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.

Power Outages | Transient (Surge)  | Sag or Swell | Noise | Harmonic Distortion | Undervoltage | Overvoltage

Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

Power Outage

Total interruption of electrical supply:

Momentary outages last from one-half second to 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) (PDF 35k)

 

Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

Transient (Surge)

A subcycle disturbance in the AC waveform, resulting in a sharp but brief increase in voltage

Surges are caused by storms (lightning), operation of utility fuses, reclosers and breakers

Internal causes are turning on or off large equipment and capacitor switching

Computer lock-up, processing errors and data loss

Burned circuit boards, electrical insulation damage and equipment damage

Surge protectors (PDF 428k)

Uninterruptible Power Supplies with built in surge suppression (PDF 35k)

Isolation transformers (PDF 32k)

Constant voltage transformer (PDF 34k)


Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

Sag / Swell

Any short-term (one-half cycle to 3 seconds) 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 (PDF 35k)

Constant voltage transformers (PDF 34k)

Voltage regulators


Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

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 (PDF 35k)

Isolation transformers (PDF 32k)

Power line filters


Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

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 (PDF 32k)

Improved wiring and grounding

Isolated loads

Line reactors


Disturbance Type

Description

Possible Causes

Symptoms/Effects

Potential Solutions

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 (PDF 35k)

Constant voltage transformers (PDF 34k)

Verify electrical connections and wiring

Relocate equipment

Reduced voltage motor starters and voltage ride-through equipment