!PPENDIX
3*
6
# ' #
&OR THE
CURRENT TRANSFORMER REQUIREMENTS
THE FOLLOWING SHOULD BE CONSIDERED
4HE SECONDARY CT CURRENT MUST DELIVER AT LEAST AS MUCH FUNDAMENTAL WAVE THAT THE STAGE ) CAN PICK UP
4HE FOLLOWING APPLIES
7ITH THE GIVEN CURRENT TRANSFORMER DATA AN ASSUMED INTERNAL BURDEN OF IE 0
I
|
0
.
|
6! 6! THE FOLLOWING RESULTS
WHERE
N
EFFECTIVE OVERCURRENT FACTOR
N
NOMINAL OVERCURRENT FACTOR
0
.
RATED BURDEN OF THE CTS
0
B
ACTUALLY CONNECTED BURDEN 6! WITH 3* PLUS WIRING
0
I
INTERNAL BURDEN OF THE CTS 0
I
)
.SEK
|
2
I
4HE SATURATION CURRENT )
3
WHICH CAN BE TRANSMITTED BY THE CTS WITHOUT SATURATION UNDER STEADY STATE
CONDITIONS IS
)
3
N
|
)
.
4HIS CALCULATED SATURATION CURRENT IS HIGHER THAN THE MAXIMUM SHORT CIRCUIT CURRENT SO THAT THE CT RE
QUIREMENT ARE FULFILLED
N
J
N
0
.
0
I
0
B
0
I
L
S
6!
6! !
!
#
4RANSFORMER
! BUS BAR OF A DISTRIBUTION NETWORK IS FED FROM A POWER TRANSFORMER WITH THE FOLLOWING DATA
RATED APPARENT POWER
3
.4
-6!
PER UNIT IMPEDANCE
U
K
PRIMARY HIGHER VOLTAGE
5
.
K6
SECONDARY LOWER VOLTAGE
5
.
K6
VECTOR GROUP
$Y
STAR POINT
EARTHED
SHORT CIRCUIT POWER AT THE K6 END
'6!
4HE FOLLOWING SHORT CIRCUIT VALUES RESULT
THREE PHASE HIGHER VOLTAGE SIDE
)
SC
! AT HIGHER VOLTAGE SIDE
THREE PHASE LOWER VOLTAGE SIDE
)
SC
! AT LOWER VOLTAGE SIDE
CORRESPONDS TO
)
+
! AT HIGHER VOLTAGE SIDE
2ATED CURRENT OF THE TRANSFORMER
)
.4
! AT HIGHER VOLTAGE SIDE
!SSUMED THE CURRENT TRANSFORMERS AT THE HIGHER VOLTAGE SIDE SHOULD BE ! ! AND AT THE LOWER VOLTAGE SIDE
!! 4HE FOLLOWING SETTINGS RESULT
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