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Study of Electromagnetic Interference on Distribution Conductors
from Parallel Transmission Line and Practical Mitigation Solutions
Mike Shen, PEng, MASc, SMIEEE
2014 IEEE PES T&D Conference
Chicago, IL, USA
1
Acknowledgement
• Appreciate the opportunity of working on NextEra Wind Farm project.
• Appreciate my co-authors, Shilpa Shah and Ramin Eftekhari, for their contributions.
2
Outline
• Introduction
• Basics of Electric and Magnetic Fields
• Joint-use Transmission Line and Distribution Line
• Induced Voltage on Distribution Neutral from Overbuilt Transmission Line
• Different Mitigation Solutions
• Summary
3
Introduction
• Renewable energy resources are increasingly built at remote rural areas.
• Developers prefer to share the ROW of existing transmission or Distribution lines and route their HV tap line along the existing ROW.
• Excessive induced voltage and current on distribution neutral and phase conductors may occur during normal operation, fault, and transient conditions of the transmission system.
4
Cont.
• Electromagnetic Interference from transmission line includes magnetic induction effect and electrostatic effect.
5
Magnetic induction
Electrostaticinduction
HV line MV or LV line
Line current
Couplingcapacitor
Basics of Electric Fields
• Point charge 𝑄 and Electric field 𝐸
• Line charges and Electric field 𝐸
• A long single phase ac transmission line and Electric field 𝐸
6
Cont.
• Vector addition of electric fields under a three-phase transmission line
7
θ1
A B C
r1 r2 r3
θ2 θ3
EA(t)EB(t)
EC(t)
P
Cont.
• Electric potential 𝑉 and the electric field 𝐸
8
Basics of Magnetic Field
• A short section current carrying wire
• A long current carrying wire
• A long single phase ac transmission line
9
Cont.
• Vector addition of magnetic fields under a three-phase transmission line
10
θ1
A B C
r1 r2 r3
θ2 θ3
HA(t)
HB(t)
HC(t)P
I (out) I I
Cont.
• Changing magnetic field and the induction voltage
11
Loop
BV
E
Joint-use Transmission
Line and Distribution Line
12
Induced Voltage from Electric Field
• Electric field under TL Phase A to ground
13
0
5
10
15
20
25
0 2 4 6 8 10 12 14 16
Tran
sve
rse
vo
ltag
e (
kV)
Seperation distance (m)
• Voltage induced on the ungrounded neutral conductor
Cont.
• Neutral conductor is 12 m from the lowest TL phase conductor.
– Ungrounded -> 486 V
– Single point grounded -> 0.3 V
– Multi point grounded -> 0.06 V
14
Induced Voltage from Magnetic Field
• Magnetic field under TL Phase A to ground
15
• Voltage induced on the ungrounded neutral conductor
0
50
100
150
200
250
300
350
400
450
500
0 2 4 6 8 10 12 14 16
Lon
git
ud
ina
l v
olt
ag
e (
V)
Seperation distance (m)
Cont.
• Neutral conductor is 12 m from the lowest TL phase conductor.
– Ungrounded -> 60.0 V
– Single point grounded -> 60.0 V
– Multi point grounded -> 14.8 V
16
Different Mitigation Solutions
• 25 ohm ground resistance
• 10 ohm ground resistance
17
0
2
4
6
8
10
12
14
16
-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 3000
Ind
uce
d v
olt
ag
e (
V)
Distribution length (m)
0
1
2
3
4
5
6
7
8
9
10
-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 3000
Ind
uce
d v
olt
age
(V
)
Distribution distance (m)
Cont.
• Bury 1 km 4/0 bare copper conductor on each end of DL
• Balancing of TL phase conductor geometry
18
0
1
2
3
4
5
6
7
-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 3000
Ind
uce
d v
olt
ag
e (
V)
Distribution length (m)
0
0.01
0.02
0.03
0.04
0.05
0.06
-3000 -2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 2500 3000
Ind
uce
d v
olt
age
(V)
Distribution length (m)
Cont.
• T/L Transposition
– Every 1000m
– Every 100m
19
0
1
2
3
4
5
6
7
8
-3000 -2000 -1000 0 1000 2000 3000
Ind
uce
d v
olt
age
alo
ng
neu
tral
(V
)
Distribution line length (m)
0.4
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
0.5
-3000 -2000 -1000 0 1000 2000 3000
Ind
uce
d v
olt
ag
e (
V)
Distribution line length (m)
Cont.
• Increase the separation distance between distribution neutral and transmission line.
• Convert overhead distribution system to shielded power cable.
20
Thank you for your attention
Questions?
21