Analysis of Power Factor Improvement Techniques in case of Non Linear System Loads.

Analysis of Power Factor Improvement Techniques in Case of Non-Linear System

Loads

• Kaustubh Nande• Abhinav Mitra• Lalitesh Vaidyar• Ritesh Ambadkar

(IIIrd Year, Electrical Engg., YCCE,Nagpur)

Definition: The power factor of an AC electrical power

system is defined as the ratio of the real power flowing to the load the apparent power in the circuit.

• Power Factor plays a crucial role in the economic operation of any system.

• Low power Factor implies low power utilization, thereby reducing the system efficiency.

• Low power factor shortens the lifespan of electrical appliances.

• The heat dissipation in the system rises proportionately by a factor equivalent to the square of the current rise.

• Electricity Boards impose a surcharge to customer if the power factor is <0.85.

• Also, Rebates are given to the customers if the power factor is maintained >0.85.

Power factor improvement in case of linear loads1. Using capacitor banks in parallel with the

system: The capacitance would try to neutralise the inductance of the system and thus the nature of the system tends closer to being resistive, thereby improving the power factor.

2. Using an synchronous condenser: An over excited synchronous motor with no load on it draws leading amperes, if the condenser is connected in parallel with the system, and thus improves the pf.

3. Using phase advancers: generally used for an IM, the phase advancers, which is an AC exciter provides exciting amperes, which neutralise the lagging stator amperes and improves the pf.

Power factor with non linear loads and sinusoidal voltage

•When the loads are non linear and current have harmonics pf cannot be calculated using the traditional methods.• I=I1•pf=cos ϕ1 ×

Power factor will be function of displacement power factor and distortion power factor.Total power factor correction can only be achieved when both displacement power factor and distortion power factor are corrected. This requires a two step process:1. Reduce the displacement angle between voltage and current.2. Reduce the total harmonic current distortion.If either of these steps is taken without the other the total power factor will be increased but it may not be high enough to reach the minimum value required by the utility.

Total power factor can be improved by decreasing the harmonic current distortion• Using filter instead of capacitor bank.• The capacitive part of the filter improves the displacement power factor, while the combination of the reactor and the capacitor bank decrease the total harmonic distortion of the current.• At tuning harmonic filter act as capacitor bank and above it behaves as inductor. At the tuning harmonic it behaves as a resistor.

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The figure below shows the behaviour of the total power factor for different values of displacement power factor and total harmonic current distortion.pf=cos ϕ1 ×

Power Factor with non-linear loads and voltage distortion.

• Traditional methods cannot be applied to power calculation.

• Neglecting the phase angles of voltage harmonics, voltage is given by

• Power factor is calculated as ×

×

• In the expression of power factor the term p/sI is relation of total active power(including harmonics) and fundamental power.

• The term is distortion power factor pfdist

• Total power factor pf total is product of p/sI and pfdist.

• Hence, when reactive power increases the phase angles between fundamental components of voltage and current increases, hence, total power factor decreases.

• Due to distortion of voltage and current increases, distortion power factor decreases, total power factor decreases.

• So, to improve the power factor:- 1.Reduce the angle between fundamental

components of voltages and currents. 2.Reduce total harmonic distortion of

voltages and currents.

Vector relationship

• Phasor diagram shows the vector relationship of P1,Q1F & S1F before power factor improvement.

• For improvement a capacitor bank QCF is added. But in case of using a capacitor bank the resonance phenomena arises with main transformer, which must be avoided.

• Use of harmonic filter improves the power factor.

The capacitive part improves displacement power factor and reactor & capacitor bank combination decreases the distortion, improving the distortion power factor and total power factor as a whole.

HARMONIC FILTERS(Frequency selective circuits)

An arrangement of linear electrical elements(R,L,C) such that the circuit is capable

of attenuating one or more frequencies depending on the values of R,L and C.

TYPES

• Active Filters(used in low voltage systems)• Passive Filters(used in medium and high

voltage systems)

ORDER OF THE FILTER = Number of energy storage components used.

• usually connected in parallel with the system• the frequency to be attenuated by a general

filter is a function of the filter parameters and hence the filter can made to attenuate a large number of frequencies by varying its parameters.

The filters might again be classified as

• High pass filters• Low pass filters• All pass filters

Types

A. Series tuned filter• intended to block the flow of harmonic

currents by providing a high harmonic series impedence.

• passes the fundamental frequency only.

B. Single-tuned filter

• intended to greatly attenuate a single harmonic component.The equation that describes its impedance behavior isZf =

• The tuning frequency of the single-tuned

filter is adjusted by f=1/2π√LC

C. First-order high-pass filter

• to achieve significant filtering to reduce the harmonic distortions, the capacitor size must be notably large.

Z =

D. Second-order high-pass filter

• this filter is generally used as a suppressor for several high-order harmonics

Z =

E. Third-order high-pass filters

the capacitor C2 is also tuned to the same

tuning frequency as the capacitor C1 with the inductor.

Z =

F. C-type filters• The C-type filter has an intermediate behavior

between the second- and third-order high-pass filters. It exhibits no loss at the fundamental frequency due to its topology. The capacitor C2 is tuned, with the inductor,to the fundamental frequency . This filter is usually utilized to filter harmonics from a lower order than the two previously explained filters.

Z =

Distribution static compensators

• Inject the pulses which are exactly 180 degrees out of phase of the unwanted harmonics , thus cancelling out the unwanted harmonics and yielding the output wave,very close in nature to the fundamental wave

Conclusion

• Both the displacement and distortion power factors need to be treated in order to maintain good the total power factor.

• Harmonic filters attenuate the harmonic frequencies and thus, an improved waveform is obtained, thereby improving the overall power factor.

• Certain other alternatives like Distribution static compensators can also be used to eliminate the harmonic components.

REFERENCES:

Power Factor in Electrical Power Systemswith Non-Linear Loads(Research thesis)By: Gonzalo Sandoval

Passive Harmonic Filters for Medium-VoltageIndustrial Systems: Practical Considerations andTopology Analysis By:Alexandre B. Nassif

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