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