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Chapter 7) 7SR23 DAD Applications Guide
©2013 Siemens Protection Devices Limited
Chapter 7 Page 19 of 42
Section 3: CT Requirements for High Impedance Protection
For the 7SR23 high impedance protection:
It is recommended that low reactance CTs to IEC60044 Class PX are used Class PX CTs have a
specified excitation characteristic and secondary winding resistance and these parameters are used to
calculate the performance of the protection in terms of primary operate current for internal faults and
stability during through fault conditions.
All current transformers should have an equal turns ratio.
The knee-point voltage of the CTs must be greater than 2 x Setting Voltage (Vs).
i.e. Required Vk 2 x I
F
(R
CT
+ R
L
) T Volts
A full explanation of how to specify CTs for use with high impedance protection is available on our Website:
www.siemens.com/energy
.
Typically the CT primary rating rated current of protected circuit (where rated current is different on each circuit
use highest rating e.g. Bus Section rating).
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 4: ...7SR23 DAD Contents 2013 Siemens Protection Devices Limited ...
Page 60: ...Chapter 3 7SR23 DAD Performance Specification 2013 Siemens Protection Devices Limited ...
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