BAR Valley Electrical Analysts - What we do and how the Power Logger works
How the Power Logger works
The Power Logger generates graphs that show the Active Power (P) (actual power usage by machinery), the Reactive Power (Q) (power being measured and charged for but not used), the Apparent Power (S) (the power being measured by the supply authority's metering equipment, Q+P, or P X PF) and the Power Factor (PF) (the amount of lag between P and S). Find out more about power factor and power factor correction.
Graph A showing low power factor (inefficient)
Graph B showing high power factor (efficient)
GRAPH A
Power Factor (PF) is measured as an average over 15 continuous minutes (as does your municipal supplier).
Peak usage Active Power (P) is 180 kVA. The Apparent Power (S) is P X PF (0.85) = 211.76 KVA
Current municipal rate is R75.50 per kVA per month, so 211.76 kVA X R75.50 = R15 987.88 per month
GRAPH B
With the correct power factor of 0.98, the equation is thus:
180 X 0.98 = 183 kVA
211.76-183 kVA = 28.76 kVA per month
This is a saving of R2 171.38 per month on your electricity bill. The kilowatt hours billed are also reduced by the same percentage.
Charges include 48-hour power analysis and an illustrated written report. Any changes that need to be made to correct the power factor must be referred to your electrical services contractor. Your contractor is welcome to contact us for any further assistance. Should you not have a contractor, we will gladly quote on fixing the power readings.
The cost includes the second monitoring of the supply after completion of the recommended work, to verify that it is correct.
All prices quoted include VAT and are subject to change without notice.
Power factor in an electrical system is the ratio between the real power and apparent power to the load. The real power is the capacity of a circuit performing the actual work. Apparent power is the product of current and voltage in a circuit due to stored energy in a load and returned to the source. Circuits containing a purely resistive load (geyser elements, stove elements, filament lamps etc.) have a power factor of 1.
Circuits containing inductors (motors, fluorescent ballasts, solenoids etc.) have a lagging power factor < 1.
Circuits containing capacitors or synchronous motors have a leading power factor which is also < 1.
In an electrical system, a load with a low power factor draws more current than a load with a high power factor for the same amount of real power transferred.
This can be shown in the formula for real power:
P = S cos∠
Where:
P is active or real power (in Watts (W), kilowatts (kW))
S is apparent power (in volt amperes (VA) or kilovolt amperes (kVA)) [S = V (volts) x A (amperes)]
cos∠ is the power factor (∠ is the angle that the amp leads or lags the volts).
This can be illustrated in the following 2 diagrams:
∠= 0°.
This means cos∠ = 1 so the power factor is 1
∠= 45°.
So cos∠ = 0.71 so the power factor is 0.71
This can also be illustrated in vectors of volts and amps
It is always desirable to keep the power factor as close as possible to 1, because you are charged by Eskom or your municipality for VA (Apparent Power) and you only consume Watts (Real or Active Power). In industry, the power factor will be lagging or leading (inductive), because of inductors (electric motors, fluorescent lamps etc.).
The most cost efficient way to correct an inductive load is to connect capacitors to the load. There are also synchronous motors with certain advantages, but they are very expensive. The amount of correction required is shown in this diagram:
