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Chapter 7) 7SR23 DAD Applications Guide
©2013 Siemens Protection Devices Limited
Chapter 7 Page 14 of 42
Calculation of Fault Setting (Primary Operate Current)
The required relay setting (87/50-1) Is can be calculated from:
POC = ( I
MAG TOTAL
+ Is ) / T = ( 6(I
MAG
) + Is ) / T
Is = POC x T – I
MAG TOTAL
= 1000/2000 – I
MAG TOTAL
Is = 0.5 – 6(I
MAG
)
The magnetising current is dependent on the relay operate voltage (Vs), this is not finalised yet so a provisional
value (Vs prov) is chosen from the above i.e. 160 < Vs < 300
Say Vs prov = 220V. From the CT magnetising curve Imag = 24mA at 220V.
Irelay = 0.5 – 6(0.024) = 0.356A (use 0.35A)
Rstab = 220/.35 = 630 Ohms
Metrosil Specification
‘C’ Value
Vs = 220V (i.e. > 100V) so a ‘C’ value of 1000 is chosen
Short Time Power Rating
Using the empirical formula
2kW
1
00
6
2000
1
00
315
4
P
V
T
I
4
P
1SEC
K
F
1SEC
For values > 8kW/s a 150mm Metrosil is required
Stabilising Resistor Specification
Continuous Power Rating
77W
P
630
x
0.35
P
R
x
I
P
CONT
2
CONT
stab
2
s
CONT
Summary of Contents for 7SR23 DAD
Page 1: ...Answers for energy 7SR23 DAD High Impedance Protection Relay Reyrolle Protection Devices ...
Page 2: ......
Page 4: ...7SR23 DAD Contents 2013 Siemens Protection Devices Limited ...
Page 60: ...Chapter 3 7SR23 DAD Performance Specification 2013 Siemens Protection Devices Limited ...
Page 225: ......