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 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