GE Multilin 565 - Page 145

CURVE INFORMATION AND TABLES
7-13
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
Trip Time
Overload
Time Dial
=+
−
L
N
M
O
Q
P
×
+− ×
−
F
H
I
K
+
−
L
N
M
M
M
M
O
Q
P
P
P
P
525
3121
08
01 3 01
1
31
525
3121
20 0 8
(.)
.( .)
(.)
NORMALLY INVERSE
Trip Time
Overload
Time Dial
=+
−
L
N
M
O
Q
P
×
+−×
−
F
H
I
K
+
−
L
N
M
M
M
M
O
Q
P
P
P
P
478
3245 7
1
0 046 2 788 0 046
1
31
478
3245 7
20 1
.
()
.(. .)
.
()
VERY INVERSE
Trip Time
Overload
Time Dial
=+
−
L
N
M
O
Q
P
×
+−×
−
F
H
I
K
+
−
L
N
M
M
M
M
O
Q
P
P
P
P
310
20415
1
0 027 1368 0 027
1
31
310
20415
20 1
.
()
.(. .)
.
()
EXTREMELY INVERSE
Trip Time
Overload
Time Dial
=+
−
L
N
M
O
Q
P
×
+− ×
−
F
H
I
K
+
−
L
N
M
M
M
M
O
Q
P
P
P
P
110
17640
05
003 05 003
1
31
110
17640
20 0 5
2
2
(.)
.(..)
(.)
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
seconds
Theoretical Trip Time
=
1092 25.
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
65,535
# trips per 65,535 cycles
=
Finally, the actual trip time would be based on this number of
cycles.
Actual Trip Time
Number of cycles per trip
=
60
EXAMPLE:
Extremely Inverse
Overload Level = 3.0 x pickup
Time Dial = 4
Theoretical Trip Time = 1.415 seconds.
Number of trips per 65,535 cycles =
1092.25 seconds
Theoretical Trip Time
=
1092.25 seconds
1.415 seconds
= 771.91
This value is then rounded off to 2 and stored in the relay’s
memory. Working backwards...
Number of cycles per trip =
65,535
Number of trips per 65,535 cycles
=
65,535
771
Now in terms of time:
Actual Trip Time =
Number of cycles per trip
60
=
85
60
= 1.417 seconds
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.
IEC A:
[]
t=
0.14
1
Multiplier
Actual Current
Pickup Current
0.02
−
×
IEC B:
[]
t=
13.5
1
Multiplier
Actual Current
Pickup Current
−
×
IEC C:
[]
t=
80.0
1
Multiplier
Actual Current
Pickup Current
2
−
×
Once the curve shape is chosen, one of the 32 time dials for
that shape should be selected. The relationship between the