A few simple steps to protect your electric motors may save you thousands of dollars.
Sometimes electrical disturbances occur on the electrical grid that are beyond Idaho Power’s control and cannot be prevented. However, electrical protection systems can reduce the likelihood of damage to your electric motors. Disturbances commonly found on power systems include:
- Transients (i.e., spikes from lightning and nearby equipment switching))
- Harmonic distortion (from variable frequency drives)
- Voltage sags and swells
- Low voltage and over voltage (due to loads switching on and off)
- Interruptions and outages
Motors are often damaged by overheating and caused by:
- Overloading the motor
- Poor air circulation, heating from adjacent motors, sun and elevation effects
- Low voltage
Over voltage can cause the breakdown of winding insulation.
A circuit breaker serves two purposes:
- Isolates faulted electrical equipment from the upstream electrical system
- Provides a means of disconnecting the electrical equipment for service
A motor starter consists of:
- Contactor: Connects/disconnects power based on the control system
- Overload relay: Opens the contactor when the motor current gets too high
The control system is either manual and/or automatic:
- Start and stop buttons and a rotary switch
- Stop button opens the motor contactor
- Start button closes contactor with rotary switch in the “hand” position
Voltage Monitor Relay
A voltage monitor relay connected to the supply voltage will automatically open the motor contactor when:
- Over or under voltage of any phase occurs
- Excessive voltage imbalance between phases occurs
- A phase is deenergized or the phases are reversed
Most voltage monitor relays include a time-delay feature that can allow the motor to restart when conditions on the power system have returned to normal.
Surge Protective Device (SPD)
The SPD helps protect the motor/electrical equipment from large voltage transients (i.e., lightning strikes).
Fluctuations below the limits of a SPD can damage motors. A surge capacitor absorbs energy from a voltage transient to help protect the motor.
A licensed electrician or contractor is your best resource for assistance with your equipment. Don’t have one? Here are some recommendations when looking to work with an electrician or contractor:
- Ask for referrals
- Check credentials
- Interview electrician or contractors and ask questions
- Contact references
- Inquire about insurance
- Get it in writing
- Keep records
- Hold final payment until job is completed
We recommend you have your electrician/contractor verify the recommended motor protection is in good working condition and do annual maintenance to your electrical equipment.
Find links to articles and resources related to motor protection below.
Find links to several guides and tip sheets associated with motors and VFDs on this Department of Energy site.
Monitor Induction Motors to Drive Power Quality
This is the first of two articles on the Plant Engineering site re: the poly-phase induction motor.
Irrigation Training and Research Center at Cal-Poly
Review this article of motors and drives, including problems associated with different power quality issues.
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