EFFECTS OF VOLTAGE FLUCTUATIONS ON ELECTRICAL EQUIPMENT

Wednesday, September 14, 2011

The undesirable effects of voltage fluctuations on electrical and electronic equipment are briefly described here. This post aims to give an overview of these effects, which are more obvious with light sources. Nonetheless, other sophisticated devices subjected to voltage fluctuations could malfunction and have reduced efficiency, which are costly in terms of downtime and rejects.

Most electrical and electronic equipment are designed to operate properly and within their specifications if the voltage supply varies within ±10% of nominal. However, some sensitive devices require stable incoming voltage for them to perform accurately, such as computers, medical laboratories, telecommunications and test equipment.

Moreover, the effects of voltage fluctuations on susceptible equipment are discussed below.

A. Light Sources

Voltage fluctuations are usually evident in nuisance variations of the light output from incandescent and discharge lighting sources. This is commonly known as flicker, which is a subjective visual impression of unsteadiness of a light’s flux, whose luminance fluctuates with time.

A rapid regular voltage change of 0.5% with a frequency of about 6 to 8 Hz can result to observable flicker in the light output of an incandescent lamp. Generally, flicker affects our brain reaction and impairs vision, leading to discomfort and deterioration in work quality. Worst case, it can even result to accidents as it affects the ergonomics of the production environment by causing personnel fatigue and reduced concentration levels.

Light sources are sensitive to voltage supply changes as the luminous flux is proportional to the applied voltage. In equation form:

Φ = VX

where:
Φ = luminous flux
V = applied voltage
X = exponent value depending on light source type

For incandescent, X is typically between 3.1-3.7. Meanwhile, X is lower at around 1.8 for fluorescent and discharge lamps. This is because incandescent lamps are more sensitive to voltage fluctuations than discharge lighting equipment.

B. Electro-heat Equipment

All heating equipment that are subjected to considerable levels of voltage fluctuation will have lower operational efficiency. For example, an electric arc furnace would require a longer melt time as compared to when voltage supply is stable.

C. Electrical Machines

Synchronous Motors and Generators

Voltage fluctuations at the terminals of these electrical machines lead to the following:

  • Increase in losses
  • Premature wear of rotors
  • Changes in torque and power
  • Hunting

Induction Motors

For an induction motor, voltage fluctuations at the terminals can cause changes in torque and slip, which affect the production process. In the worst case, fluctuations could result to excessive vibration, reducing mechanical strength and shortening the motor service life.

D. Electrolyzers

The presence of voltage fluctuations can reduce both the useful life and the operational efficiency of an electrolyzer equipment. In addition, elements of the high-current supply line can become significantly degraded, thereby increasing maintenance and/or repair costs.

E. Static Rectifiers

The effect of voltage fluctuation in phase-controlled rectifiers with DC-side parameter control is a decrease in power factor and the generation of non-characteristic harmonics and interharmonics. In the case of drive braking in an inverter mode, it can result in commutation failure and damage to system components.

F. Other Devices

Furthermore, other effects of voltage fluctuations include:

  • Computerized or automatic machines to produce defective parts
  • Unwanted triggering of UPS units to switch to battery 
  • Security system malfunction
  • Testing equipment to give inaccurate data
  • Nuisance tripping due to misoperation of relays and contactors
  • Inconsistency of motor speed

References:
Hanzelka, Z. and Bien, A. (2006). Voltage Disturbances - Flicker
IEEE 1159-1995. Recommended Practice For Monitoring Electric Power Quality

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I am an Electrical Engineer with a Masters Degree in Business Administration. My interest is in Power Quality, Diagnostic Testing and Protective Relaying. I have been working in an electric distribution utility for more than a decade. I handle PQ studies, power system analysis, diagnostic testing, protective relaying and capital budgeting for company projects.