MIL-HDBK-1025/10
loadbreak type. Switch sticks providing the minimum working and clear hot stick distance
are used to manually operate switches. They should be used for no other purpose.
Always assume that disconnect switches are not of the loadbreak type, unless you have
positive proof otherwise and then operate on the following basis.
a. Disconnect switches may be used with care to open a live line, but not under
load.
b. Disconnect switches should be used with caution to open sections of de-
energized lines, where these lines parallel other medium- or high-voltage lines. Under
certain conditions induced voltages can build up in the de-energized line and can be
dangerous to switching operations.
c. Be aware of dangers when using disconnect switches to open a tie line or to
break two parallel medium or high voltage lines.
6.5.1.2 Airbreak Switches. Gang-operated airbreak switches equipped with
arcing horns may be suitable for loadbreak operation, or they may be only capable of
interrupting the magnetizing current of transformers, the charging current of lines, or to
make and break line parallels. Airbreak switch use should be specifically stated. The
handle of the switch should be of the permanently insulated type and be effectively
grounded when operated.
a. Ground mats should be provided for the operator to stand on with both feet.
Either fixed or portable small iron-mesh mats should be used. The mats should be
electrically connected to the operating rod and the substation ground grid to equalize the
ground gradient and prevent any potential differences in case of insulation failure or
flashover. Rubber gloves should be worn by the operator.
b. The hinges of airbreak switches should be sufficiently stiff (and kept in this
condition) so that when the blades have been turned into the open position they will not
accidentally fall back on their line-side energized clips.
c. The switch should be inspected after it has been opened to see that all blades
have opened the proper distance. Single-throw airbreak switches should be opened to the
maximum amount. Double-throw airbreak switches should be opened so that the blades
clear both sides of the switch by the same amount.
d. Locks will be provided for all airbreak switch operating mechanisms and they
will always be kept locked, except when opening or closing the switch.
6.5.1.3 Interrupter Switches. Some interrupter switches are designed to be
opened under load. Metal-enclosed loadbreak switches are used in place of circuit
breakers as a more economical switching method.
55
Previous Page
