Transformer overloading

[9150]

Can someone help me out on power transformer CER, CMR ratings. How are they related to ONAN, ONAF, OFAF, ODAF, etc cooling for 40MVA up to and including 120MVA 132kV? When some says "this transformer is a CER", what do they mean? if a transformer is for example 30/60MVA does it automatically becomes a CER as well? What are the design considerations? Can someone point me to helpful documentation or standards that are easy to follow.

 

[Gr8blu]

CER = Continuous Emergency Rating
CMR = Continuous Maximum Rating

Continuous Emergency Rating
CER transformers are designed to operate at their Continuous Emergency Rating (CER) under emergency loading conditions, such as outages. The CER rating is crucial for ensuring that these transformers can handle the maximum demand during an outage without accelerating the loss of life. The design of CER transformers allows for two units to operate in parallel, with the life expectancy being not less than 40 years. The CER rating is identical for both units, ensuring that one unit can supply the total maximum demand during an outage of the other unit. The winding temperature and top oil temperature of the in-service unit must remain within specified upper limits for an ambient temperature not exceeding +5 °C. This condition is intended to compensate for any accelerated loss of life during emergency loading conditions.

Continuous Maximum Rating
The continuous maximum rating (CMR) of a transformer is the maximum load it can continuously carry without exceeding its thermal limits or other performance limitations. It's essentially the highest power, usually expressed in volt-amperes (VA) or kilovolt-amperes (kVA), that the transformer can handle indefinitely without overheating or damage. This rating ensures reliable and safe operation over extended periods.