allowed voltage drop/gain on 415volts system

It is country specific

NEC : max 5%

Canada- 5%

UK - 4%

BS now permits upto 6% drop for lighting and upto 8% for power/heating.

It is a country specific and usual 5% is applicable to India too.

But then customer is the King, and most likely he is putting the additional constraint to safeguard his equipments.

BTW: we too put the same condition (±10%) when we purchase the machinery to ensure that the system do not collapse in case of anything untowards.

"But then customer is the King, and most likely he is putting the additional constraint to safeguard his equipments."

What additional constraint?

Refer to the standards IS 13947: Part 1: 1993 or IEC 947-1: 1988.

IS 13947 - This standard is intended to serve as a guide for general requirements of all switchgear and controlgear equipment for voltages not exceeding 1000 V ac or 1200 V dc. Individual parts of this standard would cover different switchgear and controlgear items.

Hope this may help you.

While the value of 5% for Canada is accurate, it does not tell the whole story.

The requirements in Canada are as follows...

For voltage drop requirements, we break the system down to two "circuits" sections, 1) the "feeder" and 2) the "branch circuit".

The "feeder" is everything from the source of the system, either the utility demarcation point or the transformer of a separately derived system, to the branch circuit over current device.

The "branch circuit" is the run from the branch circuit overcurrent device to the load using the energy.

No more then 3% voltage drop is permitted in either section and not more then 5% voltage drop overall is permitted.

A design voltage drop of 10% is excessive. I would engineer the system for no more then 5%. Are you sure the 10% does not speak to the ability of the utilisation equipment to work with up to a 10% difference?

What is the universally accepted or practiced standard for voltage drop on a 415v system

Do you mean the voltage tolerance that a piece of electrical equipment will work on, the voltage tolerance of the grid supply or the voltage tolerance at any point on an entire system (electrical equipment and cabling), as the tolerances vary.

The project is in Bangladesh and the voltage fluctuation is very abnormal.

There is not a lot you can do about the fluctuating grid voltage unless you want (or need) to employ voltage filtering (such as UPS, voltage stabilizers or off-grid supply using generators).

Can you provide more information on your application please.

What is the universally accepted or practiced standard for voltage drop on a 415v system

1) allowed voltage drop by the supply authority or the utility provider, in this case it is the owner, the secondary voltage from the 11kv/415 transformer drops as low as 370volts due to the Primary incoming which drops to 10,000volts.

Owner insists that 10 %+- in the contract is valid.

thanks and regards.

murthy

Hi Murthy

The first thing I would ask you is this 50 hz or 60hz equipment you are working with .

If it is 50 and you want to run it on 60 you have to increase the voltage by 20% for the drive motors and then adjust any control circuits to run at the rated voltage for the coils .

I have done this many many times .

Cheers

Amos

Hi Amos, thanks for the quick reply, the equipment here are all 50hz, the problem here is that because of severe power shortage in Bangladesh, the voltage drops to as low as 370 volts from the utility side, while the equipment can still run , i believe their lifespan will be shortened. Anyway i have informed the owner of the consequences .

Thanks and regards.

Murthy

As a gross generalization, +- 10% is the spec for tolerance of equipment, meaning it will suffer no long term damage or performance issues within that range. Utilities are required to maintain +-5% (or less depending on contract, some are tighter). The overlap between the two provides a margin of safety.

Depends on what you wish to provide a quality lets say good practice install is 2.5% and the Rules ( Australia ) max 5%.

Sometimes however by reducing the VD to say 3.5% you can reduce the cable size by a whole family ie 25mm to 16mm so it is worth changing and save a considerable amount especialy when you are using big 600mm cables etc.

Rob

If the utility is going to drop that low, you had better make sure that no additional VD is introduced into the system by the distribution system inside the plant.

The following is the quote from the Indian Electricity Rules, 1956:

Rule 54.Declared voltage of supply to consumer-

Except with the written consent of the consumer or with the previous sanction of the State Government, a supplier shall not permit the voltage at the point of commencement of supply as defined under rule 58 to vary from the declared voltage:

(i) in the case of low or medium voltage, by more than 6 per cent,

or;

(ii) in the case of high voltage, by more than 6 per cent on the higher side or by more than 9 percent on the lower side,

or;

(iii) in the case of extra-high voltage, by more than 10 per cent on the higher side or by more than 12.5 per cent on the lower side.

Rule 55.Declared frequency of supply to consumer:-

Except with the written consent of the consumer or with the previous sanction of the State Government, a supplier shall not permit the frequency of an alternating current supply to vary from the declared frequency by more than 3 percent.

By the by, what is low voltage, medium voltage, high voltage & extra-high voltage, vis-a-vis the above rules? Again, I quote from IE Rule only:

Rule 2 (av)" voltage" means the difference of electric potential measured in volts between any two conductors or between any part of either conductor and the earth as measured by a suitable voltmeter and is is said to be;

" low" where the voltage does not exceed 250 volts under normal conditions subject, however, to the percentage variation allowed by these rules;

"medium"where the voltage does not exceed 650 volts under normal conditions subject, however, to the percentage variation allowed by these rules;

" high"where the voltage does not exceed 33,000 volts under normal conditions subject, however, to the percentage variation allowed by these rules;

" extra high"where the voltage exceeds 33,000 volts under normal conditions subject, however, to the percentage variation allowed by these rules;

From your name I assume that you are from India and hence I have quoted from the IE Rules. Hope the above is clear.