Snohomish County Public Utility District No. 1

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Customer Service (M-F 8a-5:30p): 425-783-1000

Electrical Disturbances

An electrical disturbance is a type of distorted electricity. An initiating event will distort electricity by changing its shape or amount.

The effect of electrical disturbances on electronic equipment and ASDs ranges from frequent trips and process shutdowns to overheated wires in the motor control center, circuit breakers panel, and system motors, which can pose a fire hazard. However, the most common effect is upset — loss of timing/control sense or process controller lockups — which may not pose a physical threat, but can be costly.

Detailed below are the most common electrical disturbances that cause power quality problems and are found in the electrical system of a typical facility.

TermDefinition
Contributing Factors These are elements within the electrical system – such as faulty or overloaded electrical wiring – that enable or help an electrical disturbance to upset or damage equipment. Most contributing factors involve incorrect and sometimes unsafe wiring and grounding practices, or wiring and grounding not up to standards because the facility is old. It would be prudent to review relevant detailed grounding procedures addressed in the National Electrical Code. Other contributing factors include damaged or misapplied cables and inadequate shielding of electronic components and equipment.
Harmonic Distortion This is caused by the power supplies of certain electronic production machinery, solid-state phase converters, electronic adjustable-speed drives, and especially programmable controllers and computer based facility systems. Harmonic distortion can overheat service transformers, facility wiring, wiring in service panels, motors, and components in some electronic production equipment.

These are commonly caused by:
- Solid-state phase converters
- ASDs
- Large power supplies
- Computers, programmable controllers
- Electronic analyzers
- Electronic lighting
Interruption in electricity (also called momentary power outage) This can last anywhere from fractions of a second to hours. Caused by lightning, downed power lines, tripped circuit breakers, and blown fuses, interruptions disrupt most ASDs, electronic and computer-based facility controllers, and the memories of unprotected facility production devices.

These are commonly caused by:
- Lightning
- Tripped circuit breaker, blown fuse
- Downed power lines
Noise This can be transmitted either through the electrical system (conducted) or through the air (radiated). “Noise” means the type transmitted through the electrical system unless stated otherwise. Communication devices such as programmable controllers, telephones, facility appliances, electronic lighting, vacuum devices, light dimmers, and ASDs, among others can cause noise. Noise interferes with communication hardware and upsets some digital operated facility equipment, but typically does not damage them.

These are commonly caused by:
- Heating and cooling equipment
- ASDs
- Communications equipment, telephones
- Loose electrical connections
- Electronic lighting
- Building transformers
Overvoltage or Undervoltage Much more rare than sags or swells, these are increases or decreases in the normal voltage level that last for seconds or minutes. These disturbances generally indicate a problem with the building electrical system such as improperly adjusted service transformers.

These are commonly caused by:

Overvoltage:
- Improper wiring and grounding
- Improper voltage tap adjustment
- Defective building transformer
- Crossed power lines

Undervoltage:
- Improper wiring and grounding
- Improper voltage tape adjustment
- Defective building transformer
- Crossed power lines
Sag This is a short (less than a second) decrease in the normal voltage level (measurement of electricity). Motors starting, energizing large kVA loads, and routine utility activities can cause sags. Sags do not damage equipment, but can cause ASDs, computers or programmable controllers to restart or lockup, and can cause timing circuits to lose memory.

These are commonly caused by:
- Starting large motors, pumps, compressors, and fans that are part of facility production systems
- Environmental control machinery
- Turning on electric heaters
- Routine utility activities
- Inadequate wiring and/or connections
Swells This is a short (less than a second) increase in the normal voltage level. Mostly caused by motors stopping, swells generally do not upset or damage electrically operated systems but can initiate the failure of a stressed component in marginally rated electronic equipment.

These are commonly caused by:
- Stopping large motors associated with facility production and environmental control machinery
- Turning off large electric heaters
- Open or high impedance wiring and neutrals
Transients (also called surges or spikes) Distortions of electricity caused by lightning, motors starting, routine utility activities, and other electronic loads. These electrical disturbances can damage the components of ASDs, programmable process controllers, and interfere with other production equipment.

These are commonly caused by:
- large motor start/stop
- lightning
- switching lights on/off
- static discharge
- routine utility activities
- facility maintenance equipment i.e. welders, electric saws, etc.
- ASDs