How to Engage Learners in a Virtual Class on Technical Topics
COVID-19 has made us rethink many things in our lives. One thing among those is education, whether we are providing it or receiving. There are some fields of study that may have easily transitioned to online, but this has proven quite challenging in technical education like electrotechnology. It’s hard enough to teach electricity in a face-to-face environment, and now we are trying to teach it in a virtual class. For example, in three-phase circuits, there are two ways of connecting loads to the supply, and both have their places, but how to we show their effects to the learners?
Here is how I taught Star vs Delta connections and their effects to my learners in a virtual class. Through this post, I would like to show that it’s possible to engage learners in virtual classes in trades and technical vocational training.
Do what you can, with what you have, where you are.
Repeat The Basics
Before I start my classes, I always build a background with fundamentals. I have found that it’s the best way to create engagement. Assuming that they know everything you have discussed in the last session is probably the biggest pitfall for losing the learners. Plus, repeating the basics never hurt anyone.
Since the class was virtual, the learners could see my camera feed, which was covering me and the whiteboard. I found the whiteboard to be one of the most important tools for my virtual classes. It’s probably a personal thing, but I find it easier to explain with it, and I’ve found that my learners respond to it quite well. I used my whiteboard to draw circuits and write the main points.
Here was my background for this topic.
Basic for my class - Single-phase and three-phase
The two most popular supplies available are single-phase and three-phase. Single-phase is straight forward, one side of the load connects to Active, the other side connects to Neutral and Earth is connected for safety but may not always be necessary. So in a normal situation, the current travels between Active and Neutral.
In three-phase systems, there are three active wires, a neutral, if the load is unbalanced and earth for safety. The active wires are also called lines that connect to the entry points of a three-phase load. We can categorise three-phase loads in two types – Balanced and Unbalanced. In this topic, I had covered Balanced loads only.
Balanced loads
Balanced loads are usually the electrical equipment that are designed specifically to work in a three-phase system, for example, a three-phase motor or a three-phase water heater. Although mostly these loads are contained in a unit, it’s not necessary. We can have three single-phase loads that have the same ratings and use them in a three-phase system.
The criteria for a balanced load are that
- Each line draws the same amount of current and
- The phase angle for each line is consistent, or the power factor for each phase is the same
You can connect balanced loads in two ways – Star or Delta. Each type of connection has specific properties and advantages.
The setup of balanced loads
A three-phase load has three separate phases inside, for example, a three-phase motor will have three windings that work together to provide the torque. A three-phase water heater, at its core, will have three heating elements that will work together to provide heating. Essentially, there are three loads inside an enclosure that work together to provide the required output.
The rule of electricity is that there needs to be an entry and an exit for the current, which means that each load must have two terminals. Since a balanced three-phase load has three separate loads inside and each must have two terminals, all three-phase loads must have six terminals internally. Manufacturers may not give you access to all six terminals for simplifying connections, but they exist.
These phases have different identifications in different countries. In Australia, the most popular ways are A, B, C or U, V, W. For the sake of consistency, I use U, V, W. This allows the terminals to have identifying labels, for example, the terminals of phase U are U1 and U2, the terminals of phase V are V1 and V2, and the terminals of phase W are W1 and W2.
The Main Subject Matter
One I had built my background, it was time to get into the main crux of the class. To explain the difference between Star and Delta, first I had to explain what each meant. So, again, using my whiteboard, I explained these. I also shared my computer screen to show them some images and calculations. I like to show the learners how to enter the numbers in the calculator; for this, I use Google’s scientific calculator.
Here goes the story
Star connection
One of the ways of connecting the three phases in a three-phase system is Star connection, also known as WYE connection in some countries. In Star connection, one terminal of each phase is joined together to form a star point, and the other terminal connects to the lines coming from the supply. So let’s say U2, V2 and W2 are joined together, this is now a star point, which means the three lines will connect to U1, V1 and W1.
The key properties of Star connection
All three-phase loads have six voltages – three line voltages and three-phase voltages. The voltage between the lines is called the line voltage and the voltage across the phase terminals is the phase voltage. Here’s what a star connected load looks like
The formula that shows the relationship between line and phase voltages in Star connected circuits is
So if the line voltage is 400V, the phase voltage will be approximately 230V. In our experiment, the line voltages are 42V, and the phase voltages are approximately 24V.
In the same way, the three-phase systems also have six currents – three line currents and three-phase currents. The current travelling in the lines, reaching the connection points on the loads are called line current.
The formula that shows the relationship between line and phase voltages in Star connected circuits is
Delta connection
Another way of connecting three-phase loads is Delta connection. In Delta, the second terminal of one phase connects to the first terminal of the next phase, and so on. This creates a triangle, and that’s why is its called a delta connection. So U2 connects to V1, V2 connects to W1 and W2 connects to U1.
The key properties delta connections
Delta connected systems also have six voltages – three line voltages and 3 phase voltages as you can see in the image below
And the formula the relates line and phase voltages is
So if the line voltage is 42V, the phase voltage will also be 42V
The six currents in the Delta connected systems are three line currents and three phase currents as you can see in the image below
And the formula the relates line and phase current is
So if the line current is 2.15A, the phase current will be approximately 1.24A.
Here Comes The Climax
So far, I covered the basics of three-phase and properties of Star and Delta connections. Now was the time to show the difference. With electricity, it’s hard to show the difference on a whiteboard or even explain it; you have to see it to believe it. So I recorded a short video where I compared the connection of three lamps in Star and then in Delta. It was so much easier to explain it.
Here’s how it went
Comparison between the effects of Star and Delta
The biggest difference between the effects of Star and Delta connected loads is the phase voltage, which then causes further differences. For example, in our experiment, the phase voltage across the lamp was 24V when it was connected in Star, even though the line voltage was 42V. When we change the same circuit to Delta, the phase voltage changes to 42V.
According to Ohm’s law, as voltage increases, the current increases if the load is kept unchanged. In our case, when we went from Star to Delta, the phase voltage changed from 24V to 42V. Because of this the current through the load increased. Increase in Voltage and Current causes the power to increase because power depends on them both.
The net result is that lamp lights brighter in Delta as compared to Star. If this were a three-phase motor, it would have produced more torque in Delta.
Well if Delta is so much better than why use Star at all? There are certain benefits of using star connection, which we will discuss in another post.
Conclusion
Virtual training doesn’t have to be difficult, but it certainly takes more work, perhaps because we are used to training a certain way. COVID-19 has made us re-evaluate the status quo. Thinking positively, it has challenged us to do things differently.
Here are the things that have made it easier for me to engage the learners in the new way of training
- Webcam and online meeting platform
- Whiteboard and accessories
- Demonstrations videos and equipment for them
I hope you enjoyed the story of Star Vs Delta and my way of explaining the differences. Please leave me a comment on how you have taught, or plan teach in your area in a virtual class.
Thanks for dropping by
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About the Author
Husnen Rupani
I help electrical training organisations increase learner engagement by designing innovative training equipment. I have a saying "Electricity - you cannot see, you cannot hear it, but by the time you feel it, it may be too late." My main aim is to turn this black magic that we call electricity into something that people can understand.
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2 thoughts on “How to Engage Learners in a Virtual Class on Technical Topics”
would have loved to see a circuit diagram of your lamp connection so you could draw attention to your main points as you did the practical exercise
Thanks for the comment Ian. You’re right, a circuit diagram in the video might have made a better impact. During the class I had drawn so many circuits, I thought I was overdoing it so I made the video with just the connections. I’m making another video for series-parallel DC circuits, Ill take your feedback onboard and message you on LinkedIn once it’s online. Thanks again.