F.G Wilson MTi 2001 PCB 2

[waross]

Hi friends.
I have a specific problem with the control card in an F G Wilson Automatic Transfer Switch.
The card is an MTi 2001, The print is dated 16 Dec, 1996.
This is a card that pre-dates the commercial release of these cards. I originally installed the card in an existing transfer switch as part of the Beta test program.
The control works well in the event of power failures, however a new issue has arisen.
The utility voltage is getting lower. Their system is short of power and is importing power. The utilization voltages are tending lower. This is a 120:208V wye system. When the line voltage drops to 110:190 Volts, prudence would dictate a transfer to backup power. Therein lies the problem.
It is quite a long way from the transformers to the transfer switch. The voltage drop in the feeders is greater than the dead band in the voltage monitor circuit of the transfer switch.
Typically, the line voltage drops to the cut-out point and the switch transfers to the backup set. As soon as the load is dropped, the voltage rises above the cut-in point.
The control card interprets this as a "Mains Return" and after 15 seconds transfers back to the mains. As soon as the load hits, the voltage drops and the ATS tries to go back on standby.
Any discussions on a work-around will be welcome.
There is a replacement transfer switch on hand. It is a different manufacturer and may or may not have the same issue. But, just sitting there, the replacement switch limits my options to a solution that will cost less than the labor to install the replacement switch. Labor is cheap here.
Given the loads on the transformer bank, it may be possible to use a dual voltage scheme.
That would be to reconnect the transformers for 240:416V and feed the other loads from the center taps of the transformers at 120:208V Then use auto transformers to drop the voltage back to 120:208 at the panel.
The information is available to check the load profiles on the transformers to see if this would remain within the rating of the transformers but this option will probably be rejected on the basis of cost.
I am thinking of some type of control system work around rather than a major hardware solution.
Thanks in advance.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[catserveng]

Bill,

I had a similar problem on a Pacific island a few years ago. I could not find an off the shelf transfer switch controller with a broad enough range to deal with the problems. I ended up making my own controller with using some Time Mark Motor Minder relays and a MicroLogix PLC, I also used a Dayton voltage sensing relay that had a real good turndown. Needed status from the ATS as to which source it was on. I also added a "Manual Return to Utility" pushbutton switch, so the operator who would come out and check on the standby after start could check the meters and decide if it was ok to put the system back on utility.

I used the motor relays because they had 3 phase sensing, so they did pretty good a seeing a real utilty problem, and the one I used also had a phase sequence sensing, since sometimes when the standby dies they would drag anything they could get their hands on and hook it up (the was not a phase rotation meter to be had on the island)this helped prevent some followon issues.

It was kinda a Rube Goldberg setup, but it gave me enough flexibility to deal with the actual site issues. Most of the ATS controllers I deal with these days want things pretty tight, and don't seem to allow much adjustment range.

If you're interested I could dig up the drawing and parts list.

Mike L.

 

[niallnz]

Why not change the location of the voltage sense the ATS uses to the output of the transformers not you main switchboard. The ATS is working correctly, and you are satisfied with its functionality. Changing the location of the sense will ensure that the generator only changes over when the utility fails.

The real problem appears to be your load growth and incoming cable size. Power factor correction at you main switchboard may help.

Cheers Niallnz

 

[waross]

Thanks Catserveng and Niallnz.
There are a few contra-indicators to moving the sense connection to the transformers.
These are the distance, access for installation and protection of the sense wires.
However the main issue is a main breaker adjacent to the ATS. We want to go to back up if the breaker trips. Maybe not the best idea but the customer insists and he is always the customer. If moving the sense connection was feasible it would be a very good solution.
I remember trouble shooting a phase rotation reversal on the standby set with a monitor with phase sequence sensing.
I haven't checked frequency with an electric clock for a few decades now. You just can't find an electric clock with a synchronous motor any more.

I am thinking of using a relay arrangement and a voltage monitor configured so that the ATS will control the drop out point, but control will then be assumed by the added voltage monitor which will control the pull in point.
Gotta go. I have an insistent 4 year old who wants me to take him bike riding. I'll elaborate more later.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Update;
Thanks for the helpful suggestions.
I will be able to easily and economically devise a circuit to use an external monitor to control the return to utility power. I won't be doing it. From past experience in this area, I anticipate that it will be defeated anyway. The generator is running and the lights are back on at the neighbors. Something is wrong with the generator again. Been there done that. I have set the voltage down to about 105 volts. The transformer taps have been pushed up by the last expert. (He didn't know how to change the voltage settings on the ATS.)
From the voltage profile I see that low voltage events are not as frequent as the customer has led me to believe. Letting the customer replace the occasional motor that may have failed because of occasional low voltage seems the best overall solution. (I have set the voltages the same on all three phases and dropped them a little.)

FYI, I have included part of the voltage log.
It is good to have good relations with the local utility.
The commercial metering department was good enough to send a tech out to the revenue meter to download two months of voltage and current readings taken at 15 minute intervals. The files were emailed to me.
The log runs from 25 February to 30 April, 2010
I have included the start and end of the logs. We don't need all 6200 data points for illustration.
Work with your local commercial metering department, there is a wealth of information available on the new electronic meters, sometimes just for the asking.

Report Title: Datos de Voltajes
Project Title:
Reference 1: Voltajes por Fase
Reference 2: Medidor No.******
Device Id: ********************
Start Date/Time: 25/02/2010 0:15
Stop Date/Time: 30/04/2010 14:00
Date Time Volts A Volts B Volts C FLAG

25/02/2010 0:15 120.36611 121.26005 125.21981
25/02/2010 0:30 122.60506 123.28828 126.60174
25/02/2010 0:45 123.22337 124.01613 127.15345
25/02/2010 1:00 120.94627 122.06556 125.028
25/02/2010 1:15 122.21293 123.35315 126.63333
25/02/2010 1:30 126.3962 127.49902 130.59862
25/02/2010 1:45 125.71396 126.6807 130
25/02/2010 2:00 124.35433 125.09197 128.34329
25/02/2010 2:15 125.52291 126.11106 129.32131
25/02/2010 2:30 125.87295 126.38038 129.41406
25/02/2010 2:45 125.69805 125.95237 128.76335
25/02/2010 3:00 125.85706 126.25371 129.1201
25/02/2010 3:15 126.17448 126.52273 129.41406
25/02/2010 3:30 126.19033 126.52273 129.35223
25/02/2010 3:45 125.28368 125.68214 128.42118

*************************************************************************************************

30/04/2010 3:45 124.996 124.64349 128.23416
30/04/2010 4:00 125.26771 124.96399 128.51459
30/04/2010 4:15 125.4751 125.20383 128.76335
30/04/2010 4:30 125.88884 125.66622 129.19752
30/04/2010 4:45 126.41202 126.17448 129.72278
30/04/2010 5:00 126.07934 125.98413 129.35223
30/04/2010 5:15 126.33289 126.20618 129.61481
30/04/2010 5:30 127.0433 126.87001 130.32268
30/04/2010 5:45 126.22203 125.98413 129.38315
30/04/2010 6:00 125.84117 125.65031 128.9496
30/04/2010 6:15 125.98413 125.74578 129.42952
30/04/2010 6:30 126.47529 126.23787 130.19985
30/04/2010 6:45 126.52273 126.26955 130.18448
30/04/2010 7:00 126.69649 126.50692 130.39939
30/04/2010 7:15 127.07478 126.82271 130.73638
30/04/2010 7:30 126.36455 126.15863 129.95384
30/04/2010 7:45 125.80938 125.63439 129.35223
30/04/2010 8:00 126.04761 125.90473 129.67652
30/04/2010 8:15 126.58594 126.58594 130.21521
30/04/2010 8:30 126.60174 126.61753 130.12302
30/04/2010 8:45 126.3962 126.41202 129.89226
30/04/2010 9:00 126.25371 126.42785 129.75361
30/04/2010 9:15 142.07041 0 196.0102
30/04/2010 9:30 0 0 0 O
30/04/2010 9:45 0 0 0 O
30/04/2010 10:00 0 0 0 O
30/04/2010 10:15 0 0 0 O
30/04/2010 10:30 0 0 0 O
30/04/2010 10:45 104.19213 105.83005 107.14476
30/04/2010 11:00 116.29273 118.23705 119.81653
30/04/2010 11:15 115.96551 118.59174 120.56533
30/04/2010 11:30 116.12063 118.11858 120.14991
30/04/2010 11:45 116.82465 118.3385 120.53215
30/04/2010 12:00 114.73448 116.29273 118.54113
30/04/2010 12:15 114.03508 116.08617 118.45674
30/04/2010 12:30 115.56816 117.4734 119.88328
30/04/2010 12:45 116.48176 117.83039 120.43255
30/04/2010 13:00 114.76933 115.96551 118.558
30/04/2010 13:15 114.8216 116.1034 118.86126
30/04/2010 13:30 114.66473 115.91376 118.65918
30/04/2010 13:45 112.65878 114.01754 116.63619
30/04/2010 14:00 114.31535 115.63736 118.38919

Period Totals Volts A Volts B Volts C

HIGH 255.99219 129.44497 255.99219
Time 22:00 1:45 22:00
Date 25/04/2010 21/04/2010 25/04/2010
LOW 40.9878 0 42.04759
Time 22:45 12:45 22:45
Date 05/03/2010 28/02/2010 05/03/2010
Average. 122.68501 122.62243 125.59303
Total Usage
Load Factor 0.47925 0.94729 0.49061

Flag Description Count
O Power Outage 56


Bill
--------------------
"Why not the best?"
Jimmy Carter