Ingenieri

National Energy Efficiency Saudi /Egyptian Program
Energy Efficiency Workshop Reyad- KSA 25 May 2009 EFFECTS OF HARMONIC ON POWER FACTOR
Dr. Eng. Mohamed H. Helal - Egypt

Abstract
The increase of use of non linear loads modern equipments that uses high frequency switching power supply that generates harmonics will require deep understanding for the effect of harmonics on power factor inorder to insure sustainable development. In this paper we investigate the effect of harmonics on power factor and show through examples why it is important to use true power factor, rather than the conventional 50/60 Hz displacement power factors, when describing nonlinear loads. This study has great priority importance especially when large quantities of CFL lamps will be used for residential andcommercial use to replace GSL lamps. The CFL (compact fluorescent lamps) are divided in 2 main categories, LPF and HPF, LPF is widely used, all LPF CFL has a Power Factor of < 60% and generates Harmonics > 100% (110~165%). Intensive use of LPF CFLs in places ware lighting loads are > 10% of total loads will lead to high losses with serious power quality harmonics that may cause damage to capacitorbanks. Power factor correction of high frequency witching loads is not possible by capacitors, Economic cost to recover losses due to High Frequency (> 5 KHz) harmonics will exceed economic limits. A good and logic solution is to set specifications that meet green lighting regulations and environmental regulations in advance. The Egyptian lighting efficiency standards 6313/2007 forbid the use ofLPF CFL.

Introduction
Voltage and current harmonics produced by nonlinear loads increase power losses and, therefore, have a negative impact on electric utility distribution systems and components. While the exact relationship between harmonics and losses is very complicated and difficult to generalize, the well established concept of power factor does provide some measure of the relationship,and it is useful when comparing the relative impacts of nonlinear loads–

providing that harmonics are incorporated into the power factor definition.

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Power Factor in Sinusoidal Situations
The concept of power factor originated from the need to quantify how efficiently a load utilizes the current that it draws from an AC power system. Consider, for example, the ideal sinusoidal situationshown in Figure 1.

The voltage and current at the load are:

Where V1 and I1 are peak values of the 50/60 Hz voltage and current, and δ1 and ϴ 1 are the relative phase angles. The true power factor at the load is defined as the ratio of average power to apparent power, or:

For the purely sinusoidal case, (3) becomes

Where p f disp is commonly known as the displacement power factor, andwhere is ( δ1 - ϴ1) known as the power factor angle.
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Therefore, in sinusoidal situations, there is only one power factor because true power factor and displacement power factor are equal. For sinusoidal situations, unity power factor corresponds to zero reactive power Q , and low power factors correspond to high Q. Since most loads consume reactive power, low power Factors in sinusoidalsystems can be corrected by simply adding shunt capacitors.

Sinusoidal Example
Consider again the case in Figure 1, where a motor is connected to a power system The losses occurred while delivering the power to the motor are (I² rms R). Now, while holding motor active Power Pavg and voltage V1rms constant, we vary the displacement power factor of the motor. The variation in losses is shown inFigure 2, where we see that displacement power factor greatly affects losses.

Figure 2: Effect of Displacement Power Factor on Power System Losses for Sinusoidal

Example (Note: losses are expressed in per unit of nominal sinusoidal case where Pf true = pf disp = 1.0

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Power Factor in Nonsinusoidal Situations
Now, consider nonsinusoidal situations, where network voltages and currents...