New Methods to Mitigate Distribution System Harmonics

University of Alberta

Alberta Power Industry Consortium

2014 Power & Energy Innovation Forum

New Methods to Mitigate

Distribution System Harmonics

By

Wilsun Xu

Power Disturbance & Signaling Research Lab


November 5, 2014


Outline

1. Background: harmonic problems faced by utility companies

2. Example research works on harmonic mitigation

3. Other power quality research activities in U of A

• Distributed micro-filter

• Zero sequence filter


1. Background 10 to 15 years ago

• Industrial customers are the main harmonic producers

• Interconnection standards have been established to limit their harmonics

Utility system

Harmonics filters

Linear & nonlinear loads

Iharmonics

Utilities have established

limits on Iharmonics flowing into

their systems at the PCC

(e.g IEEE Std. 519)

PCC – point of common coupling

Ih<Ilimit

A standard design practice

o Installation of harmonics filters inside the facility

o VFDs that generate only small amount of harmonics

• Nowadays, such loads inject little harmonics into power systems


Current situation

• More and more home appliances are becoming harmonic sources

• New “appliances” are also emerging such as PV panels and EVs

• Although insignificant individually, their collective impact can be big

• Blocks of residential loads have become main harmonic sources

0

20

40

60

80

100

120

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Harmonic order

IHD

[%

] PC 1

PC 3

PC 2

-4

-3

-2

-1

0

1

2

3

4

0 100 200 300 400 500 600

Time step

Cu

rre

nt

[A]

PC 1

PC 3

PC 2

0

20

40

60

80

100

120

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29Harmonic order

IHD

[%]

MW1 on

MW 1 off

MW 2 on

MW 2 off

-25

-20

-15

-10

-5

0

5

10

15

20

0 100 200 300 400 500 600

Time step

Curr

ent

[A]

MW 1 on

MW 1 off

MW 2 on

MW 2 off

Desktop PC Microwave

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400 500 600

CFL

-8

-6

-4

-2

0

2

4

6

8

0 100 200 300 400 500 600

Time Step

Curr

ent [

A]

Filling Water

Washing

Rinsing

Rinsing off

Spinning

Fast Spinning

Washer

1. Background


Typical spectra of a service transformer load SUB

One neighborhood

with 100 service

transformers, 3MW

“PCC”

0

2

4

6

8

10

12

3rd 5th 7th 9th 11th 13th 15th Total

Harmonic order

Cu

rre

nt

Dis

tort

ion

(ID

D,

%) Residential feeder

For this block of loads, its harmonic injection at “PCC” will exceed utility harmonic

limits. As a result, the neighborhood would not be allowed to connect to the system if it

were owned by a single owner.

Additional challenges: • The presence of 3rd and 9th harmonics (zero sequence)

• No single entity is responsible for it

• So utilities “own” the problem

1. Background Current situation


Potential Impact on Transmission Systems:

• Overload filters of HVDC, SVC and similar equipment

• Inability to energize transmission capacitors

• Resonance associated with transmission cables

1. Background Potential problems

Potential Impact on Distribution Systems:

• Overload distribution cables

• Shorten the life of distribution capacitors

• Increased capacitor/cable resonance

Potential Impact on 3rd Parties:

• Telephone interference

• Voltage induction on pipelines

• Overload customer capacitor or other equipment (e.g. wind farm)


New challenges & research needs

1. How to assess and predict the impact of distributed harmonic sources?

2. How to monitor harmonic levels in systems with distributed H sources?

New Challenge: Mass-distributed harmonic-producing loads

3. How to make the impact easier for decision-makers to understand?

4. How to mitigate the harmonic distortions in distribution systems?

• What is the proper strategy to manage the situation?

• How to impose harmonic limits on individual devices?

• What is the role of utility-side harmonic solutions?

• What options are available for system-wide or problem-focused harmonic

filtering schemes?

1. Background


• Distributed low voltage filters (called micro-filters)

• Filters dedicated to mitigate zero sequence harmonics

• Filters dedicated to prevent distribution system harmonics

from flowing into transmission systems

• Novel MV filters that may cost less than the traditional shunt

MV filters

• Resonance-free capacitors ……

New ideas under investigation at the University of Alberta

1. Background U of A research activities in harmonic mitigation


Sub-

station

3f load

Multi-grounded primary feeder

Distribution

transformers

Secondary feeder

Secondary feeder

Service drop

Service drop

House 1 House 2 House N

Feeder branch

Micro filter

• Install low voltage (micro) filters at multiple secondary systems

• Prevents harmonics from secondary systems flowing into primary systems

• How to create low cost micro filters?

• How to install them? (installation cost can be 10x of the cost of filter!)

This filter is proposed for system-wide or partial system-wide harmonic filtering

2. New method 1 – Micro Filter The concept


Meter Base

Micro Filter

Revenue

Meter Secondary feeder

House 1 House 2Point Y

Filter installation scheme Filter location in circuit

Proposed solution: Meter-collar based, 240V, plug-in active filter

• Active filtering: At low voltage, active filter is inexpensive and compact.

Estimated cost is less than $1000/each

• Micro filter is installed at only one of the houses in the secondary system

• Installation for about 30%~50% secondary systems are sufficient. Filters

can be installed gradually or partially. There is no large initial cost

Filter location

Novel Installation Scheme 2. New method 1 – Micro Filter


Extensive studies have been conducted to

1) Determine if the proposed concept can work

2) Establish design parameters for the micro filters

10m

15m

20m 30m

50m

30m

House #1

#2

#3

#4

#5

Secondary

conductor Serivce

conductors

Primary System

Ih

3rd 5th 7th 9th 11th 13th 15th TDD0

0.5

1

1.5

2

Dai

ly A

ver

age

Cu

rren

t ID

D(%

)

Harmonic order

No Filter

at Service transformer

at House 1

at House 2

at House 3

at House 4

at House 5

2. New method 1 – Micro Filter

Our research findings suggest that the micro-filter scheme is a

promising solution. The next step is to build a prototype device.

Research findings


This filter is proposed to mitigate telephone interference problems

Filter

SUB

1st neighborhood 2nd neighborhood

Parallel telephone circuit

C

A

B

C

N

C1

A

B

C

N

C2 L2

(a) (b)

9th and 15th

Yg-D (service) transformer;

25kV/600V or 25kV/480V;

300~500kVA;

Can be constructed using

3 single-phase units

Installing a filter = connecting a three-phase customer

This is essentially a

a load (customer);

This arrangement filters

both 9th & 15th harmonics;

It can be simplified by

using C1 only to filter just

the 9th harmonic.

2. New method 2 – Zero sequence filter The concept


100kVA - 14400 primary and a 277 secondary, 2 HV bushings, around $5,500.00



If this is an issue, a 2nd filter

could be installed to mitigate

upstream harmonics

Only one filter downstream

to the telephone line attracts

around 20% of the upstream

harmonic load currents

240/25 kV

Summerside

Substation

Downstream

loads

Upstream

loads

First Filter

The Telephone line

sections in parallel

with overhead lines

F1

d

LZ

u

LZ

Second Filter

(if necessary)

F2

20%uL

u dL L

Z

Z Z

21 SU Feeder (The main

source of telephone

interference in 41Ave)

2. New method 2 – Zero sequence filter Case study


1 3 5 7 9 11 13 15 Total rms0

50

100

150

200Time of the Day: 1am

Tel

lin

e V

olt

age

(V)

Harmonic order

1 3 5 7 9 11 13 15 Total rms0

10

20


Tel

lin

e V

olt

age

(V)

Harmonic order

1 3 5 7 9 11 13 15 Total rms0

10

20


Tel

lin

e V

olt

age

(V)

Harmonic order

1 3 5 7 9 11 13 15 Total rms0

10

20

30Time of the Day: 16pm

Tel

lin

e V

olt

age

(V)

Harmonic order

1 3 5 7 9 11 13 15 Total rms0

50


Tel

lin

e V

olt

age

(V)

Harmonic order

1 3 5 7 9 11 13 15 Total rms0

50

100


Tel

lin

e V

olt

age

(V)

Harmonic order

Without Filter

Transformer based filter

Two transformer based filters

Capacitor based filter

Conclusions:

2. New method 2 – Zero sequence filter Case study results

One filter at

location F1 is

sufficient

• The filter is an effective solution to mitigate telephone interference problem

• It could be useful to reduce pipeline induction as well

• The filter is very easy to construct and install

• It costs less than the traditional shunt filters

The next step is to test the filter in ATCO system


3. Other power quality related research at U of A

Power quality analysis & measurement:

• Method to assess the impact of distributed harmonic sources

• Novel sensors for measuring distribution line harmonics

• Method to detect harmonic or resonance sources

• Synchronous closing scheme for generators

• Inductive coordination of distribution line and pipeline

Power quality data analytics:

• Methods to anticipate the failure of equipment

• Method to monitor the condition of feeder capacitors

• Novel protection scheme for trip grounding


4. Conclusions

• Distributed harmonics is an emerging power quality concern

• It calls for new ideas for assessment, measurement and mitigation

• Two examples are shown to illustrate the benefits of research

On the technical subject of harmonic mitigation:

• Understand industry needs and obtain technical support/feedback

• Undertake forward-looking projects of high-risk, high-reward

nature in addition to application projects

• Provide excellent training opportunities to graduate students

On U of A research activities: The APIC platform has enabled U of A to

U of A has benefited a lot from the APIC platform as well

We thank APIC companies for their financial and technical support!

New Methods to Mitigate Distribution System Harmonics

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