power_quality_1 Seminar

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ABSTRACT
The power quality is a term used to broadly encompass the entire scope of interaction among electrical suppliers, the environment, the system and products energized, and the uses of those systems and products. It is more than the delivery of “clean” electric power that compile with industry standards. It involves the maintainability of that power, the design, the selection, and the installation every piece of hardware and software in the electrical energy system. Stretching from the generation plant to the utility customer, power quality is a measure of how the elements affect system as a whole.
This paper presents an overview of electric power quality with special emphasis on power quality problems, its adverse impacts on utilities and customers and the mitigation techniques. The wide spread usage of power electronic loads aimed at enhancement of energy efficiency and productivity has resulted in serious power quality problems such as voltage distortion due to current harmonics, flicker, voltage sag, voltage surges etc., which call for assessment and solution techniques. Here, we also discuss about two major power quality issues –grounding and harmonics and some power system components, which correct the harmonics problems. This paper broadly describes the above features along with the means for improvement of power quality.






INTRODUCTION TO POWER QUALITY
The term ‘power quality’ means different things to different people. One definition is the relative frequency and severity of deviations in the incoming power supplied to electrical equipment from the customary, steady, 50Hz sinusoidal waveform of voltage or current. These deviations may affect the safe or reliable operation of equipment such as computers and electronic instruments. It also refers to the delivery of high grade of electric service maintaining a sinusoidal load, bus voltage and current at stipulated magnitude and frequency.
As we connect electronic devices to our power system, the “quality” after power is more important. Quality can be defined in many ways. Stable voltages and undistorted waveforms are two characteristics, which are very desirable in power systems. Thus while not having a strict basis of measurement, terms like” Poor Power Quality” generally mean there is sufficient deviation from norms in the power supply to cause equipment mis-operation or pre-mature failure.

CAUSES OF POOR POWER QUALITY
The causes of poor quality can be attributed to :
 Variations in voltage, magnitude and frequency
 Variations in magnitude can be due to sudden rise or fall of load, outages, repetitive varying loading pattern in rolling mills, power electronic converters, lightning etc.
 Variations in frequency can rise of out of system dynamics or harmonics injection.

Consequently the voltage or current waveforms of a power system ceases to be purely sinusoidal in nature but consist of harmonics and other noises.

IMPACT OF POOR POWER QUALITY:
The effect of these aforesaid poor power quality problems has serious implication on the utilities and customers. Utility side impacts higher losses in transformers, cables etc. In conductors the neutral wires can burn due to the presence of third harmonics generated by non-linear loads. The power factor correction capacitors may puncture due to resonant conditions at resonant frequencies near lower order harmonics. The energy-meters, which are calibrated to operate under pure sinusoidal conditions, may give erroneous readings. The solid-state protective relays can maloperate due to poor power quality. There can be increased losses in cables, transformers and conductors.
The customer side of the power network also experience adverse effects of poor power quality. The automatic processes employing adjustable speed drives may shut down because of nuisance tripping due to even short voltage sags.. The induction synchronous motors can have increased copper and core loses, pulsating torques and overheating with derating effect.

The non-sinusoidal power supply thus reduces torque and efficiency of the motors. The computers and telecommunication equipment encounter loss of data and maloperation due to poor power supply quality. The domestic electronic gadgets such as digital clocks, VCRs and TVs are also affected by voltage distortions.

SYMPTOMS OF POWER QUALITY PROBLEMS
 Electronic controlled systems that stop unexpectedly.
 Many systems reboots required.
 Abnormal failure rate of electronic systems.
 Transformers over heating.
 Motors failing.
 PF capacitors failing.
 Test results unreliable.