Disturbance types

Power disturbances can have their source in either the utility or customer wiring system and/or equipment. These disturbances can be classified into categories that can vary in effect, duration and intensity. The chart below lists the most common categories of disturbances, their causes and some potential solutions.

Disturbance type Description Possible causes Symptoms/Effects Potential solutions
Power Outage Total interruption of electrical supply:

Momentary outages last 0.5 cycles – 3 seconds.

Temporary outages last from 3 seconds to 1 minute.

Long-term outages last longer than 1 minute.
Accidents, acts of nature, etc. which require the proper operation of utility equipment (fuses, reclosers, etc.).

Internal short circuits requiring the proper operation of a customer's breakers and fuses.

System shutdown

Loss of computer/ controller memory

Hardware damage

Product loss or damage
Uninterruptible Power Supply (UPS)
Transient (Surge) A subcycle disturbance in the AC waveform, evidenced by a sharp, brief discontinuity of the waveform. Surges are caused by storms (lightning), operation of utility fuses, reclosers and breakers, turning on or off large equipment and capacitor switching (customer and utility). Computer lock-up, processing errors and data loss.

Burned circuit boards, electrical insulation damage and equipment damage.
Surge protectors

Uninterruptible Power Supplies with built in surge suppression

Isolation transformers

Constant voltage transformer

Line reactors
Sag / Swell Any short-term (0.5 cycles – 1 minute) decrease (sag) or increase (swell) in voltage. Sags account for up to 87% of all power disturbances (according to a Bell Labs study). Major equipment shut-down and/or restart.

Short circuits

Utility equipment failure or utility switching.
Memory loss and data errors.

Equipment shutdown

Flickering lights

Motors stalling or stopping and decreased motor life.
Uninterruptible Power Supply

Constant voltage transformers

Voltage regulators

Power electronic sag correctors
Noise An unwanted high-frequency electrical signal that alters the normal voltage pattern (sine wave). Interference from radio or TV transmission.

Operation of electronic equipment.
Lock-up of sensitive equipment.

Data loss and processing errors.

Distorted audio and video reception.
Uninterruptible Power Supply

Isolation transformers

Power line filters
Harmonic Distortion The alteration of the normal voltage pattern (sine wave) due to equipment generating frequencies other than the standard 60 cycles per second. Electronic ballasts and other non-linear loads like switch-mode power supplies and variable frequency drives. Overheating of electrical equipment and wiring.

Decreased motor performance.

Improper operation of breakers, relays or fuses.
Harmonic filters

Isolation transformers

Improved wiring and grounding

Isolated loads

Line reactors
Undervoltage/ Overvoltage Any long-term change lasting more than a minute, below or above normal voltage. Overloaded wiring or equipment.

Large load swings or improper transformer settings.

Undersized wiring and faulty or poor electrical connections.
Dim or bright lights

Equipment shutdown

Overheating of motors or lights

Reduced efficiency or life of electrical equipment.
Uninterruptible Power Supply

Constant voltage transformers

Verify electrical connections and wiring

Relocate equipment

Reduced voltage motor starters and voltage ride-through equipment