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Weird voltages on transformer

Posted By: SafetyWired

Weird voltages on transformer - 07/08/13 10:55 PM

Today had a call that parking lot lights were not illuminating. Here is the set-up: Primary V 208/120 3P feeding a 75KVA transformer. Steps up to 480/277v.
From transformer, circuit goes to a photo cell controlled contactor, which than energizes a panel with lighting circuits.
Photo control working correctly. Contactor opens and closes correctly. However...with contactor CLOSED I have these voltages from phase to ground on HV side. A:210 B:340 C:340. When contactor is OPEN I have A:177 B 178 C:160 Phase to phase whether A-B or A-C or B-C is 479-481V no matter if contactor is open or closed. I have never seen this before. Any theories.
Posted By: SafetyWired

Re: Weird voltages on transformer - 07/08/13 11:16 PM

[Linked Image]
Posted By: twh

Re: Weird voltages on transformer - 07/08/13 11:20 PM

Is your 277/480 neutral grounded?
Posted By: SafetyWired

Re: Weird voltages on transformer - 07/08/13 11:23 PM

Yes. This system has been in place since 2002. All of a sudden parking lot lights do not go on. I checked bond in xfmr, and also followed electrode back to main. First thing I checked after reading screwy voltages.

I believe it is in the xfmr coils themselves. I removed HV wires off xfmr lugs for giggles to see if voltage would change with nothing connected on that side. Voltages were the same.
Posted By: twh

Re: Weird voltages on transformer - 07/08/13 11:40 PM

With 480 volts on the lines, the neutral/ground voltage isn't possible without a bad neutral or ground. I assume your lighting is 277 volts. What else can it be?
Posted By: SafetyWired

Re: Weird voltages on transformer - 07/08/13 11:44 PM

Originally Posted by twh
With 480 volts on the lines, the neutral/ground voltage isn't possible without a bad neutral or ground. I assume your lighting is 277 volts. What else can it be?


It is 277v lighting. Please clarify your response, I do not quite understanding what you are saying the way it is worded...Thanks blush
Posted By: twh

Re: Weird voltages on transformer - 07/09/13 12:08 AM

I assume the lights not working is related to the odd voltage.

With a 480/277 system, you cannot have another voltage to ground besides 277 unless the neutral or ground wire is bad. That would also explain the lights not working.

It's my best guess.
Posted By: SafetyWired

Re: Weird voltages on transformer - 07/09/13 12:34 AM

Originally Posted by twh
I assume the lights not working is related to the odd voltage.

With a 480/277 system, you cannot have another voltage to ground besides 277 unless the neutral or ground wire is bad. That would also explain the lights not working.

It's my best guess.


This could mean the coils ground too than...correct?
Posted By: JoeTestingEngr

Re: Weird voltages on transformer - 07/09/13 12:40 AM

Sure sounds like secondary neutral bonding to me.
Posted By: SafetyWired

Re: Weird voltages on transformer - 07/09/13 12:51 AM

Neutral is bonded to frame with copper band, on xfmr than lugged electrode runs from chassis to main disc. bond. I were to run a second electrode temp from bond in disc to xfmr frame, and I still do not have 277...would it mean the neutral/ground is open in the transformer itself?
Posted By: twh

Re: Weird voltages on transformer - 07/09/13 04:34 AM

If your transformer neutral is grounded, you should have a neutral and a ground at the contactor. Right?

If both, neutral and ground, have odd voltages, then the problem must be where they originate - at the transformer.

The neutral and ground are connected to the transformer neutral with a lug. That connection might be bad. Some transformers have a bolt that goes through a fibre board that connects the transformer windings to the lugs. I've often thought they were a little loose right from the factory.
Posted By: Scott35

Re: Weird voltages on transformer - 07/13/13 04:55 AM

SafetyWired;

Below are a series of preliminary Questions, which should serve to address the issues at hand.

1.: Are the Non-Functioning Lighting Fixtures High Pressure Sodium, or Pulse-Start Metal Halide?

2.: Are the Non-Functioning Lighting Fixtures connected L-N (Line to Neutral - AKA "277V"), or are they connected L-L (Line to Line - AKA "480V")?

3.: What system are the Photocell and Coil(s) of the Lighting Contactor connected to: the 208Y/120V system, or the 480V system?
(i.e.: what are the Voltage Ratings of the Photocell and the Latching Coil(s) of the Lighting Contactor)

4.: The 1 Phase Voltage readings were made L-G (Line to Ground); is there a Grounded Conductor ("Neutral") available? Measuring L-N, instead of L-G.
The Branch Circuits _SHOULD_ have a corresponding Grounded Conductor if they are intended to be 277V Circuits.

5.: Does the Nameplate on the Transformer indicate One of the following specifications:

---------------------------------------------------------
a1. Primary = 480V Delta, Secondary = 208Y/120V 3 Phase 4 Wire
a2. Primary = 208V Delta, Secondary = 480V 3 Phase 3 Wire
a3. Primary = 208V Delta, Secondary = 480Y/277V 3 Phase 4 Wire
a4. Primary = 480V Delta, Secondary = 208V (or 240V) 3 Phase 3 Wire
---------------------------------------------------------

---------------------------------------------------------
b1. Pri. = 480V, Sec. = 208Y/120V 3P 4W
b2. Pri. = 208V, Sec. = 480V 3P 3W
b3. Pri. = 208V, Sec. = 480Y/277V 3P 4W
b4. Pri. = 480V, Sec. = 208V (or 240V) 3P 3W
---------------------------------------------------------

---------------------------------------------------------
c1. Hi Volts = 480V, Low Volts = 208/120V
c2. Hi Volts = 480V, Low Volts = 208V
c3. Hi Volts = 480/277V, Low Volts = 208V
c4. Hi Volts = 480V, Low Volts = 208-240V
---------------------------------------------------------

---------------------------------------------------------
d. Primary = 208V, Secondary = 480V
---------------------------------------------------------

Per Question #1:
The Pulse Ignitors used for starting HPS and MH Lamps may have failed, resulting in Non-Functioning Lighting.

Check Lamps for obvious aging indications.
Place a known operating Lamp of equivalent Wattage in the Circuit, in lieu of the existing Lamp, then energize the Circuit.
If Lamp starts, existing Lamp was bad.
If Lamp does not start, replace Ignitor with known operating Lamp, then re-energize Circuit.
If the Lamp still does not start, proceed to "Question #2"

---BTW:---

Clients are notorious for not accurately describing the real scenario, when it comes to the failure of something.
(They tend to leave out pertinent information, eluding to extremely odd and unlikely scenarios)
Example: "The Lights Just Stopped Working" means the last functioning Light Fixture has recently stopped working, leaving the entire area dark.

Try not to be swayed by abnormal claims of sudden Doom and Gloom occurring, especially when Lighting is involved.
Simple lack of Lighting Maintenance may be the culprit, wherein the claims of "Everything Worked Until Yesterday" may have been described to you per the Troubleshooting Request, leaving you to believe there has been some type of major system failure.

Check the most apparent failure types first, then dig into least possible failure issues as necessary.

-----------------------------------------------
-----------------------------------------------

Per Question #2:
Verify if the Ballasts are connected "L-N" (277V), or "L-L" (480V).

Please indicate if the Ballasts are connected as L-N (277V), or L-L (480V).

Verify the Voltage present at the Ballast's Input Section (where the Branch Circuit connects to the Ballast)
Use a LOW INPUT Z METER for these tests, in order to obtain an accurate reading.
If you only have a typical DVM / DMM, then either leave the Ballast + Lamp connected, or use a "Wiggy" in Parallel with the DVM.

This section of questions will determine if there is any mismatching of Ballast input Voltages, what level of Voltage Drop is being experienced, and if the original Branch Circuit Wiring may have been damaged (i.e.: New Sprinklers have been installed, etc...)

-----------------------------------------------
-----------------------------------------------

Per Question #3:
If the Photocell and Lighting Contactor Coil(s) are rated as 120V or 208V, and connected to the 208V system, that makes sense of why the Controls operate properly.
In addition, if these items have a rating of 480V and are connected L-L to the output side of the Transformer, they will continue to operate properly.

If the Controls were rated for 277V, and connected L-N to the Transformer's output, the extremely Low L-N Voltage measured at Open Contactor State would not allow for the latching of the Contactor, therefore you would not be able to obtain a L-N reading with the Contactor in Latched position (AKA "Closed").


-----------------------------------------------
-----------------------------------------------

Per Question #4:
Lack of a Grounded Conductor included with the Branch Circuits, typically indicates L-L (480V) Branch Circuits, instead of L-N (277V) Branch Circuits.

In addition, the odd L-G Voltage readings point to an Output from the 75 KVA Transformer being 480V 3 Phase 3 Wire - as an Ungrounded Delta, rather than a Solidly Grounded system.

The changes in L-G Voltage on the Output of the 75 KVA Transformer when the Lighting Loads are connected, is indicative of L-L connections, and an Ungrounded system.

As measured L-G at a relatively close proximity to the Transformer, with the Contactor Open (no Ballasts connected to the Transformer), the L-G Voltage is found to be dramatically less than what would be found on a Solidly Grounded Wye system.

The Phase Voltage on a 480Y/277V system will be 277V, meaning the L-N and L-G Voltage will both equal 277V near the Transformer (within 50 feet of the Transformer; as the length increases, Voltage Drops increase too).

For this system to be a solidly Grounded "Star Point Grounded" system, the L-G Voltage would not be so dramatically effected if the Ballasts were or were not connected.
In both cases, the L-G Voltage would measure 268V - 280V

Using a High Input Impedance Meter, the measured Open Circuit L-G Voltage of 160V to 178V, and the Closed Circuit L-G Voltage of 210V to 340V, definitely points to Capacitive Coupling effects being read by the High Z Meter.

Try testing L-G with a "Wiggy" to see if there is any Voltage indication.
Most likely, the Wiggy will indicate no Voltage measured L-G, but may show a rapid pulse, then "Drains Off" to indicate zero Voltage.
If connected L-L, the Wiggy will indicate 480V, with a nice solid pull from the Solenoid!

-----------------------------------------------
-----------------------------------------------

Per Question #5:
Please describe what the Transformer's Nameplate indicates.

If you have recorded what Terminals are involved per function, this information would be helpful too.

Example:
If Terminal "X0" is connected to the Grounding Electrode System, what are Terminals "X1", "X2" and "X3" connected to?
* A branch Circuit Breaker on the 208V system?
* A branch Circuit Breaker on the 480V system?

Most likely, what you have is an Ungrounded 480V Delta output, connected to 480V Ballasts.
Ungrounded systems will place large stresses between L-G, due to Capacitive Coupling, which is seen as very large L-G Voltages.
The Integrity of Conductor Insulation, as well as any components Insulation, may easily be exceeded, as it will be subjected to excessive Voltage levels.

For Lighting components, Ignitors and Capacitors may exhibit premature failure.
Ballast Windings may exhibit flash-over, or leak to enclosures.
Lamps and Lamp Sockets may show L-G damages, instead of L-L damages.

Good luck with the Troubleshooting!

Hope this post did not confuse you.

--Scott (EE)
Posted By: Scott35

Re: Weird voltages on transformer - 07/17/13 07:59 AM

---BUMP---

Hey SafetyWired; any News regarding the Haunted Lighting System??? shocked

Hopefully there will be minimal bash, cry and mad
from a lot of dunno, making you crazy and requiring aspirin

Avoid mixing coffee and beer, as that will make you confused and tired, and eventually sleep

Ahhh, have not posted a Rebus-Oriented response in Months...
Blame my Wife for the Spontaneous Jolliness, She has been influencing me all day!!!
Neither of us have accomplished very much today - as far as Productive work... however we have accomplished to knock down a great number of items, paperwork is scattered everywhere, cellular devices have gone unanswered (oohhh), and the Cats are very freaked out! Our Duck's demeanor, however, remains unchanged.

Gotta go, as I feel as if someone may throw a Pie at me... oooppps, too late, hit by pie... now I must retaliate!!!

--Scott (EE)
Posted By: Scott35

Re: Weird voltages on transformer - 07/30/13 05:03 AM

BUMP!

SafetyWired;

Did you rectify this issue?

--Scott (EE)
Posted By: afyon

Re: Weird voltages on transformer - 03/11/14 07:46 PM

@scott35, I think you covered this issue in more detail than anybody else could. Brilliantly answered query and Id really like to say thank you to you for this since you solved my issue. I wasnt really having the issue I think the thread creator was having but the answer I was found was for question four. Once I correctly connected neutral and ground connections, all the readings I got were somehow precisely accurate.
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