|
6. |
Switch Design and
Construction |
|
a) |
Jaw Contacts
|
|
|
i) |
All jaw contacts shall be
silver to copper and designed so that wiping action is provided with a
minimum of roughening or wear on the silver surfaces |
|
|
ii) |
The design of the jaw contacts
shall be such that the resultant magnetic forces during short circuit will
tend to hold the blade in the closed position and maintain contact
pressure |
|
|
iii) |
Switch contacts shall be the
high pressure line contact type with a minimum of 100 lbs pressure on each
silver contact |
|
|
iv) |
Contact pressure shall be
maintained by separate back-up spring members independent of the main
current path. Contact members
shall be independently adjustable for proper contact deflection
|
|
|
v) |
Wear of contacts shall not result in
diminished contact performance due to reduction of contact pressure
|
|
|
vi) |
The number and size of contact fingers
shall be sufficient to ensure adequate transfer of rated current from the
blade to the jaw |
|
|
vii) |
All contacts shall be self-aligning and
self-adjusting and designed to ensure firm positive contact
|
|
b) |
Switch Blade
|
|
|
i) |
Each switch blade shall form one solid
piece and shall be so assembled that no part of the blade can move
relative to another |
|
|
ii) |
Ends of switch blades shall be completely
closed except for drain holes
|
|
|
iii) |
For rotating-blade switches, rotation and
vertical movement of the blade shall be affected by a single and simple
linkage between the rotating stack and the blade
|
|
c) |
Terminal Pads |
|
|
i) |
Terminal pads on each end of the switch
shall be located at the same height above the insulator
|
|
|
ii) |
Terminal pads shall have flat, machined
surfaces |
|
|
iii) |
Terminal pads shall be NEMA standard 2-hole
for 600 ampere switches and NEMA standard 4-hole for switches rated 1200
to 2000 amperes |
|
d) |
Switch Assembly
|
|
|
i) |
Switches of the same rating and design
shall have interchangeable parts
|
|
|
ii) |
The switch shall be so designed that when
installed, its operation will not be prevented by accumulated water,
sleet, ice, snow, dirt, or other atmospheric contamination.
|
|
|
iii) |
Metal live parts shall be non-rusting and
corrosion resistant. All
current carrying parts shall be non-ferrous.
|
|
|
iv) |
Live parts shall be designed to eliminate
sharp points, edges, and other corona producing surfaces.
Where this is impractical, adequate shields for corona suppression
shall be provided |
|
|
v) |
Live parts shall be designed to use at
least three of the four mounting holes in the insulator or insulator
adapter. |
|
|
vi) |
Bolts, screws, and pins shall be provided
with lockwashers, keys, or equivalent locking facilities
|
|
|
vii) |
No part of the switch blade or jaw
assembly, except arcing horns, shall project lengthwise beyond the
terminal pads
|
|
e) |
Switch Mechanism |
|
|
i) |
The mechanism shall be so designed that all
three blades per phase are in positive continuous control throughout the
entire operating cycle |
|
|
ii) |
Each rotating insulator stack shall have double roller or double
ball bearings in the base bearing assembly. Bearing housings shall be weatherproof. Open type bearing assemblies must be rustproof and
non-corroding, and they shall be designed to completely drain water and
moisture accumulation. |
|
|
iii) |
All roller or ball bearings shall be
greaseless or maintenance free type
|
|
|
iv) |
Rotating insulator stacks with 5” bolt
circles (115 kV and greater) shall have leveling provisions at the base of
each stack; rotating insulator stacks with 3” bolt circles (69 kV and
below) may employ shims for alignment
|
|
|
v) |
All operating pipes shall be sufficiently
rigid to maintain positive control under the most adverse conditions,
including a heavily iced switch and operating mechanism.
|
|
|
vi) |
It shall be impossible, after proper and
final adjustment has been made, for any part of the mechanism to be
displaced sufficiently, at any point in the travel, to allow improper
functioning of the switch when the switch is opened or closed at any
operating speed |
|
|
vii) |
All ferrous parts, except springs, shall be
hot-dip galvanized in accordance with ASTM A153, latest revision
|
|
f) |
Operating Mechanism |
|
|
i) |
The operating mechanism shall be positively
toggled when the switch is closed to ensure correct, complete switch
operation and to provide operating personnel with visual confirmation |
|
|
ii) |
All vertical operating shafts shall be
supported on ball or roller thrust bearings.
Guides shall be provided on the vertical shaft at regular intervals
to ensure proper operation. |
|
|
iii) |
Switches rated 161 kV and below shall be
furnished with a horizontal swing handle.
Geared mechanisms shall be acceptable, if required, to ensure
proper operation. |
|
|
iv) |
Provision shall be made for padlocking the
mechanism in the open or closed position. |
|
|
v) |
A flexible copper braid shunt shall be
provided on the operating mechanism for ground connections by Others |
|
g) |
Interrupter |
|
|
i) |
Switches
requiring load interruption capability shall utilize a vacuum interrupter
to interrupt current and to provide a confined arc when switching load,
line charging or transformer magnetizing currents |
|
|
ii) |
The interrupter
unit shall be designed to ensure high speed interruption regardless of the
operational speed of the switch |
|
|
iii) |
When not being
operated, the interrupter unit shall be out of the current path so that it
is not subject to fault currents |
|
|
iv) |
When the interrupter employs a dielectric
to enhance the interrupting rating of the enclosed vacuum bottle,
accidental loss or disposal of the dielectric shall not pose a risk to the
health of utility personnel or the environment; SF6 is not acceptable as a
dielectric |
Product
Specifications for Phase-Over-Phase GOABS®