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Recap: Our Single Phase Transmission System

As a re-cap, our transmission system circuit diagram and MATLAB Simulink model are introduced below.

The circuit illustrated in the figure below represents an equivalent power system feeding a 300 km transmission line. The line feeds a static load at its receiving end and is also provided with voltage compensation by means of a shunt reactor. A circuit breaker allows us to switch the circuit in or out of service, i.e., to energise or de-energise the line.

Figure: Simplified Transmission System Sketch

Recap: Our Simulink Model

The Simulink model contains a generator (with equivalent circuit parameters), a transmission line PI section, a load, a shunt reactor and circuit breakers controlled by a differential protection system. Several measurement blocks are also included in the model, which allow us to view the results of our simulation.

Figure: Simulink model

Recap: V&V for Modelling

In model V&V, the end product is a predictive model based on fundamental physics of the problem being solved.

The expected outcome of the V&V process is an understanding of the degree in which the modelled behaviour is representative with real-world behaviour and experimental data (i.e.: the predictive accuracy of the model).

Verification and Validation Activity

In this exercise, students shall form into pairs (or groups) and undertake various validation and verification activities on each others models. Each student shall write up their findings in a template report format that shall be submitted to both the model designer and the class lecturer.

1. Save and make a copy of your previous model. Swap this copy with your fellow students in your group.
   • Note that all students are required to undertake the validation and verification on another model that is not their own.
   • If any student is not able to form a pair with another student for any reason, please contact the course lecturer at the earliest possible time to make alternative arrangements.
2. Using the template provided, write a short report detailing the findings of your verification and validation activities.
   • The report length should not be greater than 2500 words.
   • Note that the purpose of V&V is to provide positive feedback to the model designer to assist them in improving their model, therefore, all findings (e.g.: identification of errors or inconsistencies in the model) should be presented in a clear, concise and constructive manner.
   • The template document  - P5 Coursework - Report Template provides further guidance for students. All guidance should be read in full prior to undertaking the modelling task to avoid the need for re-work.

Summary of Tasks

The following summarises the various tasks that are to be undertaken to provide a degree of verification and validation on your fellow students model. These activities shall be described in more detail in the following pages.

Check of Model Topology

The verifier should make a visual comparison of the model topology to the specified electrical system circuit diagram. In this comparison, the verifier should seek to confirm:

• All elements of the electrical system have been included in the model
• The elements of the electrical system are configured and connected correctly

In the report, students should write up which systems & subsystems have been included or omitted in their comparison and reference all source material used, e.g., course notes containing system description.

Spot Check of Model Parameters

The verifier should select a number of parameters from the specified electrical system. For each parameter individually, the verifier should confirm that the model accurately captures this parameter as a model variable.

• The number of parameters included in the spot check correlates to the degree of model verification. To act as a proof of concept for this activity, the verifier need only select 10 variables.
• Parameters should be selected from several different elements of the specified electrical system.

In the report, students should tabulate selected parameters, observed model variables and comment upon any discrepancies. Students should remember to reference all source material, e.g., course notes containing system description.

Structured Step-by-Step Analysis

The verifier should undertake a structured step-by-step analysis of the differential protection subsystem. To do this, the verifier should follow the following procedure:

• Make a copy of the differential protection subsystem and isolate the copied subsystem from any parent system.
• Using constant blocks (or otherwise) feed the isolated subsystem with various expected input signals.
• Students should feed the system with at least two signals, one expected to result in circuit breakers switching to OPEN and one expected to result in circuit breakers remaining CLOSED.
• Using measurement blocks, trace this signal as it is processed by the various blocks of the isolated system and confirm at each step that the input signal is being processed as expected.

In the report, students should describe how the signal is processed and comment on any inconsistencies.

Review of Face Validity

A review of face validity is a high-level check that the modelled system appears to operate as expected. The validator should run the simulation and check that the results generated appear ‘on the face of it’ to conform to expectations.

• Note that this activity provides only a small level of confidence that the model is an accurate representation of any system which it asserts to simulate. This activity alone would not normally suffice to validate a model but is useful in that it may quickly highlight occasions when the model appears to contains errors.
• The validator should run the model in various test conditions and view the voltages and currents measured at both Nodes 1 and 2.

In the report, students should comment upon any apparent discrepancies between the simulated behaviour and the validator’s expectations.

Comparison to Alternative Model

The validator should compare the results provided by the model that they are validating with the results that their own model generates.

• Note that in practice this activity would normally be undertaken using a model that has itself undergone rigorous verification and validation to reduce the risk of both models containing errors in common.
• The validator should compare the voltages and currents measured at both Nodes 1 and 2, when the models are configured in the same manner.

In the report, students should comment upon any discrepancies between the two sets of results.

Comparison to Simplified Mathematical Approximation

The validator should compare the results provided by the model against some simplified mathematical approximations.

• Note that 100% conformity should not be expected as it is understood that any mathematical approximations will include a large degree of inherent assumptions and simplifications. However, observation of large discrepancies may indicate that the model appears to contain errors.
• The validator should seek to compare:
• the voltage drop along the transmission line (given that the line impedance is a known parameter)
• The current flowing into Node 1 when the system is operating normally (i.e., no fault condition)
• The current flowing into Node 2 when the system is operating normally (i.e., no fault condition)

In the report, students should tabulate observed results against and their own mathematically derived results for each of the above and comment on any notable discrepancies.