Transformer Without Neutral Line

More detail would be nice:

Voltage rating of chiller.

How you know there is no neutral.

Voltage, phase, and presence/absence of neutral in the supply. Is it connected in star only, delta only, or selectable?

Thanks Tornado,

380-415 V, 3 Phase

The customer side did not have the neutral line.

Just a normal DOL connection.

Anyway, can primary transformer be two live and secondary output one line and one neutral?

this is a recommendation from my colleague, but did not understand how it work?

These two questions don't seem to be related.

A. The 380-415/3 sounds like the chiller rating, which would probably be delta. Is this also the characteristic of the supply? What sort of control circuit does the chiller have? Line-to-line (380-415 V), stepdown transformer with line-to-line primary and whatever secondary control voltage, line-to-neutral control voltage, or something else?

B. Yes, a transformer can have a primary with two live lines, and a secondary with one live and one neutral (earthed = grounded) line.

This is not yet a complete answer, because I do not yet understand all of the details.

Three phase power does not require a grounded neutral wire. The motor and additional load assembly can be successfully powered via a star or delta configuration as required. A grounded neutral will only assist if the circuit loading for one of the phases will differ from the other phases. Most of the time the three phase loading will dominate any residual single phase loading consideration that even when a neutral wire is run, the current down this wire is so small in comparison that it will draw mocking commentary here.

It is a three phase motor/ chiller. DOL contactor can be 415Volts if 230V not available.

Thanks all for the kind consideration and answer,

Anyway, normally three phase power supply to the chiller compressor and condensing fan does not required a neutral line to power up right. but to operate the control panel normally do required a live and a neutral line, the problem here is the customer side do not have the neutral line, then my colleague recommend add another transformer to the unit, then connect two live cable to the primary side, and the secondary side will output as 1 neutral and 1 live. does this work? i do need explaination to the customer?

Yes This will work,

as tornado said one line of the secondary should be wired to ground and considered as neutral.

Yes you should explain to customer, for two reasons: 1- to get paid for the transformer 2- he may can run a neutral wire from his Main distribution Panel, it is not usual not to have neutral on all the grid Good luck

Thank you very much for the information.

I am studying manufacturing engineering, however, the company assign me as a testing and eletrical engineer, i know it would be tough to learn electrical things, can anyone suggest which area should i start 1st and go through where i work for an HVAC company.

I am somewhat confused, it is unusual at least here in the United States to supply a neutral for a control circuit in three phase equipment. If I am reading your post correctly your chiller is equipped with a step down transformer.

It would be helpful if you could determine the transformers secondary voltage output or the contractors control coil voltage. Once the required secondary voltage is known you can then select a step down transformer for your application.

Yup,

Usually, the site should have a neutral line for control circuit,

But in this case the customer do not have it.

Yes, existing the chiller do have a step down transformer that change from 240v to 115v,

the solution suggested is add another 415V to 240V transformer and connect two live cable at the primary side of this transformer, then the secondary 240V and 0V will act as live and neutral line for the 240V to 115V transformer primary side.

the two live cables from power supply should be 1 of it connect to 415V and another to 0V right?

I would suggest purchasing a step down transformer to go directly from 415 volts to the required 115 volt secondary. Simply match the VA rating of the original transformer. Use any two 415 volt legs of the three phase to connect to the primary and connect the secondary in the same manner that it is currently connected.

There's no need to add the complexity of the second transformer. This should work .

would it be cheaper for a transformer 415V to 240V or a transformer 415V to 115V?

since the 240V to 115V already exist in the circuit.

Calvinlaw,

Maybe this thread also deals will the same concern, please take a look.

http://cr4.globalspec.com/thread/53686

- MS

415/√3 ≈ 240. If the existing transformer primary were wired phase-to-neutral, its secondary would be 120v. But apparently there is no neutral. The 415 x 120 transformer would be the "cleanest" choice.

Thanks.

The recommendation is submit to the superior, now depend on the customer side, one transformer or two transformer, but both case the original transformer will charge on them.

Thanks everyone for the help~!~

Please check the control wiring diagram of chiller. Then you will know whether neutral is required or not. In my experience I never used neutral line for chillers.

your question is somewhat confusing and vague.Can you copy the information plate on the chiller motor/compressor and post it for the correct reply. You should understand that in most of the cases, the quality of the answer depends upon the quality of the question.

Chaudhry

the question is quite clear and th OP get the good answer,

the issue is not with the compressor, it is with control voltage

Cheers

An autotransformer 415V in, 240V out should be considered, it needs to be only 42% of the control transformer's VA rating so will be proportionally smaller and easier to accomodate compared with the 415 to 240V double wound transformer. Also of substantially lower cost. However it's losses will be a standing loss, although only some 42% of the double wound unit.

Remember, engineering is the cost gouverned application of science. One envelope back will suffice, but your instalation cost estimates can reflect your preferences.

any 3 phase motor does not requires neutral necessarily so your chillers's compressor may not require neutral, but if there is any circulation pump of condenser fan is single phase then you will require neutral.

Now come to control circuit of the chiller, if that is 380-415v controlled, there is no need of neutral but if it is 220V controlled then you can add control transformer or bring neutral to panel depending which option is easier for you.

If there are single phase motors involved then no need of transformer you must bring neutral and use that neutral for motors and control as well.