Simulating salient pole synchronous generator runaway condition

Hello, I want to examine the runaway condition for a salient pole synchronous generator. For this, I want to remove the load while the synchronous generator is operating at full load and find the acceleration graph of the rotor and the maximum speed it will reach. How can I design this system? generator values: 850 kVA 400V 6 pole

Answer 1

[Umar]

Hi @Firat Nazar ,

To design a simulation for this scenario using tools such as MATLAB/Simulink and Simscape, you can follow these steps:

1. Modeling the Synchronous Generator: - Use the Synchronous Machine Salient Poleblock from Simscape Electrical. This block allows you to define parameters such as apparent power, voltage, and number of poles. - Set your generator's parameters: - Rated Apparent Power: 850 kVA - Rated Voltage: 400 V - Number of Poles: 6 - Configure other parameters such as inductances and resistances based on standard or fundamental parameterization.

2. Initial Conditions Setup: - Initialize your synchronous machine with load-flow analysis to establish operating conditions (real power, reactive power, terminal voltage). - Set appropriate values for rotor angle and field voltage to simulate a full-load condition.

3. Load Removal Simulation: - Implement a control mechanism (like an AVR and governor) in your model to maintain stability during load removal. - Create a scenario where you abruptly remove the load from the generator while it is operating under full load conditions. This can be done by setting up a switch or control logic that disconnects the load.

4. Measuring Rotor Dynamics: - Utilize the *Synchronous Machine Measurement* block to monitor key parameters like rotor speed, electrical torque, and per-unit measurements. - Specifically track rotor velocity (pu_velocity) as you simulate the sudden load removal.

5. Acceleration Graph Generation: - To obtain the acceleration graph of the rotor, you can derive acceleration from the change in rotor speed over time using numerical differentiation techniques. - Plot this data against time to visualize how quickly the rotor accelerates after load removal.

6. Simulation Execution: - Run the simulation for a sufficient duration to capture transient dynamics and steady-state behavior. - Ensure that logging is enabled for relevant variables to analyze results post-simulation.

Expected Results

After simulating this scenario, you should expect to see:

- An initial drop in rotor speed due to loss of electrical load. - A subsequent acceleration phase where the rotor speeds up as it is no longer opposed by mechanical loading. - The maximum speed achieved will depend on factors such as inertia of the rotor, damping effects (if any), and how quickly power is removed from the system.

Here are some additional insights to consider

Stability Considerations; The behavior of synchronous machines during transient conditions can be complex. Consider modeling damping effects if applicable.

Safety Mechanisms: In practical applications, runaway conditions can lead to mechanical failure. Implementing safety mechanisms in real-world systems is crucial.

Further Analysis: After obtaining initial results, you may want to conduct sensitivity analyses by varying parameters like inertia or field excitation levels to see their impact on runaway dynamics.

By following these steps in MATLAB/Simulink with Simscape, you should be able to effectively design a system that simulates and analyzes the runaway condition of your salient pole synchronous generator. This approach not only provides insights into its dynamic behavior but also prepares you for potential practical implications in real-world applications.

[Firat Nazar]

Thank you for the information. The purpose of doing this is to examine how much mechanical strain the generator will experience if no precautions are taken in the real world and if it experiences a sudden load change, and then I will perform a finite element analysis of the machine using the speed values ​​obtained here.

[Umar]

Hi @Firat Nazar,

I appreciate the clarity with which you have outlined your objectives regarding the examination of mechanical strain on the generator under real-world conditions, particularly during sudden load changes. Your approach to perform a finite element analysis based on the speed values obtained is commendable and will undoubtedly provide valuable insights into the machine's performance. If there are any specific parameters or additional data you require from my end to assist with this analysis, please do not hesitate to let me know.

[Firat Nazar]

Hello @Umar;

I tried to set up the model but I am not getting the results I expected and I have no idea why.

I first connected a load of 850 KW to the system, then I opened the switch and made the system equal to a load of 1 W at once. My excitation voltage is 70 Volts. I assigned a constant value of 850 KW as the generator input power. However, when the switch is opened, instead of accelerating the system, the rotor speed decreases on the contrary, I could not understand the reason for this. Would you like to help me? This is a 6 pole generator. I am sharing my Scope

[Umar]

Hi @ Firat Nazar,

I don’t have Matlab Simulink installed but can provide some suggestions if you need my help. Let me know.

[Firat Nazar]

@Umar hello again,

The simulation starts directly from the nominal speed of the synchronous generator. I cannot observe the acceleration status of the generator. Also, I eliminate the load suddenly and since I do not use any regulator, the rotor slows down while I wait for the rotor to accelerate. I could not understand this situation.What mistake could I have made in the simulation?

[Umar]

Hi @Firat Nazar,

After reviewing your comments, there are several reasons. In your Simulink simulation, the behavior of the synchronous generator can be influenced by several factors. When you eliminate the load suddenly, the generator experiences a rapid change in torque, which can lead to a transient response that may not be adequately captured if the simulation parameters are not set correctly.

One common mistake is not properly configuring the simulation time or step size, which can lead to inaccurate results during rapid changes. Ensure that your simulation has a sufficiently small time step to capture the dynamics of the system accurately.

Additionally, without a regulator, the generator's rotor may not respond as expected to changes in load, leading to a slowdown instead of acceleration. Consider implementing a speed controller or a governor to manage the rotor speed effectively during load changes.

Lastly, verify that the initial conditions of your simulation are set correctly, as starting from nominal speed without accounting for transient dynamics can lead to misleading results. Adjusting these parameters should help you observe the expected acceleration behavior of the generator.

Hope this helps.