Identification and minimization of Harmonics
- 1. IDENTIFICTION & MINIMIZATION OF HARMONICS MR. MAYUR S HIWALE
- 2. HARMONICS Distortion Or Deviation Of Prefect Sinusoidal Waveform Is Called HARMONICS OR Currents Or Voltages With Frequencies That Are Integer Multiples ( H=0,1,2,…N) Of The Fundamental Power Frequency is HARMONICS 1st harmonic: 50Hz 2nd harmonic: 100Hz 3rd harmonic: 150Hz
- 3. CONCEPT Imagine a power system with an AC source and an electrical load Figure - Power System with AC source and electrical load Load are of two types linear load or non linear load Linear loads are induction motor, heaters and incandescent lamps etc. Non linear loads are electronic loads such as diode, thyristors, Fluorescent lighting, converts etc.
- 4. Type of Load affect the power quality. Linear loads draw current that is sinusoidal in nature so they generally do not distort the waveform as shown in figure 1 Figure 1: Ideal Sine wave (current drawn by linear load)
- 5. Non-linear loads, however, can draw current is not perfectly sinusoidal (Figure ). Since the current waveform deviates from a sine wave, voltage waveform distortions are created. Figure 3: Distorted Waveform
- 6. Production of harmonics Power system harmonics: presenting deviations from a perfect sinusoidal-waveform (voltage or current waveform). The distortion comes from a Nonlinearity caused by saturation, electronic-switching and nonlinear electric loads, Figure3 - production of harmonics
- 7. Why Bother about Harmonics? 50-60% of all electrical Ac Systems in INDIA operate with non- linear type loads Power-Quality-PQ Issues & Problems Damage to Power Factor Correction capacitors Waveform Distortion can create SAG/SWELL/NOTCHING/RINGING All can cause damage effects to consumer loads and power systems due to Over-Current/Over-Voltage or Waveform Distortion Additional Power/Energy Los
- 8. Loads Producing Harmonic Electronic lighting ballasts/Controls Adjustable speed Motor-Drives Electric Arc Welding Equipment Solid state Industrial Rectifiers Industrial Process Control Systems Uninterruptible Power Supplies ( UPS )systems Saturated Inductors/Transformers LAN/Computer Networks
- 9. IDENTIFICATION OF HARMONIC IN SYSTEM Theoretical methods Harmonic Power Flow Direction Method Load Impedance Variation Method On-Line Impendence Measurement Neural Network Based Method Signal Processing Based Techniques
- 11. Calculation of THD Total harmonic distortion, or THD is a common measurement of the level of harmonic distortion present in power systems. THD is defined as the ratio of total harmonics to the value at fundamental frequency. where Vn is the RMS voltage of nth harmonic and n = 1 is the fundamental frequency
- 12. Effects of Harmonics Overheating and premature failure of distribution transformers Increasing iron and copper losses or eddy currents due to stray flux losses Overheating and mechanical oscillations in the motor-load system Producing rotating magnitude field, which is opposite to the fundamental magnitude field. Overheating and damage of neutral ground conductors Trouble sustained type Harmonics: 3rd, 9th, 15th … A 3-phase 4-wire system: single phase harmonic will add rather than cancel on the neutral conductor
- 13. Malfunction/Mal-Operation of Sensitive Tele-control and Protection Relaying False or spurious Relay operations and trips of circuit breakers Failure of the Firing/Commutation circuits, found in DC motor-drives and AC drives with silicon controlled rectifiers (SCR-Thyristor) Mal-Operation instability of voltage regulator
- 14. Power factor correction capacitor failure Reactance (impedance)-Zc of a capacitor bank decreases as the frequency increases. Capacitor bank acts as a sink for higher harmonic currents. The System-Series and parallel Resonance can cause dielectric failure or rupture the power factor correction capacitor failure due to Over-Voltages & Over-Currents.
- 15. Measuring Equipments for Harmonics Digital Oscilloscope: Wave shape, THD and Amplitude of each harmonic True RMS Multi-Meter: Giving correct readings for distortion-free sine waves and typically reading low when the current waveform is distorted Figure 4: “True RMS” Multi-Meter
- 16. Minimization of harmonics An L-C filter consists of a capacitor bank and an induction coil. The filter is designed or tuned to the predetermined non-linear load and to filter a predetermined harmonic frequency range. This is connected in parallel to the non-linear load with the objective of filtering the major harmonics generated by the non-linear load. This application is mostly used when specified for a UPS or variable frequency drive motor in a manufacturing plant. L-C Filter
- 17. Active Power Filter The active power filter (AFP) is a device that is connected in system to cancels the reactive and harmonic currents from a group of nonlinear loads so that the resulting total current drawn from the ac main is sinusoidal. Ideally, the APF needs to generate just enough reactive and harmonic current to compensate the nonlinear loads in the line, thus it handles only a fraction of the total power to the17 load. The performance of this active power filter depends on the inverter topologies and the PWM control method .Therefore, the suitable device in developing the AFP is “Pulse Width Modulated (PWM)” inverter by using IGBT or MOSFET devices. There are two kinds for active power filter such as series and shunt filters.
- 18. Phase Shifting A harmonic minimizing using transformer is a new power quality product for minimizing harmonic problems in electrical distribution systems. This type of transformer has patented built-in electromagnetic technology designed to remove the most harmful harmonics from the 3rd through 21st. The technique used in these transformers is call phase shifting . These transformers can be used to reduce existing harmonics in line current system. This same application can be designed into new construction to prevent future harmonics problems.
- 19. Conclusion The harmonic distortion principally comes from Nonlinear-Type Loads. The application of power electronics is causing increased level of harmonics due to Switching!! Harmonic distortion can cause serious Failure/Damage problems. Harmonics are important aspect of power operation that requires Mitigation!! Over-Sizing and Power Filtering methods are commonly used to limit Overheating Effects of Sustained Harmonics.