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Join Date: Jun 2016
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Zenith Transfer Switch VT Issues

07/12/2017 6:17 PM

Zenith GE 1200 Amp Closed Transition Switch has voltage sensing issues. (600vac 3-phase circuit.) It will sense a huge voltage imbalance on utility lines, thereby causing 500KW Genset to run unecessarily. Transfer switch is controlled by Entelligard 250 Electronic Controller. Voltage will read correctly around 600vac, but anything above or below that number, reading is out by 10% or more. Has anybody run into this issue before? We have calibrated multiple times,not getting better results.

I have inserted a link to schematic of Controls Power Supply. Can anybody explain why they have the voltage Xformers set up this way? (When looking at control board only 2 Xformers are visible.) Shouldn't there be 3 vts to correctly sense a 3phase circuit?

Ironically enough, when the voltage was dangerously high a few weeks ago (750vac, confirmed by 2 fluke meters) only 630vac was sensed. We had to switch on genset manually.

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Guru

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#1

Re: Zenith Transfer Switch VT Issues

07/12/2017 8:32 PM

Is it possible you have the wrong sensors installed? Is it possible something is interfering with the signal? Is it possible the sensors have been damaged?

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Active Contributor

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#2
In reply to #1

Re: Zenith Transfer Switch VT Issues

07/12/2017 8:54 PM

This unit came prewired from the GE factory. We only connected all main power lines.

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#3
In reply to #2

Re: Zenith Transfer Switch VT Issues

07/12/2017 9:14 PM

Maybe you need them to show you how to set it up so it works....or attend a training session to qualify yourself.....

Section 7

http://apps.geindustrial.com/publibrary/checkout/DEP-148A?TNR=Renewal%20Parts%7CDEP-148A%7Cgeneric

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#4
In reply to #3

Re: Zenith Transfer Switch VT Issues

07/13/2017 2:58 AM

Yep. Nothing beats interaction with the Original Equipment Manufacturer for solving problems with its equipment.

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Guru

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#5

Re: Zenith Transfer Switch VT Issues

07/13/2017 9:14 AM

Ref. REH question about why 2 transfos in "V" are used, rather than 3. It is cheaper and if you have a 3 wire system @ 600V, adequate. Theoretically, you can get the third line-line voltage with an instrument VT from the "open" secondaries or by a calculation using the angle between the two voltages you have.

I do not have any knowledge of the Zenith system, but since you write "voltage transformers", not "potential transformers", maybe you are in the 50Hz world.

So I wonder...

  1. Are the transfos XN. and XE. (maybe XN2, XE2 were not changed) made for 60 Hz & saturating on 50 Hz??
  2. Is there a 50/60 Hz selection by link or software which has not been applied?
  3. Are you getting frequency variations from normal, USA system is 60 +/- 0.02 Hz, so they tend not to consider frequency effects?
  4. Are your VTs connected where voltage fluctuates with load from what it should be, because someone thought it was easier & quicker to connect to the nearest point?
  5. Did someone fix the display to read correct, then make a "quick getaway" because they could not fix a problem?
  6. Have you checked carefully to see if the voltages (in Zenith figure 19 you linked) between the [transfo secondary] 3 wires identified by "2 Phase Source 1 Sensing" (wires 803, 804, 807) and corresponding 3 wires for Source 2 are in proportion to their primary voltages and the busbar line voltages they should measure?? You have mentioned one time when you got 750V busbar & 630 displayed, but have you made a planned systematic check? I think the secondary voltage is 10V line-line but bad drawing has put the numbers "1" over the wires.
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#8
In reply to #5

Re: Zenith Transfer Switch VT Issues

07/14/2017 2:46 PM

Thanks for the detailed reply.

1- This is a 600 volt 3phase 4-wire 60 hz system. All componenets are marked 60hz.

2- Not aware of any hz selector switches or menus.

3- Hz are very consistent at 60.

4- Controls power supply is connected directly to 1200 amp bus, so no voltage drop issue.

5- I have calibrated display numerous times to read correctly, only to see it performing even worse the next day.

6- I think this is the issue. The primary voltages today read 585v,612v, & 613v respectively.. At the same time the secondary voltages were at 11.74v, 11.77v, &12.25v, so the proportions are certainly not correct.

We're now trying to get GE to send us a new CPS, after finding out that the current one is a replacement unit. What is a refurbished $500 part, doing inside a brand new $100000 piece of equipment???

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Guru

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#9
In reply to #8

Re: Zenith Transfer Switch VT Issues

07/15/2017 6:29 AM

OK, thanks.

yr 1- OK

yr 2- Fig 6 of manual referenced by yr document has Fig 6 with JP3 for frequency

3- OK

4- Not even a fuse in path !!??

5- something drifting about badly.

6- Comes out as HV/LV 49.8, 52, 50.04 for 585, 612, 613. The 52/612 is the odd one. Remember that you only actually have two voltages in the V -- for the diagram you gave the XN1 and XN2 transfos. I would measure at the transfo HV & LV terminals and compare ratios XN1 to XN2.

Do you get errors just on mains supply indication from XN1,XN2 or also on generator - which would be XE1, XE2??

I am suspicious that XN1, XE1 also supply control power - not just "10V winding" potential - a bad connection will have more current (varying maybe) and volt drop.

HV terminal 21 feeds both transfos & high resistance would affect both voltages.

Look carefully at LV voltages & ratio to HV terminals of transfo - a fluctuating reading not seen at HV may be due to a bad connection inside windings - sparking will upset electronics.

I had a intermittent, deteriorating voltage/frequency indication problem eventually traced to the lugs on the transfo on a printed board where the solder had cracked. Pushing/pulling wiring & transfo found fault after fluctuating LV voltage at instruments fed by transfo found. Resoldering fixed problem.

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Power-User

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#6

Re: Zenith Transfer Switch VT Issues

07/13/2017 11:42 PM

The 2 transformers are sensing as an open Delta, which would be fine if you didn't have a load or supply that is loading between one of the lines and ground. What sort of circuit configuration is the utility supply and the load? Open deltas are used in most 3 phase switchgear PT drawers and also most utility installations for medium voltage. Using this for low voltage would not be a problem unless you have improper connectiuon madein either supply or load.

Go back to when the problem first started and look at what changes were made right before then. I would vote for a phase to ground load that should have been connected to the neutral instead. I would say call GE-I&SE but they have probably changed the name by now. The phone used to be 800-533-5885.

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Power-User

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#7

Re: Zenith Transfer Switch VT Issues

07/14/2017 12:55 AM

This should not be the case, but your results are consistent with the following issue.

Can you assure your waveform is sinusoidal?

The circuit used for voltage measurement in industrial equipment usuallu measures the FILTERED RECTIFIED voltage, instead of RMS voltage, because of easier control and higher reliability. The relationship between RMS and AVG is called form factor. Therefore, different waveforms mean different rate between voltage measured with Digital Multimeter and measured with industrial machine.

If this were the issue, calibration would not help (unless it is voltage dependent).

If you do not know your waveform, measure it with an oscilloscope.

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