110v transformer problem

[Crosswire]

Was called to look at a 3phase 400/110v 10KVA transformer on a building site. The workers had been complaining their power tools ran slow.

Found 230v on all 3 phases and 400v between all phases.

Transformer output was 55v between phases. Healthy transformer on floor above, (which was on same feed) showed 110v between phases.

Found another transformer and swopped it over. Problem remained.


Now, either I've swopped one faulty transformer for a second faulty transformer, or their is another problem..

What would cause a transformer to output , only 55v between phases and not 110v?



All ideas appreciated

 

[Plonker 3]

Whats the output KVa rating of the transformers, whats the KVa rating of the power tools being used?

 

[itselectric]

Are you sure you have 400v between phases, is it not possible one of your input phases is out. Did you measure the voltage with transformer plugged in, or did you measure supply only. masure voltages at source in case you have a phase down

 

[Darkwood]

Do the correct testing sequence for the supply not forgetting a lost phase will still show as 230v as it feeds back through the TX winding.... Disconnect from TX and test is necessary to eliminate false positives.

The supply may still test ok but an upstream poor termination may manifest issues only under load conditions.... re-test ensure 3ph supply and that all sequences of LINE/LINE test show 400v.

If you do find a phase down following the correct test procedures then give yourself a slap! ...you should know better about testing sequence of 3ph..:bucktooth:

Note! -- 2 different TX's used same symptoms point to supply issues!

 

[Crosswire]

Lost phase was my first thought.

I did measure with T/X still connected, but that upstream T/X on the floor above worked fine with the same power tools , and showed 110v between phases on output side, whereas the first transformer showed 55v between phases on output side.

Will recheck phases again tomorrow, and if there is a phase down will commit ritual suicide so as to restore the honour of my family..........

Remember they are on same supply, looped from the first T/X (faulty) to the second T/X (fine)

Trannies are 10KvA , didn't check power tools but are standard 110v builidng site tools, nothing special.

 

[Darkwood]

OK then prime suspect is a terminated phase loop from TX1 been poor hence TX1 ok TX2 not... List all results for us if phases are ok!... Test the loop cable for damage.

When something gets initially confusing its easy to miss the obvious and skip vital testing without realising.


T.U.R.D.

-Test it
-Understand it
-Retest it
-Decide

 

[Crosswire]

OK then prime suspect is a terminated phase loop from TX1 been poor hence TX1 ok TX2 not... List all results for us if phases are ok!... Test the loop cable for damage.

No is other way round , TX 1 not working, TX 2 is fine.. This is what is confusing me.

 

[Darkwood]

Swap TX1 with TX2 or another TX you know is ok... Do the TX's have integral fusing maybe a fault on the connected equipment has taken out a fuse in the original and then as the fault still existed again in the replacement.

Test off load first and PAT check loads before plugging in.

As you have multiple outputs fro a 3ph Tx the outputs will be balanced across 3phases so i assume not all outputs have L-L 55v.

 

[Marvo]

.....T.U.R.D.

-Test it
-Understand it
-Retest it
-Decide

Hats off to you for getting that past the potty mouth detector. Did you just make that up or is it how you were taught? I think I'm going to steal it and use it either way

 

[Darkwood]

Hats off to you for getting that past the potty mouth detector. Did you just make that up or is it how you were taught? I think I'm going to steal it and use it either way

Totally made up lol ... was thinking if you don't follow it you may end up in it

 

[Crosswire]

Swap TX1 with TX2 or another TX you know is ok... Do the TX's have integral fusing maybe a fault on the connected equipment has taken out a fuse in the original and then as the fault still existed again in the replacement.

Test off load first and PAT check loads before plugging in.

As you have multiple outputs fro a 3ph Tx the outputs will be balanced across 3phases so i assume not all outputs have L-L 55v.

Hmm maybe, didn't see any internal fuse but will look again tomorrow. All of the 16amp outlets and both of the 32 amp outlets showed 55v across phases on output, despite having 400 across phases on supply side.

Thanks for the input though, is a real baffler. What is weird is that the 110 lights ( which are plugged into one of the outlets) are working fine. Will have to go into more detail tomorrow, it is doing my head in

 

[Knobhead]

You should be getting 63.5V to earth on the 110V side.

What current is being drawn? 52A max per 110v phase.

Supply size?

Too many unanswered questions.

Out of interest what meter are you using for your tests?

 

[Crosswire]

You should be getting 63.5V to earth on the 110V side.

What current is being drawn? 52A max per 110v phase.

Supply size?

Too many unanswered questions.

Out of interest what meter are you using for your tests?

Current not measured, supply 32 amp MCB , meter was basic Dilog 2 prong tester, Fluke 1653 too impracticable to carry round all day for basic voltage measurements.

Time also a factor on busy site. When multiple trades cannot work , it is often quicker (and therefore more economic) to quickly replace equipment than to carry out lengthy and detailed test procedures. This is , unfortunately, the reality of life on a site with deadlines to hit.

If I cannot suss it in 10 mins tomorrow, a new single phase T/X will go in, and a new cable run.

 

[Engineer54]

If I cannot suss it in 10 mins tomorrow, a new single phase T/X will go in, and a new cable run.

You're an expensive fella to call in then!! lol!!

 

[Bobster]

Tools running slowly, have you looked at volt drop?


Edit: I must read threads properly. Where on the circuit are you measuring for voltage?

 

[ian.settle1]

OK then prime suspect is a terminated phase loop from TX1 been poor hence TX1 ok TX2 not... List all results for us if phases are ok!... Test the loop cable for damage.

When something gets initially confusing its easy to miss the obvious and skip vital testing without realising.


T.U.R.D.

-Test it
-Understand it
-Retest it
-Decide

Better than SNAFU

 

[Crosswire]

You're an expensive fella to call in then!! lol!!

Yup, but new T/X went in, all up and running. Job done.