Calculation of Multiplication Factor of Energy Meters

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

87 thoughts on “Calculation of Multiplication Factor of Energy Meters”

  1. 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.

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

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

  2. 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

    Reply
  3. 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?

    Reply
  4. 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

    Reply
  5. 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

    Reply
    • 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!

    • 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

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

    Reply
    • 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

  7. 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.?

    Reply
  8. 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

    Reply
    • 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?

    • I have Schneider conzerv 6400NG energy meter.
      CT is 75/5.5A
      PT is 33000/110V
      Please told me how to read unit in meter and what is multiple factor

  9. 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

    Reply
  10. 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 ?

    Reply
  11. 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

    Reply
  12. 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.

    Reply
    • 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.

  13. 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

    Reply
  14. 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,

    Reply
    • 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.

    • 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

    • Dear Sir,

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

      Thanks and regards

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

  15. Dear Sir,

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

    Thanks and regards

    Reply
  16. 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.

    Reply
  17. A METER OF
    MADE TO I.S.S. 2705/1992
    (RATIO : 2000/5A VA : 15 CLASS : 1.0
    FREQ : 50 Hz
    LINE VOLTS : I.L.0.66/3.0KV

    SO WHAT WILL BE M.F RATIO OF THIS

    Reply
    • I have a meter written on it x/5A,3×58/100V externalC.T ratio300/5 ,external PT ratio11000/110V what will be the multiplying factor ?pl lam in need of this information

  18. we had come a cross one issue at our plant. In CT panel, the connection which is going to meter, phase and neutral got interchanged. Hence though we use power, 1/3 only getting by meter. Inspection done by EB and they said , henceforth major changes in power cost. EB said they only did mistake while giving connection in few years back. Can you give some suggestion to how to tackle
    thanks

    Reply
    • This is a big mistake by EB. The connection needs to be immediately changed. Also, ask EB to replace the meter as meter might have got damaged due to wring wring connection.

  19. Hi. Hallo. HT METERING PANEL. 60 KVA CT RATIO 5/1A
    PT RATIO 11KV/√3/110V/√3
    VOLTAGE READING. 62.36
    CURRENT IN AMPS 0.432
    How to calculate input voltage.

    Reply
  20. Sir can you explain in detail calculation of MF with
    External CT ratio = 200/1A
    External PT ratio= 11kv/110v
    Meter CT ratio= -/1A
    Meter PT ratio= 11KV/110v

    Reply
  21. If CMD changes CT coils are also to be changed , is it so. Why?

    My CMD us 350Kva .derating to 250Kva.

    Present CTR. 20/1,. ptr. 11kv/110v

    Reply
  22. HI I am vijayakumar i have one dought

    my self have one DG (eg 500kva or 250 kva ) i want select the coil

    how to select the ct coil if have any formula plse share me

    Reply
  23. I have a 3 phase 415V kwhr meter where CT ratio is shown 100/5a and on kwhr meter , it mentioned 400/5a , what will be the multiplying factor ?

    Reply
  24. I have a 3 phase 4wire, 110v energy meter where CT ratio is 300/1A and the meter is installed on an 11KV panel. Can I use a P.T of 33000/110 volts to connect the meter ? what effect will it have on the reading?

    Reply
  25. my question is, we have connected CT of 100/5 with 3 phase 4 wire static meter of -/5 A. How the actual KWH will be calculated. pls help

    Reply
  26. we have connected external CT Ratio 400/5 and external PT Ratio 11000/110 then meter CT ratio 400/5 and meter PT Ratio 11000/110 what will be the MF

    Reply
  27. 400volt 5(6)amp genus meter ct ratio200/5 amp.meter display show voltage r-110 v,y-300 v,b-300 v.amp average 78/phase.maximum femand-56kw.so how many kwh we loss.

    Reply
  28. my question is, we have connected CT of 100/5 & PT of 11KV/110 with 3 phase 4 wire static meter of -/10 A & -/110 How the actual KWH will be calculated. pls help

    Reply
  29. Please help me in entering PT values in programmable energy meter.
    Connecting meter in LT side having phase to phase voltage 440V and phase to neutral 220V.

    Thanks in Advance.

    Reply
  30. Aoa dear all please tell me how to calculate multiplying factor for 400v LT energy meter
    My CT ratio is 600/5 and phase voltage is 400v

    Reply

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