DIFFERENCE BETWEEN NOMINAL RATING AND CONTINIOUS RATING

[subash148]

What is the exact difference between NOMINAL RATING and CONTINIOUS RATING? What does the transformer name plate and the generator name plate shows; NOMINAL RATING OR CONTINIOUS RATING? When we say transformer is rated at some voltage and current; are we talking about NOMINAL RATING or CONTINIOUS RATING?

 

[jghrist]

The nominal load current rating is a continuous rating.

 

[7anoter4]

It is a difference from “rotating machine” standard definitions and transformer standard definitions.
The IEC 60034-1 Standard for Rotating electrical machines – Part 1: Rating and performance defines:
3.1 rated value = a quantity value assigned, generally by a manufacturer, for a specified operating condition of a machine.
3.9 duty = the statement of the load(s) to which the machine is subjected, including, if applicable, starting, electric braking, no-load and rest and de-energized periods, and including their durations and sequence in time.
4.1 Declaration of duty =
It is the responsibility of the purchaser to declare the duty.
4.2.1 Duty type S1 – Continuous running duty=
Operation at a constant load maintained for sufficient time to allow the machine to reach thermal equilibrium, [see Figure 1]. The appropriate abbreviation is S1.
[That does not mean at the "rated load" only "continuously"].
So, what is written on name plate is the “rated” value.
The same IEC 60076-1 Standard for Power transformer :
3.4.1
rating
those numerical values assigned to the quantities which define the operation of the transformer
in the conditions specified in this part of IEC 60076 and on which the manufacturer's
guarantees and the tests are based.
However it is a remark:
4.1 Rated power
The transformer shall have an assigned rated power for each winding which shall be marked on the rating plate. The rated power refers to continuous loading.