Frequent energizing of transfromer in solar field

[tigre1983]

Hello,

I am working for a solar company, they plan on creating a 900mw solar field. There has been talk about turning off all the power distribution equipment at night to save money. (No-load current, magnetic flux, hysteresis and eddy current losses)

What are your thoughts on 30 years of de-energizing and re-energizing transfromers every morning and night? (11,000 times)

I am under the impression that this may reduce the life of the transfromer. Anyone have an data that shows this?

Thanks for your help.
Cameron

 

[davidbeach]

You're going to pump a lot of water into places you don't want water with all that thermal cycling. Assuming that you really meant MW, not mw, you are looking at some fairly high voltages and will find your equipment to have a much more reliable life if it spends nearly its entire life at thermal equilibrium.

 

[itsmoked]

Very interesting question. I too await some wisdom on this.


You could always use synchronous starting and stopping to leave the magnetics in a known state and start them at the correct time. I suspect that would remove the cycling issue.

Bring up the transformer from the LV side.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[tigre1983]

Yes 900MW, my bad.

The site will have 1000-1500 total transfromers. Starting with hundreds of small ones going from 575vAC-5kvAC, all the way up to the large 500kvAC output units that take it to the grid.

I agree with your statment of "more reliable life", but what does that really mean? Will we have many failures over the 30 year life? A few? One?

How could I quantify the reduction in reliability of frequent cycling of the transfromers?

 

[tigre1983]

itsmoked-
Thats an interesting idea, it would reduce the mechanical stresses, however like david said the thermal loading from operation at day/off at night would still be quite a problem.

I am not sure I could bring them up from the LV side, we need the grid to start the system every morning, we have lots of inductive loads(motors) to start in the morning as the system tracks the sun.

 

[busbar]

How about a different approach—specifying transformers with very limited no-load losses? It may likely save on switchgear wear and tear in the process.

 

[cranky108]

Another thought which usually isen't used in the power industry is the dry type transformer. That should help on the wet oil in the transformer issue.
However there is a limit on size of dry type transformers.

 

[davidbeach]

Actually keeping water out of the oil is probably the least of the worries and standard dry type (not cast coil) would be even more of a problem. I was thinking cables, terminations, switchgear, and the like. Let it run hot during the day and then cool off at night, followed by the same endlessly will drive a certain amount of moisture in every time it (any of it) cools off. Seems to me to be asking for trouble.

Oil filled transformers are designed to breathe and so have desiccant in breather lines. Switchgear can be provided with space heaters. Cables and terminations are out there on their own.

Another consideration with transformers, of all types, is the physical expansion and contraction associated with the thermal cycling. Your cores will wear and become loose over time where that is not generally a consideration.

 

[cranky108]

Maybe we should ask about the averege humidity levels. Then that should come into play.

You are right that the thermal cycling would loosen most of the transformer parts over time. However this should be part of the duty spec of the transformer, and would surely increase the cost of same.

If switchgear is used keeping the heaters on would reduce some of the issues with breakers, and cable terminations.

 

[davidbeach]

Whether or not any portion of the equipment ever gets below the dew point during the thermal cycle is much more important than the average humidity level. In a desert the average humidity may be very low, but steel still at overnight temperatures may well be below the dew point as the outside air warms up in the morning.

 

[jghrist]

Besides the thermal problems, you will be subjecting the system to large inrush currents every day. If you try to energize the whole system at once, the total inrush may be very high (as much as 12 times full load for each transformer). For transformers in series (say 500-34.5 kV then 34.5-5 kV then 5 kV - 575 V) all experiencing inrush at the same time, you may get close to through fault levels of current on the 500 kV transformer. This would definitely lower the life, but I don't know how you would quantify it.

 

[edison123]

I would add that all those switching surges do no good to the insulation. May be you need to tell the manufacturers that you intend to torture their babies day in and day out (pun intended).

 

[tigre1983]

Thanks everyone for the feedback so far.

Area is Southern CA desert. Barstow. Very hot and dry most of the time, untill the monsoon season.

Does anyone know of any documents or regulations talking specificly about frequent energizing of transformers and expected life?

Thanks everyone.

 

[prc]

I think frequent energising and deenergising is not a problem for T & D equipments and already such applications are there.Eg transformers in a pumped storage hydroelectric plant is subjected to such stresses everyday with a reversal of power flow also.Traction supply transformers feeding overhead rail and arc furnace transformers are subjected to frequent short circuits running to several tens a day.Manufacturers take care of such onerous conditions and design for it.

 

[itsmoked]

Good point prc. Motors which are more fragile than a stationary wad of iron and windings can cycle many times a day for decades.

Keith Cress
kcress -

http://www.flaminsystems.com