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TRANSFORMER POWER FACTOR TEST
2

TRANSFORMER POWER FACTOR TEST

TRANSFORMER POWER FACTOR TEST

(OP)
Good day.

I have an arc transformer (42 MVA, 13,2 kV / 557 V).  The high voltage winding in near the core and the low volgate winding is over it.

3 years ago the power factor was:  
1. AT          0,59  AT VS EARTH + AT VS BT
2. AT  GST     0,63  AT VS EARTH
3. AT-BT (UST) 0,56  AT VS BT
4. BT          0,45  BT VS EARTH + BT VS AT
5. BT  GST     0,15  BT VS EARTH
6. BT-AT (UST) 0,52  BT VS AT

The transformer was outdoor for three years (without tension) and Actualy the power fator is:

1. AT          0,61  AT VS EARTH + AT VS BT
2. AT  GST     0,74  AT VS EARTH
3. AT-BT (UST) 0,52  AT VS BT
4. BT          1,16  BT VS EARTH + BT VS AT
5. BT  GST     3,33  BT VS EARTH
6. BT-AT (UST) 0,51  BT VS AT

Why reason the mesure number 5 , the power factor of 0,15 in the past in now 3,33  ?

Can I energizer the transformer?



 

Juan C. Castro G.
High Voltage Electrical Engineer

RE: TRANSFORMER POWER FACTOR TEST

A power factor greater than unity is not possible: it varies from zero lag through unity to zero lead. What are you measuring?
  

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If we learn from our mistakes I'm getting a great education!
 

RE: TRANSFORMER POWER FACTOR TEST

The power factor test is not really greater than 1, 3.33 is really 3.33% which is a bit high.  NETA spec's states that it should be <2%.

I don't quite trust your test results and would like to see them all.  For the watts and ma's Test 4 - test 6 should equal test 5.  This tells if your test results are correct.  

Your results show that the high and low side to ground are 1.16 while the low to ground by itself is 3.33 which strikes me as unusual.

Was every thing off the low side during testing?  Were the bushings cleaned?  Is this an oil filled transformer or dry type, I assumed that it was oil.  What voltage was the low side tested at?

What do you get for a megger reading on the low side?  Did you do a PI?
 

RE: TRANSFORMER POWER FACTOR TEST

(OP)
Hi pwrengrds, thanks for your answer

The transformer is in oil, in HV there are three clean bushings and in LV there are no bushings, the terminals of LV are a few slides (platens) that go out across a bakelite, the transformer was outdoor during three years and and I belive that is moisture (humid) in the bakelite

The data transformer are:

42 MVA
13200 V  / 557 V
Arc transformer
Windings of HV is near the core and windings of LV is over HV

3 years ago the power factor was:  
1. AT        74,7 mA   10,6 W   0,59 PF  (AT VS EARTH + AT VS BT)  
2. AT  GST     31,5 mA   4,74 W  0,63 PF  (AT VS EARTH)
3. AT-BT (UST)  43,20 mA   5,86 W   0,56 PF  AT VS BT
4. BT          54,6 mA   5,94 W   0,45 PF   (BT VS EARTH + BT VS AT)
5. BT  GST     11,08 mA   0,43 W   0,15 PF   (BT VS EARTH)
6. BT-AT (UST)   43,52 mA   5,51 W    0,52 PF (BT VS AT)

The transformer was outdoor for three years (without tension) and Actualy the power fator is:

1. AT          78 mA  4,82 W   0,61 PF  (AT VS EARTH + AT VS BT)
2. AT  GST     33,1 mA   2,48 W  0,74 PF (AT VS EARTH)
3. AT-BT (UST) 44,3 mA   2,32 W   0,52 PF  (AT VS BT)
4. BT           58,7 mA  6,82 W   1,16 PF  (BT VS EARTH + BT VS AT)
5. BT  GST     14,14 mA   4,71 W  3,33 PF  (BT VS EARTH)
6. BT-AT (UST)  44,3 mA   2,28 W  0,51 PF  (BT VS AT)


Why reason the mesure number 5 , the power factor of 0,15 in the past in now 3,33 ans the Wattios  were 0,43W and now 4,71 W ?

Thanks


 

Juan C. Castro G.
High Voltage Electrical Engineer

RE: TRANSFORMER POWER FACTOR TEST

It wouldn't suprise  me if the bakelite was wet, being outdoors for years.  It would explain the high readings on the low side.  Any way to take them off and retest or get them replaced?  

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