Motor Drive Systems and Maintenance 347
Motor Drive Systems and Maintenance describes the major components found in motor drive systems and best practices for system maintenance. A motor drive system typically consists of a variable frequency drive and a three-phase AC motor used to power a driven unit. The motor connects to the driven unit through a drive train. Because there are many mechanical and electrical components, motor drive systems are prone to various faults that interrupt operation and lead to downtime. Following a proactive maintenance approach can be a very effective method of preventing and dealing with system faults.
Motor drive systems are used for many industrial applications. When operating motor drive systems, understanding how they work and how they can potentially fail is essential. In addition, understanding motor drive maintenance prepares users to operate machinery effectively, reducing downtime and manufacturing costs.
Number of Lessons 18
- Motor Drive Systems
- Variable Frequency Drives
- Three-Phase Motors
- Drive Trains
- Load Types
- Motor Drive System Components Review
- Motor Drive System Faults
- Troubleshooting and Maintenance
- Proactive Maintenance
- Inspection Measurements
- Testing Tools
- Measurement Tool Categories
- CAT Designations
- Proactive Maintenance and Measurements Review
- Inspection Routes and Frequency
- Operational and Shutdown Inspections
- Maintenance Teams
- Final Review
- Describe a typical motor drive system.
- Describe the components of a variable frequency drive.
- Identify major components of a three-phase AC motor.
- Identify different types of drive trains used in motor drive systems.
- Distinguish between constant torque, variable torque, and constant horsepower loads.
- Describe common faults that occur in motor drive systems.
- Distinguish between reactive and proactive maintenance approaches.
- Lists the steps for implementing a proactive maintenance program.
- Describe measurements for proactive maintenance inspections.
- Distinguish between different testing tool levels.
- Distinguish between the IEC’s four measurement categories.
- Distinguish between the IEC’s four measurement categories.
- Describe inspection routes and frequency for proactive maintenance.
- Contrast operational and shutdown inspections.
- Describe the responsibilities of various members of a proactive maintenance team.
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.
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.
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.
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.
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.
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.
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.
A grounded metal strip that serves as a common connection between several circuits. Bus bars are found in electrical boxes and distribution panels.
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.
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.
The measurement category used for single-phase receptacle-connected loads. CAT II installations include appliances, tools, and long branch circuits.
The measurement category used for three-phase distribution circuits. CAT III installations include hard-wired equipment and distribution panel devices.
The measurement category used for three-phase circuits at the mains. CAT IV installations include electric meters, primary overcurrent protection devices, and outdoor conductors.
A mechanical system consisting of a chain and toothed wheels called sprockets. Chain drives are used to transmit motion from one sprocket to another.
A series of linked metal rings used to transmit motion. Chains are designed to mesh with toothed wheels called sprockets.
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.
Able to act as a path for the movement of electricity. Conductive components form magnetic fields when energized.
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.
A maintenance instrument used to fix issues and faults. Corrective tools are used while systems are shut down.
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.
Consisting of people with a wide range of expertise. Cross-functional teams include people from a variety of departments within an organization.
The flow of electricity. Current strength is called amperage and is measured in amperes (A), also called amps.
Any type of information gathered about an application or process. Data is often in the form of values or numbers.
Direct current. Electricity that flows in one direction. DC does not reverse the direction of flow.
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.
A connection of three conductors that forms a triangular series circuit. Delta connections are used in three-phase power systems.
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.
A drawing that illustrates the parts or operation of something. Diagrams use pictures and symbols to represent components.
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.
DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.
A drive train system that uses a straight shaft to connect the motor immediately to the output device. Direct drives require precise, rigid alignment.
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.
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.
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.
The complete loss of performance in a component or a system. Failure can result from electrical and mechanical faults within a system.
A problematic condition that interferes with a component or system's ability to function as intended. Faults may lead to failure and safety risks.
A flat projection that protrudes from the bottom of a motor's housing. The foot of the motor rests or mounts on the foundation.
The flat surface upon which a motor sits. The motor's feet may simply rest on the foundation or be mounted to it.
The number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).
A force that resists motion between two objects that are in contact with each other. Friction generates heat and increases wear between components.
A mechanical system consisting of two or more gears. Gear drives make it possible to alter the output speed and torque of a motor.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The maintenance role responsible for dealing with mechanical faults. The Industrial Mechanic deals with overheating components, mysterious breaker trips, and recurring motor failures.
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.
Examination of a component or system to ensure that it is operating correctly. Inspection for proactive maintenance involves measuring and comparing various parameters.
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.
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.
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.
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.
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.
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.
Excessive clearance between mechanical components. Looseness can occur between rotating and/or stationary parts.
The application of lubricants, such as grease or oil, to machines. Lubrication reduces friction and wear between mechanical components.
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.
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.
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.
A device that measures electricity. Meters may measure many different values, including voltage and current.
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.
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.
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.
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.
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.
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.
An electrical testing instrument that produces a visual representation of a voltage or current waveform. Oscilloscopes are also called scopemeters.
The electrical current sent from one device to another. The output signal produced by the inverter provides voltage to the motor.
A component that protects circuits from excess current flow to prevent overheating and fires. Overcurrent devices include fuses and circuit breakers.
A state in which the level of current exceeds the recommended level for a device or circuit. Overloading can cause overheating and equipment damage.
The greatest magnitude of a waveform. Peaks can be positive or negative.
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.
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.
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.
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.
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.
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.
A metal ring that houses the steel balls in a bearing. Races have grooves along which the balls roll.
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.
A device into which an electrical conductor can be plugged. Receptacles include common wall outlets.
A device used in an electrical circuit to convert AC power to DC power. Rectifiers allow electrical current to flow in only one direction.
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.
Replacing the windings in an electric motor. Rewinding is the responsibility of the Industrial Electrician.
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.
The rotating part of a motor. The rotor connects to an output shaft that drives the load.
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.
An electrical testing instrument that produces a visual representation of a voltage or current waveform. Scopemeters are also called oscilloscopes.
A testing instrument that provides quick measurements used to identify changes or issues. Screening tools are the first instruments used during inspection.
The point where electricity enters a building. A service entrance switchgear has metering equipment and devices for overcurrent protection and electrical control.
The rotating part of a motor that transmits torque to the load. The shaft turns loads such as pumps and fans.
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.
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.
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.
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.
1Φ. Alternating current power that consists of only one voltage. Single-phase power is typically used for simple applications like lighting and heating.
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).
The stationary part of a motor. The stator houses the motor's rotor and windings.
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.
A sign or mark that represents something else. Symbols are often used to represent components in diagrams.
The specific temperatures produced by a component. Thermal signatures can be used to identify abnormal temperature conditions.
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.
A limit at which a given parameter is no longer within tolerance. Thresholds identify readings as acceptable or unacceptable.
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.
The allowable range of variation for a specific measurement. Tolerance sets the boundaries used to determine whether a measurement is acceptable or problematic.
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.
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.
A general direction in which something is developing. Trends indicate changes in data over time.
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.
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.
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.
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.
A rapid, continuous, repetitive motion in a machine or other structure. Vibration can negatively affect mechanical operations.
A screening tool that takes basic vibration measurements. Vibration meters determine whether or not problematic vibration is occurring.
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.
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.
The shape of the wave produced by an electrical signal. A waveform's shape depends on the method used to produce the current.
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.
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.
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.
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.