GE I-44233
TIME OVERCURRENT RELAYS
TYPE IAC66K
DESCR IPTION
The type IAC66K relay is similar to the IAC51B except:
(1) the U-magnet construction has been altered
to give a very l ong time operating characteristic, Fig. 1; (2) the tap ranges are shown in Table I, and (3)
the relay has two instantaneous units, one standard unit, and one special high dropout unit. The standard
is mounted in the front of the relay while the special unit is mounted in the rear. The internal connections
are shown in Fig. 3 and the outline and panel drilling in Fig. 7.
APPLICATION
The Type IAC66K relay is used for motor protection. Typical external connections for motor protection
are shown in Fig. 4. The recommended settings for the three units are as follows:
P.U. SETTING
MULTIPLES OF
UNIT
FULL LOAD CUR.
T IME OVERCURRENT UNIT
51
1.15 to 1.4
NORMAL DROPOUT INST.
OVERCURRENT UN IT
50/IOC-A
8 to 15
H IGH DROPOUT INST.
OVERCURRENT UNIT
50/IOC-B
2 to 3
Based on these settings, the ratings of the three units should be chosen as follows:
MOTOR FULL
RECOMMENDED RATINGS
LOAD CURRENT
51 UNIT
50/ IOC-A
50/IOC-B
UNIT
UNIT
0.8 -
1.7
l - 2
10 - 40
2 - 6
1.4 - 2.6
1.5- 3
10 - 40
4 - 12
l.B - 4.3
2. 5 - 5
20 - 80
4 - 12
1.8 - 4.3
2 - 6
20 - 80
4 - 12
2.9 - 5.0
4 - 8
20 - 80
4 - 12
When adjusted as shown above, the relay operates as follows:
1. For overloads, the 51 unit times out, picking up external auxiliary 51X, which rings the alarm
bell.
2. For locked rotor, the 50/IOC-B unit will pick up instantaneously and the 51 unit will pick up
with time delay. When both units have operated, the breaker is tripped to cause shut down of
the motor.
3. For a fault, the 50/IOC-A unit will pick up instantaneously to trip the breaker and cause shut
down of the motor.
These instructions do not
p
urp
o
rt to
cover
all details or variations in
equipment nor to provide
for
every possible contingency to be met in connection with installation,
operation or maintenance.
Should
further information be desired or should particular problems arise which are not covered s ufficiently
for
the purchaser's purposes,
the matter
should be referred to the General Electric Company.
To the extent required
the
products described herein meet applicable
ANSI,
IEEE and
NEMA
standards;
but no such assurance is given with respect to local codes and ordinances because they vary greatly.
3
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