Re: Latest MMC Calculations...

Hi Stefan,

I too was wondering how to combine the lifetimes.  I was thinking of
combining them like parrallel resitors.  Suppose you have three life times
of 10000, 1000, and 5000 hours.  1/(1/10000 + 1/1000 + 1/5000) = 769 hours.
 Seems reasonable to me...



At 04:39 PM 7/14/99 +0200, you wrote:
>Hi Terry, all,
>the "15th_power-law" is a very interesting find. I looked over
>the formulas, you posted at 
>You wrote:
>> These equations have the life estimates for corona, temperature, 
>> and Dv/Dt
>and you calculate the lifetimes L1, L2, L3.
>But don't you think that all those three major factors play
>a role TOGETHER in decreasing the lifetime? In my opinion, the 
>lifetime reduction factors should be multiplied as each one is 
>decreasing the lifetime at the same time.
>For the example you give at
>I would say that the total lifetime is more like
>  1e6 x (Life1/1e6 x Life2/1e6 x Life3/1e6),
>which works out to 96 hours instead of 6576 hours which
>was the lowest single value (Life1).
>I'm not sure if the three factors should be of equal weight. 
>On the other hand, if you give some weight to the factors,
>the product should always be a stronger criteria than any single 
>factor. As you can't tell which factor is the most important one,
>I think the equal weight is most probably the right one, isn't it?
>Only other solution could be a weight that depends on the factors
>themselfes, such as "if the temperature dependent reduction actor is
>below 1/1000, then it is negligible (weight = 0), otherwise the 
>weight = 1".
>This view shortens the predicted life dramatically (in your example from
>6576 hours down to 96 hours, which is factor 69.
>But as said - I'm not sure here but it seems logical to me (remember
>the reduction of the rated AC-voltage with increased frequency due to the
>frequency dependent heating of the cap).
>Any more thoughts on this? 
>Cheers, Stefan
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