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POWER ELECTRONICS GENESIS,TRENDS AND IMPROVEMENTS
Introduction:
- Power quality means how pure is the quality of power being used without abnormalities.
- In this paper we are going to seethe factors causing in the production of harmonics, the types of harmonics, their effects and problems caused by them.
- The solution for the reduction is the use of filters.
Power quality deterioration:
- Linear loads- The current consumed is directly propotional to supplied voltage.
- Non-linear loads- The high frequency components consume non-sinusoidal current.
- These high frequency components are called as harmonics.
- Harmonic voltages are superimposed over the pure supply voltage causing distortion in voltage.
Sources of Harmonics:
- Switched mode power supplies.
- Fluorescent lighting ballets.
- Variable speed drives.
- Uninterrupted power supply.
- Magnetic cored devices.
- Electric arc furnaces.
Effects of harmonics:
Nuisance:
§Transformer noise
§Communication noise
§Communication noise
Economics:
§Reduction in life
§Increased cost
§Reduction in life
§Increased cost
Damage:
§Over heating
§Over voltage which results in capacitor and machine failure.
Being linear loads, capacitors do not generate harmonics but they tend to amplify existing harmonics.
§Over voltage which results in capacitor and machine failure.
Effects on capacitors and machines:
Capacitor:
Being linear loads, capacitors do not generate harmonics but they tend to amplify existing harmonics.
Motors:
The high frequency harmonics produce more core loss in motor than the power frequency, which results in increased heating of the motor core.
Generator:
Generators have greater heating effect, because of its higher reactance and impedance.
Advent of Harmonic Filters:
Passive Filters:
Limitations:
- Provide certain amount of reactive power which is not desirable.
- Sensitive to frequency and network changes.
- Used to filter only one harmonic component.
Active Filters
- Open loop control
- Closed loop control
- Active filters overcome the performance of passive filters.
- The compensating current created by a three phase IGBT inverter bridge that is able to generate any given voltage waveform with PWM technology.
- IGBT bridges uses a DC voltage source realized in the form of DC capacitors.
- Closed loop filter directly its effect on the filtration by comparing the resultant waveform with the pure one with the help of feedback signal.
Benefits of Active Filters:
- Reduced energy costs
- Elimination of higher and lower order harmonics
- Improve load power factor
- Voltage improvement and stability
- Surge and transient protection
- Reduce voltage unbalance
- Reduce power line losses
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