OPAL-RT RT14 Conference: Experience in power plant with RT-LAB BERTA test bench

The 7th International Conferenceon Real-Time Simulation TechnologiesMontreal | 9-12 June, 2014

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Marc LangevinOPAL-RT TECHNOLOGIES

[email protected]

Some experiences in power plants with

RT-LAB BERTA Test Bench

mailto:[email protected]


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A Real-Time Regulator, Turbine and Alternator Test Bench for Ensuring Generators Under Test Contribute to Whole

System Stability and Facilitating Model Identification

Marc Langevin, eng., Ph.D.

OPAL-RT TECHNOLOGIES, Montréal


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The Needs of the Industry

• Better understanding of generator behaviors in case of major system frequency disturbance;

• Better modeling of turbines and speed governors, for improved accuracy of transient stability studies;

• Better speed governor settings for improved frequency stability.


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Requirements

• Transmission system owner’s requirements for power plant operation:

• NERC’s Standard Mod-027;

• IEC’s international standard 60308;

• Hydro-Québec’s transmission system;

• Dynamic model identification and validation;

• Frequency stability improvement


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NERC’s Standard Mod-027

• Requirement #2 of 5:

• "Each Generator Owner shall provide, for each applicable unit, a verified turbine/governor and load control or active power/frequency control model, including documentation and data ... to its Transmission Planner in accordance with the periodicity specified in MOD-027 Attachment 1"


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IEC`s International Standard on Testing of Control Systems for Hydro Turbines

• "The principle of the simulator can be described as follows: a signal, representing the speed/frequency variations which would occur if the unit were supplying an isolated load, is developed by calculation from the measured electrical power output of the generator. This simulated speed/frequency signal is then delivered to the controller in place of (or in addition to) the actual speed/frequency signal."


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Hydro-Québec’s transmission system requirements

• As a member of NPCC (Northeast Power Coordinating Council), Hydro-Québec Production needed to provide to Hydro-Québec TransÉnergie, the Québec transmission grid owner, the required models and parameters for the hydraulic turbine and speed governors. These models must be in accordance with IEEE standard “Dynamic Models for Steam and Hydro Turbines in Power System Studies” and “Hydraulic Turbine and Turbine Control models for System Dynamic Studies".


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What is BERTA?

• A test bench specially designed for testing speed/power control on site and/or in laboratory;

• Driven by a real-time simulator capable of generating frequency signals to be injected in the speed governor:

• Open loop tests with pre-programmed frequency signals;

• Closed loop tests using a frequency signal computed in real time according to the generator power variations resulting from a load disturbance in a simulated islanded mode of operation.


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Standard Operation Set up in a Power Station


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Test Set up in a Power Station


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• Experimentation in hydro power plant


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Model Validation: open loop test• Simulated

• frequency

• deviation


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The speed governor block diagram


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Model Validation: open loop test

Equivalent gate

set point variation

and actual gate

displacement:

∆ 𝑆𝑃 = −∆𝐹𝐵𝑝


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Model Validation: open loop test


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Model Validation: the importance of closed loop tests


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Model Validation : the importance of closed loop tests


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Model Validation : the importance of closed loop tests

-5%

load

ste

p


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Closed loop test: the PSS emulator


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• Experimentation in gas power plant


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Closed loop test: detection of instability in islanded operation


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Closed loop test: after new settings


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• Experimentation in a diesel power plant.

• Some test sessions can be very arduous.

• There is no miracle. You need to be very well prepared.


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Open loop test: frequency signal


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Open loop test at speed no load

• A first test to validate the speed pick-up modeling


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Open loop test

• Description:

• P0 = 135 kW

• Delta F simulated = +0.001 p.u.

• Dead-band = ±0.2 Hz

•Expected result:

• Valve will close by 0.025 p.u. because of 4% droop value

• Power will decrease according to the valve opening


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Open loop test

•Actual result:

• Valve first closed by 0.015 V, but came back to its initial value;

• Power first dropped by 0.02 p.u. and finally went back to its initial value

•Possible explanation:

• A limitation on minimum power?


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Steady state characteristics: very important to know before tests


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Open loop test

• Description:

• P0 = 1289 kW

• Delta F simulated = +0.002 p.u.

• No dead-band

•Expected result:

• Valve will close by 0.05 p.u. because of 4% droop value

• Power will decrease according to the valve behavior


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Open loop test

•Actual result:

• Valve closed by 0.03 V;

• Power decreased by 0.03 p.u.


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Open loop test

•Actual result:• Valve closed by 0.03 V;

• Power decreased by 0.03 p.u.


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Closed loop test


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Closed loop test


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Closed loop test


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Closed loop test

• Simulated mechanical power


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Test conditions not good enough

• Mechanical power model hard to estimate because:

• The tested unit is relatively large compared to the whole power system;

• The power system frequency is continuously oscillating. This means that the tested unit speed is also oscillating;

• The electric power oscillates against all the other units in the power system. Hard to tell what comes from where;


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Closed loop: Fourier analysis


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Closed loop: Fourier analysis

• Zoom at lower frequencies


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Example of recommendations

• Following a hard test session:• All the missing information regarding the speed governor and the diesel prime

mover characteristics should be requested from the manufacturer. This information is necessary for building an accurate model of the speed governor and the prime mover;

• Other tests should be conducted at higher power values;

• Some frequency sweep tests in open loop should be conducted;

• Power system stabilizers should be implemented and carefully tuned for frequencies between 0.2 Hz and 6 Hz;

• New speed controller settings should be implemented in order to avoid the use of the speed control derivative gain. Close loop tests should be conducted with these new settings.


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Example of recommendations

• Following a good test session in a hydro power plant:

• Use the speed controller model of figure XX;

• Use the non linear model of the Francis turbine with the following parameters:• Tw = 3.2 s;

• Phi = 0.045;

• Gross head = 1.045 p.u.

• And the following polynomials:• 𝑄 = 0,0071 𝐺3 − 0,588 𝐺2 + 1,8467 𝐺 − 0,268

• 𝑃 = −1,0296 𝑄3 + 1,523 𝑄2 + 0,5685 𝑄 − 0,0658

• The current speed governor settings seem appropriate (or do not seem appropriate) for ensuring the unit to contribute adequately to the power system frequency stability.


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Frequency Behavior in a Multi-Machine System

• The synchronous interconnection transfers the stabilizing energy from the stable units to the unstable units

• But does not stabilize a power system where most of the units would be unstable in an islanded system

• Conclusion: each unit should be set to be stable in islanded operation mode. That’s the speed governor job

• Please, do not resort to load shedding to make up for the inefficiency of your frequency control systems


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Three Important Principles to Consider when Adjustinga Speed Governor

• Speed governor should be set to ensure the generating unit stability in an islanded power system, even if it is synchronized to a powerful grid;

• Control parameters should be set for quick and stable frequency recovery;

• Speed governor must avoid contributing to natural electro-mechanical power oscillations.

Software

OPAL-RT RT14 Conference: Experience in power plant with RT-LAB BERTA test bench