Wind Energy and Protection

Roy Moxley
Thanks to Reigh Walling, Walling Energy Systems Consulting LLC
You See Wind Machines Everywhere
(30 miles North of Pullman)

82 GW Capacity in the US as of January 2017

Wind Turbines
Self Protecting

Size Increasing (today up to 8 MW)

No Zero Sequence

No (Presently) Negative Sequence

Type 1 and type 2 induction generator wind turbines
Basic operation of type 1 and 2 – typical configuration
Type 1 and 2 IG wind turbines
Advantages/disadvantages
Type 3 – Doubly-fed induction generator (DFIG)
Basic operation of DFIG – typical configuration
Type 3 – Doubly-fed induction generator (DFIG)
Advantages/disadvantages
Full-Converter (type 4) system
What are the advantages of the Full
Converter system?
Type 4 Variable-speed, full-converter wind
turbine-generator
Advantages/disadvantages
Comparison of WTG Designs to Comply with
Interconnection Requirements
Comparison of Type 4 with Synchronous
(conventional) generation
Advantages and Disadvantages of
Conventional generation
Reactive capability characteristic
of synchronous generator
Modeling Full Converter Machines –
Reactive Capability
Reactive capability characteristic of
full-converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Reactive capability characteristic of full-
converter wind turbine
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
Curves for different terminal voltages
(example)
What Are Common Reactive Control
Requirements ?

Existing:
 Voltage Regulation
 Reactive Power Control (constant Q)
 Power Factor Control (constant ratio of
Q to P)

 Reactive Control without Active Power

Production
 Voltage Regulation (adjustment of
reactive power to satisfy voltage regulation
schedule)
 Reactive Power Control All are
capabilities currently provided on a routine
basis by synchronous generators, except
reactive power control without active power
production (“synchronous condenser
operation”), which typically requires extra
equipment.
Wind Plant Reactive Power and
Voltage Control
Wind Plant Voltage Control – Reactive Droop

Typical Droop of 1% to 5%
Option for Voltage Deadband
Exercise – Draw Rough Sketch:
How does a full-converter wind park compare with a
synchronous generator for steady-state voltage control?
Voltage control: Fast response to change in
reference

Wind plant response very comparable to synchronous generator response.

WTG response very similar to excitation system response.
Summary – How Full-Converter WTGs provide
Reactive Power Control
 What Are Common Active Power Control
Requirements

Existing:
• Power Output (Curtailment) Control
• Ramp Rate Control
• Curtailments
• Start-up
• Regulation Up for Underfrequency
• Adjustable Droop
• Regulation Down for Overfrequency
• Adjustable Droop
• Low Voltage Ride Through
• High Wind Ride-Through
• Rate Variation Control
Ramp rate control - smooth, controlled
transition from one output level to another
Frequency Droop Control - Primary
Frequency Response
Frequency response – Simulations calibrated with
test in Electric Reliability Council of Texas (ERCOT)

Much faster than fossil

response, which may require
over a minute to fully
respond.
Low-voltage ride-through (LVRT)
Rate Variation Control
Transient underfrequency response (“inertial
response”)
Delta control – operate with a constant delta below
maximum output
 High Wind Ride Through (HWRT)

High wind speeds (above 25 m/s) caused widespread tripping in the past;
Summary – How FC WTGs provide Power
Control (existing and anticipated)
Modeling for power system analysis
Type 3 WTG Fault Performance
Type 3 WTG Performance During
Crowbar Activation
Model Limitations
Comparison of FC WTG with Synchronous Generation
to Comply with Interconnection Requirements
 Future Developments (Present Weaknessess)

• Weak grid controls for sustained stable operation in

systems with SCR < 3 (SCR = 3-phase short circuit MVA at
regulation point / aggregate turbine MW)
• Power oscillation damping for inter-area power
oscillations.
• Sub-synchronous resonance damping for series
compensated systems
• Isochronous operation – standalone operation These are
capabilities that can presently be provided by synchronous
generators.
 Protection Design Excercise

230 kV Line 75 miles long

2 mi. 2 mi.

25 mi. 25 mi. 25 mi.

Assumptions:
$200,000 per installed 230 kV breaker
$100,000 + $10,000/MVA for installed transformer
$25,000 per installed 34.5 kV breaker
$150,000 per mile 34.5 kV line
$10,000 per mile for fiber
$50,000 per microwave link
$20,000 per installed relay
 Protection Design Excercise
10kA fault duty 5kA fault duty
1000A load → 230 kV Line 75 miles long

2 mi. 2 mi.

25 mi. 25 mi. 25 mi.

25 – 3 MW 25 – 3 MW
Type 4 machines Type 4 machines
 Considerations
10kA fault duty 5kA fault duty
1000A load → 230 kV Line 75 miles long

• Distance Relays have been shown to have unreliable reach if wind

machines are radial due to SubSynchronous factors
• Line Current Differential can go up to 6 terminals
• Infeed is unreliable from wind farms (overcurrent complications,
distance reach trouble)
• How much added fault “exposure” is being added, compared to the
total line length?
Each generator has its
advantages and
disadvantages, but
Full Converter WTGs
generally have many
advantages and few
major disadvantages.
If we could only
control the wind…
Protection Considerations
Distance Relay with Inverter Current

IZ-Vop

Vpol
 Current Differential
I  I A  I B each I is the summation of:
ImI  Ii = ICT-Err.+ ISignal-Err.+ISync-Err.

I A

I Re s _ min  Trip if differential current exceeds sum of

   IA measurement errors
I Diff  I A  IB added by safety margin IRes_min
I Res  I  I Res_min

I B  ReI 
IB

Slide 69
Alpha Plane Current Differential
Differential More Secure but
Adds Communications
Let’s Calculate the Business Case of
Tap versus Substation

$750,000 -
Plus –
$1,500,000 for 3
New Line Relays
installed 230 kV
New Bus Relay
breakers +
New Feeder Relay
buswork,
Buswork
switches…
Construction Time

Slide 72
 Look at Business Case of Tap –vs-
Substation

What does a
Splice Cost ?

Slide 73
Provisos, Limitations, Exclusions…
Up to 6 Terminals, 64kbps Channels to Each Relay
Tapped Loads
Photo Voltaic

Major Industrials

Wind Farm
 Apply Built-in Distance for Backup

Relay 2
Relay 3

Relay 1
Relay 4

Relay 6

Relay 5
Set Reach to Inside Line With Maximum Infeed –
But What About Faults Beyond That ?

Relay 2
Relay 3

Relay 1
Relay 4

Relay 6

Relay 5
 Sequential Tripping Clears Strongest Source
First – Best Stability Response

Relay 2
Relay 3

Relay 1
Relay 4

Relay 6

Note: Shape shows reach, not

characteristic of the relay
Relay 5
 Power Swing Detection
Typical impedance trajectory
Z(ϑ = 0°)

 ϑ = 40°
X normal load condition

 ϑ = 120°
dangerous for
distance protection

Zone Z1  ϑ = 180°
unstable power swing
 out of step tripping
Z(ϑ = 40°)
φ
Z(ϑ = 180°) R
Z(ϑ = 120°)

Slide 78
 Traditional Power Swing
Blocking and Tripping
Z(ϑ = 0°)

Blinder
Blinder

Zone Z1

φ
Z(ϑ = 180°) R
Z(ϑ = 120°)
 Impedance trajectories of
3-machine power-swings

Slide 80
 Zero Setting Power Swing
Detection

OR
impedance in
power swing area

monotony power swing

AND detected

continuity

smoothness

Slide 81
 Measure Power Swings Like a
Human Would

 power swing if
ΔR1 and ΔR2 and
ΔX1 and
 power ΔX2if
swing
haveand
ΔR1 same
ΔR2direction
or
X
ΔX1 and ΔX2
ΔX1 have same directions
ΔX2
ΔX2 ΔX11 ΔX2
 no power swing if
ΔR2
ΔR1 and ΔR2 and
ΔR2 ΔR1
ΔX1 and ΔX2 have
ΔR2 ΔR1 different directions

R
Slide 82
Swing
Center
Voltage
Method
Out of Step Blocking 180°System
Separation
 Quick Quiz
What will the voltage across the
breaker contacts be if tripped on
the line between ZS and ZR ?

180°System
Separation
 Quick Quiz
What will the voltage across the
breaker contacts be if tripped on
the line between ZS and ZR ?

A. 2 X L-L Voltage

180°System
Separation
 Quick Quiz pt 2
What would you expect to
happen when the breaker tries
to open at 2 X L-L Voltage?

180°System
Separation
 Quick Quiz pt 2
What would you expect to
happen when the breaker tries
to open at 2 X L-L Voltage?

A. Restrike !!

180°System
Separation
 Quick Quiz pt 3
What would Generators (type 1
or 2 wind machines) during a
restrike ?

180°System
Separation
 Quick Quiz pt 3
What would Generators (type 1
or 2 wind machines) during a
restrike ?
A. Serious
Damage Possible

180°System
Separation
 Quick Quiz pt 4
What would happen to capacitor
banks energized by a restriking
breaker ?

180°System
Separation
 Quick Quiz pt 4
What would happen to capacitor
banks energized by a restriking
breaker ?
A.
Failure…Explosion
…Fire…

180°System
Separation
 Replacing Nuclear with Wind

High Availability Non-Dispatchable

High Inertia Low Inertia
Dynamic Voltage Support No Dynamic Voltage Support
Significant Fault Contribution Minimal Fault Contribution

Page 95
 Massive
Wind Farms
Installed and
Planned for
the North Sea

8 GW Installed and 2.9

Awaiting Installation
 Loss of Northern Power Plant

Power
Oscillation

Loss of 80%
Power
Transfer

P=V1V2sinΘ/X

Page 97
System Impact of a Line Trip

Loss of 50 MW Power Transfer

Loss of 13 MVar

Page 98
Power Plant Trip in Southern Area

Loss of about 600 MW

Page 99
 Impact of System Changes
On Protection Settings

Fault Duty – Overcurrent Pickup

Critical Clearing Time, Breaker Failure

Load Changes – Load Encroachment

Overcurrent Coordination

Load Balance – Islanding Considerations

Power Swing Settings
 Adaptive Protection ?

• How Are Settings Changed ?

• What is Protection Impact during setting
changes?
Real – World Distribution Example
Provide Overcurrent Settings for Breaker B
Settings if Breaker B knew Status of Breaker C ??
 Headlines Impact
System Stability

Note the Concentration of

Nuclear Plants along the West
Edge and the SouthWest
 Current Account Balance

2013 2023
Bulk Power Flows
Adjusting to Dynamic Load Limits
Changing Setting Groups and Files
 In Service Application Considerations
Setting Groups and Setting Files
Loss of Protection during Group Change ?
Time Required for Setting File Input ?
Security of File Transfer

Time Required
Control Center Calculations
Data Transmission
Time inside relay
 In Service Results

• Setting Groups and Setting Files

No Loss of Protection during Group Change

Security of File Transfer

Time to Transfer and Implement New Settings File

10 Seconds for Control Center Calculations and transmission
1 second within the relay

Security
Encrypted files to Station and to Relay
Backup / Fallback Settings Always in Place
Wind is Here to Stay
 Protection Considerations
• Fault Response
• System Response
• Out of Step Impacts
• Coordination Impacts
• Connection Costs
Questions ?