Power Quality Issues


Power Quality Issues

Quality of the power is decided by the end users. If the power equipment works satisfactorily for given supply then power is at good quality. If it doesn’t functions well or fails to work, then power quality is bad. Reasons for bad power quality or power quality issues are discussed below.

  • Flicker :

Flickers are short duration voltage changes, resulting from switching, short circuits and load changing. The permissible magnitude of light flicker is regulated by International Standards, based on perception criteria. Excessive flicker can cause migraine and is responsible for some instances of the so-called ‘sick building syndrome’.

  • Voltage sags and swells :

Voltage swells occur due to transfer of loads from one source to another, sudden rejection and application loads.Flickering is a low frequency problem that occurs mainly at starting or low voltage conditions. Flickering is due to low voltages or frequency that can be observed by the human eye. Voltage sags and swells results in malfunction of equipments, loss of efficiency of motors, insulation failures, fluctuation of light illumination, tripping of relays and contractors, etc.

Voltage sag or dip is the decrease of voltage levels from nominal values at power frequency. It lasts from about half of a cycle to several seconds. Low voltages are due to several factors like electrical motors, arc furnaces, utility problems, flickering etc.

  • Harmonics :

Harmonic nature of voltage and currents is the deviation from the original or pure sine waves. Harmonic frequencies are integral multiples of fundamental frequency and are very common in electric power systems. Order of harmonics is 1th, 3rd, 5th, 7th, 9th.

The fundamental waveform is superimposed by odd harmonics, which results in the distorted wave forms. These harmonics have serious effects on various electrical equipments such as overheating of cables and equipments, interference with communication lines, errors while indicating electrical parameters, probability to produce resonant conditions, etc.

Major nonlinear loads produce odd harmonics and even harmonics are produced due to uneven operations of the electrical devices like transformer magnetizing currents contains the even harmonic components.

  • Grounding :

Earthing of installations and equipment is an issue that crosses the boundaries of the various disciplines involved in the construction and equipping of a modern commercial or industrial building.

LighSystem must protect electronics by providing a low impedancepath to interconnect equipment. Proper cable routing, zoningand shielding are important aspects and serve the purpose ofpreventing sources of disturbance from interfering with the operation of electrical equipment.

  • Electrical Transients :

These are also sometimes called as spikes, surges, power pulses, etc. These occur due to atmospheric disturbances like lighting and solar flares, fault current interruptions, switching the loads, switching capacitor banks, switching power lines, etc.

Some of the devices are designed with transients in mind but most of the devices can handle few transients depends on severity of the transient and life of equipment. These transients are limited by surge protection suppressors, filters and other transient suppressors as shown in figure.

  • Power Factor :

Power factor is a power quality issue in that low power can sometimes cause equipment to fail. In many instances, the cost of low power factor can be high; utilities penalize facilities that have low power factor because they find it difficult to meet the resulting demands for electrical energy.

Operating in a high power factor environment ensures that the power system is functioning efficiently. It also makes economic sense. Apparent power in an electrical system can be defined as being equal to voltage times current. Power factor may be viewed as the percentage of the total apparent power that is converted to real or useful power.


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