Re: Help w/ Chokes
At 09:10 PM 5/30/96 -0600, you wrote:
>From jim.fosse-at-bdt-dot-comThu May 30 21:03:21 1996
>Date: Fri, 31 May 1996 01:11:04 GMT
>From: Jim Fosse <jim.fosse-at-bdt-dot-com>
>Subject: Re: Help w/ Chokes
>On Thu, 30 May 1996 12:50:18 -0600, Tesla List
><tesla-at-poodle.pupman-dot-com>, you wrote:
>>>From MSR7-at-PO.CWRU.EDUThu May 30 12:41:19 1996
>> My search for a suitable potential transformer continues.....
> I've read of people blowing potential transformers.
>Distribution transformers on the other hand, none. Distribution
>transformers are designed to survive near lightning strikes and
>therefor have a secondary voltage rating of several hundred thousand
>volts. I've not found references to exact limits yet.
> Richard? Malcolm? Robert? Wallace? et al?
Dear Jim: My Westinghouse Reference Book on distribution systems has, as
its Chapter 6 a reference to "conventional transformers" and to Completely
Self Protecting Transformers. "The 'conventional' transformer is so
designated because it has no integral lightning, fault, or overload
protective devices supplied as a part of the transformer. These protective
devices must be separately purchased and mounted." * * * " Completely
self-protecting transformers are self-protecting from lightning or line
surges, overloads, and short circuits. Lightning protection of the primary
winding is accomplished by lightning arresters mounted directly on the
transformer tank. Each external primary bushing which is not permanently
grounded has its own lightning arrester. Lightning protection of the
low-voltage secondary winding is obtained with gaps across each secondary
busing. No secondary arresters are required because the normal secondary
voltage is not sufficient to sustain a gap breakdown wnhich is initiated by
a lighntning stroke. The arresters on the primary are usually of the
Overload protection is accomplished by circuit breakers inside the
transformer tank. The breakers are coordinated thermally with each
individual rating to follow closely the true copper temperature of the
coil;s. This is accomplished by having the secondary current flow through
a bi-metal of the breaker and also by placing the bi-metal in the same path
of oil flow used to cool the windings. Excessive temperature of the
bi-metal (hence of the coils) causes the breakers to trip to the open
position. Most CSP transformers have a red warning light built into the
external breaker operating handle to indicate overheating of the windings;.
The signal light comes on when the transformer winding termperature reaches
the ASA temperature limit for Class A insulation. If the warning light goes
unheededand the winding termperature increases to a deangerous level, the
breaker will trip."
Following a tripping, the breaker can be reset with the external
operating handle. For most CSP transformers the handle cn be set to an
"emergency" position, which recalibrates the breaker trip setting and
permits carrying out increased load until the transformer can be changed out.
Internal protective links between the primary winding and the
primary bushings isolate the transformer in event of an internal fault. The
purpose of the links is to protect the remainder of the primary system from
a faulted transformer and also to minimize the possibility of having an oil
fire develop in a faulted transformer. "
PLEASE NOTE: B.L. Lloyd who wrote this chapter was describing the
fault protection when used as a stepdown transformer, not when hooked up
backwards for use in a Tesla Coil. The chapter goes on at length to
describe distribution transformer temperature and short-circuit standards,
Designation of Voltage Ratings of Windings and an explanation of Terminal
Markings and Polarity but it is far too much for me to keyboard and I do not
have a scanner that is of the current generation. I will be happy to
duplicate the 46 pages of the chapter in hard copy for one or two of those
who would like it and cannot get access to a copy of this manual. Let me
know your snail-mail addresses. Wallace Edward Brand