On Load Tap Charger (OLTC) vs. Automatic Voltage Regulator (AVR)

How much variation in incoming voltage.If the variation is high it may be better to go in for OLTC .

Thanks nesubra and chaterpilar.

The variation is likely to be around + 5%. Broadly speking, the load profile consists of 2200 TR, VRF central airconditioning system and highly sophasticated scientific equipment besides light load and other mixed load. I am supposed to recommend techno-commercially optimum design.

The variation of +- 5% is not much.OLTC for the transformer of size you are mentioning may make the transformer expensive.Other areas could tolerate the variation except the scientific instruments for which alone AVR may be enough.This could be cost effective in combination with a off load tap changer may be sufficient.May be you can have a slightly more taps combination like +-7.5% or However working out with actual costs I think you will be able to arrive at the right choice

It depends..on the sensitvity of your load.

For robust loads OLTC is good, provided you are not going to parrallel the transformers.

I would use a combination.

OLTC and use surge protectors for individual sensitive loads.

cheers.

I would use the AVR setup. All three of your transformers are the same size although load per phase on the feeders will vary slightly. From the voltages I suspect that you are not in the USA so you are dealing with a 240/380 three phase secondary system. That is great as your load per phase per feeder is well balanced. Therefore, you can use one AVR per phase in front of your transformer and have one spare AVR in the substation to use when you need to do maintenance on any of the other AVRs. The OLTC selection will boost your equipment cost and will create more work for your maintenance and field people. You have to take the transformer out of service to perform maintenance on the OLTC which could create a problem for load management on a day when the system is heavily loaded. Just my opinion; it is your substation.

vagabond

I would definitely like to agree with your thought regarding maintenance in the long run. The civil construction part (substation building and foundations for the transformers, whose capacity is already frozen) of the project is under progress already.

You know, scientific institutes keep evolving with time, every now and then new load is added to the system. yet, I have taken steps to ensure reasonably balanced load on all the three phases, at least theoritically.

After all this discussion, I am inclined towards AVR, however I haven't yet worked out the cost. Once I do that, I'll let you know the percentage difference of cost between the two possible options.

Kind regards,

When you are considering cost please consider the cost of maintenance. I can't prove it; but, my experience has been that my crews spend more time doing maintenance on OLTCs than they do on AVRs.

Hi, J Kamal,

I feel you are very much inclined to go for transformer with High voltage automatic voltage regulator.(AVR) Hope you have the financial sanction already.It is a better proposition. In addition to providing voltage stability it will also save on your recurring energy consumption. In a case study submitted by M/s Andrew Yule & Company Brentford unit Electrical division ( They are a reputed government of India enterprise ) they claim that for a 1500 KVA installation for 10 % under voltage there is approximately Rs 190000/ annual saving . The initial extra cost difference can be recovered in three to four years and there after there will be a reoccurring saving. The maintenance charges for HV voltage regulation will be much less compared to LT voltage regulation. You can get the initial extra capital cost from the manufacture. They normally give complete data for preparation of project report.

Thanks for the valuable inputs Mr. Abraham, you know finance is not a constraint for a prestigious India Govt. project. Energy saving is another positive dimension to choose AVR.

Kind regards,

Hi J kamal,

Normally my experience with Government of India organisations is the finance people make the road blocks in innovative projects with their reasoning of cost effectiveness (except in R& D of M of D) that is why I asked about finance .In those cases I used to project the actual financial saving to convince them for recommending for financial sanction and it used to work well.

As regarding Brentford Automatic Voltage Regulators , they have a manufacturing range up to 33 kV and 7500 KVA capacity .for 3 phase 50 Hz system. They take care of wide range of voltage fluctuations with voltage correction up to + / - 1 % accuracy and I have verified it also. Being a government of India unit it will be much easier to negotiate also.( Out of own experience )There are only few manufacturers in India who manufacture AVR at 33 kv. and large kVA rating ) While calling for enquiry you must specify the following details:-

Capacity in kVA , Band width of input voltage variation ( minimum and maximum supply voltage variation), output voltage required, application ( type of load and details of load )

With thoose information they can make a technically suitable tailor made offer for you.

For low voltage AVR Automatic Electric Company is reputed manufacturer and their product is found to be most efficient and ,maintenance free.

Thanks again Mr. Abraham. Of course, I'll take care of the parameters specifically spelled out by you. LV AVR is ruled out.

Kind regards,

I can understand the economics of OLTCVs AVR .But energy saving?while it is true that by maintaining rated voltage losses can be reduced and there is saving.But this can be achieved with OLTC as well.In fact the additional losses in the avr will make it more inefficient compared to OLTC.Also you are adding additional Inductance which needs additional capacitors to compensate to maintain power factor.Could you please clarify.

One thing to consider is the break in output power when the tap changer goes from tap to tap, this could cause some loads to malfunction. You may also want to consider a ups system.

Hi,

Normally for any ASVRs the tap changing will be automatic. The Incomimng High Voltage will be stepped down to a control voltage of 110 V to adjust the tap. There will be a potentiometer control raise/lower tap which will snese the incoming and outgoing voltage and accordingly the tap will be cahnged.

One important aspect is the ASVR never be used for Volatge Transformation wheras this is intended to the regualte the voltage of the feeder.

Also, ASVRs are not for intended for parallel operation.

N.Suresh

AVR

can we add OLTC in low tension side. actually in our distribution system, we deal with 33 kV , 11 kV and 440 V voltages. there r transformers of rating 33/11 kV, 20 MVA and 22/11 kV 10 MVA, 11/440 , 990 kVA. and we r using OLTC for regulating the voltage on HT side. can u explain that can we use OLTC on LT side. what r advantages or what is technical difference between the two( i.e. using OLTC on HV side or LV side).

OLTC is is used on HV side as the current is lower.On the LV side the contacts will have to handle higher current (In the inverse of voltage ratio)This could make OLTC expensive, possibilities of arcing and deterioration of Oil, frequent maintenace.