3 Phase Generator Transfer Panel Not Sensing Power Failure

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dbrown98500

dbrown98500

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West Palm Beach Florida
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Director of Engineering
Good afternoon all. I have a transmitter site fed by Florida Power and Light with 3 phase power. Occasionally we will have a power failure on one leg of the 3 phase and the transfer panel will not sense the failure. If I manually start and transfer the load, all is good. I have been told the reason for the lack of sensing the failure is that we have a "corner grounded three phase" circuit feeding the building and the transfer switch cannot sense it when the "grounded phase" is the one with the failure ???

Does anyone have any advice on how to get the transfer panel to operate automatically correctly on all three phases regardless of which one is lost ??? It is an ASCO transfer panel btw.....

I sure appreciate the advice.

Dave
 
You may need to get a phase loss relay that will monitor the negative sequence voltages.

You can find these from many manufacturers but don't be surprised at the cost of some of them. I have used ones from Basler and Schweitzer, but I think you might find some dedicated ones in small DIN rail packages.
 
get three control relays with whatever coil voltage the power is.

wire a relay A-B, B-C, and C-A.

wire normally closed contacts from each relay in parallel to the ATS switch command input. if any relay drops out, the ATS will operate.
 
Diversified / ATC makes a nice line of phase loss/reversal/under voltage relays. Or call your ATS mfg they may have a relay that would work
 
Before you: Ass | u | me I would do a simple test to determine if it is a true Corner Grounded Delta service. Take a voltmeter and measure:
Phase A to gnd = ?
Phase B to gnd = ?
Phase C to gnd = ?
One of the readings will read zero if it's corner grounded. Then you can proceed with what Jim suggested, but 3 phase sensing on on transfer switch is usually done on a phase to phase basis, not phase to ground. This is an interesting question. So what happens to the 3 phase to phase voltages if the grounded phase is lost? Maybe nothing because you can still read 3 phases with just 2 xfmr windings such as in an Open Delta configuration! An Open Delta circuit is a cheap way of using just 2 xfmrs in control circuits to produce a 3 phase voltage, usually for metering or V sensing.
Can you provide the catalogue # and serial # of the ASCO ATS or take a pic of the nameplate? I need to look at the schematic/ wiring diagram before we can see just how the 3 phase sensing is accomplished.
 
The negative sequence relay will even work if one if the fuses blows on the primary side.

If your process must run during power losses, and it must since you paid for a generator, then what is a few $k to stay in business?
 
I still have my doubts that the system was not designed for a loss of phase (single phasing) condition.
We need the nameplate info to see the voltage sensing circuit.
 
ptonsparky said:
The company that sold and/or installed that unit should be fixing it. That's a BS issue.
Click to expand...
The last one I worked on was a design and build. The contractor never considered the loss of a unity side fuse. At least they had specified a multifunction relay as part of the automatic throw over scheme.

Took me 18 hours of travel and 3 minutes on-site to implement.
 
jim dungar said:
The last one I worked on was a design and build. The contractor never considered the loss of a unity side fuse. At least they had specified a multifunction relay as part of the automatic throw over scheme.

Took me 18 hours of travel and 3 minutes on-site to implement.
Click to expand...
But you know what you are doing. That usually makes it a lot easier. And quicker. :)
 
Thank you all, I will head out to the transmitter site and check the nameplate on the transfer switch etc... interesting to note our competitor has an Onan transfer switch and we have the ASCO but they both have the same issue.
 
dbrown98500 said:
Yes, always on the primary side of the FPL transformer. It's a fairly remote site and we are the only customers on the line running about a mile in...
Click to expand...
Talk to your phase loss relay manufacturer. Sensing a primary side single phase with a delta secondary is sometimes harder than it first seems.
 
Jim makes some excellent points and recommendations.
Do you know the configurations of the windings and core of the FPL transformer? It can have a significant influence on what the secondary side does in response to the loss of a phase on the primary.

On pg. 1-2 in the paper at the first link below it says:
"The response to an open-conductor condition depends on transformer construction. Table 1... shows the voltage response of unloaded and/or lightly loaded transformers for various transformer winding and core configurations to an open phase (A) on the primary. As can be seen in the table, under no-load conditions delta connected primaries and wye primary transformers that do not have a delta connection on their secondary/tertiary or are not a core-form transformer result in low voltages on their primary and secondary. Whereas, the wye connected primaries that have a delta connection on their secondary/tertiary or are core-form transformers, recreate the voltage to 1 pu in the open phase. This illustrates the fact that certain transformer configurations may not require the same protection needed for those transformers that recreate the voltage."

http://www.pes-psrc.org/kb/published/reports/K11_8.70_OpenPhaseDetectionNuclear.pdf

https://selinc.com/api/download/124320
 
Hey again all, so I travelled out to the site and obtained the following information and pictures. I was also wrong, it is a Lakeland transfer switch.

On the transfer switch phase sensor...
A to ground is 132.0v
B to ground is 156.7v
C to ground is 135.2v

A to B is 243.7v
B to C is 243.3v
C to A is 241.5v


FPL transformer
FPL Transformer.jpg

Lakeland phase sensing relay
Transfer Switch Phase Monitor.jpg


Secondary transformer
Secondary Transformer Schematic.jpg

Secondary Transformer
Secondary Transformer.jpg

Transfer switch nameplate
Transfer Switch Nameplate.jpg
 
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