The many forms of power disturbances

April 17, 2012

Sophisticated semiconductor technologies and digitally controlled industrial processes are the backbone of today’s economy. As the capabilities of these technologies expand, so does their level of complexity, which in turn increases their sensitivity to even the slightest power quality problems.

When lights turn off unexpectedly and computers shut down, it is obvious that a power interruption or outage is to blame. The power will eventually turn back on and so will your lights and computers. While the immediate visible effect of the power disturbance may be easily reversed, damage to the sensitive electrical circuits from the sudden loss in power might go undetected for a long time. Two of the most often cited consequences of frequent exposure to power quality problems are data corruption and reduced equipment lifetime, both of which are often not apparent immediately but only over time as subsequent events intensify the damage.

Many power problems originate outside of the facility. Causes range from lightning to power grid switching operations. However, on/off switching of heavy machinery or HVAC equipment, faulty distribution components or even static electricity can create many power quality issues inside the facility, too.

Since many power problems are not as easily diagnosed as power interruptions, the following table provides a starting point to understand the most common power disturbances, what to look out for, where they originate and how to mitigate the problem or avoid undesirable effects. In general, it is always a good idea to check the electrical grounding and bonding first, since grounding issues can lead to a variety of seemingly mysterious problems.

Disturbances Causes Effects Prevention
(Surge, Spike, Impulse)

Fast voltage spike
· Lightning

· Electrostatic discharge

· Switching of inductive loads

· Poor grounding

· Utility fault clearing
· Corruption or loss of data

· Physical damage to equipment or reduced product life

· System halts

· Proper grounding
Interruptions (Outage)
Complete loss of supply voltage or load current
Instantaneous: 0.5 to 30 cycles
Momentary: 30 cycles to 2 s
Temporary: 2 s to 2 min
Sustained: > 2 min
· Electrical grid damages

· Load changes

· Utility faults

· Circuit breaker tripping

· Component failures

· Automatic circuit reclosers (at utility level)
· Corruption or loss of data

· Equipment damage or reduce product life

· System shutdown
· Regular equipment maintenance to reduce potential internal sources


· Redundant systems
Sags/Undervoltage (Brownout)
Drop in voltage below 90%
Sag: 0.5 cycle to 1 min
Undervoltage: > 1 min
· Startup loads

· Utility faults

· Load changes

· Equipment faults

· Configuration issues
· Corruption or loss of data

· Equipment shutdown

· Equipment overheating
· Power conditioner


· Adding dedicated circuits for large startup loads or alternative power sources

· Use of adjustable speed drives (ASD)
Noise/ Electromagnetic Interference (EMI)/ Radio Frequency Interference (RFI)
Unwanted radiated electromagnetic field or conducted voltage or current
· Radio transmitters

· Faulty equipment

· Ineffective grounding

· Proximity to EMI/RFI source
· System stop

· Data errors or loss

· Equipment malfunction or reduced component life

· Signal distortions
· Remove transmitters

· Reconfigure grounding

· Reduce proximity to EMI/RFI source

· Increase shielding

· Filters

· Isolation transformer

If you have a particular power quality problem or would like to learn more about appropriate prevention measures, please contact us at 208-772-8515.

Susann Ferrari 

Technical Writer, Protection Technology Group

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