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Understanding Power Disturbances: Power Quality Terms Guide

Power Disturbances Guide

Power and energy management are important for many reasons. Power quality can determine equipment life, efficiency in the workplace and how costly energy bills are. For these reasons, it is crucial for facilities to understand power disturbances and the impact they have on productivity and the health of an organization’s equipment. There are a lot of factors that are involved in power quality, but that doesn’t mean power management has to be difficult for end users.

Following is a quick reference guide of some power disturbance terms and their causes and solutions.


Transients are short power disturbances with high magnitudes of current and voltage. Usually these disturbances range from 50 nanoseconds to 50 milliseconds. Although these disturbances last a very short amount of time, they can reach thousands of volts and amps. These bursts of energy contain high voltages that can be very damaging to low voltage systems.

Transients are most commonly caused by lighting strikes, which are more common than you may realize. According to the MPSS Institute of Occupational Safety and Health, lighting strikes Earth 100 times a second, meaning facilities should always consider this natural event a threat.

Although Transients are extremely short disturbances, they can do a lot of damage. Transients can cause lighting failure and damage to motors and other electrical equipment. Properly installed Transient Surge Suppressors can help avoid the effects of Transients.


Overvoltage is when a voltage level exceeds the normal level. In order to qualify as an Overvoltage, the voltage level has to increase 110% – 120% at rates longer than a minute.

Overvoltage is caused a few different ways. High distribution voltage due to incorrect settings on transformers, switching off large loads, or over-correction of voltage drops can all be determining factors. Overvoltage primarily affects electrical equipment. Consequences include equipment malfunction, failure, reduced operational life and overheating. This disturbance is most commonly corrected by making adjustment to transformers and installing voltage regulators.



Undervoltage is a decrease in voltage. Usually, the decrease is 80% – 90% of the normal and the time periods last greater than one minute. Undervoltage is caused by heavy loaded circuits, heavy loads turning on and capacitor banks switching off.

Similar to other disturbances, Undervoltage causes equipment malfunction, overheating and shorter operational life. These issues can be solved by installing Voltage Regulators.


Frequency Variation

Frequency variation, as the name suggests, is the change in power system frequency from the normal range. This disturbance is usually a result of unstable power sources or emergency generators.

The effects of Frequency Variation can include equipment shutting down or malfunctioning or data loss. To solve the problems Frequency Variations cause, the power sources causing the issues need to be fixed and replaced, if required.



To work properly, voltage and current waveforms need to be perfect sinusoids. When a wave strays from the perfect sinusoid, harmful harmonics form. If power systems are designed to handle harmonics, then there aren’t many issues.

Harmonics are the result of currents that have waveforms that do not match the one of the supply voltage. These different waveforms can stem from lighting and office equipment, heavy machinery, etc.


Voltage Swells

Voltage Swells are short increases in voltage. These swells are typically 110% – 180% of the normal level. Voltage Swells are most commonly caused by system fault conditions and when large loads turn off.

Voltage Swells can be very harmful to a facility’s equipment. Damaged power supplies, hardware failure and shutdown are common results of voltage swells. In order to correct these issues, facilities should install Uninterruptible Power Supplies, Constant Voltage Transformers and Dynamic Voltage Restorers.


Voltage Sags

Voltage Sag is caused when a voltage level decreases between 10% – 90% of the normal range. This type of disturbance in common in power management because it is mainly caused by bad weather and utility equipment. Voltage Sag can also be caused by switching heavy loads on/off.

Electrical equipment takes the biggest hit from Voltage Sags. This disturbance can shutdown systems and decrease efficiency and the life cycle of equipment. Voltage Sag can be solved a few different ways. In order to prevent Voltage Sags, facilities can incorporate Uninterruptible Power Supplies to protect equipment.


Voltage Unbalance

Voltage Unbalance is a voltage variation in a power system where the voltage magnitudes or the phase angle difference between them aren’t equal.

Voltage Unbalance is most commonly caused by internal factors in a facility, such as facility loads that are different than others. The most common problem caused by Voltage Unbalance is motor damage from overheating. Solutions for this type of disturbance include active filters and connecting single phase loads on all three phases.


Voltage Interruptions

Voltage Interruption is when a voltage supply level is interrupted, causing the level to drop for a certain duration.

Voltage Interruptions are usually caused by damage to electrical supplies. Damages could be the result of weather, animals, falling trees, etc. The result of these damages can include equipment malfunction, which can lead to production downtime and loss of resources.

Please contact us for more information on how we can help achieve your energy management goals.




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