protection functions guide.pdf
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TRANSFORMER PROTECTION
TRANSFORMER PROTECTION
¡
Protection functions :
•
49 : thermal overload
•
50/51 : phase overcurrent
•
50N/51N : earth fault protection
•
59N : neutral voltage displacement
•
67 : directional overcurrent
•
67N : directional earth fault
•
27 : undervoltage
•
27R : remanent undervoltage
•
59 : overvoltage
•
50/51 : tank earth leakage
•
64REF : restricted earth fault
•
87T : differential protection
¡
Protection functions :
•
Main characteristics
•
Protection by circuit breaker
•
Logic discrimination
Division - Name - Date - Language
2
TRANSFORMER PROTECTION
¡
Main characteristics :
•
Transformer energizing inrush current :
Ie
t
e
i (t) = I e
î
e
(t): current peak value as a function of
time
Î
e
: value of maximum peak, i.e. the first
peak
e
e
t
e
: damping time constant
•
Inrush current at high voltage end of TRIHALtransformers:
Power in kVA
160
250
400
630
800
1000
1250
1600
2000
$
ne =
Ie
In
10.5
10.5
10
10
10
10
10
10
9.5
te (s)
0.13
0.18
0.25
0.26
0.30
0.30
0.35
0.40
0.40
Division - Name - Date - Language
3
TRANSFORMER PROTECTION
¡
Main characteristics (cont'd) :
•
Vector group :
Va
Va
VC
a
A
VA-VB
VA
11
b
B
VB
C
c
VA-VB
Dy11
Division - Name - Date - Language
4
TRANSFORMER PROTECTION
¡
Main characteristics (cont'd) :
•
For earth fault :
JA
During the fault
:
Ia
IA
n.Ia = N.JA and IA = JA
a
A
IB
Ia = Icc three - phase
b
B
IA = -IB = 0.58 . Icc three - phase / k
c
C
k : transformer ratio = 0.58 . N / n
n
N
Division - Name - Date - Language
5
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