15
I.B. 8926-1A
CURRENT TRANSFORMERS
When current transformers are used with overload
relays, the current through the overload relay heater
is related to the motor full-load by the inverse of the
current transformer ratio.
WARNING:
Do not ever remove heaters from Size 5
and larger starters to check unit operation. These
starters use current transformers to drop the current
to the range of the size 1 overload relay. Operation
with heaters removed will not interrupt voltage to the
motor and will generate dangerous voltages in the
open secondary of the current transformer.
MOTOR CIRCUIT PROTECTOR (HMCP)
AFTER INSTALLATION OF THE CONTROL
CENTER, EACH MCP MUST BE ADJUSTED TO
ACTUAL MOTOR FULL-LOAD AMPERES (FLA) SO
THAT IT WILL TRIP AT ANY CURRENT WHICH
EXCEEDS STARTING INRUSH. This setting
provides low-level fault protection. The first half-
cycle inrush will vary with the motor characteristics.
Motors with locked-rotor currents of six times motor
full-load amperes will usually require an
instantaneous magnetic setting of 7 to 11 times
motor full-load amperes to prevent tripping when
starting.
Fig. 25 HMCP Magnetic Adjustment
A cam to accept a small narrow-blade electrician’s
screwdriver is near the lower left corner and around
which are eight lettered adjustment points, calibrated
in trip amperes. See Figure 25. Adjustment should
never exceed 13 times FLA which is in accordance
with NEC requirements for magnetic-trip-only
breakers.
Adjustment should be made as follows:
1. Obtain FLA from motor nameplate.
2. Multiply FLA by 13.
3. Set the cam to the highest trip setting which does
not exceed the calculated figure of Item 2. This is
the maximum setting that should be used.
4. Depress and turn the screwdriver adjustment
counter-clockwise one setting at a time, until the
breaker trips in starting and then adjust upward
one setting position. This will insure that the
circuit will open instantly on any current above
the motor inrush, usually 7 to 11 time FLA.
The PUSH-TO-TRIP button checks the tripping
function and is used to periodically exercise the
operating mechanism. The button is designed to be
operated by using a small screwdriver.
Freedom 2100 MCC’s are supplied with Type HMCP
motor circuit protectors having an interrupting rating
to match the short-circuit withstand rating of the bus
bar system. For HMCP’s in 225, 400, and 600
ampere frame sizes, the magnetic-trip adjustment is
set for each pole. A three-pole HMCP has three trip
settings to adjust. Place all three poles at the same
setting.
CURRENT LIMITERS FOR USE WITH TYPE
HMCP AND FD BREAKERS
The addition of the current limiter provides
interrupting capacity above the range handled by the
HMCP in motor starters or by FD thermal-magnetic
feeder breakers.
Each HMCP or FD breaker rated up to 150 amps
has its own current limiter to provide coordinated
protection against faults up to 100,000 amperes, rms
symmetrical.
Built-in trip indicators in each phase immediately
show when a fault has blown the current limiter and
tripped the circuit breaker. This provides protection
against single phasing.
After interrupting a fault,
the current limiter will require replacement.
After
the fault has been cleared, the current limiter is
replaced by the removal of three screws. The
breaker can then be reset to provide for subsequent
high overcurrent protection.
Содержание Freedom 2100 Series
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