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The worst power factor results you have experienced

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    The worst power factor results you have experienced?

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    Cast core dry type GSU. 44KV/6.6KV. Tested two identical units and both had these numbers or worse. Been sitting deenergized since last November. Fans and heaters don't work, unsurprisingly. Tested again after the units had the doors off and a chance to breathe fresh air and the numbers dropped to around ~9 or so. Brought in external heaters to dry them out but I won't be able to go back for testing, unfortunately. I'll ask the crew to keep me updated, if they test again. Engineering is actually okay with the second set of results not posted here.

    Both units have core ground issues as well. Engineering wants to fix the core ground issue before energizing. In a quick search, we found a black magic marker that was burned up, probably from the late 90's on one core and a 3/4 nut on the other core. Still didn't fix the core ground issue. No telling what the guys will find next week!

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    Quote Originally Posted by rofo42 View Post
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Name:	Screenshot 2021-06-10 202126.png 
Views:	12 
Size:	178.8 KB 
ID:	508

    Cast core dry type GSU. 44KV/6.6KV. Tested two identical units and both had these numbers or worse. Been sitting deenergized since last November. Fans and heaters don't work, unsurprisingly. Tested again after the units had the doors off and a chance to breathe fresh air and the numbers dropped to around ~9 or so. Brought in external heaters to dry them out but I won't be able to go back for testing, unfortunately. I'll ask the crew to keep me updated, if they test again. Engineering is actually okay with the second set of results not posted here.

    Both units have core ground issues as well. Engineering wants to fix the core ground issue before energizing. In a quick search, we found a black magic marker that was burned up, probably from the late 90's on one core and a 3/4 nut on the other core. Still didn't fix the core ground issue. No telling what the guys will find next week!
    After looking at the numbers my first question was going to be about any grounding issues. I had -15% PF once on a shielded liquid-filled transformer, main issues were moisture and grounding as well. Keep us posted on any updates!

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    High Power Factors

    I would perform calibration verification to make sure that the test set is working properly. Please note that the currents and watts for lines 3 and 4 do not match. Line 3 is the actual CHL (inter-winding) while line 4 is the calculated. Lines 2 and 3 the CH + CHL should equal line 1, CH+CHL, and they do not add correctly. There is an issues for the low side CHL as the watts do not match.

    Are the transformers properly grounded?
    Was the ground from your test set connected to the ground on the transformer being tested?
    Was there a jumper placed from the test equipment ground back to the chassis ground on the test set?
    If you used the blue LV lead try a test with the red LV lead. The same holds true for using the blue lead.
    Cast core transformers can be a pain as often times you can have negative numbers.
    An excellent paper on testing dry type transformers can be obtained by contacting your Doble client service engineer. Your CS engineer can also review the results and provide feedback.

    A PI is not valid on oil filled transformers but curious if you performed a PI on these units?

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