Power Quality

Power quality…what it is, and how voltage regulators can help.

Power quality problems come in all sorts of shapes and sizes.

Commonly, power problems are defined as spikes, surges, sags, brownouts, outages and harmonics.

Definitions of terms

From the start, it must be stated that the term utility power problems is a term used to classify power problems, because AC power comes from utility companies. Actually, a very small percentage of the power problems experienced can be laid at the door of the utility company. In North America, the power that is supplied from the power lines to a facility is generally the cleanest power in the world. Normally, facilities only begin to experience power problems once the power is used inside the building.

The most common type of power problem is:

Auto Reclosures

When current exceeding the capabilities of the system are detected, power is removed temporarily to clear the problem. This may happen multiple times in a row. If the temporary removal of power does not help, then the wire/feeder must be isolated and de-energized until the problem can be discovered. This is usually done by patrolling crews.

These types of temporary faults occur all the time. A branch contacting the line in a high wind, an animal making contact with the wire and ground (ex. a squirrel sitting on a transformer and reaching up to contact the energized top of the transformer bushing), lightning, and tracking during a rain storm (i.e. surface wetness can conduct electricity temporarily shorting out an energized device) are all examples of occurrences that may cause a temporary fault.

The idea is that the system will react automatically and avoid damage and a lengthy outage for a problem that is very difficult to detect by observation, especially temporary situations. By de-energizing the system temporarily through an auto reclosure, these faults can clear themselves and prevent a device from failing due to overload.

Electrical Noise or Transients (spikes)

These disturbances are high frequency voltage spikes, typically in the microseconds range. Electrical Noise or Transients are magnified by poor grounding of plant equipment, and are caused by arcing, lightning hits, or use of certain types of equipment such as welders, elevators, copiers, etc. The next major power problem is:

Fluctuating Voltage (sags/surges)

Fluctuating voltages can also be termed voltage sags or surges. These types of disturbances are short-term under or over-voltage conditions that can last from one cycle to several cycles. This occurs when motors start up suddenly, drawing current from the line. They are also caused by lightning strikes, fault clearing, and from power factor switching. Another problem is:


Brownouts happen less frequently than transients or fluctuating voltage, but are much more noticeable when they occur. Brownouts seem to occur on those hot muggy days in the heat of summer when everyone has air conditioner turned on full blast.

Brownouts are defined as longer-term under-voltage conditions lasting from several seconds to several hours, depending on the cause. This type of disturbance can typically be measured with a standard digital or analog voltmeter. They are caused by faults, large changes in the load (such as air conditioners), long-term regulation problems, utility grid overload, or within the power grid.

With the increasing use of non-linear loads (such as personal computers, variable frequency drives, industrial DC power supplies, etc.) comes the very real problem of:


If load is attached to the utility and distorts the input line currents, as all non-linear loads do, high frequency or harmonic currents are generated. These harmonic currents travel along the surface of conductors, cutting down the cross-sectional area.

Because the resistance has increased, the power dissipated in the conductor goes up. The net effect is a fire hazard, because conductors are not sized for harmonic currents.

The main culprits for this deadly power problem are switch mode power supplies (which are installed in virtually every computer), variable speed equipment, and other non-linear power supplies.

Blackouts or Power Outages.

Power outages are a total interruption of electrical power. These problems are solved by additional means other than equipment installed inside a facility. The causes of power outages are over-loads, faults, storms, internal or external power distribution failure, or something as unfortunate as a squirrel getting caught in a transformer.