Winding Temperature Rise by ANSI 2

[iskar2000]

Winding Temperature Rise by ANSI

Hi all,
Please somebody to say me what is different between 55 and 65 C temperature rise when design a transformer. How to decide what of the two values to use.

 

[jwerthman]

55 deg. C rise was the older rating standard for liquid filled power transformers. As newer and higher temperature insulation systems were developed, the allowable temperature rise was increased to 65 deg. C. For many years, most transformers were specifed with a dual rating of 55C/65C. The rating at the 65C rise was 112% of the rating at 55C rise. Transformers can still be specified in this manner and some users still prefer this approach. It was quite common to utilize the 55C rating for normal load and the 65C rating as an emergency load or margin for future growth.

Virtually all transformers today utilize insulation systems that are rated for 65 deg. C rise. In the interest of saving initial investment, most transformers today are purchased for straight 65 deg. C rise. A transformer rated for 65 deg C will be less expensive than one of the same kVA but rated for 55 deg. C rise.

 

[busbar]

May I suggest there is some tendency to spec 55°C rating for cases where some reliability/headroom is desired? Compare a burger stand on a freeway exit favoring the 65°C-rise unit, where padmount transformer dimensions have been standardized as almost a commodity item in utilities. A set of articulated secondary-unit substations fitted with drawout air-frame circuit breakers, for a 24/366 data center, may be appropriate for 55°C-rise units.