power_quality_2 Seminar

[born_for seminars]

ABSTRACT:
THE UBIQUITOUS APPLICATIONS OF POWER ELECTRONIC EQUIPMENTS RESULTED IN POWER QUALITY PROBLEMS, SUCH AS VOLTAGE DISTORTION DUE TO HARMONICS GENERATED IN SUPPLY CURRENTS OF VARIOUS ORDER ENERGY EFFICIENT ELECTRONIC EQUIPMENTS AND NON LINEAR LOADS ON VOLTAGE AND CURRENT WAVE FORMS. THE POWER QUALITY IS OF INCREASING CONCERN OF ELECTRIC UTILITIES ,SINCE THE ILL EFFECTS OF HARMONICS CAUSES THE DETERIORATION OF VARIOUS SENSITIVE ELECTRONIC AND ELECTRIC EQUIPMENT DESIGNED TO OPERATE ON PURE SINUSOIDAL WAVE FORM OF A.C. SUPPLY AT RATEDVOLTAGE AND FREQUENCY. HARMONIC DISTORTION AND SUBSEQUENT EQUIPMENT DAMAGE ONE OF THE MOST SERIOUS POWERQUALITY PROBLEMS NOW A DAYS . THE THREE MAIN IMPORTANT FACTORS RELATED WITH POWER QUALITY ARE UTILITY, CUSTOMER AND EQUIPMENT MANFACTURERS. THE AIM OF THIS PAPER IS TO TAKE A OVERVIEW OF DIFFERENT SOURCES OF HARMONIC GENERATION , THEIR EFFECTS, MEASUREMENT AND ELIMINATION TECHINIQUES TO BRING THE TOTAL HARMONIC DISTORTION WITHIN PERMISSIBLE LIMIT BY USING HARMONIC SUPPRESSOR SYSTEMS .


INTRODUCTION:
Harmonic Voltages and Currents are the integral multiples of the fundamental frequency. In
India ,for 50Hz. frequency of second harmonic is 100Hz, third harmonic is 150Hz. and so on.
Though the applied voltage is sinusoidal because of their nonlinear characteristics the current drawn by them is non sinusoidal. This non sinusoidal current after passing through the low impedance of power causes distortion in sinusoidal voltage which can be split up as sinusoids of the different frequencies, which when added together results in original distorted waves. Advancements in power electronics caused the use of such a equipment in power system at LV,MV,HV and EHV levels increasing at a faster rate, harmonics is negative by product of this development. Utility of nonlinear loads resulted in large harmonics in supply currents causing distortion of the voltage wave form resulting in deterioration of power quality.
Deviation from sinusoidal shape is generally expressed in terms of harmonic components. All the harmonic current deteriorates the performance and impose various problems. Therefore , identification of sources of harmonic are important.
Sources of harmonics:
Harmonics of different orders generated when connected power system network by different sources as below:
• The non linear loads such as inverter fed adjustable speed drive.
• The use of powerfactor correction capacitor creates parallel or series resonance problems increasing the harmonic distortion.
• Process control and solid state power conversion equipments.
• Energy efficient compact flourescent lamps.
• Use of AC and DC adjustable speed drives
• Static VAR compensators.
• Transformers produces very high levels of harmonics when they are initially energized, the so called in rush current will generate harmonics of several orders.
• Cycloconverters,Lift control system,Traction,AC voltage regulators, UPS, Battery chargers.
The following are the undesirable effects of harmonic on the operation of different equipment connected to power system network. The effect of harmonic depends on harmonic voltages and currents are the integral multiples of the fundamental frequency.

EFFECTS OF HARMONICS:
• 1.The duration presence of long duration harmonic cause more serious effects on the various equipments connected to the power system .
2. Amplitude of harmonics ….large amplitude harmonics of short duration under resonance condition cause dielectric breakdown due to over voltages.
Now a days various devices and equipment being measured applications are more sensitive compared to the past.
• The capacitor used for power factor correction and in different filters decreases resulting in increasing in current drawn by capacitor beyond permissible limits. The capacitor acts as sink for harmonic currents resultant effect of harmonics is overloading , hence over heating increases dielectric stress and increase the power lost. The thermal failure of capacitor may take place because of higher temperature.
• Non sinusoidal power supplies results in reduction of torque of induction motor
• It will increase interference with telephone , communication and logic circuits.
• Error in reading of induction type energy meters which are calibrated for pure sinusoidal A.C power.
• Higher order harmonics causes voltage stress and carona .
• Presence of harmonics in power system network can cause additional losses in power system network, overheating of transmission lines, transformers and generators etc.,
• Malfunction or even failure of electronic or computer controls.
Hence it is clear that day by day the increase in harmonic contents will impose new problems on operations of electronic equipment . The energy efficient electronic equipment that will be produced in future trends result in poor performance due to the voltage distortion. Hence it is essential to have the proper coordination between the supply authorities and consumers regarding the power quality problem, their causes and results and solutions available to eliminate them.
IMPORTANCE OF HARMONIC MEASUREMENTS:
• Meaurement provides the real time information about the power system network to utilities, consumer and designer .Filters designed after harmonic measurements are technically better and economical.
• Measurement provide information to analyze the combined effect of harmonic generated by different loads on power quality.
EQUIPMENT USED FOR MEASUREMENT OF HARMONICS:
In these systems it is necessary that the signal input to the harmonic analyzer should faithfully represents the voltage and current signals to be analysed Hence the accuracy of Transducer used in harmonic measurement is very important. Measurement of the harmonic current is performed by using current transformer up to 50th harmonic without any problem.
I) Capacitive voltage transformer offers considerable error in the transformation ratio at harmonic frequencies .The error is significant even for harmonics of order below 25.
II) Potential transformer
III) Switchable capacitive voltage divider (CVD) . For each phase of the system with capacity to reproduce harmonics other than 50Hz accurately .
IV) The AC system measurement in the frequency domain are carried out by a harmonic analyzer equipped with grade signal conditioners and ADC. The harmonic analyzer are microprocessor based high precession instrument using fast fourier techniques to analyze the input signal.