1
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
2
Acknowledgement
• Appreciate the opportunity of working on
NextEra Wind Farm project.
• Appreciate my co-authors, Shilpa Shah and
Ramin Eftekhari, for their contributions.
3
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
4
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.
5
Cont.
• Electromagnetic Interference from
transmission line includes magnetic induction
effect and electrostatic effect.
Electrostatic
induction
Magnetic
induction
Coupling
capacitor
Line
current
HV line
MV or LV line
6
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
7
Cont.
• Vector addition of
electric fields under
a three-phase
transmission line
A
B
C
θ1
r1
θ2
r2
θ3
r3
P
EC(t)
EA(t)
EB(t)
8
Cont.
• Electric potential 𝑉
and the electric field
𝐸
9
Basics of Magnetic Field
• A short section
current carrying wire
• A long current
carrying wire
• A long single phase
ac transmission line
10
Cont.
• Vector addition of
magnetic fields under
a three-phase
transmission line
A
B
C
I (out) θ1 I θ2 I θ3
r1
r2 r3
P
HA(t)
HB(t)
HC(t)
11
Cont.
• Changing magnetic
field and the
induction voltage
Loop
V
B
E
12
Joint-use
Transmission
Line and
Distribution Line
13
Induced Voltage from Electric Field
• Voltage induced on
the ungrounded
neutral conductor
25
20
Transverse voltage (kV)
• Electric field under
TL Phase A to ground
15
10
5
0
0
2
4
6
8
10
Seperation distance (m)
12
14
16
14
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
15
Induced Voltage from Magnetic Field
• Voltage induced on
the ungrounded
neutral conductor
500
450
400
350
Longitudinal voltage (V)
• Magnetic field under
TL Phase A to ground
300
250
200
150
100
50
0
0
2
4
6
8
10
Seperation distance (m)
12
14
16
16
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
17
Different Mitigation Solutions
14
12
Induced voltage (V)
• 25 ohm ground
resistance
16
10
8
6
4
2
0
-3000 -2500 -2000 -1500 -1000 -500
0
500
1000 1500 2000 2500 3000
Distribution length (m)
9
8
Induced voltage (V)
• 10 ohm ground
resistance
10
7
6
5
4
3
2
1
0
-3000 -2500 -2000 -1500 -1000 -500
0
500
1000 1500 2000 2500 3000
Distribution distance (m)
18
Cont.
6
Induced voltage (V)
• Bury 1 km 4/0 bare
copper conductor on
each end of DL
7
5
4
3
2
1
0
-3000
-2500
-2000
-1500
-1000
-500
0
500
1000
1500
2000
2500
3000
Distribution length (m)
0.06
0.05
Induced voltage (V)
• Balancing of TL phase
conductor geometry
0.04
0.03
0.02
0.01
0
-3000 -2500 -2000 -1500 -1000 -500
0
500
Distribution length (m)
1000 1500 2000 2500 3000
19
Cont.
– Every 1000m
7
Induced voltage along neutral (V)
• T/L Transposition
8
6
5
4
3
2
1
0
-3000
-2000
-1000
0
1000
2000
3000
1000
2000
3000
Distribution line length (m)
– Every 100m
0.5
0.49
Induced voltage (V)
0.48
0.47
0.46
0.45
0.44
0.43
0.42
0.41
0.4
-3000
-2000
-1000
0
Distribution line length (m)
20
Cont.
• Increase the separation distance between
distribution neutral and transmission line.
• Convert overhead distribution system to
shielded power cable.
21
Thank you for your attention
Questions?