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TILT test A to C short

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Sparkyette

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Location
Washington State
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Electrician
During commissioning of a data center a TILT test was performed on five separate transformers being fed from their own generators. Each test indicated a short between A and C phase. The test itself was physically performed at the line side bussing inside of the building. There are eleven parallel feeds for each phase and ground. There is no neutral. This was my first experience on commissioning and my first experience using the TILT meter. After reading their literature and after conducting an online search for an explanation I am reaching out to this forum. The readings cannot be a coincidence. Any thoughts or explanations?
 
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hillbilly1

Senior Member
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Had to look that one up, never heard of it before. Looks to be similar to a meg test, so was both primary and secondary disconnecting means open? If not, probably reading through a load or generator winding.
 
synchro

synchro

Senior Member
Location
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EE
Are there any power factor correction capacitors on either the primary or secondary side of the transformers that remain connected during the testing?
 
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Sparkyette

Member
Location
Washington State
Occupation
Electrician
synchro said:
Are there any power factor correction capacitors on either the primary or secondary side of the transformers that remain connected during the testing?
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I do not know. However, that is what I was leaning towards as an explanation. It is my understanding that these large backup generators have a capacitor or capacitors in order to allow a generator to come up to full speed. If that is so, why only a short between phase A and C? Do generators only need one capacitor in order to come up to speed? Also, is A to C the typical place for the capacitor?
 
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ramsy

Roger Ruhle dba NoFixNoPay
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Joethemechanic said:
Hmmmmmm, interesting

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Watched the entire presentation, and this was my understanding.

Unlike a Megger, the proprietary TILT is a low voltage tester, which won't detect high resistance faults, and would be destroyed by energized lines.

The disclaimer at the 12:00 minute mark clarifies "Partially Failed" issues are not detected. I believe this referrs to the higher-resistance faults.

The "OK" idiot light is designed to differentiate xfmr coil resistance from shorts, which a Megger will read as Ohms without an idiot light.
 
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Sparkyette

Member
Location
Washington State
Occupation
Electrician
Joethemechanic said:
Hmmmmmm, interesting

Click to expand...

ramsy said:
Watched the entire presentation, and this was my understanding.

Unlike a Megger, the proprietary TILT is a low voltage tester, which won't detect high resistance faults, and would be destroyed by energized lines.

The disclaimer at the 12:00 minute mark clarifies "Partially Failed" issues are not detected. I believe this referrs to the higher-resistance faults.

The "OK" idiot light is designed to differentiate xfmr coil resistance from shorts, which a Megger will read as Ohms without an idiot light.
Click to expand...
The video is appreciated. It explained a few things for me. The situation I was faced with was slightly different. I did not have the transformer in front of me. Instead, all five backup generators were/are connected to their respective transformers outside of the building. All five transformers have their parallell feeds (each phase has eleven copper wires, 500s?) and grounds (no neutrals) landed on busbar at the line side of the respective main breakers inside the building. I took readings inside of the building during non energized conditions. The video hints that I need to double check the breakers and ensure all five breakers are in the open position thereby not reading a short through a connected load. The video also suggests I need to disconnect the primary side of the transformer. Am I interpreting this correctly?
 
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Sparkyette

Member
Location
Washington State
Occupation
Electrician
synchro said:
Are there any power factor correction capacitors on either the primary or secondary side of the transformers that remain connected during the testing?
Click to expand...
I do not know. I shall check tomorrow at work. Would that explain reading a short between only A and C phases? Or should I expect to see shorts on A-B A-C B-C?
 
Joethemechanic

Joethemechanic

Senior Member
Location
Hazleton Pa
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Electro-Mechanical Technician. Industrial machinery
Sparkyette said:
The video is appreciated. It explained a few things for me. The situation I was faced with was slightly different. I did not have the transformer in front of me. Instead, all five backup generators were/are connected to their respective transformers outside of the building. All five transformers have their parallell feeds (each phase has eleven copper wires, 500s?) and grounds (no neutrals) landed on busbar at the line side of the respective main breakers inside the building. I took readings inside of the building during non energized conditions. The video hints that I need to double check the breakers and ensure all five breakers are in the open position thereby not reading a short through a connected load. The video also suggests I need to disconnect the primary side of the transformer. Am I interpreting this correctly?
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Yeah most of us are still looking into this TILT tester thing. We normally go about things with a megger.

I would assume that your readings on all three phases would be consistent . I think the capacitor question was just to understand the circuit for troubleshooting tests.

How big of transformers? What voltages? Wye or delta?
 
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Sparkyette

Member
Location
Washington State
Occupation
Electrician
Joethemechanic said:
Yeah most of us are still looking into this TILT tester thing. We normally go about things with a megger.

I would assume that your readings on all three phases would be consistent . I think the capacitor question was just to understand the circuit for troubleshooting tests.

How big of transformers? What voltages? Wye or delta?
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I will look tommorrow to see how big, the voltages, wye/delta, etc.
 
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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Sparkyette said:
Why only between A and C of all five transformer/generator pairings?
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If the generator breaker is open, there may be a voltage sense wire tied onto the load side of its breaker, which may be causing the reading. If these generators are connected in parallel, it might be something to tell the generator controller that voltage is present? Check for control wires coming off the load side of the breaker. I’ve done up to 2 meg generators, but have only worked on one that was paralleled, and I didn’t wire it.
 
Joethemechanic

Joethemechanic

Senior Member
Location
Hazleton Pa
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TwoBlocked

TwoBlocked

Senior Member
Location
Bradford County, PA
Occupation
Industrial Electrician
Sparkyette said:
Why only between A and C of all five transformer/generator pairings?
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Wouldn't an "A" cable crossing over and landed on a "C" terminal (and another one from "C" to "A") cause this? Isn't that one of the things the TILT tester checks for? What reading do you get with a regular ohm meter?
 
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