Increase of the Rate of Change of Frequency (RoCoF) and its … · 2017. 12. 12. · • The ESB group is one of the largest wind generators in Ireland, and ESB has been involved

Increase of the Rate of Change of Frequency (RoCoF) and its impact to

the Conventional Power Generation in the Island of Ireland

or

Transient stability of conventional generating stations during times of

high wind penetration on the Island of Ireland

September 2015, International Energy Studies Workshop, Rome, Italy

Marios Zarifakis, Electricity Supply Board, Dublin, Ireland

www.esb.ie

TCD

© 2015 ESB, TCD

2 esb.ietcd.ie

Real Frequency Event, 27.04.2014, DBP

Frequency and

Power traces

Pnom=390MWFrequencyPower Output

3 esb.ietcd.ie

Contents

1. Introduction of the Irish Grid and ESB

2. Government targets and policies

3. Rate of Change of Frequency (RoCoF) and the Grid Code Definition

4. Mathematical models

5. Impact to generating plant and grid

6. RoCoF impact studies with manufacturers

7. Frequency oscillations

4 esb.ietcd.ie

Contents








5 esb.ietcd.ie

ESB – Electricity Supply Board

• Vertically Integrated Utility

• Involved in most types of generation

• The first ESB generation plant (in 1927) was a hydro

station at Ardnacrusha

• The ESB group is one of the largest wind

generators in Ireland, and ESB has been involved in

development, construction and management of

Irelands wind resources since the 1980s.

• Large international business.

• ESB owns a number of international power stations

and has O&M contracts for several other generation

stations.

6 esb.ietcd.ie

Transmission System Ireland

7 esb.ietcd.ie

European Transmission System

ROCOF Project Board Meeting

8 esb.ietcd.ie

Contents








9 esb.ietcd.ie

Increase of sustainable energy sources

EU 2020 Policy

20% of the EU’s energy demand to be from renewable sources by 2020

Irish Government Targets

40% of Ireland’s total electricity consumption to be met by renewables

TSO’s DS3 Programme

Safe and secure power system with high levels of renewable generation

10 esb.ietcd.ie

Operating Zones

11 esb.ietcd.ie

System and Wind Generation

ROCOF Project Team Meeting

Areas where Wind Generation had to be curtailed

12 esb.ietcd.ie

Timeline

13 esb.ietcd.ie

ESB Generation

Focus

Perspectives and Dependencies

EirGrid & SONI

Focus

Mechanical Issues

Turbine Integrity

Generator Integrity

Security of supply

Voltage Stability

Loading of Lines

14 esb.ietcd.ie

Contents








15 esb.ietcd.ie

Frequency Scale

50Hz

49Hz51Hz

Generation Consumers

16 esb.ietcd.ie

Generation-Load Balance

Generation

Load

48.5

49.0

49.5

50.0

50.5

51.0

-2 -1 0 1 2 3 4 5 6 7 8

Fre

qu

en

cy (

Hz)

Time (s)

Sample Low Frequency RoCoF

Frequency (Hz)

17 esb.ietcd.ie

Frequency and the Rate of Change of Frequency

Frequency

RoCoF=𝑑𝑓

𝑑𝑡

RoCoF

18 esb.ietcd.ie

RoCoF mathematical definition

(simplistic view)

𝒅𝒇

𝒅𝒕=

𝒇𝒏𝑷

𝟐𝑯𝒔𝒚𝒔𝒕𝒆𝒎𝑺𝒃With:

𝑓𝑛= System Frequency

𝐻𝑠𝑦𝑠𝑡𝑒𝑚= System Inertia

𝑃 = Lost load or generation

𝑆𝑏= MVA rating of the system

GenerationConsumers

50Hz

19 esb.ietcd.ie

Proposed Definition of RoCoF

The new definition by both TSOs, EirGrid and SONI, for the Grid Code is:

“remain synchronised to the Transmission System for a Rate of Change of Frequency

up to and including 1 Hz per second as measured over a rolling 500 millisecond

period”

Mathematical Definition of RoCoF

𝑹𝒐𝑪𝒐𝑭𝑨𝑽𝑬𝑹𝑨𝑮𝑬 =∆𝒇

∆𝒕

𝑹𝒐𝑪𝒐𝑭𝑰𝒏𝒔𝒕𝒂𝒏𝒕𝒂𝒏𝒆𝒐𝒖𝒔 =𝒅𝒇

𝒅𝒕

20 esb.ietcd.ie

RoCoF Trace

21 esb.ietcd.ie

Definition of RoCoF (500ms window)

Ardnacrusha (AA), Aghada (AD), Cathaleen’s Fall (CF), Louth (LOU), Carrickmines (CKM), Great Island

(GI), Ballylumford (BALLY) and Poolbeg (PB) (*1)

Maximum RoCoF measurements for different time windows

RoCoF values at various substations (trip of EWIC) (Eirgrid Study 2012)

Problem: Generator sees actual values…

22 esb.ietcd.ie

RoCoFAverage with Δt = 100ms and Δt = 500ms

23 esb.ietcd.ie

Contents








24 esb.ietcd.ie

Conventional Swing Equation

𝜏𝑎 = 𝜏𝑚 − 𝜏𝑒𝑙 = 0

𝐽𝑔𝑒𝑛 𝜔𝑚 𝑡 = 𝜏𝑚 − 𝜏𝑒𝑙

with 𝜔𝑚(𝑡) = 𝛿(𝑡)

𝐽𝑔𝑒𝑛 𝛿 𝑡 = 𝜏𝑚– 𝜏𝑒𝑙

Introducing 𝐻 =1

2𝐽𝜔2

𝑆𝑁

2𝐻

𝜔0

𝛿 𝑡 +𝐾𝐷𝜔0

𝛿 𝑡 = 𝜏𝑚 − 𝜏𝑒𝑙

And with 𝜏𝑒𝑙 =𝑘

𝜔0𝐵𝑅𝐵𝑆 sin 𝛿 𝑡

2𝐻

𝜔0


𝛿 𝑡 +𝑘

𝜔0𝐵𝑅𝐵𝑆 sin 𝛿 𝑡 = 𝜏𝑚

2𝐻

𝜔0


𝛿 𝑡 + 𝑘𝐵𝑅𝐵𝑆𝛿 𝑡 = 𝜏𝑚

25 esb.ietcd.ie

Negative ROCOF, Steam Turbine

0.25 Hz/s & 4 s 0.5 Hz/s & 2s 1 Hz/s & 1s 2 Hz/s & 0.5s

26 esb.ietcd.ie

Positive ROCOF, Steam Turbine

0.25 Hz/s & 4 s 0.5 Hz/s & 2s 1 Hz/s & 1s 2 Hz/s & 0.5s

27 esb.ietcd.ie

Real Frequency Event, 27.04.2014, DBP

Frequency and

Power traces

Pnom=390MWFrequencyPower Output

28 esb.ietcd.ie

Magnetic Field in a Synchronous Generator

Stable conditions:

Tel=Tmech

or

0=Tmech - Tel

Dynamic conditions:

J𝛼 = Tmech-Tel

J 𝜔 = Tmech-Tel - KD𝜔J 𝜔 = Tmech - kBSBRsin𝛿 - KD𝜔

29 esb.ietcd.ie

BR

BS

No gravity!!!

30 esb.ietcd.ie

G

1G

2Grid

Turbine Torque

Turbine Torque

To create the equation of motion using Lagrange

Damping depends on speed deviation!

Asynchronous effect!

31 esb.ietcd.ie

Swing Equation for light systems

𝑑

𝑑𝑡

𝜕𝐾𝑒𝜕(𝑞 11)

𝜕𝐾𝑒𝜕(𝑞 12)

𝜕𝐾𝑒

𝜕(𝑞 13)

𝜕𝐾𝑒

𝜕(𝑞 14)

⋮

𝜕𝐾𝑒𝜕(𝑞 𝑛1)

𝜕𝐾𝑒𝜕(𝑞 𝑛2)

𝜕𝐾𝑒

𝜕(𝑞 𝑛3)

𝜕𝐾𝑒

𝜕(𝑞 𝑛4)

−

𝜕𝐾𝑒𝜕𝑞11




⋮

𝜕𝐾𝑒𝜕𝑞𝑛1




+

𝜕𝑃

𝜕(𝑞 11)

𝜕𝑃

𝜕(𝑞 12)

𝜕𝑃

𝜕(𝑞 13)

𝜕𝑃

𝜕(𝑞 14)

⋮

𝜕𝑃

𝜕(𝑞 𝑛1)

𝜕𝑃

𝜕(𝑞 𝑛2)

𝜕𝑃

𝜕(𝑞 𝑛3)

𝜕𝑃

𝜕(𝑞 𝑛4)

+

𝜕𝑉

𝜕𝑞11

𝜕𝑉

𝜕𝑞12

𝜕𝑉

𝜕𝑞13

𝜕𝑉

𝜕𝑞14

⋮

𝜕𝑉

𝜕𝑞𝑛1

𝜕𝑉

𝜕𝑞𝑛2

𝜕𝑉

𝜕𝑞𝑛3

𝜕𝑉

𝜕𝑞𝑛4

=

𝑄11

𝑄12

𝑄13

𝑄14

⋮

𝑄𝑛1

𝑄𝑛2

𝑄𝑛3

𝑄𝑛4

=

𝑢𝑑

𝑢1𝑞

𝜏𝑚𝑔𝑒𝑛

0

⋮

𝑢𝑑

𝑢𝑛𝑞

𝜏𝑛𝑚𝑔𝑒𝑛

0

32 esb.ietcd.ie

Model verification


Real event

Model

33 esb.ietcd.ie

Frequency trace depends on system inertia

34 esb.ietcd.ie

Contents








35 esb.ietcd.ie

Swings depend on electromagnetic torque

36 esb.ietcd.ie

Restrictions

Updated?!

37 esb.ietcd.ie

Reactive power influences swings (MP1)


305MW

100MW

with higher reactive power

the damping is stronger

38 esb.ietcd.ie

Calculations with parameters ± 1Hz/s & 1.2s

Operational Point RoCoF,

duration

Remarks

1.) P=305 MW; Q=180Mvar -1Hz/s;

1.2s

The generated active power increases to 540MW. Generator

experiences 150% of rated stator current. The stator current limiter

in the AVR is triggered.

2.) P=305MW; Q=0Mvar The generated active power increases to 503MW. Generator

experiences 140% rated stator current. The stator current limiter in

the AVR is triggered.

3.) P=305MW; Q=-120Mvar The generated active power increases to 530MW. The stator

current limiter in the AVR is triggered. The reactive power triggers

the under-excitation limiter and under-excitation protection. I>

protection picks up.

4.) P=100MW; Q=-160Mvar The reactive power triggers the under-excitation limiter and the

under-excitation Protection.

1.) P=305 MW; Q=180Mvar +1Hz/s;

1.2s

ΔP/Δt is substantial and can lead to trigger the “Remote Breaker

Opening” logic which would close the control valves.

2.) P=305MW; Q=0Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker


3.) P=305MW; Q=-120Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker


4.) P=100MW; Q=-160Mvar ΔP/Δt is substantial and can lead to trigger the “Remote Breaker

Opening” logic which would close the control valves. Reverse

Power Pick up (-125MW). Torsional Oscillations become more

evident on low loads.

39 esb.ietcd.ie

Shaft line, exact modelling required for all stations

Higher RoCoF values might trigger

Eigen-Frequencies

Analysis for impact at turbine

and generator components

40 esb.ietcd.ie

Risks related to mechanical integrity

Torsional oscillations can create stresses to:

• Couplings

• Rotors and shafts

• Turbine blades

• Generator rotor end bells

• Generator stator end windings

41 esb.ietcd.ie

Impact on lifetime is unknown

Life time and maintenance

analysis to be undertaken

42 esb.ietcd.ie

Technical Risks

Technical Risks

• Controller & Operational Issues

• Turbine/Governor Controller

• AVR/PSS Controllers

• Protection Systems

• Turbine Protection

• Generator & Transformer Protection

• Mechanical Integrity

• Turbine Components

• Generator Components

• Lifetime Assessments

• Electrical Integrity

• Impact of Auxiliary Systems

• Motors, Fans, Pumps

Action

• Studies to be completed to assess impact

• Modelling Scenarios

• Rotor Dynamic Analysis

• Operational Analysis

• Internal Modelling work

• Torsional Probes

• Matlab/Simulink Model Build

• Digsilent Study

43 esb.ietcd.ie

Mechanical Integrity Consequences

RoCoF Event

Reduced Component Life Time

Consequential Machine Damage

Decreased overhaul intervals and

Increased Inspection Requirements

Forced Outage

44 esb.ietcd.ie

Operational Consequences

ROCOF Event

Further loss of Electrical Power Generations

Cascade Tripping Event

Load Shedding in the system

System Brown/Black Out

45 esb.ietcd.ie

Real Event, Poolbeg CT 15 @ 65 MW

46 esb.ietcd.ie

Contents








47 esb.ietcd.ie

Study Scope

Type MW

(Exp)

Unit

#

Studies

Required

Study

Priority

CCGT 2094 4 4* 1

Peat 228 2 1 1

Coal 855 3 1 1

Gas 258 1 1 3

OCGT 517 6 2 3

Pump Storage 292 4 1 1

Hydro 206 17 2 3

12 studies to be completed

Timeframe for Priority 1 Units 18 months

48 esb.ietcd.ie

Timeline going forward

● Studies required to demonstrate compliance

– High priority – 18 months - high run hours, frequently constrained on, frequently run during high

wind

– Mid priority – 24 months - units not in other categories

– Low priority – 36 months - low run hours, infrequently constrained on, infrequently run during

high wind

– Exempt units – units soon to retire, very low runs hours or units which in EirGrid’s operational

experience have ridden through high RoCoF events in the past

ESB will need to be compliant (or derogated/exempted) by these dates to

ensure it incurs zero penalties.

49 esb.ietcd.ie

Project Timeline

2010 – 2012Consultation Period

• Risk Paper

• OEM Engagement

• Understanding & Education

• Financial Appraisal

• Regulatory

2013 – 2014CER ROCOF Paper

• Consultation Paper

• Decision Paper

• KEMA Challenge Study

• No Cost Recovery Position

• Procurement Strategy

2014 – 2016Studies•Tender Process•Priorities 1 studies•Digsilent Study•Matlab/Simulink Model•Torsional Probe Analysis• Quality & Validation

2016 – 2018Post Studies

• Level of Compliance

• Level of Investment

• Development of individual Business Cases

• Implementation

That’s it??

50 esb.ietcd.ie

Contents








51 esb.ietcd.ie

Real Event, DBP, 26.12.2014

• C30 in Coolkeeragh Trip at 22:38

• DB1 MW; Hz

• 7 Min Oscillation

• Pk-Pk: ~0.3 – 0.4 Hz

• Period of Osc: 15 s (0.066 Hz)

52 esb.ietcd.ie

Typical Turbine Generator control circuit

53 esb.ietcd.ie

Response to a sinusoidal disturbance

Currently installed turbine controllers need major attention….

Output of controllers

swing almost in

phase with

disturbance which

amplifies the

disturbance

54 esb.ietcd.ie

Real event in Germany (Rhein-Ruhr Region)

55 esb.ietcd.ie

Questions?

Fragen?

ErwthseiV;

Thank You

and

Grazie

Footer

57 esb.ietcd.ie

Acknowledgements

Models used:

Matlab from Mathworks with Simulink and SimPowerSystem

Literature:

“Power System Stability and Control”, Prabha Kundur

“Handbook of Electrical Power System Dynamics”, M. Eremia, M. Shahidehpour

“Elektrische Schaltvorgaenge”, Reinhold Ruedenberg

Various publications by Eirgrid and CER (www.eirgrid.com and www.cer.ie)

DNV GL Study on ESB Fleet

Some animations were used from www.wikipedia.de, Dreiphasenwechselstrom

Contributions by:

Prof. Dr. William T. Coffey, Trinity College Dublin, Ireland

http://www.eirgrid.com/

http://www.cer.ie/

http://www.wikipedia.de/

Increase of the Rate of Change of Frequency (RoCoF) and its … · 2017. 12. 12. · • The ESB group is one of the largest wind generators in Ireland, and ESB has been involved

Documents