×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

F.G Wilson MTi 2001 PCB
2

F.G Wilson MTi 2001 PCB

F.G Wilson MTi 2001 PCB

(OP)
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

RE: F.G Wilson MTi 2001 PCB

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.  

RE: F.G Wilson MTi 2001 PCB

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

RE: F.G Wilson MTi 2001 PCB

(OP)
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

RE: F.G Wilson MTi 2001 PCB

(OP)
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

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources