GE Multilin 565 Instruction Manual page 145

Below are the 565 Timed Overcurrent Curve Equations. Over-
load values from 1.03 to 20.0 times pickup and Time Dials
from 1 to 32 may be entered into these equations.
MODERATELY INVERSE
L
3121
= +
N M
Trip Time 525
−
( Overload
NORMALLY INVERSE
L O
3245 7 .
= +
N M Q P
Trip Time 478
−
( Overload 1 )
VERY INVERSE
L O
20415 .
= +
N M Q P
Trip Time 310
−
( Overload 1 )
EXTREMELY INVERSE
L
17640
= +
N M
Trip Time 110
−
( Overload 0 5 . )
The preceding four equations, and the three IEC equations,
represent the theoretical trip times for the 565 and not the
actual trip times. This is because the relay uses look up tables
where a 16 bit number (0-65,535) is stored. This number
represents the number of trips per 65,535 cycles or 1092.25
seconds. The relay does not store the theoretical trip times in
memory and as a result there are rounding off errors. The
following will simulate how the relay operates. By performing
these operations on the theoretical trip times, you can calcu-
late the exact 565 trip times for various overload levels and
time dials. First of all, calculate the number of trips per 65,535
cycles. This is based on the theoretical trip time.
Number of trips per 65,535 cycles
Since only integer numbers can be stored in the 565 look up
tables, this value must be rounded off. Working backwards
with this rounded off value, the number of cycles before a trip
occurs can be calculated.
Number of cycles per trip
Finally, the actual trip time would be based on this number of
L
F
Time Dial
+ − ×
M M
0 1 . ( 3 0 1 . )
H
O
31
×
Q P
3121
M M
0 8 . )
+
525
−
N
( 20 0 8 . )
L
F
Time Dial
+ − ×
M
0 046 . ( . 2 788 0 046 . )
H
M M
×
3245 7 .
+
478
M
−
N
( 20 1 )
L
F
Time Dial
+ − ×
M 0 027 . ( . 1 368 0 027 . )
H
× M M
20415 .
+
310
M
−
N
( 20 1 )
L
F
Time Dial
+ − ×
M M 0 03 . ( . 0 5 0 03 . )
H
O
×
Q P
M M 17640
2
+
110
−
N
2
( 20 0 5 . )
1092 25 . seconds
=
Theoretical Trip Time
65,535
=
# trips per 65,535 cycles
CURVE INFORMATION AND TABLES
cycles.
Actual Trip Time
EXAMPLE:
O
− I
1
P P
K
Extremely Inverse
P P
Overload Level = 3.0 x pickup
Q
Time Dial = 4
Theoretical Trip Time = 1.415 seconds.
− O
I
1
P
K
Number of trips per 65,535 cycles =
31
P P
P
Q
This value is then rounded off to 2 and stored in the relay's
memory. Working backwards...
− O
I
1
P
K
31
P P
P
Q Number of cycles per trip =
Now in terms of time:
O
I
−
1
P P
K
31
P P
Actual Trip Time =
Q
IEC CURVES
Three new curve shapes, IEC A, IEC B, and IEC C, are now
present in addition to the standard Moderately Inverse, Nor-
mally Inverse, Very Inverse, and Extremely Inverse shapes.
The formulas below characterize the IEC curve shapes.
t =
IEC A:
t =
IEC B:
t =
IEC C:
Once the curve shape is chosen, one of the 32 time dials for
that shape should be selected. The relationship between the
Number of cycles per trip
=
60
Theoretical Trip Time
1092.25 seconds
=
1.415 seconds
= 771.91
Number of trips per 65,535 cycles
65,535
=
771
Number of cycles per trip
85
=
60
= 1.417 seconds
0.14
×
Multiplier
[ ]
0.02
−
Actual Current 1
Pickup Current
13.5
×
[ ] Multiplier
−
Actual Current 1
Pickup Current
80.0
×
Multiplier
[ ]
2
−
1
Actual Current
Pickup Current
1092.25 seconds
65,535
60
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