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Capacitors,Power Quality, Harmonic filters,Powerquality, Solutions, APFC.
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How The Internal Fuse Protect The Good Element |
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Capacitor with interal fuses during failure
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Capacitor withinternal fuses
after operation of the fuse |
How the internal fuse protect the good elements
Analysis of interal fuse is made on two parts :
The first one, practically impossible to occur, when failure of the interal element
occurs on the moment of zerovoltage in the capacitor terminals:
and the second one, much likely to occur, when failure occurs on the moment
of the pack of voltage. In the first case, zero voltage,
there is no energy in the interal elements and therefore the fule link will only
count on failure current for it's operation. This condition is shown in fig.3,where
voltage and current values appear on the subsequent moments to failure,
unit operation of the interal fuse. |
Discharge of energy in parallel
element that failed |
In the example of the figure the current through the interal fuse will be 16
times (1.25 * 12) the normal current of the interal element, capable to
make it opetate for few cycles. If this capacitor would have on interal
fuses, the current through the external fuse, would only be 1.33 times
the normalcapacitor current, insufficient to make it operate.
In second case, when failure occured in the peak of voltage on fail
current exists to operate the internal fuse, however stored energy exists
in the element in parallel, which will discharge on the element which
failed and it's fuse link,according to figure.
Evidently what occur most times is that failure occurs close to the
peak voltage,when there is a contribution of a high amout of enegy
and a fail current to operate the link.
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After the operation of the interal fuse, operating condition of the capacitor
is one shown in figure, when the remaining elements in parallel with the one
hat failed, will work withan overvoltage, foreseen in the design of
the capacitor and the other groups will work with a voltage below the rated one.
It is possible to affirm that, besides the fact the capacitor is sized to operated
with admissible overvoltage,the first element to fail is the weakest one of them and
that, as a consequences,the remaing one for being better will have to support such
permanant overvoltage. |
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© Copyright 2007 Shreem Capacitors Pvt.Ltd. All Rights Reserved. Capacitors,Power Quality, Harmonic filters,Powerquality, Solutions, APFC.
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