02a_Basis stator ground fault protection.pdf
Post on 12-Jan-2016
38 Views
Preview:
Transcript
The year of Profitable Growth
Global network of innovation
Basis of Stator-Ground-Fault Protection
Power Automation 2
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Presenter: Dr. Hans-Joachim Herrmann PTD PA13Phone +49 911 433 8266E-Mail: Hans-Joachim.Herrmann@siemens.com
Generator ProtectionBasis of Stator-Ground-Fault
Protection
Power Automation 3
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Test Results showing Effects of Arc Burning on Stator Core Laminations during Ground Faults
Power Automation 4
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Methods of Neutral-Point Connection (1)
? Isolated or high ohmic groundedAdvantage: Small fault currentsDisadvantage: High transient overvoltage at
intermittent ground faults(2.5 – 3.5 ) Vph-E
? Compensated or reactive groundedAdvantage: Small fault currents on the fault
locationDisadvantage: Transient overvoltage
(<2.5Vph-E),Higher costs
Standard application
Very seldom; in older plants used
< 10 A
< 10 A
Power Automation 5
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Methods of Neutral-Point Connection (2)
?Low ohmic groundedAdvantage: Lower transient overvoltage,
95 to 98% protective range ofSEF protection
Disadvantage: Great damages to generatorsat longer fault duration
? Solidly (effective) groundedAdvantage: Low transient voltage, better
measuring conditions for theprotection
Disadvantage: Great damages to generators,Leakage zero sequence currents
Application in industrial plants
Application at low voltage generators
G
< 200 - 400 A
Power Automation 6
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Voltages in Case of an Ground Fault
Voltage without ground fault
VL3,E VL3,E = VL31
VE = -VL1,E
VL1,E = 0
VL2,E = VL21
Voltages at the point of a ground fault at phase L1
? VLx,E ... phase-ground-voltage
? no displacement voltage (VE = 0)
? VL,E voltage decreases in the faulty phase (min ?? 0)
? VL,E voltage in the both “healthy” phasesare increase (max ?? ? phase-to-phase)
? VE displacement-voltage(can be measured at star point to ground)
MMVL1,E
VL2,E
L1L2L3
ABC
Power Automation 7
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Currents in the Case of an Ground Fault
Model:
Equivalent voltage VE at the point of fault
IE =3 ?IE/3 = 3 ??VE/ZE
IE/3 ... ground fault current in one phase
ZE ... ground impedance at one phase
Vector diagram: ground fault in phase L1
VL3,E
VL2,E
IE =3V0
1
j? CE
= 3V0 ??j? CE
=3 VE
ZE
IC,2
IE
IC,3
L1L2L3
IC 33V0 =3VE
UE
IE/3
IE
ZE
L1L2L3
~ ~ ~
Power Automation 8
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Correlation from Ground Fault Location
Displacement voltage VE (V0) and ground current IE (3I0) as a function of the fault location of an ground fault in the machine winding.
IE= 3VE
ZE
VE
VL2,EVL1,E
VL1,E VL2,E
VE ZE
VE
At faults close to the star-point the displacement voltage and the ground currents become small
Power Automation 9
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Generators Connected via an Unit Transformer to the Grid
? generator is galvanic isolated
? under the assumption of an ideal transformer, the displacementvoltage caused by an ground fault, can only be measured at the generator
GGG
Power Automation 10
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Unit Connection: Elimination of the Disturbance during a Ground Fault on the High Voltage
Groundingtransformer
üTR =
CLCG CTr
CK
VEO ?VN
3
(Limb transformation ratio)
VGen
31003
5003
VV
? ?R
RPrim
ü3
2TR
?VR
Problem: grid ground faults cause disturbancesdue to the coupling capacitancebetween the two transformer windings
Solution: attenuation by means ofa load resistor
Note:At solidly grounded transformer the VE0 is
appr. 80% of VN/?3
(Safety margin, if solidly grounding is open)
Power Automation 11
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Unit Connection - Influence onto the Coupling Capacitance
VR,prim Rprim
CK
VC
VEO
VR,prim???Rprim VEO1Rprim + j? ?CK
Example: CK = 10 nF VEO = 220 kV3
VR,prim ??265V
?
??? ???
???? 665
3RR
2TR
Primü
VN,G = 10,5 kV R = 5 ?
üTr = 34,6
? VR,sek ??23V
? 23V500V
? 4,6% disturbanceinfluence
CE.
equivalent circuit disturbance voltage
CG+CL+CTr neglected
VEO displacement voltage on the high voltage sideCK three phase coupling capacitanceRprim primary load resistorüTr grounding transformer ratio
Power Automation 12
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Unit Connection with Neutral Transformer
This design is very often used outside Germany, mostly at small generators
Generator Unit transformer
Rsek=Rprim
ü2TR
Design of Rprim so that the fault current is < 10A
R
VR
ÜTR =VGen
3VR
A high secondary nominal voltage VR (250V - 500V) is selected in order to avoid very small load resistors.
Power Automation 13
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Generator Connected Directly to the Grid
? machines are galvanic connected
? displacement voltage caused by an ground faultcan be measured in all locations
G G G M
Power Automation 14
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Direct Connection -Directional Stator Ground Fault Protection
L1 L2 L3
L1
L2
L3
CEIC + IR
Ohmic currentboost
IC
IR
ICL2
ICL1
3I0
3V0
VL1 VL2
Network
3i0 ?3V0
? DFT ?3V0>, 3I0>
? Direction(?3V0, 3I0)
Groundingtransformer
Power Automation 15
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Fault Currents in Case of a Direct Connection
G1
G2
IMess
IMess
Power Automation 16
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Fault Currents in Case of a Direct Connection with Grounding Transformer
G1
G2
IMeas
IMeas
Grounding transformer
Ohmic currentRB
Power Automation 17
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Ground Current Detection via a Toroidal Current Transformer and Holmgreen Connection
Toroidal Current Transformer
IE3 per phase
I´E
L1 L3L2
IE
? I3 ~
Holmgreen connection(separate cores)
Holmgreenconnection(common neutral return connector
Sensitivity is limited
Problem:Large CT ratioleads to small currents on thesecondary side
IE3 per phase
L1
L3
L2
I´E
(IE = 3 I0)
? magnetic additionof ground currents,
? principle is sensitive
Power Automation 18
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Directional Stator Ground Fault Protection Directional Characteristic
Power Automation 19
Power Transmission and Distribution
Power AutomationProgress. It‘s that simple.
Directional Stator Ground Fault Protection - Logic
top related