On Thu, 11 Sep 2003 12:23:38 GMT, Roland Perry wrote:

In message , Chris Game
writes
If the line went into overload
protection at a fraction of what it should have done, a simple test
of the line during commissioning (at 50% of rating) would have shown
this.

I wonder how you test 2500 amp circuits on load when a large section of
south London only draws half of that. What's the dummy-load going to
look like?

You don't need 275,000v to inject a test current through the current
transformers. Protection testing is done at both primary and secondary
levels. A primary injection set may produce lots of amps, but at a
relatively low voltage. Testing on the secondary side only uses a few
amps.