Chapter 7) 7SR23 DAD Applications Guide
©2013 Siemens Protection Devices Limited
Chapter 7 Page 16 of 42
2.2.2
Example 2 – Restricted Earth Fault Protection
Figure 2-7
Example System – Restricted Earth Fault
Plant Data
See diagram above.
Settings Requirements
Rated current = 10 x 10
6
/ ( 3 x 11000) = 525A
Assigned through fault current (rated stability limit) = 16 x load current = 8.4kA, or, as specified by the user.
Required Fault Setting (Primary Operate Current):
10 – 25% of protected winding rated current, or
As specified by the user.
Required P.O.C. = 53 - 131A. Say 60A.
Line CT (LCT) and Connection Details
Turns ratio (T)
1/600
Voltage Knee Point (V
K
)
350V
Magnetising Current (Imag) @ V
K
40mA
CT secondary resistance (R
CT
)
7.5 Ohms
CT lead loop resistance (R
L
)
0.15 Ohms max.
Neutral CT (NCT) and Connection Details
Turns ratio (T)
1/600
Voltage Knee Point (V
K
)
300V
Magnetising Current (Imag) @ V
K
50mA
CT secondary resistance (R
CT
)
6 Ohms
CT lead loop resistance (R
L
)
0.15 Ohms max.
Summary of Contents for 7SR23 DAD
Page 1: ...Answers for energy 7SR23 DAD High Impedance Protection Relay Reyrolle Protection Devices ...
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Page 60: ...Chapter 3 7SR23 DAD Performance Specification 2013 Siemens Protection Devices Limited ...
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