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Assignment (30% of Module)

ES097A – Operation and Control of Power Systems

February 2023

Part 0 Navigation in ETAP

ETAP is a software package commercially available for the power industry to conduct analyses to support power system planning, design and operation. It is donated to the University of Warwick for students to gain some experience of using such software. ETAP has been installed on all PCs in The School of Engineering computer rooms. It can also be accessed remotely as described in Moodle in an email from Mark Hewson of the Engineering IT Office.

ETAP includes on-line help and tutorials. This assignment is designed to help you access the basic functionality of ETAP.

Step 0 Open up the StarExample project and edit it

ETAP manages studies as projects. A project contains the base system configuration and component parameters. Case scenarios are then applied to the project to investigate the system response in such scenarios.

As the first of the assignment, open up the example project through the directory path: ‘…C:\ETAP 20xx\Example-Other\StarExample…’.

Then edit the project with the following changes:

- Change in ‘Project-Standards’ to IEC and 50 Hz.

- Change Transformer T1 voltage ratio to ’11 kV/0.4 kV’.

- Change the nominal voltage of Bus 1,3 to 11 kV and that of Bus 2 to 0.4 kV.

- Change the length of Cable1 to ‘500 m’ and choose underground cable: BS6622, 3-core, with cross-section area of 95 mm² per-phase.

- Change the induction motor a 400 V, 50 Hz, 4-pole machine with similar power rating. Choose NEC motor if prompted.

- Add a static load of 200 kW at unity power factor to Bus 2, ignore adding any switchgear.

- Change the voltage setting of the ‘slack’ bus from 12.47 kV to 11 kV.

This model approximately represents the radial feeder running from the University of Warwick primary substation (near the Estates) to Warwick Sport. The 200 kW static load represents the lighting and administration loads etc. and the 100 HP induction motor represents that in the air ventilation system.

Save your edited project. And your system should look like Figure 1.

Part 1 Power System Analyses

Step 1 Load flow study (10% mark)

Conduct a load flow calculation in ETAP, and tabulate the bus voltages against the corresponding nominal values, and the branch current against the corresponding ampacities or ratings.

Step 2 Fault level analysis (15% mark)

Calculate the fault levels at Buses 1, 2 and 3, and compare the results with ratings of the Fuse 1, CB3, CB4 and CB5. Analyse why CB5 would be needed. Please take into account the transients of the fault current (3-phase metallic), including the DC component.

Figure 1  The modified project system

Step 3 Direct-on-line starting of induction motor (20%)

Direct-on-line starting of a large induction motor from standstill always needs special attention as the will draw a significant amount of current from the supply. The starting current is predominantly reactive. Please investigate the effects of starting the 100 HP induction motor on the system voltages.

In industry, while starting individual large induction motors have to be specifically considered, it is also common that a large number of small induction motors are supplied from the same bus or transformer. Although these motors can be started from standstill sequentially, power system design and operation still needs to carefully manage the situation when the power supply is disturbed by a fault in the upstream network, and the voltage is initially lost or reduced but subsequently restores. Please conduct research and depict how this could happen in practice and describe the techniques that may be used to solve the problem.

Step 4 Protection coordination (25%)

Fuses and circuit breakers are all set as over current protection devices. Their response times are all inversely related to the current that the devices are sensing, after pick-up. Investigate, in ETAP, the protection characteristics of CB4, Fuse1 and CB3 are set for coordinated actions against a solid 3-phase short-circuit fault on Bus2. Explain how the coordination is achieved.

In ANSI standard, conduct a protection coordination check, with a metallic 3-phase fault applied to Bus2. Record the operation times of CB4, Fuse1 and CB3.

In IEC standard (61363), conduct a fault analysis with a metallic 3-phase fault applied to Bus2. Record the waveforms of fault current through CB4, Fuse1 and CB3. Check against their protection characteristics to determine the operation times.

If the fault location is moved to Bus1, what is fault clearance time by CB3? If this time needs to be halved, how should the protection characteristic of relay OCR2 be modified? How would this affect the coordination with other protection characteristics against other fault scenarios?

Step 5 Embedded generation (30%)

Suppose that Warwick Sport would like to install a 2 MW (electrical), CHP, 50 Hz, 400 V, synchronous generator connected at Bus2 or Bus1. The generator is driven by a Rolls-Royce gas turbine. Analyse how the connection should be made. And also analyse the impacts of this addition on the voltage, fault levels and protection coordination.

Part 2 Report

Submit a report of about 3000 words with no more than 10 figures or tables to document the way in which you have conducted the investigations, your critical evaluation on the results obtained and your insightful analyses regarding the meaning of the results.