# Diary of a Trainee Electronics Engineer: February 2017

**Bewley lattice diagrams, laser cutting inductions and first electronics experiences (again!)**

At the beginning of the month I had a fair few assignments which needed to be handed in towards the end of February and I knuckled down with these, so that I wouldn’t have as much work to do over half term. I think the two highlights to my half term were my little sister coming into work with me, as well as having a day trip to Ripon, followed by Masham to visit the Black Sheep brewery.

As I mentioned, my younger sister came into work over half term so she could try her hand at the very basics of electronics and programming, using the Genuino Starter Kit which she was bought as a gift for Christmas. To read more about this please see the post First Electronics Experiences (again!).

### Learning to laser Cut (Again?)

In last months Diary of a trainee Electronics Engineer I mentioned that I ran an introduction to laser cutting for the members of the Hebden Bridge hackerspace, Bridge Rectifier, in January. Towards the back end of February there was a public laser cutting workshop held at the hackerspace, where people of all capabilities were invited to book in for a one hour slot which introduced them to using Inkscape and the laser cutter, before they were able to have a go at laser cutting for themselves.

This time instead of running the workshop I was there to lend a helping hand and support the members who I previously ran the induction for. Since the introduction I gave back in January, members of Bridge Rectifier have come on in leaps and bounds, experimenting with many different types of cut, speeds and powers in order to becoming laser cutting pros.

Overall I can say the public workshop was a great success! We had people from a wide range of skill sets and backgrounds come down and have a go at laser cutting. As we could only accommodate so many attendees per time slot, there are already names down for the next laser cutting workshop!

### Bewley lattice

Recently in the Further Electrical Power unit of my HND, we have been studying Bewley lattice diagrams, a section which I have found particularly interesting. This is a method of graphical representation for determining wave values in transient analysis.

When disturbances occur in power networks it is inevitable that high frequency transient signals will be subsequently generated. Many fault location algorithms have been developed for the monitoring of power quality, as this is essential in power generation, transmission and distribution.

Here a Bewley lattice diagram can be used to diagrammatically illustrate the position, direction and motion of each incident, reflection and transmitted wave at every moment in time. Using a diagram to illustrate this overcomes the complexity of keeping track of multiple successive reflections at various junctions.

*Image source: The Department of Electrical Engineering, University of Moratuwa *

Publications of Bewley lattice diagrams include those for the study of:

- Electromagnetic transients
- Fault location in distributed systems
- Calculation of transient fault currents
- Calculation of transient fault voltages

*Image source: The Department of Electrical Engineering, University of Moratuwa *

In the diagram above we see a plot of the transmission line voltages with respect to the time of each reflection. A plot of transmission line currents would look very similar to the plot of the voltages.

We were taught several steps in order to derive our own Bewley lattice plot with transmission line voltages and currents with respect to the time of each reflection, for our individual student parameters as stipulated in the assignment brief for this unit. These steps can be found below.

The load must be removed to begin with.

Step 1 – Calculate the transmitted voltage between Rg and Zo like so:

Step 2 – Calculate the coefficient of the reflection figure (Г) at the load ( ГL).

Step 3 – Calculate the bounce back wave.

Step 4 – Calculate the reflection coefficient at the generator.

Step 5 – Calculate the reflected wave back to the load via the transmission line.

Step 6 – Repeating the process at the load, calculate the reflected wave back to the generator.

Step 7 – Calculate the propagation delay of one reflection.

Step 8 – Calculate from the generator to the load using the reflection coefficient Гg.

Step 9 – Calculate from the load back to the generator using ГL.

Step 10 – Calculate the bounce back to the load from the generator using Гg.

Step 11 – Finally we consider the last bounce back from the load to the generator using ГL.

Step 12 – We can now calculate the currents.

From the above calculations we are now able to plot the Bewley lattice diagram and the transmission line voltages and currents, with respect to the time of each reflection(please refer to diagrams above.)

### New Projects!

During February I spent a bit of time working on something new and exciting. I began by looking at what it is compromised of, as well as its specifications, before moving onto recreating previous projects using it. There will be a blog post on this released soon, so be sure to keep an eye out !