Calculation example 1
Verify that the existing CTs fulfil the requirements for the REG670 generator
differential protection in the following application.
~
GDP
Ext fault
CT1 CT2
I
tf
I
tf
IEC11000215-1-en.vsd
IEC11000215 V1 EN
Figure 348:
Generator data:
Rated apparent power: 90 MVA
Rated voltage: 16 kV
Short circuit impedance: 25 %
The existing CTs (CT1 and CT2) have the following data:
• CT1: 4000/1 A, 5P10, 15 VA, the secondary winding resistance R
ct
= 5 Ω The
rated burden:
EQUATION2529 V2 EN (Equation 284)
• CT2: 4000/1 A, class PX, the rated knee point e.m.f. E
k
= 200 V, R
ct
= 5 Ω
From the data the E
al
can be calculated:
• CT1:
( ) ( )
= × × + = × × + =
al sr ct b
E ALF I R R 10 1 5 15 200 V
EQUATION2530 V2 EN (Equation 285)
where ALF is the CT accuracy limit factor.
• CT2:
1MRK 502 071-UEN - Section 24
Requirements
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 749
Application manual
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