8-8
B30 BUS DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
SLOPES AND HIGH SET THRESHOLD
CHAPTER 8: APPLICATION OF SETTINGS
8
where
T
1
is a primary system time constant
T
2
is the secondary CT time constant, which can be estimated by the following equation:
Eq. 8-6
where
N is the CT ratio
V
s
is the CT voltage at 10 A exciting current obtained from the CT excitation curve
CT limiting factor K
S_LIM
is defined by the following equation:
Eq. 8-7
where
I
p
is the maximum CT primary fault current
The figure illustrates the K
s
CT saturation capability curve and K
S_LIM
limiting factor.
Figure 8-5: Determining CT time-to-saturate
CT time-to-saturate (t
SAT
) is determined as a projection of the intersection of the K
s
CT saturation capability curve and
K
S_LIM
CT limiting factor, as shown in the figure.
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
1
, t
2
...t
n
–
Use equation 8-5 to calculate the corresponding K
S1
, K
S2
…K
Sn
–
Calculate K
S_LIM
using equation 8-7
–
Compare each K
S
value with K
S_LIM
. If K
S
at the given time instance t
i
is less than K
S_LIM
, it means that true t
SAT
is
greater than t
i
, otherwise it is less than t
i
Summary of Contents for b30
Page 10: ...x B30 BUS DIFFERENTIAL SYSTEM INSTRUCTION MANUAL TABLE OF CONTENTS ...
Page 486: ...5 278 B30 BUS DIFFERENTIAL SYSTEM INSTRUCTION MANUAL TESTING CHAPTER 5 SETTINGS 5 ...
Page 616: ...iv B30 BUS DIFFERENTIAL SYSTEM INSTRUCTION MANUAL ABBREVIATIONS ...
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