2500KVA Transformer Daily Switching

"... £5000 at 12 hours/day."

So if you consider a potential risk of even a £50,000 transformer repair (likely more than that) after just 5 years of doing this madness, you will have saved only £25,000 ... and that's not even considering the lost revenue from down time when the transformer is being repaired!

ROI = -50%... even the worst accountant would see the folly in that.

Can we include a capacitor or inductor during starting to reduce starting current surge.

I agree with your advice. It is absolutely not advisable to switch off the transformer every night. It can be further advised to add fixed capacitance of suitable capacity along with APFC (if installed ) at Substation to avoid low PF penalty. APFC cannot operate under no load condition of the transformer .

Excellent idea! You may also want to consider having the ability to switch in added inductance to improve PF during instances wherein the supply power system is capacitive in nature.

In a Substation normally PF is maintained by switching capacitance with the help of APFC . When the transformer remain idle under no load conditions the PF correction will not be taken care of by the APFC and the capacitance will remain cut off . So correctly calculated Capacitance have to be connected in addition to the Capacitance controlled by the APFC . When the load is switched on the additional requirement of Capacitance will be added to requirement only by APFC .The value of the un controlled capacitance have to be correctly designed so that no inductance need to be added as PF will remain with in limits and never go leading. I had to keep the transformers idle and faced the low PF penalty and had to solve the issue and had carried out corrective measures.

You need to quantify first the scenario.

How much would it cost per day for the energy consumed if the transformer stay's online 24/7. This is should be first on the set of condition. You could easily estimate this by the heat dissipated of the transformer. It would be the difference of transformer and ambient temperature (which I assume you have this on monitoring daily as part of predictive maintenance program)

If you have the estimate how much, equate it with hiring a professional (including fringe benefits plus) the tendency of wrecking the unit as per on-off condition.(High in rush current every turn on condition)

I believe answering these questions will certainly influence your decision.

You said.

"due to reduction in night shift load we want to OFF this transformer in night and again switch ON at morning"....

So you've not completely shead the load, only reduced it.... so the Transformer is STILL powering machines, lighting, maybe A/C units, etc. So by turning it off, you will not only (hopefully) save on the losses, but completely shut down part of your factory/office/facility.

So why don't you just turn off everything that is NOT being used, install low power lighting, switch off un-used A/C units, install PIR detectors to switch lights on and off.

There is a whole world of power conservation methods you can employ BEFORE you start switching off power transformers, as previously stated by others before me.

Educate your staff to switch off lights, computers, A/C's, install timers on lights, switch off outside lights of not used or needed, switch off warehouse lights if not needed.

Transformer and circuit breaker damage/maintenance will soon negate your savings.

Discussion is interesting. What is the difference between switching of the transformer and removing (reducing ) the load?

Suppose primary is kept energised , but all loads on secondary are disconnected or load is removed / minimized- is this same as - remove supply to primary side also?

Why I am asking this question is - someone has said, if you completely shut off the transformer, moisture may affect the oil quality etc. Even if the primary alone is kept energised also- moisture may still affect the oil.

xyz,

You are correct, the temperature will cycle due to the load (and climatic changes), the oil will expand and contract, air will move in and out of the tank, bringing moisture. Standard constant full-load temperature rise is about 55 Celsius.

We do not know the transformer rating plate data or specification, which would probably give the magnetising & load losses - it is likely the resistive load losses are about twice the magnetising (core) loss.

The extra effect of power off for 12 hours may be a lot less significant than whether the transfo has a working, well maintained, de-hydrating breather and whether the oil has been cleaned and moisture removed at intervals by a suitable machine.

Not being vibrated 12 hours per day could be some compensation for the temperature cycling effect. Transformers bolted-on to generators which operate on/off for peak lopping experience de-energised times & heating cooling cycles.

However, the considerable stresses at energisation are the big objection to turning off at night - as I wrote, it is as "beneficial" as applying a secondary short circuit daily.

The only way I can conceive for energising the transfo gently is - if the second or other transfo in the plant has the same phasing and is nearby - and the subject transfo is energised on the LV windings via resistance [from the other transfo] - to limit the inrush current before closing the HV breaker & opening the LV resistor breaker.

This would require some big 415V motor size breaker gear and some careful control design, the transfo magnetising power will be about 125 kVA, which cost must be compared to the annual saving.

67model

Here we are referring to a big transformer rated at 2500 KVA. But India, load shutdown or load shedding is a very common thing. In non-urban areas 10 to 12 hour power almost daily shutdown is quite common. Obviously transformer life will be far lower than the declared life. I don not know whether the utilities limit shut down to distribution level only and keep live the higher voltage level transformers. Hence in this context, I was curious to understand various related issues affecting transformer life etc.

For pre planned load shedding in India normally the corresponding breakers only are disconnected ( LT and 11 kV ) . It affects the life of the breakers and distribution transformers.It is inevitable considering the short fall of energy production specially during summer and during short supply of coal to generating stations. To avoid frequent breakdowns such breakers and transformers are put on regular preventive maintenance schedule . When such timely preventive maintenance is not carried out there are frequent breakdowns especially in remote villages. Considering the present short fall of Electrical energy production in India the timely preventive maintenance is the only solution.