Calculation Of Settings; Icw51A And Icw52B Relays - GE ICW51A Instructions Manual

CALCULATION OF SETTINGS
ICW51A AND ICW52B RELAYS
Consider a 3-phase 13.8 KV, 2,500 KVA diesel
driven generator for which
it
is desired to provide
protection against motoring. Assume that the 3-
phase motoring real power losses for this machine
are given QY the manufacturer as 15 per cent of the
full load KV A rating. Thus, the 3-phase motoring
power is (2500) (0.15)
=
375 KW
Since the full load current on this unit is:
2500
102.5 primary amperes,
=
13.8
V3
assume that 150/5 CT's are employed. Assume
also that the PT's provide 120 secondary phase-
to-phase volts with a 120/1 ratio.
The 3-phase secondary motoring power taken
by the generator is:
Primary Watts
=
375000
Secondary Watts
=
-----=---------
(CT Ratio)(PT Ratio)(30)(120)
=
104 Watts
Refer to Fig. 2 showing the operating time
curves of the relays and select an operating time
which is long enough to override system swings and
which will not hinder the process of synchronizing
the unit onto the system.
RIGHT·H~D CDNT4CTS
7
50
-
'0"
SET TO a.OSE "'1 THESE
PERCENTAGES OF T~
T
VALUE.
30
,.
..
17
u
j
TIME TO a.OSE .,,.,T
7
;x:'~~~~~~~~
FROM TN' VALUE.
~/
I
II
7
/
V
/
/
V
II
./
II
/
-
0
22
I
;$
20
c--
-<
0)
10
co
1l
C")
-
~
10
C")
ill
bO
z
-
,.
....
~
~
;:
"
10
V
/
V
v
/
I--
V
V
L.--
Power Relays Type ICW GEH-2056
Assume that a 2.0 second operating time is
desired. Fig. 2 gives a number of combinations of
time dial setting and multiple of tap that will yield an
operating time of 2.0 seconds. If it is desired to set
the pick up for 25 secondary 3-phase watts, this will
give a multiple of tap setting of
104
25
=
~.16
From Fig. 2 set the time dial at approximately
3.6
to obtain 2 seconds operating time.
The tap setting of 25 watts may be obtained with
either the 15-60 watt relay or the 25-100 watt relay.
Either range may be used as long as the maximum
load current does not exceed the continuous rating
of the relay selected. In this case maximum full
load secondary current is:
102.5 X
5
150
=
3.41 secondary amperes
Thus, either range may be used.
The target seal-in units in these relays have
two taps. The available taps, operating currents,
and resistances for this unit are given in the section
under RATINGS. Since the higher of the two taps
has the lower resistance,
it
should be used except
when the minimum trip current through the unit is
less than 1.5 times tap value. In this case the lower
tap should be used.
IS"
T I ME
1'0
CLOS£ LEFT CJ)NT ACTS "lEN POWER
\
IS $lJOO[NLY INCREASEO FROM ZERO.
\
7
\
7
r - -
r-..
\J.
1\
/
' " RI QiT.HIHD
CONTACTS SET TO
a.OSE AT THESE
\
I
~
PEACENTN;ES OF
T~ VIt.UE
\~ ...........
~
I"
.........
r--
~
~
........
f'..-
t.-
"-
~
"' - --
.....
eo"
t--lEFT CXlNTACTS a.OSEO
1511
10 20 3Cl .to 50
eo
70
eo
to 100 110 120 130
,.«)
1 !O Ito 170 lID '10 200
PER CENT OF POIllER R£WI RED TO CLOSE LEFT ceJrilTACT
Fig. 3 Typical Time-Watt Characteristics Of ICW52A Relay With Rated Voltage Applied
7