3 wind and solar plant performance

Not for distribution without permission.Voltage at POI Wind Plant Power Output Voltage & Reactive Power Controls Actual measurements from a 162MW wind plant Wind Plant Voltage • Regulat

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Power Systems & Energy Course: Wind and Solar Plant Performance

Jason MacDowell

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Application Characteristics Single WTGs Large Farms Multiple Farms Low Penetration High Penetration

LVRT Protection Volt/VAR Control Primary Frequency Response

Grid Requirements Evolution

Fast Frequency Response

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Load & Wind Measurements

Feeder circuit trips

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Grid Friendly Wind Power Plant

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Wind Turbines and Reactive Power Control

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Reactive Power…Voltage control VIDEO

The Sources and Sinks of Reactive Power

The Reactive Power Balance must be struck on a local basis

Courtesy of National Grid Co, UK

Flow to Other Areas

Heavily Loaded Overhead Lines

Inductive Compensation

Transformers

Generators Consumer Loads

Flow from

Other Areas

System Load Voltage

The Reactive Power Tank

Current leads

voltage or

“overexcited”

Current lags voltage or

“underexcited”

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Reactive/Voltage Requirement Variations

• Fixed power factor

• Power factor range (permissive)

• Dispatched reactive or pf, within pf range

• Voltage regulation, within pf range

– May regulate local or remote bus

P Q

Permissive Range

Required Range

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GE 1.5 MW Reactive Capability

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WTG Reactive Power Capability

Terminal Bus

P gen

Q gen

WTG

Reactive Power for Voltage Support

• Steady-state PF range - 0.90 under-excited/0.90 over-excited

• Dynamic range meets or exceeds steady-state range

• WTG reactive capability often sufficient to satisfy PF

requirements at POI

• VAR capability reduced at low power due to units cycling off-line

Rating Point

Active Power

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Hierarchical Control Philosophy

Individual WTGs have fast, autonomous, self-protecting regulation of their terminal voltages

• Individual WTGs will always respond rapidly and correctly for grid voltage events

WindCONTROL provides plant-level controls to meet performance

requirements (e.g., voltage regulation) at the point-of-interconnection (POI)

• Sends supervisory reactive power commands to individual WTGs to ‘trim up’ initial individual WTG response

• Coordinates other substation equipment (e.g., switched shunt capacitors)

• Interfaces with utility SCADA

• Accepts commands (e.g., voltage reference setpoint) from utility system operator

Voltage Regulation

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LTC

Plant Level Control System

plant supervisory control

shunt devices if necessary

eliminates need for SVC,

STATCOM, or other expensive

equipment

SCADA

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Voltage at POI

Wind Plant Power Output

Voltage & Reactive Power Controls

Actual measurements from a

162MW wind plant

Wind Plant Voltage

• Regulates Grid Voltage at

Point of Interconnection

• Minimizes Grid Voltage

Fluctuations Even Under

Varying Wind Conditions

• Regulates Total Wind Plant

Active and Reactive Power

through Control of Individual

Turbines

Average Wind Speed

Voltage and Reactive Power Regulation

Like A Conventional Power Plant

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Power Factor Specification

• Typical power factor requirement variations:

under-excited to avoid ambiguities)

• Even where voltage regulation is required, a pf or reactive

range is specified

• Difficult to achieve some seemingly simple pf requirements

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Must supply

or absorb reactive over this entire range

A well thought-out code

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Wind Plant vs Wind Turbine Reactive Capabilities

Wind Plant pf capability  wind turbine pf spec

Extra compensation provided to make up the difference

variable reactive capability

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Steady-State Reactive / Voltage Analysis Inputs

• Reactive characteristics of WTG

– As a function of power

– As a function of voltage at WTG terminals

• Voltage range of point-of-interconnection

– Reactive or pf spec may vary with voltage

(see next slide)

• Operating voltage range of WTG

• Topology of collector system

• Impedances of substation and unit transformers,

collector cables, HV line

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Voltage-Dependent Power Factor Spec

Type of Requirements Main transformer operation Capacitor

compensation

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Voltage-Dependent Power Factor Spec

15.000 -15.000

-45.000 -75.000 [Mvar]

1.1500 1.1000 1.0500 1.0000 0.9500 0.9000 [p.u.]

Wind Farm V Q Diagram (EN): Reactive pow er ref erence (at Pn) in Mv ar / Voltage at PCC in p.u.

Wind Farm V Q Diagram (EN): Reactive pow er at PCC in Mvar / Voltage at PCC in p.u.

Wind Farm V Q Diagram (EN): Total Reactiv e Pow er of All Wind Turbines at LV Level in Mvar / Voltage at PCC in p.u.

15.000-15.000

Wind Farm V Q Diagram (EN): Reactive pow er ref erence (at Pn) in Mv ar / Voltage at PCC in p.u

Wind Farm V Q Diagram (EN): Reactive pow er at PCC in Mvar / Voltage at PCC in p.u

Wind Farm V Q Diagram (EN): Total Reactiv e Pow er of All Wind Turbines at LV Level in Mvar / Voltage at PCC in p.u

reactive power

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POI Reactive Power Range: effect of load level

75.000 45.000

15.000 -15.000

V-Q Q_WTG Date: 8/19/2014 Annex: /5

75.00045.000

15.000-15.000

• Higher I 2 X at high power

• WTG reactive power range can

be:

– function of active power

– function of voltage at WTG

terminals

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POI Reactive Power Range: effect of compensation

Figure 5-1: VQ curve with neutral tap positions at 0.5pu active power

75.000 45.000

15.000 -15.000

75.000 45.000

15.000 -15.000

75.00045.000

15.000-15.000

• Capacitors usually not required

• If required, typically at 34.5kV substation

• Capacitors can be controlled with WC

With capacitors Without capacitors

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POI Reactive Power Range: effect of OLTC

75.000 45.000

15.000 -15.000

75.00045.000

15.000-15.000

• On Load Tap Changer (OLTC) on if really needed

• Considered for “4-corner” requirements

• Wide voltage control band preferred to reduce

operations

75.000 45.000

15.000 -15.000

OLTC on main transformer Fixed tap on main

transformer

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Classical Power Limit

Normal Range

P Margin

Power Limit

Unstable

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Why is it the single most important factor?

• Maximum short circuit (I.e max kI sc or min X sc )

dictates breaker duties, many equipment ratings (later lecture)

• Minimum short circuit (I.e min kI sc or max X sc )

dictates worst sensitivities, e.g dV/dC, dV/dP, etc (we’ll look at this some more below)

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Steady State considerations

Insufficient margin and challenging operation in PF control

Plant level voltage control improves network voltage

stability performance in constrained transmission systems

Voltage Control

PF Control

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Wind Farm P, Q, V Relationship

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WindFREE TM

Reactive Power Control

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May 23, 2006

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150 0

0 1500

WindFREE Reactive Power

• Wind Turbine converter can

deliver reactive power

(kVAR) without wind (kW)

• Benefits weak grids and

systems with high wind

penetration

• Voltage support continues

without active power

generation…even following

trips

Active Power (zero)

Reactive Power Field Test Results (2.5 unit)

Reactive Power - even without wind:

A valuable option – An unreasonable requirement

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WindFREE Reactive Power Control Concept

Wind turbines generally operate

unless:

• Low wind speeds

• High wind speeds, resulting in

sudden turbine shut-down

• Abnormal grid conditions

Controls in GE’s Multi-MW allow continued delivery

of reactive power (kVAR) without wind (kW)

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active power reactive power

Voltage (medium voltage side)

Field Tests from Operating Multi-MW Turbine

Grid voltage influenced by a non-operating turbine

Turbine out of operation:

no active power produced

1 Initially turbine supplies

1100 kVAR; voltage 101%

2 Turbine kVAR command ramped down to zero;

voltage declines about 1%

3 Turbine kVAR command stepped up to 200 kVAR; slight voltage rise

4 Turbine kVAR command stepped up to 1100 kVAR; voltage jumps up about 1%

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-200 100 400 700 1000 1300

power reactive power

Turbine continues constant supply of reactive power

during start up and operation

Field Tests from Operating Multi-MW Turbine

Turbine kVAr

Turbine kW

Turbine Starts

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Economic Benefits

Wind plants with WindFREE Reactive Power Control

Reduce Grid Capital Costs

• Avoid requirement for other dynamic reactive power

equipment

• Avoid transmission system reinforcements

Reduce Grid Operating Costs

• Avoid requirement to run un-economic generation to meet

stability and voltage regulation requirements

• Reduce losses and other costs associated with poor voltage regulation

• Reduce consequential costs of grid instability

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Wind Turbine Fault Tolerance

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Ride-Thru Capabilities

 Remains on-line and feeds

reactive power through

system disturbances

 Meets present and emerging

grid requirement with

Low/Zero Voltage Ride

GE's Standard WindRIDE-THRU Offerings

0 20 40 60 80 100 120

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LVRT reduces amount of generation lost during faults

• Improves system stability

• Reduces likelihood of cascaded tripping

• Reduces likelihood of system collapse

LVRT enables a WTG to continue operation during faults

• Improves system availability and reliability

• Increases annual energy yield

• Increases revenues from energy sales

• Prevents overloading of other parts of the network

• Enables meeting the spinning reserve requirements

LVRT Advantages

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Ride-Thru Capabilities

Medium voltage bus drops to 0.0

Power recovers to disturbance level in <200ms

pre-GE's Standard WindRIDE-THRU Offerings

020406080100120

3-phase zero retained voltage, 200ms fault:

(GE Standard ZVRT offering) P, Q (Mw,Mvar)

Field Test Results (2.5 unit)

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3-phase 18.5% retained voltage, 700ms fault:

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Transient Stability

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