TRANSFORMER POWER FACTOR TEST 2

[juanccga]

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

 

[ScottyUK]

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!

 

[pwrengrds]

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?

 

[juanccga]

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

 

[pwrengrds]

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?