Energy Meters are one of the important instrument to account for energy imported / exported in an industry. In Power Generating Stations, the cumulative reading of such energy meters are used for the calculation of total Million Units (MUs) of energy exported. On the basis of MUs, total revenue generated by the Station is calculated. Thus reading of Energy Meter is quite important to be recorded, accounted and audited.

As we know that,

Power = VICosØ where Ø is power factor.

Therefore, an Energy Meter shall take current and voltage as an input. Current and voltage input is extended through metering core of Current Transformer (CT) and metering core of Potential Transformer (PT). Based on this input, the energy meter calculates and display amount of energy imported / exported.

Let us take an example. Suppose the energy meter is connected in STAR connected system having CT ratio of 200/1 A & PT ratio of 220 kV / 110 V (phase to phase value). Assume power factor to be unity for the sake of easy understanding of Multiplication Factor.

Calculation of Multiplication Factor of Energy Meters

So, the current and voltage input to meter will be 1 A (phase to neutral current) and 110 V (phase to phase). Let us convert the input current and voltage to phase to neutral value.

Phase Voltage = 110/1.732 = 63.5 V

Phase Current = 1 A

Per phase power calculated by the Energy Meter assuming power factor to be unity

= 63.5 x 1 x 1 Watt = 63.5 Watt

Hence, total power as displayed in Meter = 3xPer Pahse Power

                                                                  = 3×63.5 Watt

                                                                  = 190.5 Watt

Energy Meter displays the cumulative energy imported / exported in Wh. Hence, energy displayed by meter assuming 190.5 Watt of power is supplied for 1 hour

= 190.5 Wh

Is this the actual power? Definitely not.

Actual power = 1.732x220x200x1 kW  (Three phase power)

                      = 76208 kW

Actual energy for 1 hour in watt hour = 76208 kWh

This discrepancy in the actual power and power displayed in energy meter is due to the fact that meter is taking CT and PT secondary value as input for its calculation. To overcome this discrepancy, we need to have a Multiplication Factor of Energy Meter.

Calculation of Multiplication Factor:

Multiplication Factor of Energy Meter is calculated as below

Multiplication Factor = (External CT Ratio x External PT Ratio) / (Meter CT Ratio x Meter PT Ratio)

You can find the meter CT and PT ratio in the manufacturer manual. Usually both the ratios are 1.

Let us calculate the Multiplication Factor for our example.

Here,

External CT Ratio = 200/1

External PT Ratio = 220 kV / 110 V

Hence,

Multiplication Factor (MF) = (200×220 kV) / (1×110)

                                 = 400,000

Thus the difference of meter reading must be multiplied by the above Multiplication Factor to get the actual amount of energy imported / exported for our example.

To conclude, as an energy meter shows the cumulative energy imported / exported in Watt Hour, therefore the difference of meter reading taken at two different point of time gives the net energy imported / exported. Let this difference in meter reading is n Wh for the given period.

Then the actual energy imported / exported during that period  

= n x MF Wh

= n x MFx10-3 kWh

= n x MFx10-3 Units

50 thoughts on “Calculation of Multiplication Factor of Energy Meters

  1. Tshewang Dorji says:

    Supposing my CT ratio is same but the PT ratio differs. Then how should i calculate the M.F. let as assume CT ratio is 200/1 external and meter side but PT ratio for external is 220/100 and at meter side 220/110. High light on it please.

    1. admin says:

      One meter will only have one CT and one PT input. Therefore the method for calculation of multiplication factor will remain same.

  2. Biswajit Som says:

    for multifunctional meter multiplication factor required or not

    1. admin says:

      For Multifunctional meter it is not required. But is better to refer the manufacturer’s manual.

  3. aurel says:

    hello friends. i need your opinion
    i habe recently installed a 6kV switchgear, having doubts for the energy measyrement.
    the old energy meter had a MF =100
    The VTs are 6kv/100 V CTs are 300 A/5
    so the MF should be (6 × 300 ) / ( 5× 100) = 3.6 ?
    is this right??
    the metter shows 1.2 kWh
    so should i multiply this value with 3.6?

    thanks

    1. Ranjeeth says:

      U will get mf as 360 not 3.6

    2. Ananda says:

      Yes u r right Mr. Aurel made the calculation with 6. That should be 6000. Then the answer would be 360.

  4. aurel says:

    regarding my post of some minuits ago
    a did a mistake in calculation.
    for my switchgear PT ratio are 6000/100 CTs ratio 300/ 5A the meter ratio are both set at 1
    so my MF is ( 6000 * 300)/(5* 100) =3600 ?
    my new energy meter shows 2.2 kWh the last 24 hours
    so the real value is 2.2 * 3600?

    1. admin says:

      Thank you Aurel for asking. Yes, you need to multiply the energy meter reading by 3600 (for kWh or Unit conversion) for getting the actual energy consumption by auxiliaries. You can download Multiplication Factor Calculator for Energy Meters for your future use and reference. Please share the post if you like it.

  5. joy says:

    if you apply for 1MW at a plant, VT ratio 11kv/110,CT ratio 50/5. how do u find the multiplying factor

    1. admin says:

      Thank you for asking. You can download Multiplication Factor Calculator for Energy Meters for calculation.

  6. Pema Tamang says:

    Please help me.
    the external CT ratio is 50/1A, external PT ratio is 33kV/110V
    meter CT ratio is -/5A, meter PT ratio is -/110V.
    What should be the multiplying factor?
    Help will be highly appreciated

    1. admin says:

      The Multiplication Factor (MF) for Energy Meter will be 15,000. The MF to convert meter reading in kWh (Unit) = 15. You can download Multiplication Factor Calculator for Energy Meters for calculation for your future use.

  7. akhil krishna says:

    external ct ratio 200/1,external pt ratio 66kv/110
    meter ct ratio 400/1,meter pt ratio /110v
    mf will be????

    1. admin says:

      Thank you for asking. You can download Multiplication Factor Calculator for Energy Meters for calculation. If you still find problem, please reply.

  8. Egbodor Peter says:

    Please I have a question,
    We have a meter at the at the transmission substation (132/33kv) and another meter on the 33kv feeder some kilometers away for inter-boundary metering.
    The issues now is this, the reading from the inter-boundary meter is higher than that the meter at the transmission end is picking.
    How can this be possible and how can I be able to resolve it? Those the CT rating has a part to play in this?
    Thanks

    1. admin says:

      What is the CT and PT ratio for Substation Meter and feeder meter? Please revert so that I can help you. If possible can you send me a simplified single line diagram for Meter connection for both substation and feeder? Thank you!

    2. Kamlakar Singh says:

      132kv/33kv ka P.T. ratio kitne volt hoga

    3. admin says:

      PT kis side laga hai, agar 33 of side hai to ratio 33 kv/110 v hoga Aur agar 132 kv side hai to 132 kv/110v hoga

  9. PRANJAL BORTHAKUR says:

    A Meter of /110v , / 5A having external CTR300/1 and PTR 66kv/110v and interposing Ct 1/5A. Pls advice whether Mf = 36000

    1. admin says:

      where does this interposing relay coming into picture in your system?

    2. PRANJAL BORTHAKUR says:

      The secondary of 300/1 CT is connected to the primary of interposing CT n secondary of interposing CT is connected to a HT meter of /5A

    3. admin says:

      In this case, the MF of Energy Meter will be = (300/5)x(66×1000) / 110 = 36000

  10. J. U. Parmar says:

    11kv feeder external CT ratio 300/5,external pt ratio 11 kv/110 v, meter ct ratio – /5,meter pt ratio /110 v, what is m. F.?

    1. admin says:

      It will be 6000.

  11. J. U. Parmar says:

    Sir, your anser is not match in formula 11kv /110 v*300 /5/110 v*5=10.8
    Your anser is 6000
    We use 60m.f.in our 66kv substation in 11kv outgoing panel
    What right 10.8,6000,60?
    Please calculation me

    1. admin says:

      See, (11x1000x300) / (5×110) = 6000. It may be that you are using MF to convert into into million Units. Check where you are using MF and then change the data accordingly. Can you pls send me detail for your 66 kV substation so that I may check why the MF is 60 in that case?

  12. Sartaj says:

    I have to calculate MF of summation meter…yard CT ratio for feeder 1 is 300/1 and for feeder 2 is 300/1. Also, summation meter ke current transformer ka CT ratio 50/1 hai. And summation meter se pehle install 4 abt meter having CT ratio 600/1….
    Then, how to calculate MF of summation meter?? Please reply with details

    1. admin says:

      Please send SLD.

  13. ayad aziz says:

    I have a meter type MK6E with nominal current In= 1(10) Amps & Vn = 3*57-240 volt but the external CT = 100/5 & external PT = 20000/100 … please can you tell me how much is the multiplication factor ?

  14. JAGRUP KUMAR says:

    We have one 3 phase 4wire energy meter installed in our distribution network. On Energy meter facia MF-20 is written at bottom of meter 200/5A is written. There is no CT connected inside meter box. However we have connected one external CT of 300/5 in meter connection. Now what will be overall multiplying factor to calculate overall reading.

    Pl reply

    1. admin says:

      What is the PT ratio connected to the Meter?

  15. JAGRUP KUMAR says:

    No PT is connected. three phase 415 V supply is directly connected to meter.

    1. admin says:

      It will be great if you can mention the meter make and model number so that i can check.

  16. JAGRUP KUMAR says:

    Great
    Make- Capital,AC 3 Ph 4WIRE for unbalanced load
    Type-RR47
    Meter MF- 20 (written on meter facia)
    At bottom of meter facia 200/5A is mention.
    we have externally connected only CT having ratio 300/5. NO PT only 3 phase supply 415 V is connected. what will be the meter overall MF.

    1. admin says:

      I could not find the manual of the energy meter. However, if the power is being supplied through 415 V line and general calculation is considered then multiplication factor should be 60.

  17. K. Purushothaman says:

    Hi
    A
    I’m k. Purushothaman
    How can I identify PT Ratio in selec MFM376 Meter.. I’m using this meter in control panel. Please clear my doubt sir. CT RATIO is 250/5

    1. admin says:

      Is this the meter installed? If installed, then pls check in the meter console for voltage.

    2. NS says:

      if the input is 440/240 volt there is no need of PT ratio, your MF will be 50

  18. LALTHANZUALA says:

    Hi
    Kindly clarify the correctness
    The external CT ratio is 200/1A, external PT ratio is 132kV/110V and
    meter (Secure Make) CT ratio is -/1A, meter PT ratio is 132kV/110V
    We are using MF as 200
    If not correct, please show detail calculation

    Thanks & Regards
    Lalthanzuala,

    1. admin says:

      The MF will be 240,000. However, the MF to convert meter reading into kWh (Unit) will be 240. For detailed calculation, you are requested to refer the article.

    2. LALTHANZUALA says:

      Dear Sir,

      External CT Ratio = 200/1

      External PT Ratio = 220 kV / 110 V

      Hence,

      Multiplication Factor (MF) = (200×220 kV) / (1×110)

      = 400,000

      From the above calculation, how do you get 220 for External PT Ratio

    3. admin says:

      PT ratio is 132 kV/110V for your case. CT ratio is 200/1.

    4. LALTHANZUALA says:

      Dear Sir,

      what about the Meter CT and PT ratio. Why it is not considered in the MF calculation?

      Thanks and regards

    5. admin says:

      As mentioned by you, it is 1. Meter CT and PT ratio is also considered. Please check the formula for multiplication factor.

  19. LALTHANZUALA says:

    Dear Sir,

    what about the Meter CT and PT ratio. Why it is not considered in the MF calculation?

    Thanks and regards

    1. admin says:

      It is considered.

  20. NS says:

    MF=(33*50)/1*110=15
    Meter reading should be multiplied by 15.

  21. kayser Ahmed says:

    In our 33/0.415 KV 0.5MVA S/s Installed Elite 440-442 model. PT primary/Secondary = 33000/110 & CT primary/Secondary = 75/5 . Multiplying Factor is 4500 . But Why Installed Company Multiply with only PT Ratio (300) and KWH From meter.

  22. Manjunath says:

    11kv Bank external CT ratio 800/1,external pt ratio 11 kv/110 v, meter ct ratio 200/1,meter pt ratio 66kv/110 v, what is m. F.?

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