"Mark Brader" wrote in message
...
Has anyone here read it? Is it worth buying??

I have posted this capsule review here befo

| * London Under London: A Subterranean Guide, by Richard Trench(!!)
| and Ellis Hillman(!), 2nd edition, pub.1993 John Murray, P240mM,
| ISBN 0-7195-5288-5.

| The worst single sentence is probably this, in the section on electric
| power: it contains at least 4 clear errors and probably more, depending
| on how you count!
|
| ! High voltages generate immense heat, known as superconductivity and
| ! caused by the resistance set up within the cable by the alternation
| ! of the current -- particularly if the cables are laid underground.

Ha ha! Let's count the errors:

- it's the power loss (I-squared R) that generates the heat, so it's the
fact that high currents are being passed rather than the high voltage
applied which causes it

- superconductivity occurs are very low temperatures (approaching 0 kelvin)
not at very high temperatures - this error is a classic

- any "resistance" that is dependent on the fact that it's AC rather then DC
is impedance, not resistance; the heating is actually a simple I-squared R
and would be the same for AC and DC - the impedence of a straight piece of
wire would be negligible.

- no mention of the skin effect whereby AC flows only in the outer "skin" of
the wire rather then throughout the whole cross-section - I'm not sure how
significant this is at only 50 Hz

However its assertion that the problem with heating is worse when the cables
are underground is correct - firstly because the heat is insulated by the
ground so the temperature will be higher, and secondly because higher
temperatures will cause greater resistance and so more resistive heating.