Slopes And High Set Threshold - GE B30 UR Series Instruction Manual

9.4 SLOPES AND HIGH SET THRESHOLD

where
I is the maximum CT primary fault current
p
The figure illustrates the K
CT time-to-saturate (t
SAT
K CT limiting factor, as shown in the figure.
S_LIM
Practically, CT time-to-saturate can be obtained by either of the following methods:
• Method 1 — Download the "CT Time-to-Saturate Estimator.xlsm" spreadsheet from the GE Multilin web site, located
under Support > Support Documents > B30 Bus Differential System. Enter the required system and CT parameters to
obtain the CT time-to-saturate.
• Method 2
•Define several time instances t
•Use equation 9-5 to calculate the corresponding K
•Calculate K
S_LIM
•Compare each K
greater than t
Columns 6 and 7 of the table below summarize the DC saturation threat for the fault on C-1. CT-4, CT-6, CT-7, and CT-8
may saturate due to the DC components and may generate spurious differential signal for both the North and South bus
relays depending on the bus configuration. The saturation will not occur before 5.02 ms and will be detected by the Satura-
tion Detector.
The transient saturation of the CTs due to the DC component may be neglected when setting the slopes of the characteris-
tic as the saturation is detected and the relay uses the current directional principle. It must, however, be taken into account
when setting the high set (unbiased) differential element.
Table 9–4: EXTERNAL FAULT CALCULATIONS ON C-1
CT I
FAULT
CT-1
9 CT-2
CT-3
CT-4
9-8
CT saturation capability curve and K
s
Figure 9–5: DETERMINING CT TIME-TO-SATURATE
) is determined as a projection of the intersection of the K
, t ...t
1 2 n
using equation 9-7
value with K . If K at the given time instance t
S S_LIM S
, otherwise it is less than t
i i
(KA) I (A SEC)
FAULT
14.0 116.67
0 0.00
6.0 25.00
5.0 25.00
B30 Bus Differential System
limiting factor.
S_LIM
, K ...K
S1 S2 Sn
is less than K
i
T (MS) AC
DC
SATURATION
40 Yes
N/A No
5 No
30 No
9 APPLICATION OF SETTINGS
CT saturation capability curve and
s
, it means that true t
S_LIM
DC T (MS)
SAT
SATURATION
Yes 5.02
No N/A
No N/A
Yes 26.37
GE Multilin
is
SAT