TransFormer Surge Arrestors

[J.B. Wood]

Hello, everyone. In July 2012, in the aftermath of the derecho storm
that clobbered the Washington, DC metro area many pole-mounted medium
voltage power distribution transformers had to be replaced for various
reasons. In my area of Arlington County I noticed that the replacements
don't have the customary surge arrester that is usually bolted to the
side of the transformer case. For the record the MV system in my
neighborhood is of type 34.5/19.9 kV.

Again, I'm referring to the arrestor, not the fuse/cutout combination
that connects the transformer primary side to the feeder. Is this a
cost-cutting measure? Thanks for your time and comment. Sincerely,

 

[Don Kelly]

Hello, everyone. In July 2012, in the aftermath of the derecho storm
that clobbered the Washington, DC metro area many pole-mounted medium
voltage power distribution transformers had to be replaced for various
reasons. In my area of Arlington County I noticed that the replacements
don't have the customary surge arrester that is usually bolted to the
side of the transformer case. For the record the MV system in my
neighborhood is of type 34.5/19.9 kV.

Again, I'm referring to the arrestor, not the fuse/cutout combination
that connects the transformer primary side to the feeder. Is this a
cost-cutting measure? Thanks for your time and comment. Sincerely,

You may find that the surge arrestor is not necessarily mounted on the
transformer but is a separate unit near it (typically looks like an
insulator between the fuse and the transformer but there will be a lead
to ground (probably to the ground on the transformer).

 

[J.B. Wood]

You may find that the surge arrestor is not necessarily mounted on the
transformer but is a separate unit near it (typically looks like an
insulator between the fuse and the transformer but there will be a lead
to ground (probably to the ground on the transformer).

Thanks for the informative reply, Don. I looked again and all I can
observe between the transformer HV (primary) terminal and the MV feeder
is the usual series combination of a manual-reset cutout and a fuse.
Also, the replacement transformers, unlike those they replaced, have a
(plastic?) shroud that covers about half the length of the transformer's
HV terminal insulator.

The surge arrester's principal function is to protect against lightning
strikes (or perhaps induced potential from unusual sunspot/auroral
activity) so I suppose it could be left out without undue risk for power
outages and equipment damage. Or perhaps the replacement units are more
robust and don't require an arrester. Sincerely,

 

[Don Kelly]

Thanks for the informative reply, Don. I looked again and all I can
observe between the transformer HV (primary) terminal and the MV feeder
is the usual series combination of a manual-reset cutout and a fuse.
Also, the replacement transformers, unlike those they replaced, have a
(plastic?) shroud that covers about half the length of the transformer's
HV terminal insulator.

The surge arrester's principal function is to protect against lightning
strikes (or perhaps induced potential from unusual sunspot/auroral
activity) so I suppose it could be left out without undue risk for power
outages and equipment damage. Or perhaps the replacement units are more
robust and don't require an arrester. Sincerely,

The setup can vary from utility to utility- Here only an arrester and a
fuse are used-no cutout. The fuses are in tubes and, if I recall
correctly the fuse holder acts as a cutout. Some appear to have the
arrestor and fuse on a common mount. An underground MV cable has fuse
and arrester on the pole where the cable goes down.

 

[Nightcrawler®]

Related question: When I was a kid, seemingly older pole transformers
often had a thing attached to the pole under the transformer that looked
like a large acorn. I don't remember how wires were attached to it other
than it was attached to the ground lead running down the pole, but what
could this have been? Perhaps a surge arrestor attached to the secondary?

If I recall correctly, that is where the old transformers made their center
tap to ground bond. Modern transformers usually have those on the lower part
of one of their sides. As with the new, there is a bus bar that worms its way
up the guts to the "neutral".