Upload
kris
View
98
Download
0
Embed Size (px)
DESCRIPTION
Performance of Industrial Network improved by Low Resistance Neutral Treatment. Ralf Heitbreder Volkswagen AG Germany. Steffen Schmidt Siemens AG Germany. Structure of 6 kV system. 110 kV. 6 kV switchgear (with circuit breakers). 0.4 kV busbar. - PowerPoint PPT Presentation
Citation preview
1Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Performance of Industrial Network improved by Low Resistance Neutral Treatment
Ralf Heitbreder
Volkswagen AG
Germany
Steffen Schmidt
Siemens AG
Germany
2Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Structure of 6 kV system 110 kV
6 kV switchgear(with circuit breakers)
0.4 kV busbar 6 kV unit substation (with load interrupter switches and HV fuses)
3Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
IC=100A
transient earth fault relay
IC=100A
transient earth fault relay
Initial state (isolated neutral)
- unreliable operation of transient earth fault relays - high overvoltages (transient and power frequent)- high fault current over a long time
virtually every earth fault results in multi-pole fault- high voltage dips in 0.4 kV system in case of multi-pole 6 kV fault- man power needed for fault location and switch off
4Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Steps of Investigation
• Measurements for data acquisition– Zero sequence impedance; Reduction factor of cable shield
– Earthing and touch Voltages
• Calculation of earth fault currents
• Comparison of variants of neutral treatment– Effects on operation; Risk of fault propagation
– Devices for fault detection and protection
– Neutral devices
– Compliance with touch voltage criteria
• Installation of proposed variant of neutral treatment
• Commissioning and earth fault test
5Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Measurements for data acquisitionItestCurrent source
A VItest U
6 kV cableNYFG(b)Y
V
remote stationfeeding station
V
measurement of earthingand touch voltages
A Isheath
A Iearth
measurement of earthingand touch voltages
Results:
• Z0 1,5 /km + j 1,5 /km
• rE = 0,60 ... 0,80
• UE 20 V/kA
• UB 10 V/kA
Results:
• Z0 1,5 /km + j 1,5 /km
• rE = 0,60 ... 0,80
• UE 20 V/kA
• UB 10 V/kA
6Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Improved operation with isolated neutral
+ no interruption of supply + no cost for neutral devices
- high fault current over a long time risk of multi-pole fault - high overvoltages (transient and power frequent) risk of double fault- new capacitive directional earth fault relays necessary- man power needed for fault location and switch off
IC=100A
capacitive earth fault relayIE> = 50 A
IC=100A
capacitive earth fault relayIE> = 50 A
7Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Operation with earth fault compensation
+ no interruption of supply+ small earth fault current low risk of multi-pole fault
- high overvoltages (transient and power frequent) risk of double fault- new wattmetric earth fault relays and window-type transformers
necessary- high costs for neutral earthing transformer and arc suppression coil - man power needed for fault location and switch off
IRest<10A
wattmetric earth fault relaywindow-type current transformer
ICoil = 140 AIRest<10A
wattmetric earth fault relaywindow-type current transformer
ICoil = 140 A
8Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Low impedance earthing 2000 A
+ fast fault clearing low risk of multi-pole fault+ no transient overvoltages low risk of double fault+ existing overcurrent-time relays with phase fault detection can be used
- setting of phase fault detection must changed to -smaller starting currents (to detect earth faults) and -higher delay times (to prevent tripping by inrush currents)
- voltage dips of up to 10 % in 0.4 kV system in case of 6 kV earth faults- unselective or no tripping of HV fuses
Ik1,max=2kAIk1,min=0,77kA
overcurrent-time relay(phase fault detection)t» = 0,3 s
Ik1,max=2kAIk1,min=0,77kA
overcurrent-time relay(phase fault detection)t» = 0,3 s
9Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Low impedance earthing 500 A
+ fast fault clearing and low fault current low risk of multi-pole fault+ no transient overvoltages low risk of double fault+ low voltage dips in 0.4 kV system in case of 6 kV earth faults
- new overcurrent-time relays with earth fault detection necessary
- unselective or no tripping of HV fuses
Ik1,max=500AIk1,min=310A
overcurrent-time relay(earth fault detection)IE> = 200A; tE> = 0,3 s
Ik1,max=500AIk1,min=310A
overcurrent-time relay(earth fault detection)IE> = 200A; tE> = 0,3 s
10Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Comparison of Investment Costs
Isolated neutral
Earth fault compensation
Low impedance earthingIk1 = 2000 A
Low impedance earthingIk1 = 500 A
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
cost for protection devices
costs for neutral device
11Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Equipment used for low impedance earthing
Neutral earthing transformer
Neutral resistor
12Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Results of the short-circuit test
R
6 kV0,4 kV
voltages 6 kV system
voltages 400 V system
earth fault current
13Schmidt DE Session 2 – Block 1 – Paper 17
Barcelona 12-15 May 2003
Operational experience
• low impedance earthing (Ik1 = 500 A) is in operation for more than 2 years
• 2 earth fault were selectively cleared by protection relays
• no unselective tripping in response to earth fault starting
• no sensible voltage dips in 0.4 kV system during 6 kV earth faults