Motor Drive Systems and Maintenance 347

AC

Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times per second, or 60 hertz (Hz), in the US.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current switches direction 60 times per second, or 60 hertz (Hz), in the US.

baseline

Initial data collected while a system or component is in working order. Baseline readings are compared to future readings in order to detect potential faults.

bearing

A friction-reducing device that allows one moving part to glide past or rotate within another moving part. Bearings use a sliding or rolling mechanism to reduce friction.

belt drives

A mechanical system consisting of a flexible belt and at least two fixed pulleys that is used to transmit motion. Belt drives are low maintenance and do not require lubrication.

belts

A loop of flexible material that is used to transmit motion. Belts are made of various materials and come in different types, such as flat belts, round belts, and V-belts.

branch circuits

The part of a distribution system that consists of circuit conductors. Branch circuits are located between the final overcurrent protection devices in the distribution panel and the loads being powered.

bus bars

A grounded metal strip that serves as a common connection between several circuits. Bus bars are found in electrical boxes and distribution panels.

capacitors

A device that stores electrical energy and releases it when needed. Capacitors are used to filter electricity in the DC bus of a variable frequency drive.

CAT I

The measurement category used for protected electronic equipment and circuits that do not connect directly to the mains. CAT I installations are no longer specified by the International Electrotechnical Commission.

CAT II

The measurement category used for single-phase receptacle-connected loads. CAT II installations include appliances, tools, and long branch circuits.

CAT III

The measurement category used for three-phase distribution circuits. CAT III installations include hard-wired equipment and distribution panel devices.

CAT IV

The measurement category used for three-phase circuits at the mains. CAT IV installations include electric meters, primary overcurrent protection devices, and outdoor conductors.

chain drives

A mechanical system consisting of a chain and toothed wheels called sprockets. Chain drives are used to transmit motion from one sprocket to another.

chains

A series of linked metal rings used to transmit motion. Chains are designed to mesh with toothed wheels called sprockets.

circuit breaker

A safety device that detects overcurrent in a circuit. Circuit breakers open circuits to prevent overloading and overheating.

complex indirect drives

A drive train system that uses flexible couplings in addition to gears, belts, and/or chains to connect the motor and output device shafts. Complex indirect drives also include additional components to support the couplings.

conductive

Able to act as a path for the movement of electricity. Conductive components form magnetic fields when energized.

conductors

A material or element that allows electricity to flow freely. Conductors are used to connect electrical components.

constant horsepower load

CH load. A load that requires a consistent amount of horsepower at all times. Constant horsepower loads require high torque at low speeds and low torque at high speeds.

constant torque load

CT load. A load that requires a consistent amount of torque at all times. With constant torque loads, horsepower changes as speed changes but torque remains the same.

corrective tools

A maintenance instrument used to fix issues and faults. Corrective tools are used while systems are shut down.

coupling

A component that connects two shafts in a mechanical system in order to transfer motion. Couplings may be used to attach the motor and driven unit shafts in a motor drive system.

cross-functional

Consisting of people with a wide range of expertise. Cross-functional teams include people from a variety of departments within an organization.

current

The flow of electricity. Current strength is called amperage and is measured in amperes (A), also called amps.

data

Any type of information gathered about an application or process. Data is often in the form of values or numbers.

DC

Direct current. Electricity that flows in one direction. DC does not reverse the direction of flow.

DC bus

The part of a variable frequency drive that filters electricity flowing from the rectifier to the inverter. The DC bus uses capacitors to smooth out ripple and electrical noise.

delta

A connection of three conductors that forms a triangular series circuit. Delta connections are used in three-phase power systems.

diagnostic tools

A testing instrument that provides more detailed information about the cause of a problem. Diagnostic tools are used to analyze problems that have been identified during screening.

diagrams

A drawing that illustrates the parts or operation of something. Diagrams use pictures and symbols to represent components.

diode

An electronic device with two terminals that allows electric current to flow in only one direction. Diodes use polarity to control current flow.

direct coupled drive

A drive train system that uses a flexible coupling to connect a motor shaft to an output device shaft. Direct coupled drives do not require precise shaft alignment and are commonly used for pumps.

direct current

DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.

direct drive

A drive train system that uses a straight shaft to connect the motor immediately to the output device. Direct drives require precise, rigid alignment.

distribution panel

A grouping of electrical devices that divide upstream electricity into separate circuits to reach individual components downstream. Distribution panels consist of fused switches, circuit breakers, and other devices.

drive train

A group of mechanical components used to transmit power from a motor to an output device. Drive trains connect the shaft of the motor to the shaft of the driven unit.

drive train

A group of mechanical components used to transmit power from a motor to the driven unit. Drive trains connect the shaft of the motor to the shaft of the driven unit.

driven unit

The machine or device powered by a motor drive system. The driven unit may also be called the load because it provides resistance to the motor.

electrical noise

An AC power line disturbance caused by sudden changes in the load. Electrical noise is problematic because many electronic devices cannot differentiate between an intended electrical pulse and an unintended electrical spike.

failure

The complete loss of performance in a component or a system. Failure can result from electrical and mechanical faults within a system.

faults

A problematic condition that interferes with a component or system's ability to function as intended. Faults may lead to failure and safety risks.

foot

A flat projection that protrudes from the bottom of a motor's housing. The foot of the motor rests or mounts on the foundation.

foundation

The flat surface upon which a motor sits. The motor's feet may simply rest on the foundation or be mounted to it.

frequency

The number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).

friction

A force that resists motion between two objects that are in contact with each other. Friction generates heat and increases wear between components.

gear drives

A mechanical system consisting of two or more gears. Gear drives make it possible to alter the output speed and torque of a motor.

gears

A round or cylindrical mechanical component with teeth that is used to transmit power. Gears are designed to mesh with one another in order to alter the speed, torque, or direction of mechanical energy.

graphs

A diagram that represents the variation of one value compared to another. Graphs are useful for identifying changes in a value that occur over time.

hard-wired

Having wires that are physically connected to other devices or wires so as to consistently function the same way. Hard-wired equipment performs the same tasks over and over again.

horsepower

hp. A unit used to measure power in large electrical devices such as motors. One horsepower equals 33,000 foot-pounds (44,748 joules) of work per minute, or 746 watts.

housing

A protective cover designed to contain or support a component. The housing of an electric motor is a metal enclosure that protects the internal motor parts.

IEC

International Electrotechnical Commission. An organization that governs electrical equipment standards in Europe and other countries outside the U.S. The IEC outlines the four measurement categories, or CAT designations, used to rate electrical testing equipment.

IEC 61010

A standard written by the International Electrotechnical Commission that outlines the four measurement categories used to rate electrical testing equipment. IEC 61010 categories are based on the amount of voltage available and potential transients in the installation.

indirect drives

A drive train system that uses additional components such as gears, belts, and chains to connect the motor and output device shafts. Indirect drives offset the motor and output device and may also use flexible couplings.

Industrial Electrician

The maintenance role responsible for dealing with electrical faults. The Industrial Electrician deals with excess power consumption, motor shutdown and overheating, and repeated motor rewinds.

Industrial Maintenance Manager

The maintenance role responsible for resolving overall maintenance issues. The Industrial Maintenance Manager deals with tasks that involve replacing equipment and lost production time.

Industrial Mechanic

The maintenance role responsible for dealing with mechanical faults. The Industrial Mechanic deals with overheating components, mysterious breaker trips, and recurring motor failures.

infrared cameras

A thermal inspection device that uses infrared technology to produce a visual representation of temperature conditions. Infrared cameras provide images of a component's thermal signature.

inspection

Examination of a component or system to ensure that it is operating correctly. Inspection for proactive maintenance involves measuring and comparing various parameters.

inspection routes

A list of points in a system that outlines the order and content of an inspection. Inspection routes group tasks by category, such as thermal or vibration inspection.

insulated gate bipolar transistors

IGBT. An electrical device used to rapidly switch power on and off. Insulated gate bipolar transistors are used for pulse width modulation in variable frequency drive inverters.

insulation

A material that does not conduct electricity and is used to cover electrical conductors. Insulation contains current to prevent excess leakage and other faults.

insulation resistance testers

A diagnostic tool that supplies a low DC voltage to a conductor to measure the current leakage rate. The insulation resistance tester uses the current leakage rate to calculate the resistance of the insulation.

International Electrotechnical Commission

IEC. An organization that governs electrical equipment standards in Europe and other countries outside the U.S. The International Electrotechnical Commission outlines the four measurement categories, or CAT designations, used to rate electrical testing equipment.

inverter

A device that converts DC power into a signal that resembles AC power. Inverters often use pulse width modulation to output pulsed DC that the motor interprets as AC.

laser alignment tool

A corrective instrument that provides visual guidelines and instructions for how to re-align misaligned shafts. A laser alignment tool can also be used to diagnose misalignment.

leakage current

The current that flows through the insulation of a conductor to ground. Leakage current increases as insulation degrades.

leakage current clamps

A screening tool that measures the amount of current leaking from a conductor. Leakage current clamps can be used while equipment operates.

load

The opposition to an applied force, such as a weight or resistance. The load may also refer to the driven unit since it provides resistance to the motor.

local distribution systems

The circuits that deliver power to separate areas and components within a building. Local distribution systems include fixed equipment installations and distribution panels.

logging function

A feature that allows testing tools to repeatedly measure and record various parameters over time. The logging function of a power quality analyzer allows it to monitor systems for intermittent or long-term faults.

looseness

Excessive clearance between mechanical components. Looseness can occur between rotating and/or stationary parts.

lubrication

The application of lubricants, such as grease or oil, to machines. Lubrication reduces friction and wear between mechanical components.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

main disconnect switch

A heavy, spring-loaded switch on an electrical panel, such as a distribution panel, that cuts off power to a circuit within a facility. Main disconnect switches are used to ensure that a system is de-energized before maintenance.

mains

The power lines in a distribution system that supply electricity from the utility to buildings. Mains connect to the main switchgear in a building to provide power to a motor.

measurement categories

A grouping of electrical equipment organized by the amount of available voltage and potential transients in the installation. Measurement categories are used to rate testing tools.

meters

A device that measures electricity. Meters may measure many different values, including voltage and current.

misalignment

A condition in which the shafts of a motor and a driven unit are offset or angled. Misalignment can cause damaging vibration in a machine.

monitoring tools

A testing instrument that measures the same parameter repeatedly over time to identify changes. Monitoring tools are typically installed in a system and set to signal when they detect a certain change.

motor drive

An electronic device that regulates the power supplied to a motor. A motor drive, such as a variable frequency drive, can be used to control the speed and torque of a motor.

motor drive system

The combination of an electric drive and the motor it controls. Motor drive systems typically use variable frequency drives and three-phase AC motors.

motor failures

A situation that occurs when a motor turns off and is no longer able to operate. Motor failures are more severe than motor shutdowns because a failed motor cannot be reset in its present state.

motor shutdowns

A situation that occurs when a motor turns off and stops operating but may be reset. Motor shutdowns may result from system faults or be scheduled as part of a maintenance program.

National Electrical Code

NEC. The standard for minimum safe electrical installations in the United States. The National Electrical Code is adopted in some form as law in all 50 states.

operational inspections

Maintenance and testing tasks that can take place when a motor or system is running normally. Operational inspections include screening and diagnostics for thermal, vibration, and power quality issues.

oscilloscopes

An electrical testing instrument that produces a visual representation of a voltage or current waveform. Oscilloscopes are also called scopemeters.

output signal

The electrical current sent from one device to another. The output signal produced by the inverter provides voltage to the motor.

overcurrent devices

A component that protects circuits from excess current flow to prevent overheating and fires. Overcurrent devices include fuses and circuit breakers.

overloading

A state in which the level of current exceeds the recommended level for a device or circuit. Overloading can cause overheating and equipment damage.

peaks

The greatest magnitude of a waveform. Peaks can be positive or negative.

planned downtime

A scheduled stop in production that is often used for machine maintenance. Planned downtime is preferable to unplanned downtime, which is usually caused by machine failure.

polarity

Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.

power quality analyzer

A testing tool that measures levels and characteristics of electrical power. A power quality analyzer can be installed in a system to act as a monitoring tool.

power transmission

The movement of energy from a source to an output device that performs work. Power transmission can be performed in many different mechanical systems, including gear trains, belt drives, and chain drives.

predictive maintenance

PdM. A maintenance approach that involves testing and monitoring each machine individually in order to predict failures. In predictive maintenance, periodic readings are compared to baseline readings in order to identify problems.

preventive maintenance

PM. The practice of performing standard maintenance functions on a scheduled basis in order to prevent breakdowns. Preventive maintenance tasks are usually determined by the age of the equipment.

proactive maintenance

The practice of incorporating both preventive and predictive maintenance approaches. Proactive maintenance leads to increased production and reduced downtime.

pulse width modulation

PWM. A method of producing a signal that resembles an AC waveform by turning a series of electrical switches on and off. Pulse width modulation produces the output signal that a variable frequency drive sends to a motor.

races

A metal ring that houses the steel balls in a bearing. Races have grooves along which the balls roll.

reactive maintenance

RM. The practice of performing immediate maintenance on a machine only after it becomes damaged or problematic. Reactive maintenance is also known as run-to-failure and is not a cost-effective long-term maintenance approach.

receptacles

A device into which an electrical conductor can be plugged. Receptacles include common wall outlets.

rectifier

A device used in an electrical circuit to convert AC power to DC power. Rectifiers allow electrical current to flow in only one direction.

relay

A device that controls one circuit by opening and closing the contacts in another circuit. Relays can be used to disconnect a motor from its power source under overload conditions.

rewinding

Replacing the windings in an electric motor. Rewinding is the responsibility of the Industrial Electrician.

ripple

Fluctuation of voltage that results from the AC voltage supplied to a variable frequency drive. Ripple must be eliminated before the voltage reaches the inverter.

rotor

The rotating part of a motor. The rotor connects to an output shaft that drives the load.

run-to-failure

The practice of performing immediate maintenance on a machine only after it becomes damaged or problematic. Run-to-failure is also known as reactive maintenance and is not a cost-effective long-term maintenance approach.

scopemeters

An electrical testing instrument that produces a visual representation of a voltage or current waveform. Scopemeters are also called oscilloscopes.

screening tools

A testing instrument that provides quick measurements used to identify changes or issues. Screening tools are the first instruments used during inspection.

service entrance

The point where electricity enters a building. A service entrance switchgear has metering equipment and devices for overcurrent protection and electrical control.

shaft

The rotating part of a motor that transmits torque to the load. The shaft turns loads such as pumps and fans.

shaft imbalance

A condition in which a rotating part rotates around a point other than its center. Shaft imbalance can never be completely eliminated, but it can cause mechanical issues if it is out of normal range.

shutdown inspections

Maintenance and testing tasks that must take place when a motor or system is not operating. Shutdown inspections generally concentrate on the motor and load of a motor drive system.

shutdowns

A period of time during which a machine or system is de-energized and not operating. Shutdowns interrupt production, but they are necessary to perform certain inspection and maintenance tasks.

single phasing

A condition in which one of the phases of a three-phase motor does not conduct electricity. Single phasing leads to 14% of all motor failures.

single-phase

1Φ. Alternating current power that consists of only one voltage. Single-phase power is typically used for simple applications like lighting and heating.

speed

The rate at which an object travels in a given period of time. In motors, speed reflects rotational movement and is measured in revolutions per minute (rpm).

stator

The stationary part of a motor. The stator houses the motor's rotor and windings.

switchgear

A freestanding assembly of electrical panels with metering equipment, overcurrent devices, and other protective devices. Switchgears receive power from the utility mains at the service entrance and distribute it to smaller circuits downstream.

symbols

A sign or mark that represents something else. Symbols are often used to represent components in diagrams.

thermal signature

The specific temperatures produced by a component. Thermal signatures can be used to identify abnormal temperature conditions.

three-phase

3Φ. Alternating current power that consists of three overlapping voltages. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.

threshold

A limit at which a given parameter is no longer within tolerance. Thresholds identify readings as acceptable or unacceptable.

tiered maintenance

A method of using a smaller group of people to develop maintenance tasks that are carried out by a larger workforce. In tiered maintenance, the smaller group also analyzes the data gathered.

tolerance

The allowable range of variation for a specific measurement. Tolerance sets the boundaries used to determine whether a measurement is acceptable or problematic.

torque

A force that produces rotation. Torque is measured in pound-feet (lb-ft.) in the English system and newton-meters (N-m) in the metric system.

transients

A momentary surge of power that causes a circuit to experience extremely high voltages for a short period of time. Transients can damage motors and other electrical devices.

trends

A general direction in which something is developing. Trends indicate changes in data over time.

troubleshoot

To systematically eliminate the various components of a system, circuit, or process from consideration in order to locate a malfunctioning part. Troubleshooting problems after system failure is considered reactive maintenance.

unbalance

A condition in which the phases of three-phase power differ in current or voltage magnitude or do not have a phase displacement of 120 degrees. Unbalance is expressed as a percentage.

unplanned downtime

An unexpected stop in production due to maintenance, mechanical failure, or other processing problems. Unplanned downtime can lead to safety problems and production losses.

variable frequency drive

VFD. A device that converts incoming 60 Hz AC power into other desired frequencies. Variable frequency drives can be used to control the speed of AC motors.

variable torque load

VT load. A load that requires different amounts of torque and horsepower at different speeds. Variable torque loads require torque and horsepower to increase as speed increases.

VFD

Variable frequency drive. A device that converts incoming 60 Hz AC power into other desired frequencies. VFDs can be used to control the speed of AC motors.

vibration

A rapid, continuous, repetitive motion in a machine or other structure. Vibration can negatively affect mechanical operations.

vibration meters

A screening tool that takes basic vibration measurements. Vibration meters determine whether or not problematic vibration is occurring.

vibration testers

A diagnostic tool that indicates the location, severity, and frequency of vibration in a mechanical component. Vibration testers use sensors to measure machine vibration in three different directions.

voltage

The electrical force or pressure that causes current to flow in a circuit. Voltage is measured in volts (V) and is also called electromotive force.

waveform

The shape of the wave produced by an electrical signal. A waveform's shape depends on the method used to produce the current.

windings

Wire wrapped around a core or into a coil that is used to conduct current. Windings create the magnetic field in a motor that makes the motor work.

wye

A connection of three conductors in which one end of each conductor is connected to a common central point. Wye connections are used in three-phase power systems.