes in operating characteristics of various control components.

Drive Controller An electronic device that can control the speed, torque, horsepower, and direction of an AC or DC motor. This device is also called a variable-speed drive.

Drive End of a Motor The end (D.E.) that carries the coupling or driving pulley.

Driver A circuit that adjusts the reference signal to the correct level. It could also be considered the circuit that controls the "firing" of an IGBT. Driver circuits turn the power device on and off. With an IGBT, less current is required to turn the device off compared with an SCR.

Duty Cycle The relationship between the operating and rest times or repeatable operation at the different loads.

dv/dt The term dv/dt comes from differential calculus and means the derivative of v (voltage) with respect to t (time). It is the instantaneous rate of change in voltage with respect to time. To conform to the mathematical definition, the dv/dt of a voltage pulse should be defined as a function that describes the rate of change in voltage at any time during the duration of the pulse. In most discussions of motor insulation voltage stress, the term dv/dt is applied to the average rate of voltage change as voltage rises from 10% to 90% of the peak voltage or:

time rise

0.8 ge peak volta dt dv ×

=

The rate of change in voltage versus a rate of change in time. Specially designed resistor-capacitor networks can help protect the SCRs from excessive dv/dt, which can result from line voltage spikes, line disturbances, and circuit configurations with extreme forward conducting or reverse-blocking requirements.

Dwell The time spent in one state before moving to the next. In motion-control applications for example, a dwell time may be programmed to allow time for a tool change or part clamping operation.

Dynamic Braking--See Braking

Eddy Current--Currents induced in motor components from the movement of magnetic fields. Eddy currents produce heat and are minimized by lamination of the motor poles and armature. In transformers, it is the current that circulates in the metallic core material. This current is a result of electromotive forces induced by a variation of magnetic flux. Magnetic flux is a condition produced by the movement of voltage induced in an electrical conductor.

EEPROM--EEPROM is an acronym for electrically-erasable programmable read-only memory. The EEPROM is the non-volatile memory that stores all parameters, even when power is removed. (Sometimes referred to as E2 PROM).

Efficiency Ratio of mechanical output to electrical input indicated by a percentage. In motors, it is the effectiveness with which a motor converts electrical energy into mechanical energy.

Electromagnetic Compatibility (EMC) Electromagnetic--Compatibility is the ability of a device or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to anything in the same environment. To achieve EMC, the immunity of all equipment in the environment must be higher than the emissions from any source in the environment.

Electromotive Force (EMF) Electromotive force is a way of expressing voltage or potential difference.

Electromagnetic Interference (EMI) This is an abbreviation for electro-magnetic interference. This characteristic occurs during the switching of electronic power supplies and is similar to a radio wave. If the EMI signal is strong enough, it will cause unwanted reference signals or "noise" in other electronic equipment, such as drives.

Electrostatic Discharge See ESD

----p332

Representation of EMC Immunity and Emissions Limits

EPROM--EPROM is an acronym for erasable programmable read only memory. The EPROM is a circuit that can be erased with ultraviolet light, then reprogrammed with electrical pulses. It is essentially where the drive software exists-the section that controls semiconductor firing signals, etc.

Enable To allow an action or acceptance of data by applying an appropriate signal to the appropriate input (e.g., to allow the drive to start).

Enclosure The housing in which the control is mounted. Enclosures are available in designs for various environmental conditions.

Encoder--A device that produces a serial or parallel digital indication of mechanical angle or displacement. Essentially, an encoder provides high-resolution feedback data related to shaft position and is used with other circuitry to indicate velocity and direction. The encoder produces discrete electrical pulses during each increment of shaft rotation.

There are two types of encoders available: absolute and incremental. The absolute encoder provides multiple-channel coding of shaft position, with the output in a unique binary code. This type of encoder costs more than an incremental one because of the complexity of the circuit.

The incremental encoder consists of magnetic or optically-coupled electronic devices inside a case. These devices give out a number of pulses that correspond to speed and direction. This type of encoder has a disadvantage when used in positioning. When power is lost, this device also loses its starting point.

Error--Difference between the set-point signal and the feedback signal. An error is necessary before a correction can be made in a controlled system.

ESD--ESD is an acronym for electrostatic discharge. Electrostatic-discharge cautions indicate situations in which static electricity can damage circuit boards without any visible signs of damage. Precautions listed in an AC drive installation start-up manual must be followed when installing or removing circuit boards. As little as 50 V of static charge can damage a gate-emitter junction or a microcircuit in a "chip." Humans don't feel a discharge unless it is over 3000 V of static charge. Therefore, it is imperative that ESD grounding devices are worn when working on drive circuitry with the power off. By the time a human would feel ESD, the circuitry on the board could be damaged and not repairable.

FCC (CFR47) Limits from the Code of Federal Regulations. Defines the limits of radiated energy (expressed as RFI-radio frequency interference) from computing devices. These limits indicate protection from interference when receiver located at least 10 m from the RFI source.

Feedback This part of a system provides an actual operation signal for comparison with the set point to establish an error signal used by the regulator circuit.

Feedback Loop The feedback loop provides the self-corrective signal necessary to tell the drive to adjust output to the motor. The motor performs the required adjustment in speed or direction. The feedback loop is critical to the automatic accurate operation of the system. Because the feedback loop is directly connected to the motor or machine, it provides an exact representation of speed.

Fieldbus The word field indicates that we are dealing with the field level, the lowest layer of automation hierarchy, where the field devices like sensors and actuators are used. The word bus tells us that these communication devices are connected to a common connecting point instead of point-to point connections.

Field Range--The range of motor speed from base speed to the maximum rated speed.

With AC drives this is also referred to as the above base speed range or constant horsepower range. With DC drives, this indicates the area where above base speed operation is a result of weakening the shunt field flux.

Field Weakening Point On AC drive systems, this is the point at which the output voltage no longer increases even though the output frequency is increased. Operation above this point results in reduced motor torque capability while the out put kVA remains constant.

Filter A device that passes a signal or a range of signals and eliminates all others.

Flash Prom This is a memory chip imbedded on a circuit board similar to an E2 PROM™. This memory can contain drive parameters and values and can be upgraded to a new software version through fiber-optic communications.

Flux Vector Flux-vector drives use a method of controlling torque similar to that of DC drive systems, including a wide speed-control range with quick response.

Flux-vector drives have the same power section as all PWM drives, but use a sophisticated closed-loop control from the motor to the drive's microprocessor. The motor's rotor position and speed is monitored in real time via a resolver or digital encoder to determine and control the motor's actual speed, torque, and power produced.

Firmware This is a series of instructions in an EPROM. The instructions are used for internal processor functions only and are transparent to the drive opera tor.

Floating Ground An electrical common point that is not at earth-ground potential or the same ground potential as circuitry it is associated with. A voltage difference can exist between the floating ground and earth ground.

Flying Start The inverter (AC drive) searches for the frequency that corresponds to the motor speed and synchronizes with it smoothly. Some modern inverters will even find a motor rotating in the opposite direction.

Form Factor A figure of merit that indicates how much rectified current deviates from pure (non-pulsating) DC. A large departure from unity form factor (pure DC) increases the heating effect of the motor. It is expressed as IRMS/IAV (motor-heating current/torque-producing current).

Four-Quadrant Operation--The four combinations of forward and reverse rotation and forward and reverse torque of which a regenerative drive is capable. The four combinations are (1) forward rotation/forward torque (motoring), (2) forward rotation/reverse torque (regeneration), (3) reverse rotation/reverse torque (motoring), and (4) reverse rotation/forward torque (regeneration).

Frame Size The physical size of a motor, usually consisting of NEMA-defined "D" and "F" dimensions at a minimum. The "D" dimension is the distance in quarter inches from the center of the motor shaft to the bottom of the mounting feet. The "F" dimension relates to the distance between the centers of the mounting feet holes.

Frequency The number of cycles generated each second. The unit of measurement is hertz (Hz). (1 hertz = 1 cycle per second) Frequency Converter ( AC Drive) Equipment to convert single- or three-phase alternating voltage into alternating voltage with another frequency or phase number. The frequency converter typically consists of a rectifier and an inverter. Main types are direct converter and indirect converter.

Frequency Resolution (Analog) This is the minimum step in motor frequency the drive can deliver in relation to the analog input. The smaller the step, the finer the control. This becomes important for fine speed control in conveying systems. Frequency can also be set with the panel, but as the process is usually controlled by the analog input, panel frequency setting is not as important.

Full-Load Torque The torque necessary to produce rated horsepower at full-load speed.

Gate The control element of an SCR (silicon-controlled rectifier). When a small positive voltage is applied to the gate momentarily, the SCR will conduct current (when the anode is positive with respect to the cathode of the SCR). Current conduction will continue even after the gate signal is removed.

Gateway --An electronic device that is used to translate one form of data to another form of data. It could also be considered an electronic "interpreter." It interprets the protocol of a device such as a PLC.

General-Purpose Motor--This motor has a continuous Class "B" rating and design, listed and offered in standard ratings with standard operating characteristics and mechanical construction for use under usual service conditions without restriction to a particular application or type of application. These types of motors are not recommended for use with variable-frequency drives.

Group--In many AC and DC drives, a "group" is a category of parameters. Groups identify parameters by their functionality.

GTO Gate turn-off or gate turn-on power semiconductor device.

Hall Effect Sensor A transducer that produces a voltage feedback proportional to the magnetic field generated in a conductor. The magnetic field is proportional to the current flow in the conductor and is used in drives in the current limit circuit. The benefit of this type of sensor is the ability to very accurately measure AC current at low-frequency output.

Harmonic The component frequency that is an integral of the fundamental frequency (i.e., 60 Hz). For example, the 3rd harmonic is 60 × 3 or 180 Hz.

Harmonic Distortion -- A condition that exists in a power-distribution system due to the switching of equipment power supplies (computers, etc.) This "distorting" of the AC sine wave occurs wherever an electronic device (computer, drive, etc.) draws current in short pulses. Drives, for example, draw current only during a controlled part of the incoming voltage waveform. This process improves the efficiency, but causes harmonic distortion (currents) which could cause overheating in transformer neutrals. The harmonic currents would show up as an AC waveform that no longer looks like a pure sine wave. The voltage and current waveforms are no longer related. They are therefore called nonlinear.

Head --A measurement of pressure, usually in feet of water. A 20-foot head is the pressure equivalent to the pressure found at the base of a column of water 20 feet high.

Horsepower-- A measure of the amount of work that a motor can perform in a given period of time (see Appendix B, "Formulas and Conversions").

Hunting -- Fluctuations in motor speed that can occur after a step change in speed reference (either acceleration or deceleration) or load.

Hysteresis Loss -- Laminated iron materials offer some resistance to becoming magnetized.

This resistance results in energy being expended. Hysteresis loss in a magnetic circuit is the energy expended to magnetize and demagnetize the core.

IEEE Standard 519 -- An Institute of Electrical and Electronics Engineers standard that indicates the guidelines for harmonic control and inductive reactance of static power converters. This guide recommends limits of disturbances to the AC power distribution system which affects other equipment and communications.

Impedance -- The total opposition to AC that occurs in a circuit. This opposition (indicated by Z) is sometimes referred to as an "AC resistance." It is actually the combined product of resistance, inductance, and capacitance. Because of the inductor and capacitor part of the circuit, impedance is very frequency-sensitive.

IN -- This notation abbreviates the current at which the drive trips and on which current settings the trip point is based.

Induction Motor -- An AC motor that has the primary winding on one member (usually the stator), which is connected to the power source. A secondary winding on the other member (usually the rotor) carries the induced current. There is no physical electrical connection to the secondary winding.

Inertia -- A measure of a body's resistance to changes in velocity, whether the body is at rest or moving at a constant velocity. The velocity can be either linear or rotational. The moment of inertia (WK^2 ) is the product of the weight (W) of an object and the square of the radius of gyration ( K2 ). The radius of gyration is a measure of how the mass of the object is distributed axis of rotation. WK^2 is usually express in units of lb-ft^2.

Instability -- Characteristics of a system where there is an output but no corresponding input.

Insulated Gate Bipolar Transistor (IGBT) -- A current-operated power device that incurs lower losses than standard bipolar transistors. This results in increased switching frequencies and requirements for smaller heat sinks. Smaller gate currents can control large motor currents. Higher switching frequencies reduce the amount of audible motor noise and allow for smoother motor control (compared with low switching rates of 1 kHz and below). These devices allow a drive to operate at near "triples" control. They also allow the motor to develop high starting torque with 100% load capability.

Integral Horsepower Motor -- A motor built in a frame having a continuous rating of 1 HP or more.

Intelligent Power Module (IPM) -- This module includes the drive and protection circuits in a compact unit that is attached to the heat sink. IPMs offer increased reliability and lower losses because the IGBTs within the module have lower power losses.

Intermittent Duty Motor -- A motor that never reaches maximum temperature, but is permitted to cool down between operations.

Inverter -- A term commonly used for an AC variable-frequency drive. An inverter is also a term used to describe a particular section of an AC drive. The section uses the DC voltage from a previous circuit stage (DC bus Bus) to produce an AC current or voltage having the desired frequency.

Inverter Duty Motor -- This type of motor is designed to be operated on variable-frequency drives.

An inverter duty motor design includes phase insulation paper between the first few turns of stator windings. In addition, the stator windings are form wound (windings are laid exactly parallel next to each other). This increases inductance in each length of winding. An inverter duty motor also has winding insulation of a high-voltage class (e.g., 1600 V).

Inverter Spike-Resistant (ISR) Wire -- A trademark of the Phelps-Dodge company applied to a new magnet wire insulation that provides an increased level of protection from voltage peaks. This type of wire is found in some motors powered by adjustable frequency drives.

IP-Classes-- Protection of equipment against ingress of water or solid bodies such as dust. IP stands for ingress protection. Examples: IP00 indicates no water protection, no guards; IP54 indicates protection against damaging dust accumulation and against splashing water from any direction.

IR --This notation abbreviates the constant torque rated output current, in amperes, of an AC drive.

IR Compensation --This term is used in DC drive systems and relates to the voltage drop across the armature (E = I × R). It is a way to compensate for the loss in speed because of additional load on the motor. This compensation provides a way to improve the speed-regulation characteristics of the motor, especially at low speeds. Drives that use a tachometer-generator for speed feed back generally do not require an IR compensation circuit because the tachometer will inherently compensate for the loss in speed. In AC drives, IR compensation is a parameter that allows the motor to develop extra torque at motor speeds between 0.1 Hz and the set field weakening point.

This term is also used in variable-frequency drives, referring to improved speed regulation through additional volts per hertz control.

IRSQ --This notation stands for the rated variable-drive output current, in amperes, of an AC drive.

Isolation Transformer--A transformer that electrically separates the drive from the AC power line.

An isolation transformer provides several advantages: It enhances protection of semiconductors from line voltage transients; reduces disturbances from other solid-state control equipment such as drives without isolation transformers, time clock systems, electronic counters, etc.; and allows voltage matching of line power and drive input power (either step-up or step down transformer).

I 2T (Thermal Protection) --The ability of an AC drive to calculate the motor heating from the operation history.

Jogging --Momentary motor movement by repeated contact closures (e.g., using a single pushbutton).

Joystick Control --Joystick control allows you to use a joystick for external speed and direction drive control through an analog input. Typically, the center joystick position is zero speed and movement of the control causes forward or reverse direction.

Local Area Network (LAN) --A privately owned network communication channel, which is used for connecting communication equipment (e.g., data processing, drives, PLCs, etc.) This system is usually in a limited geographical area.

LED (Light Emitting Diode) --A solid-state device used for signal indication on the manual control and the I/O module.

LED Display --An alphanumeric display consisting of an array of LEDs (light emitting diodes).

Limit Switch --An electrical switch positioned to be actuated when a certain motion limit occurs. The switch then opens a contact that may then be used as a digital input to an AC drive.

Line Reactor --Reduces the amount of electrical noise fed back to the AC power line. It reduces the line notching (absence of power) caused by switching of power conversion devices (phase controlled rectifiers such as SCRs). Line reactors also serve to limit the current surge seen by the DC bus capacitors.

This surge happens when a voltage surge occurs to the input of the drive.

When a voltage surge occurs, a large current surge will occur as the bus capacitors charge to the peak voltage of the surge. The higher the surge level, the quicker the capacitor will charge (the surge may be 5 to 10 times higher than normal operating current). When the capacitors reach an overvoltage level, the drive shuts down. Line reactors, connected in series with the drive input, limit the magnitude of the current surge. The capacitor charges at a slower rate, thereby not allowing the capacitor to reach the voltage trip level.

Line Voltage-- The input voltage that provides power to the drive. Line voltage is connected to the terminals L1, L2, and L3 (U1, V1, and W1 ). Also refer to Sup ply Voltage in this glossary.

Linear Acceleration/Deceleration-- This drive circuit controls the rate at which the motor is allowed to accelerate to a set speed or decelerate to zero speed. On most drives, this circuit is adjustable and can be set to a particular application.

Linearity --A measure of how closely a characteristic follows a straight line function.

Linear Load --Any type of electrical equipment that does not change the voltage or current waveform. This load does not distort the AC sine wave. Examples of this type of load include standard incandescent lights and AC induction motors.

Living Zero--The living zero function allows an AC drive to detect a loss of reference signal. This function operates in many drives when a "minimum AI1" parameter is set to a value greater than 0.3 V/0.6 mA. You can then super vise the presence of a control signal by setting an "AI < min function" to Warning or Fault. A Warning or Fault message will then display if the analog input falls below the set minimum.

Load Sharing -- This is an application where the shafts of several motors are mechanically connected together through the load. If the load is shared unevenly, one or more motors may be overloaded while the others operate lightly loaded. With DC motors, load sharing can be adjusted by adjusting the field currents of the individual motors. With AC motors, there is no com parable means of adjusting the load sharing. Load sharing with AC motors is determined by the mechanical design of the driven equipment, the placement of the motors, and the motor torque-speed curves. Since the AC motor torque-speed curve dictates that the motor speed must decrease when the torque speed increases, motors will share the load evenly if the mechanical connection among the motors prevents them from operating at different speeds.

Locked-Rotor Current--Current taken from the line with the rotor at standstill (at rated voltage and frequency). This is the starting current when the motor is connected to the load.

Locked-Rotor Torque--Torque that a motor will develop for all positions of the rotor (with rated voltage applied at rated frequency).

Logic Control -- Controlling the power switching devices to obtain adjustable frequency. It also controls the firing sequence to maintain phase coordination and the output voltage to produce the required V/Hz ratio. The driver subsection adjusts the reference signals to the correct level. The power output control subsection automatically adjusts the switching of the power output sub section. Monitoring devices for overcurrent and bus Bus voltage level report to the control logic.

M-Z >>