Power Systems
The value of off diagonal elements is

 sum of admittances connected at bus i
 sum of admittances connected at bus j
 which is connected between bus i and bus j with negative sign
 which is connected between bus i and bus j with positive sign

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Power Systems
The draft tube is provided to

 raise the water surface of the stream to create an artificial head.
  increase the acting head on the water wheel.
None of these
 reduce the effect of water hammer.

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