Power Factor Across Transformer
- Thread starter adamscb
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No mention of PFC other than yours. We need confirmation PFC is involved and the actual data to proceed down that path.
There is no PFC in the substation. And the load is mostly inductive, it's a large industrial plant (40 MVA total, with about 27 coming from on-site generation, so we're buying around 13 MVA).
If the transformer is a delta primary, wye secondary, could it be the phase transformation that's causing this? These types of transformers have a 30 degree phase change correct?
If the transformer is a delta primary, wye secondary, could it be the phase transformation that's causing this? These types of transformers have a 30 degree phase change correct?
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The phase change in a transformer should equally affect both voltage and current and so should have no net effect on power factor.
The POCO power factor metering is on load side. Right? If so, it is only to be ascertained whether they are recording a leading power factor. If yes, it answers your OP query. If no, it is likely defective metering.
Julius Right
Senior Member
- Occupation
- Electrical Engineer Power Station Physical Design Retired
It is not important if 69 kV or 13.8 kV is towards the utility, indeed.
Let's say 13.8 kV it is the supply side. The rated current of 40 MVA is 1673.5 A but actually only 13 MVA is required so only 543.9 A. If the transformer impedance voltage is 11% then X=13.8^/40*11/100=0.5237 ohm [since X/R >10 we may neglect R].
Then the reactive power across the transformer is 3* 543.9^2*0.5237=464.75 kVA.
However, a no-load current of 3% [50 A] considered entirely reactive will require SQRT(3)*50*13.8=1200 kVAR.
The load power factor -let's say=0.9 then Qload=sqrt(1-0.9^2)*13000=5666.6 kVAR.
The total supplied reactive power will be 5666.6+1200+464.75=7331.3 kVA.
sin(psi)=7331.3/13000=0.4716
pf=cos(psi)=sqrt(1-0.4716^2)=0.8258[8.24% less] viewed from utility side.
Let's say 13.8 kV it is the supply side. The rated current of 40 MVA is 1673.5 A but actually only 13 MVA is required so only 543.9 A. If the transformer impedance voltage is 11% then X=13.8^/40*11/100=0.5237 ohm [since X/R >10 we may neglect R].
Then the reactive power across the transformer is 3* 543.9^2*0.5237=464.75 kVA.
However, a no-load current of 3% [50 A] considered entirely reactive will require SQRT(3)*50*13.8=1200 kVAR.
The load power factor -let's say=0.9 then Qload=sqrt(1-0.9^2)*13000=5666.6 kVAR.
The total supplied reactive power will be 5666.6+1200+464.75=7331.3 kVA.
sin(psi)=7331.3/13000=0.4716
pf=cos(psi)=sqrt(1-0.4716^2)=0.8258[8.24% less] viewed from utility side.
sparknarc
New member
- Location
- North Carolina
Engineer
Engineer
I was wondering if your meter and the utility meter KW, KVA, KAR readings agree. You have already stated the PF does not agree. If these other values do not agree (taking into consideration the transformer losses which should not be significant) you more than likely have a meter setup problem. Does you meter provide you with a phasor diagram? This diagram would help you to determine if the phase orientation of the voltage and currents are correct. If the orientation of the voltages and currents are incorrect the meter will read incorrectly and could possibly give you bad PF readings.
Engineer
I was wondering if your meter and the utility meter KW, KVA, KAR readings agree. You have already stated the PF does not agree. If these other values do not agree (taking into consideration the transformer losses which should not be significant) you more than likely have a meter setup problem. Does you meter provide you with a phasor diagram? This diagram would help you to determine if the phase orientation of the voltage and currents are correct. If the orientation of the voltages and currents are incorrect the meter will read incorrectly and could possibly give you bad PF readings.
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