INSTITUTE OF INTEGRATED ELECTRICAL ENGINEERS
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A CLOSER LOOK AT POWER FACTOR ADJUSTMENT, DOES NGCP REALLY NEED TO GET RID OF IT? R. F. Corpuz, G. R. Pagobo
Abstract—This study investigates Power Factor Adjustment as implemented by NGCP. It looks into the details of its formulation and concludes if it is profitable for NGCP to remove or carry on power factor adjustment.. Index Terms—Power Factor, Reactive Power, OATS Rules, Power Factor Adjustment
I. I NTRODUCTION HAT is power factor? In a power system, two types of power are actually transmitted. The first is the real power measured in MW and the second is the reactive power measured in MVAR. Ordinary loads such as heaters and incandescent bulbs consume real power (MW). Motors and transformers require reactive power (MVAR) in addition to MW. The vector sum of MW and MVAR is called apparent power measured in MVA. The relationship between the three power values is shown in Figure 1.
W
Figure 1.
II. R ATIONALE , W HY D OES NGCP C HARGE P OWER FACTOR A DJUSTMENT ? With reference to Figure 2 , each power value in the power triangle corresponds to a value of current. Thus a “current triangle” could be drawn. Figure 3 shows the current corresponding to each type of power.
Figure 3.
The Power Triangle
Power factor (pf) is the “factor” that is multiplied to the apparent power (MVA) to get the real power (MW). In mathematical terms: M V A × pf = M W
(1)
MW MV A
(2)
pf = cos(θ)
(3)
pf =
Figure 2. For the same MW, as MVAR is increased, θ increases. The power factor or cos(θ) decreases
So power factor is the cosine of the angle between the apparent power and the real power. With more motor loads connected to the system, more reactive power (MVAR) is needed. The net effect is an increase in angle θ and consequently, the MVA is increased. Figure 2 shows increasing angle θ as MVAR is increased. Note that as θ increases, cos(θ) or the power factor decreases. Low power factor degrades the quality of transmission line performance.
Currents Corresponding to Each Type of Power
Why does NGCP charge Power Factor Adjustment? The answer to that question can be found in Figure 3. Recall that NGCP’s power bill to its customers is based on MW or demand. Thus it is charging its customers payment for wheeling energy corresponding to IM W of current. Note from Figure 3 that the actual current that passed through the line was IM V A which is greater than IM W . . Thus to compensate for the extra current due to MVAR which passed though the transmission lines, Power Factor Adjustment is collected. III. T HE O RIGIN OF P OWER FACTOR A DJUSTMENT F ORMULA Since Power Factor Adjustment is intended to compensate for the extra current passing through the transmission lines, its quantity should be proportional to IM V A . From the Equation 3: pf = cos(θ) =
IM W MW = MV A IM V A
(4)