HOW TO DETERMINE AMOUNT OF kVAr REQUIRED
ANALYSIS OF UTILITY BILLS
Monthly utility bills should be studied and analyzed. Since loads vary from month to month, or season to season, it is good practice to consider the last twelve months of bills. Most utility providers print out the average power factor for the month, and the total active energy consumed during that billing period. However, with some utility providers, power factor may not be obvious on the monthly bill. Myron Zucker, Inc. (MZI) experienced staff has the expertise to provide detailed utility bill analysis. The average active power for the billing period can be calculated by dividing the total active energy consumed by the total number of hours of the billing period.
With values of active power and power factor known, the power triangle diagram can be developed and the reactive power can be determined. To improve the power factor to 100%, the value of reactive power determined from this analysis is equal to the capacitance of the PFCC in kVAr. Sizing of PFCC can also be determined by the use of Table 1, which simplifies the calculations.
INSTRUCTIONS FOR USING TABLE 1:
- Find the billing (original) power factor in the first column.
- Read across the first row for the desired power factor.
- Find the multiplier value where the above two values intersect.
- Determine the PFCC capacitance in kVAr by multiplying the average active power by the multiplier value.
EXAMPLE:
The utility bill shows an average power factor of .72 with an average active power of 627 kW. How much capacitance in kVAr is required to improve the power factor to .95?
STEPS:
- Locate .72 (original power factor) in column (1).
- Read across desired power factor to .95 column.
- Find the multiplier value of .635 where the above two values intersect.
- Multiply the average active power of 627 by .635 (627 kW x .635 = 398 kVAr).
- Select a 400 kVAr to improve power factor to 95%.
Once capacitance is determined the next task is to determine the PFCC mounting location.