Issue with Transformer and spa not working

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A.Randazzo

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Miami
(work was done by a former electrical contractor)
I have a rooftop panel - 3ph 208v 200A, on the panel I have a 2P 100A breaker feeding a 25kva transformer with a secondary output voltage of 240, this leads to a 2P 60A GFCI breaker. The secondary load is a jacuzzi 230v 42A load.

Problems - Transformer is hot to the touch, spa pumps working (2 motors each 230v 11A) but no heat,

Q- Is the transformer big enought to handle this load?
Q- When calculating a voltage increase (208v primary to 240v secondary) are the calculations different than as stated below?

Multiply KW by 1000/voltage and then by power factor.
25kw x 4.16(1000/240) = 104 x .90 = 93.6 Amps -- Is this correct?
 
42A x 230V = 9660VA = 9.66 kVA, assuming single phase.
25 kVA tranformer size is OK.
Dry type transformers normally run hot to the touch.
Q- When calculating a voltage increase (208v primary to 240v secondary) are the calculations different than as stated below?

Multiply KW by 1000/voltage and then by power factor.
25kw x 4.16(1000/240) = 104 x .90 = 93.6 Amps -- Is this correct?
Click to expand...
I'm not sure what you mean by calculating voltage increase. I also don't know where the 4.16 comes from in your calculation,but the result is 104A without the 4.16. Transformer rating is kVA, not kW, so you don't need the power factor if you know the load in amps.
 
Ok...few doubts...


a) Is your transformer 3phase or 2 phase ? What is the secondary line to line voltage when on load?

It seems the input is 208 volt Line to line to transformer and desired output is 240 volts....and if this is the case then you have one leg not being used at all.

b)Is this transformer a standard make or custom built for this spa? If it is a standard make can you attach a snap of it's name plate please..?

c) Can you check the secondary voltage before and after the Jacuzzi is put ON?

d) What is the secondary load (amperes) pumps and heaters.....and all included?

The size (25 kva) looks OK but there can be other issues which can be brought forward by the tests i suggested..

A 2phase 240 volt 25 kva transformer should not be loaded more that 42 amps which is 80 % of its full load capacity (52 amps).

Cheers.
 
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FYI. based on a maximum ambient temperature of 40 deg Celcius, a transformer windings insulation threshold is a maximum of 150 deegree celcius above ambient temp. Of course you will havee to check the transformer specifications for the correct temperature rating of the winding insulation
 
chaterpilar said:
Ok...few doubts...


a) Is your transformer 3phase or 2 phase ? What is the secondary line to line voltage when on load? 2 phase

It seems the input is 208 volt Line to line to transformer and desired output is 240 volts....and if this is the case then you have one leg not being used at all. - primary side phase a to b has a voltage of 213V using H1 & H4, the secondary has a output of 240V X1 & X4, X2-X3 to grounded conductor, this goes directly to a cold water pipe then to building steel)

b)Is this transformer a standard make or custom built for this spa? If it is a standard make can you attach a snap of it's name plate please..? GE 9T21B9120

c) Can you check the secondary voltage before and after the Jacuzzi is put ON? Tomorrow

d) What is the secondary load (amperes) pumps and heaters.....and all included?2x11A 230v pumps 1x20A 230v heater

The size (25 kva) looks OK but there can be other issues which can be brought forward by the tests i suggested..

A 2phase 240 volt 25 kva transformer should not be loaded more that 42 amps which is 80 % of its full load capacity (52 amps).
Click to expand...
 
Yes..they come in 80 C/115 C/ 150 deg C "rise" ratings @ 40 deg C ambient.

In case your transformer is 80 deg rise rated transformer then the max you should have is 120 deg C.

This is the reason why name plate snap would help.

You may use a Infra red thermometer as "touch" can be deceptive.

Cheers.
 
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