and motor control center molded case breakers for a fault on a feeder
circuit. Information on primary relays and molded case breakers will be
supplied to the Contractor. The 2 power supply circuit breakers and the
bus tie circuit breaker shall be electrically interlocked so that only 2 of
the 3 breakers can be in the closed position at the same time. A local
test control switch shall be provided for each electrically-operated
circuit breaker which shall be electrically interlocked through cell
switches or secondary disconnects to prevent breaker operation except when
the breaker is in the test position. Sufficient breaker auxiliary switch
contacts and cell switches shall be provided to accomplish the required
breaker control and interlocking system as shown. At least 4 auxiliary
switch contacts shall be provided on each breaker. At least 2 spare
auxiliary switch contacts, one normally-open and one normally-closed, shall
also be provided on each electrically-operated breaker.
2.5.4.3
Feeder Air Circuit Breakers
Feeder breakers shall be independent manually-operated type with
manually-charged stored energy closing mechanism and with frame sizes as
indicated, and shall be rated 600 volts AC. Circuit breakers with
600-ampere frames shall have a short-circuit interrupting capacity of not
less than 22,000 rms symmetrical amperes at 600 volts AC. Each feeder
breaker, except as specified otherwise, shall be provided with a
solid-state direct-acting overcurrent tripping device consisting of a
long-time-delay element and a short-time-delay element. The
long-time-delay trip elements for direct-acting overcurrent tripping
devices shall be adjustable over an approximate range of 80 to 110 percent
of the trip ampere rating. The short-time-delay trip elements, for the
direct-acting overcurrent tripping devices shall be adjustable over a range
of approximately 4 to 10 times the ampere rating. Manually-operated
drawout type circuit breakers shall be fitted with suitable operating
handles, preferably of the pistol grip type, or vertical lever type,
designed to close the breaker with a rotary motion of less than 180
degrees. All breakers shall be designed for tripping by a rotary motion in
the opposite direction or by pressing a readily accessible trip button.
The operating handles shall be easily removable when it is necessary to
open the compartment door and easily replaceable for operating the breaker
in the withdrawn or test position. Duplicate feeder breakers shall be key
interlocked. Each breaker shall be equipped with a conspicuous mechanical
target visible with the breaker in the normal operating position to
indicate whether the breaker is open or closed and shall be provided with a
manually-reset bell alarm contact to energize the annunciator circuit only
when the breaker is automatically tripped on a fault or overload. The
circuit breaker for the powerhouse crane feeder shall be manually-operated
type equipped with a 125-volt DC shunt trip attachment for emergency
operation from remote stations.
2.5.4.4
Automatic Bus Transfer
The stations shall be provided with automatic bus transfer. The automatic
transfer arrangement shall be as shown by the schematic diagrams and shall
incorporate the following (normal operation will be with both supply
breakers closed and the bus tie breaker open):
a. Loss of voltage on one bus shall cause the associated supply
breaker to trip and the bus tie breaker to close.
b. Automatic transfer control will cease to function if either of the
supply breakers or the bus tie breaker trip on overcurrent.
SECTION 16404A
Page 18
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