Ground Fault Protection Resonance Neutral
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Transcript of Ground Fault Protection Resonance Neutral
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7/29/2019 Ground Fault Protection Resonance Neutral
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Power System Protection
grounded systems
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Professor at Norwegian Univ. Science and
Technology Dept. Electrical Engineering Power system transients and protection
g vo age eng neer ng, s ress ca cu a ons
Recent focus on Power Transformers
Sabbatical at MTU
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Solid vs. resonance neutral
+ No over-voltages in faultsituations
- Undefined voltages to ground.High at resonance.
+ Ideall zero fault current. Arc
- g au curren
+ Easy fault detection
+ Ground faults ersist
self-extinguish.
- Difficult fault detection/location.Requires special competence
Fast trip and reclosing
- Poor power quality
and maintenance.
- In dynamic systems the coilmust adapt. Expensive
- Extra stress .+ Can continue to operate duringground fault. Increased power
ualit .
Safety issues: down/broken
conductors
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How can be reduce fault current further
from isolated neutral systems?
.
Resonance principles:
C L
I
+
V
-
L=-1
Cg
21 I V j C LC
j L j L
At resonance (2LC=1) the current is zero
g
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CurrentI0: SumIa,Ib,Ic
Summing the current numerically
I0Loweraccuracy
Residual connection
Summation transformer
3I0
differences3I0
(Toroidal/Rogowski coil)
a, ,
c
Open delta 3V0
Neutral point (isolated or resonance earth)V0
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Inductance added in the neutral point
Compensate for the capacitive current through Cg
; help
the arc self extinguish
changes (Petersen-coil (patent from around 1920)
Adjust air gap The coil changes it value incrementally and notice how the
neutral voltage changes. From a theoretical curve the resonance
point is estimated.
Over-compensation preferred to limit VN Avoid resonance also when parts of the system become
disconnected
The unit Ampere is used to quantify the coil;IL=Vp/L
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Variable inductance
h2V
hVpaN
TRENCH
Vpa
L
Increases with
resistance
VN Normal
operation
esonance
No-fault situation
L~
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First attempt to analyze the
neutral voltage
normal operation. Set U0 pick-up above this limit I V V C
V
h2Vpa
pa
2( )
( )
b N p a
c N p a
I V h V j C
I V h V j C
L C
03 ( ) 3
0? ?
Na b c N
N
I I I I V j Cj L
V3I0
At resonancej3C+1/jL=0 and the neutral
Need to add sophistication here
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Effect of asymmetry and
conductive line chargingN Increases with
Va
h2Vpa
paasymmetry and
resistance
VN Normal
C+CL GC
point of
operation
2
( ) ( )
( ) ( ( ) )
a N p a
b N p a
I V V G j C
I V h V G j C C
Resonance
No-fault situation
IL~1/LOver-comp.Under-comp.
20
2
3 ( ) 3 ( ) ( )
c N p a
Na b c N N p a
p a p p
VI I I I V G j C V h V j C
j L
h V j C V V C ,m ax
3 3 1 / 31
N N Ns dG j C j C j L Gj
u u
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Resonance grounded system
during fault (L=constant)
2(1 3 ) aV L CN A
Vpa
+If
3G2(1 3 )
f
f gj L R L CRf3Cg
L
0 2(1 3 )
pa
N
f g
V Vj L R L C
Vpa at resonance,
also for largeRf
elements (G||1/Rf) affect fault current and VN
to find the fault (identify faulty feeder)
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From ATP simulations
In reality the resonance peek is typically lower and measurements are required
25
30
35
V]rm
s
Stay away from this
resonance area
10
15
20
tralvoltage[
Fault0k
Fault3k
NofaultLCC
0
5
0 2 4 6 8 10 12 14 16 18 20
Ne
1pu
Normal point
of operation
100 k
U
V
SAT
Y
LCC
50. km
WRITE
max
50. km
LCC
50. km
LCC
50. kmM1
Coil"current"[A]0.1 nF 0-3k
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Directional over-current relay
resonance grounded systems Start when V0 goes above a fixed limit; pre-
measure the coil response max(VN,healty);
After a delay connect resistorR (|| toL)
nd
VNea y
0
Trip zone set based on natural conductive
current and asymmetry
IL
I01
I02
-I0
For each feeder
V0
I03LR
CG
V00CG I0L
I
Trip zone
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The resistive component ofI0 (in phase
with V0) is used
Trip zone
- 0
I0CGI
- 0
For each feeder
0
R
Healty feeder
0
I0R
R
Faulty feeder
I0CG r p zone
03 ( )
i a i b i c iI I I I 0
3 ( )
3 3 /
i a i b i c iI I I I
V G C V V R
0
13 ( ) 3 ( )
t i t iV G G j C C
j LAngle quite close to 90
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V0>Vlim (type 59G over-voltage relay)
and in correct quadrant (4th)? > m ype rec ona over-curren re ay
+
67N (I0>Ilim)
52 trip-
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Used in the 132 kV resonance earthed s stem
Measure the transient surge and use time ofarrival principles
Communication required
Trip the two relays that first identify the fault ens t ve to stur ances e g tn ng