Experience from Tests of Frequency Containment Reserve delivery for Generating Units

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1 Experience from Tests of Frequency Containment Reserve delivery for Generating Units Evert Agneholm Senior principal engineer DNV GL Adjunct professor University West 02 April DNV GL 02 April 2019 SAFER, SMARTER, GREENER

2 Outline Test equipment Tests performed and experiences gained Hydro units Gas turbines Thermal units Governor feedback signal Backlash How to tune and optimize Experiences from nuclear plants Summary 2

3 Test equipment Replaces the normal frequency signal with a synthetic frequency signal as specified in the FCR requirements Is small and portable Can be connected during operation Is flexible to cover different governor types Can also be used for testing island operation capability Can be used for FCR verification tests Together with theoretical work for optimizing the frequency control 3

4 Test equipment Based on a general and flexible platform from National Instruments Presently programmed to test governor response (and also AVR response) High sampling frequency (50 khz) Outputs: ± 10 VDC ± 20 ma or 4-20 ma 110 VAC single phase (through an amplifier) Other type of VAC and VDC through an amplifier 4

5 Hardware 5

6 Tests performed DNV GL has performed tests on Tens of hydro units Several gas turbines Several thermal units Tests have been performed to verify FCR Island operation capability Voltage control 6

7 Turbine governor feedback signal Depending on the governor feedback signal the response can vary significantly Guide vane feedback (hydro) Regulator output Active power The governor feedback affects Applied frequency test signal as specified in the FCR requirements Unit response, i.e. MW/Hz Stability margins 7

8 Example from a Pelton turbine using guide vane feedback The relationship between guide vane opening and active power is not constant for hydro units. This means that the gain (reglerstyrka) is not constant for the operating range if not using active power feedback. Generally the gain Decreases with the loading for Pelton and Francis turbines Increases with the loading for Kaplan units Gain (MW/Hz) Active power [MW] 8

9 Example from a thermal turbine using active power feedback The relationship between valve opening, regulator output and active power is not constant for thermal units. Normally manufacturer try to linearize. The gain in MW/Hz is constant when using active power feedback Frequency change (Hz) Change of active power, regulator output and valve opening(%) 9

10 Frequency step response test to verify steady state activation and backlash Example from a Francis turbine in Myanmar Due to backlash ΔP 1 ΔP 2 and ΔP 3 ΔP 4 10

11 What is backlash? 11

12 How can we see backlash? Backlash affects Amplitude Phase shift In the FCR requirements amplitude and phase are of importance 12

13 Frequency step response test to verify steady state activation and backlash Example from a gas turbine in Sweden using active power feedback Gain in MW/Hz constant Backlash in the fuel valve corresponds to several percent 13

14 Backlash impact in island operation - gas turbine T(s) Frequency (Hz) Active power (MW) Phase shift (degrees) Amplification (db) Time (s) f (Hz) 14

15 Tune the frequency control to fulfil FCR requirements (1) There are many different parts in a production unit that can affect/limit the frequency control and the possibility to fulfil the FCR requirements Model the important parts affecting the frequency control and estimate the parameters Physical models The turbine governor and its parameter settings are the most important part and also easy to change If possible try to validate the model by tests Perform simulations of the planned FCR-tests using the dynamic simulation model and evaluate the results Try to find parameter settings in the dynamic model fulfilling the FCR requirements Start with the governor Estimate impact from other parts 15

16 Tune the frequency control to fulfil FCR requirements (2) Perform tests according to the FCR requirements Measure and evaluate the tests Important to measure as many signals as possible to use for validating the dynamic model If fulfilling the requirements the prequalification is finished If not fulfilling the requirements redo previous steps now with a better validated dynamic model Active power (MW) Test Simulation Frequency step ±0.1 Hz Time (s) 16

17 Optimize the frequency control Estimate costs for participating in frequency control Reduced power production du to allocating capactity for up regulation Reduction in production due to not operating at best efficiency Wear and tear Changing direction of opening/closing valve/guide vane Changed position Increased risk for breakdown and stand still costs Simulate typical frequency cycles of days, weeks or years Estimate the specified parameters/costs Find optimum based on several different choices of governor settings fulfilling the FCR requirements 17

18 Example from nuclear power plants using power control In previous FCP projects it was found that some Swedish nuclear power plants use active power as feedback signal in the governor and that the power control is very fast Power control measure the electric power out from the generator. The electric power out from the generator consist of mechanical power and the change of kinetic energy If having a dimensioning fault the frequency derivative can be as high as ±0.3 Hz/s Assume a unit with rated power 1000 MVA and H=7 MWs/MVA. The change in kinetic energy then corresponds to PP = dddd 2 SS HH = dddd ff 0 50 = 84 MMMM/unit If having a fast power control using power feedback this is contra productive for the power system 18

19 Summary It is important to have a good knowledge of the production unit and its limitations Sometimes it is rather easy to see that FCR requirements cannot be fulfilled without doing test To tune the unit to fulfil the requirements it is recommendable to first build up a dynamic simulation model and then simulate the FCR tests to evaluate if the requirements are fulfilled During the tests it is common that non linearities are found that have a negative impact on the performance During tests it might be necessary to tune parameters in the governor Optimizing the frequency control can create further values but requires knowledge of what is causing the costs for frequency control 19