Electrical Maintenance for Motor Drive Systems 348

“Electrical Maintenance for Motor Drive Systems” provides a comprehensive overview of the common power quality issues that occur in motor drive systems and the methods used to inspect and resolve these issues. Electrical maintenance involves inspecting input power, DC bus output, leakage current, and insulation resistance as well as checking for overloading, single phasing, electrical unbalance, transients, harmonics, and thermal abnormalities.

Many industrial applications rely on motor drive systems to power output devices. Motor drive systems consist of complex electrical components and require sufficient power quality to function correctly. Power issues in any system component can cause the entire system to malfunction and fail, leading to lost production time and increased costs. This class prepares users to effectively operate and maintain motor drive systems to minimize downtime and economic losses.

Class Details

Class Name:
Electrical Maintenance for Motor Drive Systems 348
Version:
2.0
Difficulty:
Advanced
Number of Lessons:
23

Class Outline

  • Power Quality
  • Electrical Testing Tools
  • Input Power Measurements
  • Diagnosing Input Power Problems
  • Motor Overloading
  • Single Phasing
  • Input and Motor Faults Review
  • Electrical Unbalance
  • Diagnosing Input Unbalance
  • Diagnosing Output Unbalance
  • DC Bus Output
  • Unbalance and Output Signal Review
  • Transients
  • Diagnosing Transients
  • Harmonics
  • Diagnosing Harmonics
  • Transients and Harmonics Review
  • Leakage Current and Insulation Breakdown
  • Insulation Inspection
  • Insulation Resistance Testing Methods
  • Thermal Inspection
  • Thermal Abnormalities
  • Insulation and Thermal Inspection Review

Objectives

  • Describe power quality in motor drive systems.
  • Describe common electrical testing tools used with motor drive systems.
  • Describe best practices for measuring input power in a motor drive system.
  • Describe input power inspection.
  • Describe motor overloading inspection.
  • Describe single phasing inspection.
  • Calculate electrical unbalance percentages.
  • Describe input unbalance inspection.
  • Describe output unbalance inspection.
  • Describe DC bus output inspection.
  • Describe transients.
  • Describe transient inspection.
  • Calculate harmonic values.
  • Describe harmonic inspection.
  • Describe leakage current.
  • Describe insulation inspection.
  • Distinguish between common insulation resistance testing methods.
  • Describe thermal inspection.
  • Describe common causes of thermal abnormalities in motor drive systems.

Job Roles

Certifications

Glossary

Vocabulary Term Definition
A Ampere. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.
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.
AC coupling An input option on an oscilloscope that displays only AC signals. The AC coupling option provides a more detailed look at the ripple in a waveform.
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.
ammeter A device that measures amperes in an electrical circuit. Ammeters that have built-in current clamps are called clamp meters.
amperes A. A unit of measurement that indicates the amount of current flowing in a circuit. Amperes are also called amps.
amps A. A unit of measurement that indicates the amount of current flowing in a circuit. Amps are also called amperes.
arcing Overheating that occurs when electricity flows from one surface to another. Arcing is dangerous because it can cause injuries to operators and damage to equipment.
audible Able to be heard by the human ear. Audible noise in a motor drive system may increase if the system experiences harmonics.
average A number expressing the central or expected value within a set of values. The average of a set of values is equal to the sum of the values divided by the number of values in the set.
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.
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.
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.
capacity The amount of electricity that a conductor can carry safely. Capacity indicates how much current can flow through a device without it overheating.
circuit breaker A safety device that detects overcurrent in a circuit. Circuit breakers open circuits to prevent overloading and overheating.
clamp meter An ammeter or multimeter that includes a built-in current clamp. Clamp meters can be used instead of DMMs and clamp accessories to measure current.
cold spots A point within a system or component at which the temperature is lower than the surrounding temperature. Cold spots may be caused by unbalance and other electrical faults.
conductors A material or element that allows electricity to flow freely. Conductors are used to connect electrical components.
contactors A type of relay that uses a small control current to operate contacts and energize or de-energize a load. Contactors are used in motor starters.
contacts Conductive points in a circuit that allow current to flow when they are connected, or closed. Contacts that are open prevent electricity from flowing.
contaminants Damaging foreign material, such as dirt or debris, that causes wear to machine components. Contaminants can lead to insulation breakdown.
current The flow of electricity. Current strength is called amperage and is measured in amperes (A), also called amps.
current clamp An accessory device used with electrical meters to measure current. A current clamp closes around a conductor to quickly measure current.
current draw The amount of current a load demands from its power source. Current draw depends on the amount of resistance the load provides.
current unbalance A condition in which the phases of three-phase power differ in current magnitude. Current unbalance is often caused by voltage unbalance.
cycle The time it takes for alternating current to flow, pause, reverse direction, and then pause again. One cycle is considered to be one complete 360° waveform.
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.
DC coupling An input option on an oscilloscope that displays both DC and AC signals. The DC coupling option measures ripple and the absolute voltage of DC.
delta A connection of three conductors that forms a triangular series circuit. Delta connections are used in three-phase power systems.
digital multimeter DMM. A device that can measure voltage, current, and resistance. Digital multimeters are the most versatile and common meters used today for electrical maintenance.
diode An electronic device with two terminals that allows electric current to flow in only one direction. Diodes are used by VFD rectifiers to convert AC power to DC power.
direct current DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.
distortion The deformation of an electrical signal's waveform. Distortion may be caused by harmonics.
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.
distribution system An electrical circuit that provides power from the utility to specific end destinations. The distribution system sends power along the mains to the service entrance of a building.
DMM Digital multimeter. A device that can measure voltage, current, and resistance. DMMs are the most versatile and common meters used today for electrical maintenance.
downstream Moving in a direction away from the power supply in an electrical circuit. Power quality tends to suffer as it moves downstream.
downtime A period of time when production stops, often due to mechanical failure or maintenance needs. Downtime can be planned or unplanned.
efficiency losses The reduction of energy due to natural effects, which cause the energy output to be less than energy input. Efficiency losses can be minimized with good design, but no system is 100% efficient.
electric shock The flow of electricity through the body. Electric shock can be fatal.
enclosure The metal frame or case of an electrical device such as a motor or drive. The enclosure protects the wiring inside the device.
feed A circuit conductor that provides power from a power supply to one or more branch circuits. One feed may serve several loads, and changing conditions on one load can affect other loads on the feed.
filters Electronic devices designed to keep any internally generated noise within the electronic equipment from affecting adjacent equipment via the shared AC power lines. Filters often experience leakage current.
first harmonic The waveform provided by the power supply. The first harmonic is also known as the fundamental.
flashover An electrical explosion of heat and light that occurs when a short circuit forms between exposed conductors. Flashover may be caused by voltage transients.
flat-topping A disturbance in a waveform that causes the peak to become overly rounded and resemble a flat line at the top. Flat-topping in the mains' supply can cause low DC bus voltages.
frequency The number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).
full load amps FLA. The maximum current a motor uses when producing full torque and horsepower. The full load amps value can be multiplied by the service factor to approximate the motor's service factor amps.
fundamental The waveform provided by the power supply. The fundamental is also known as the first harmonic.
ground A source that absorbs stray electrical charge. Ground may refer to the earth or another large conducting body, such as a motor housing, that serves as a source of zero electrical potential.
ground fault circuit interrupters GFCIs. A type of switch that is disabled if the electricity comes into contact with water. Ground fault circuit interrupters should be used whenever there is a risk of electricity contacting water.
grounding conductor The wire that provides a low-resistance path to ground for fault currents. Grounding conductors are usually bare copper or covered with green insulation.
harmonics An extraneous waveform superimposed over the fundamental waveform. Harmonics occur in groups and create distortion.
harmonics Extraneous waveforms superimposed over the fundamental waveform. Harmonics occur in groups and create distortion.
hertz Hz. A unit of measurement indicating the frequency of alternating current. One hertz is equal to one cycle per second.
hot spots A point within a system or component at which the temperature is higher than the surrounding temperature. Hot spots may be caused by high-resistance connections, unbalance, and other electrical faults.
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.
Hz hertz. A unit of measurement indicating the frequency of alternating current. One hertz is equal to one cycle per second.
IEEE 519-2014 A standard that lists the acceptable levels of distortion for harmonics. IEEE 519-2014 was created by the Institute of Electrical and Electronics Engineers (IEEE).
impedance The effective resistance to current flow in an AC circuit. Impedance should be the same in all phases of a motor.
induction motors An AC motor in which power is connected only to the stator. Induction motors are the most common motors used for industrial applications.
infrared IR. Invisible rays of light energy emitted by heated objects. Infrared light can be used to capture a visual representation of an object's thermal signature.
infrared cameras A thermal inspection device that uses infrared technology to produce a visual representation of temperature conditions. Infrared cameras are also called thermal imagers.
infrared thermometers A thermal inspection device that uses infrared technology to measure temperature. Infrared thermometers provide a numerical reading of an object's thermal signature.
Institute of Electrical and Electronics Engineers IEEE. An international organization that creates standards for working with electricity and electrical components. The Institute of Electrical and Electronics Engineers defines the acceptable levels for different harmonics in IEEE 519-2014.
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 tester 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.
intermittent Occurring at periodic intervals. Intermittent electrical issues can be monitored with the logging function of a PQA.
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.
jaws Movable parts that allow a device to open and close around an object. The jaws of a current clamp allow the clamp to close around conductors.
kilovolt kV. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. One kilovolt is equal to 1,000 volts.
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.
loads The opposition to an applied force, such as a weight or resistance. 'Loads' also refers to the devices a motor powers since they provide resistance to the motor.
local distribution system 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.
low-pass filter function A setting that allows low-frequency signals to pass through and blocks high-frequency signals. The low-pass filter function on an oscilloscope emulates a motor's impedance characteristics and filters the waveform to give a realistic reading of the effective voltage at the motor terminals.
magnitude The size of a wave. Magnitude is the highest positive point on the wave and the maximum positive value.
main disconnect switch A heavy, spring-loaded switch on an electrical 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.
maximum deviation The greatest existing degree of difference between a specific value and a set of values. Maximum deviation can be found by subtracting the specified value from the value furthest from it or subtracting the furthest value from the specified value.
mega-ohms MΩ. A unit of measurement that indicates the amount of electrical resistance in a circuit. One mega-ohm is equal to 1,000,000 ohms.
megger A device used to measure resistance in insulation. Meggers are also called megohmmeters.
megohmmeter A device used to measure resistance in insulation. Megohmmeters are also called meggers.
milliseconds One thousandth of a second. Transients last between a few milliseconds and a few nanoseconds.
motor disconnect A device used to control when power is delivered to a motor. The motor disconnect can be used to isolate the motor from the greater electrical circuit.
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 systems 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 starter An electrically operated switch that starts a motor when actuated. Motor starters provide the startup current for a motor.
multi-channel oscilloscopes An oscilloscope that can be used to measure multiple conductors at once. Multi-channel oscilloscopes are used to measure output unbalance.
nameplate A label attached to a device, such as a motor, that displays manufacturer-provided ratings and information. Nameplates include information such as voltage and current ratings and full load amps.
nanoseconds One billionth of a second. Transients last between a few milliseconds and a few nanoseconds.
neutral wire The conductor that returns power back to its source and completes a circuit. The neutral wire is usually covered with white insulation.
nominal values The specified operating level for an electrical variable. Nominal values determine the appropriate ranges for variables such as voltage, current, and frequency.
ohms Ω. A unit of measurement that indicates the amount of electrical resistance in a circuit. Ohms can be measured by megohmmeters.
optimization A systematic process of adjusting a device's operating conditions to maximize efficiency. Optimization helps prevent faults like electrical unbalance.
oscilloscope 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 of a VFD provides the voltage that the motor receives.
overcurrent A situation in which excess current flows in an electrical component. Overcurrent conditions are also called overloading conditions.
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.
peak The greatest magnitude of a waveform. Peaks can be positive or negative.
phase displacement The separation of the three phases in a three-phase system. The phase displacement should always be 120 degrees.
point-in-time data Information gathered at one instance by taking a single measurement. Point-in-time data reflect present conditions rather than long-term or intermittent conditions.
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.
power quality analyzer PQA. 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.
PQA Power quality analyzer. A testing tool that measures levels and characteristics of electrical power. A PQA can be installed in a system to act as a monitoring tool.
probes A device attached to an electrical testing instrument that uses a conductive tip to connect to an electrical component. Probes connect to conductors and terminals.
ramp voltage test A method of measuring insulation resistance by applying increasing voltages and taking several readings. A ramp voltage test typically takes five readings in a five-minute period.
readout A display that indicates the measurements taken by a testing tool. The readout may display measurements in numbers or in images.
real-time data Information gathered over a period of time by taking multiple measurements. Real-time data reflect long-term and intermittent conditions and allows for trending.
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.
reflections An unwanted electrical signal cast by an original electrical signal traveling in the opposite direction. Reflections may be whole or partial copies of the original waveform.
resistance The opposition to current flow. Resistance is measured in ohms (Ω).
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.
RMS Root mean square. The square root of the arithmetic mean of a set of values. The RMS indicates the effective average of the values.
root cause The true origin of a problem, as opposed to any resulting symptoms or effects. Identifying the root cause of a problem is an important aspect of troubleshooting and maintenance.
root mean square RMS. The square root of the arithmetic mean of a set of values. The root mean square indicates the effective average of the values.
sags A short decrease in voltage of more than 10% below the normal rated level. Sags last between one-half an AC cycle and one minute.
scopemeter An electrical testing instrument that produces a visual representation of a voltage or current waveform. Scopemeters are also called oscilloscopes.
service entrance The point where electricity enters a building. A service entrance switchgear has metering equipment and devices for overcurrent protection and electrical control.
service factor SF. The amount of additional load above a motor's rated horsepower that the motor can withstand for short periods of time. The service factor can be multiplied by the full load amps value to approximate the motor's service factor amps.
service factor amps SFA. The amount of current a motor will use when experiencing the amount of overload specified by the service factor. Service factor amps is approximately equal to full load amps multiplied by service factor.
short circuit A situation in which current takes a shorter, unintended path between two conductors. Short circuits cause excess current flow.
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.
spot insulation test A method of measuring insulation resistance by applying a voltage and taking a single reading. A spot insulation test typically takes one minute.
stator The stationary part of a motor. The stator houses the motor's rotor and windings.
subpanel An enclosed collection of electrical devices used to control electricity as it travels downstream to separate circuits and components. A subpanel contains devices such as switches, fuses, and circuit breakers.
superimposed Placed over or above something else. Harmonics are additional waveforms superimposed over an original, or fundamental, waveform.
surge arrestors A device that protects electrical circuits and equipment from transients by regulating voltage on the line. Surge arrestors react quickly to high-voltage conditions to protect against damages.
switching electronic loads A power supply component that includes built-in devices that turn on and off to convert AC to DC. Switching electronic loads can cause transients within a building.
terminals A connecting point in an electrical circuit or device to which a wire can be attached to connect a component. Electrical measurements are often taken at terminals.
THD Total harmonic distortion. The combined effects of a fundamental's harmonics, from the second to the 50th. THD is expressed as a percentage.
thermal imagers A thermal inspection device that uses infrared technology to produce a visual representation of temperature conditions. Thermal imagers are also called infrared cameras.
thermal signatures 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.
time-resistance test A method of measuring insulation resistance by applying a constant voltage and taking several readings. A time-resistance test typically takes readings every 10 seconds during the first minute of testing and then takes a reading every minute for 9 more minutes.
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.
total harmonic distortion THD. The combined effects of a fundamental's harmonics, from the second to the 50th. Total harmonic distortion is expressed as a percentage.
transformer An electromagnetic device that increases and decreases the voltage of electrical power. Transformers often increase voltage for power lines and then decrease voltage for the power to enter a facility.
transient 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.
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.
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.
V Volt. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as electromotive force.
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.
vibration A rapid, continuous, repetitive motion in a machine or other structure. Vibration can negatively affect mechanical operations.
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.
voltage drop A decrease in voltage that occurs as electricity passes through resistance. Voltage drops occur as voltage travels through a circuit.
voltage notches A disturbance in a voltage that appears as an indentation in the normal waveform. Voltage notches last for less than one-half of an AC signal's cycle.
voltage suppression devices An electronic component used to protect circuits and electrical systems from transient voltages. Voltage suppression devices work by weakening or diverting transients.
voltage unbalance A condition in which the phases of three-phase power differ in voltage magnitude. Voltage unbalance often causes current unbalance.
volts V. A unit of measurement that indicates the amount of electrical force or pressure in a circuit. Volts measure voltage, which is also known as 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.
wear The gradual removal of material on a surface caused by contact and friction. Wear is both a cause and an effect of faults in motor drive systems.
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.