thread238-497878 hello I want the

[zaboli]

thread238-497878
hello I want the k value in the I2t=k formula for a 21MW/11KV generator made by GE (MS5001 type). can you help me?

 

[Gr8blu]

What the formula is telling you is that the square of the PER UNIT CURRENT (I) multiplied by the TIME IN SECONDS (t) is a constant. This is for determining relative thermal stress by indirectly calculating the amount of heat introduced into the winding.

For example: the nameplate reads some rated current (i.e. 1.0 per unit) and a service factor (typically unity). That means it can carry that amount of current indefinitely without undue thermal stress. Now let's assume you have some sort of short-term overload requirement - say, 1.5 per unit. How long can you operate there?

(1 pu)^2 * (t) = (1.5 pu)^2 * (tx)

Thus tx = 0.44 * t

Also realize it takes about 300 seconds for a conductor in a rotating machine to reach stable operating temperature. That means that for all intents and purposes, "constant" is 300 seconds. Using that value for "t" in the above ratio, tx becomes 133 seconds, or just over 2 minutes. That ALSO means there is ZERO current required for the remaining 3 minutes or so. If the loading is not zero, we have to look at the RMS value over that 300 second window.

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