Power Transformer Overloading

[afeldman]

I am carrying out a research about Power Transformers Overloading worldwide. It is well-known that overloading reduces power transformers life span. In Brazil, electric utilities established a penalty fee for large consumers that do overload power transformers. I am doing a research that aims discover how other electric utilities, all over the world, are managing the life span reduction of their power transformers due to consumer overloading.

Does anyone know contact information of USA/Canada or other electric utilities that can have such information to me? I had already obtained information from PJM Consortium (USA).

I would be most grateful for this help.

Alexander Feldmann - MSc
Electric Engineer - Researcher - PESC/COPPE/UFRJ
Universidade Federal do Rio de Janeiro
Rio de Janeiro - RJ - BRAZIL

 

[busbar]

An applicable reference may be IEEE Std C57.91-1995 – Guide for Loading Mineral-Oil-Immersed Transformers Table of contents at

http://standards.ieee.org/reading/ieee/std_public/description/dtransformers/C57.91-1995_desc.html

Ordering info for PDF at

http://shop.ieee.org/store/product....qu=%28%24all+C57.91%2D1995%29&mh=10&sh=0&ae=1

 

[afeldman]

Dear busbar,

Thanks for your kind reply. Actually I am aware of IEEE standards and other ANSI standards and IEE/IEC resolutions.

The point is: I need contact information (preferably e-mail addresses) of electric utilities or consortii of electric utilities, in order to send them a questionary about their set of rules (if any) involving the management of power transformers life span due to operation in overloaded conditions.

If you can help me in this matter, I would be most grateful.

I am looking forward to your and others reply.

Alexander Feldmann - MSc
Electric Engineer - Researcher - PESC/COPPE/UFRJ
Universidade Federal do Rio de Janeiro
Rio de Janeiro - RJ
BRAZIL

 

[jbartos]

Suggestion: Normally, transformers are protected according to their nameplate ratings and industry standards, e.g. IEEE 242, so that there is no transformer overloading. However, in some instances, perhaps on temporary basis, the transformer iron and winding temperature transient constant may be and are considered for the transformer short time overloading purposes. It is not quite clear from the original posting in which direction the research is heading. Please, would you be more specific?

 

[afeldman]

Dear jbartos,

Sometimes, transformer operation has to afford short periods of overload due to distribution/power system conditions, e.g. in a failure recovery. Other times, large consumers do overload power transformers for short periods.

In this second case, assuming that all protection schemes were correctly set-up and are working well, we still have the life span reduction due to consumer's (purposely/accidentally) overload imposed to that transformer. For this event, electric utilities in Brazil had developed a penalty fee to be charged to that consumer or consumers that imposed such overload condition, after a complete investigation process. This is part of the agreement between the electric utility and the consumer, provided this consumer is quoted as "heavy consumer".

What the research aims is to learn what is done outside Brazil with that "heavy client" that happens to cause an overload condition to a power transformer and so reducing its life span or even ruining it.

We had already learned that there is no general rule applying to that matter, except those IEEE/ANSI standards (and others) that do apply to operation and protection.

But we could see nothing about the penalization of the agents of overloading conditions (strictly speaking: the consumer that overloads the transformer).

I hope I made myself clear.

Thanks for your kind reply and help.

Alexander Feldmann - MSc
Electric Engineer - Researcher - PESC/COPPE/UFRJ
Universidade Federal do Rio de Janeiro
Rio de Janeiro - RJ
BRAZIL

 

[SidiropoulosM]

We are an electric utility in the Pacific Northwest and we allow our transformers an emergency overload of 20% above nameplate rating for up to half an hour.

I don't understand what you mean by "large consumers overloading our transformers". Here in the USA electric utilities have an obligation to provide power during peak load conditions to all customers, small and large. We forecast their peak loads and plan our system so that we are able to satisfy all demand under normal and adverse conditions. Only in cases of extreme multiple contingencies do we disconnect customer load in order to preserve the integrity of the system.

I hope this helps.

Michael Sidiropoulos

 

[afeldman]

Dear SidiropoulosM

Thanks for your kind and extremely clear explanation. You helped me quite a lot. It is difficult to explain you all the circumstances that surround Brazilian electric power systems, since they were government-owned for a long time span. Only recently the electric utilities were privatized, and our energy market is still heavily regulated.

Our research is aiming show the governmental regulatory agencies what is being done in this matter worldwide, in comparison to what is being done here in Brazil.

I sincerely appreciated your help.

Alexander Feldmann

 

[davidbeach]

Customers can not overload utility transformers, but utilities can undersize transformers. The only way it could be the customer's fault is if they increase their service size without notifying the utility.

Utilities often use a transformer smaller than the rating of the customer's service size, based on the utility's experience with similar types of loads, but it is the utility's responsibility to size the transformer to the service, and if they under estimate the real loading on the service it is their problem.

 

[jbartos]

Suggestion: The transformer can be protected that it is safe as it possibly can be. Then, there overload does not materialize. As some of the above postings indicate, the transformer overloads are permitted in emergency. Apparently, the transformer protective devices are either adjustable to allow this overload, or the transformer is protected such that the overload for a specified time materializes. However, this is the transformer operator/owner prerogative (to capitalize on the poor-transformer suffering leading to a shorter life-cycle).

 

[edison123]

I do believe, all power transformers are designed for continous 10% overload albeit with higher temp rise and thus lower life.

In India (where like your country, energy privatization is a stumbling progress), the heavy consumer has to install his own transformer. That way, the utility does not have to worry about transformer burn-out.

However, if the consumer exceeds in contracted KVA demand, then there is a heavy penalty. This is to protect the system integrity.

 

[busbar]

There is a US electric utility, Pacific Gas and Electric, that publishes its”Electric Rule 2.” §F. INTERFERENCE WITH SERVICE outlines the utility’s policy on load character like inrush, power factor and harmonics. See:

http://www.pge.com/customer_services/business/tariffs/doc/ER2.doc

 

[jbartos]

Suggestion: The India system integrity principle appears to hold true in USA too except those transformers that are supplied by the Utility.