March† 1996††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Volume 2†† Issue 4
POWER FACTOR CORRECTION
††† For many Prince Edward Island production operations, the fastest, easiest way to reduce the electric bill is to improve the plantís power factor.†
††† Inductive loads such as motors and lighting system ballasts reduce the typical production facilityís uncorrected power factor from the ideal 100 per cent to perhaps 70 or 80 per cent at peak demand.† When the power factor is 100 per cent, current and voltage peaks occur at the same time ó an ideal situation in which real power (kW) equals kilovolt-amps (kVA), and the electric utility bills you only for the real power that you use.†
††† When the power factor drops below 100 per cent,† kVA and kW are no longer equal.† The kVA figure exceeds the kW figure, and since production facilities are normally metered and billed in kVA, the business ends up paying a significant dollar penalty.
††† Inductive loads cause current peaks to lag (come after) the voltage peaks.† In the figure below, the current waveform lags the voltage waveform by one-eighth of a cycle.† That amount of lag exists when the power factor is 71 per cent.
††† Capacitors installed across the line cause current peaks to lead (come before) the voltage peaks.† The solution to the power factor problem is to put just the right amount of capacitance across the line.† When you do that, the come before tendency just balances the come after tendency.† The voltage and current peaks are brought back together once again, the power factor returns to 100 per cent, and the electricity bill goes down.
In actual practice the power factor is not usually brought back all the way to 100 per cent, but is corrected to 90 or 95 per cent.†† The figure chosen often depends on the fine print of the electric rate description which defines how that facility is billed.† With some Maritime Electric rates, for example, correcting power factor beyond 90 per cent has no economic advantage.
HOW MUCH CAN I SAVE?
††† Naturally, in order to know just how much you could save by correcting power factor it is necessary to analyze your particular situation.† Still, it is possible to get some sense of the magnitude of potential savings from a series of power factor studies done on nine Island food processing plants.† These studies assumed that each plantís power
factor would be brought from its existing value of 70- or 80-some per cent up to 95 per cent.† The results are summarized in the table below:
††ANALYSIS OF P.F. CORRECTION POTENTIAL
OTHER MONEY-SAVING BENEFITS
††† Improving a facilityís power factor reduces the cost of power, but it also has other beneficial effects that can sometimes be of great value.
Increased System Capacity
††† When it is time to expand a plantís production activities it is often necessary to increase the capacity of the electrical service entrance as well ó and doing this can be expensive.† One of the benefits of power factor correction is that it frees up service entrance capacity, giving the facility some capacity ďhead room.Ē†
††† Letís assume, for example, that a plant has an electrical service entrance rated at 200 kVA.† Letís also assume that demand actually does reach 200 kVA at times, and that the power factor at those times is 70 per cent.† Under these circumstances the full capacity of a 200 kVA service entrance is required to serve a plant load of only 140 kW.† If power factor was corrected to 90 per cent, the kVA demand would drop from 200 kVA to just 156 kVA (140 kW divided by 0.90).† This would free up 44 kVA of service entrance capacity that could be used to serve expanded plant needs.
††† PF-correction capacitors can be installed either at the service entrance or at major low-PF loads such as large motors.†† When this latter option is taken, power bus current within the plant is reduced.† This frees up bus capacity,† making it possible for the existing in-plant distribution systemto carry additional loads.
Improved Voltage Levels
††† Because improving power factor reduces service entrance current, there is less voltage drop within the power companyís distribution transformer and less drop on power company feeder lines.† This causes the voltage level at the service entrance, and within the plant, to increase slightly.† When individual motors are compensated there can be an additional voltage rise due to reduced voltage drops within the plantís own distribution system.
Reduced In-plant Power Losses
††† Reduced voltage drops within the plantís distribution system also mean reduced power losses within that system.† In some situations these savings can be significant.† If, for instance, a large motor is located a long distance from the service entrance, it may make economic sense to reduce feed circuit losses by putting the PF-correction capacitors right at the motor rather than at the service entrance.
SOUNDS HOPEFUL.† WHAT DO I DO NEXT?
†††† If you want to look into the pros and cons of power factor correction, the first step is to get an accurate measurement of your facilityís power factor at the time when electrical demand is highest.† If the Energy and Minerals Section has already done an electrical energy audit of your business, the report you received may contain this figure.† If, however, things have changed significantly since those measurements were taken, or if they were not taken when plant electrical demand was at its peak, additional measurements may be needed.† To discuss additional metering, call Mike Proud or Ron Estabrooks at 368-5010 (toll free).† We can arrange to come out and attach equipment that will monitor your electrical usage for a period of time, and then create the needed load and power factor profiles for you.†
††† In the next issue of $mart Energy User we will discuss the rest of this process: getting the technical advice you need, selecting the best correction option, and pricing out the job.