After a long wait, Hwange Power Station’s unit 7 went live and was synchronized. And that is where we lost a lot of our brothers and sisters. What exactly is synchronization?
So the simple definition of synchronization is we need to ensure the properties of one system match the properties of the system that it is to be married with.
That is the importance of synchronization, especially with power-generating units. The power station is a very formidable force. And so if a unit is just connected to the power station without matching the parameters of this running power station, something will get fried and spoiler alert, it’s not the power station.
The power station itself is usually comprised of several power generating units which are all connected to a common point called a bus bar. This will ensure that when the power leaves the station and enters the grid, the grid sees it as a single source. This bit will come in handy soon. Now we just need a tiny introduction to electricity.
So the electricity we get from the grid is in the form of alternating current. This means that if we have a live and a neutral, the live constantly oscillates above and below the neutral. At its peak, the voltage value is 220V (RMS) on either side of the neutral inside our homes. In Zimbabwe, this oscillation happens 50 times a second giving us what is known as a frequency of 50Hz.
This is where those properties for synchronization come from. And there are 4 of them. Frequency, Phase sequence, phase angle, and Voltage magnitude. Fair warning it’s about to get super technical but I’ll do my best to keep it simple.
Frequency is the easiest. Remember those cycles we talked about? The unit that we are connecting to the bus bar should have a frequency that exactly matches the frequency on the bus bar. If the bus bar is at 50.023Hz, the unit must match this.
If you ever took a look at a power station and cables coming from a power station, you may have noticed that they are always 3. Each wire is referred to as a phase. Fun fact, the 3 colors you see on ZESA vehicles are the industry colors for the 3 Phase electrical system. Now a generator outputs 3 phases of electricity and all 3 of them have to be perfectly matched to the 3 phases on the bus bar. Red on red, Yellow on yellow, and blue on blue. Similar to wiring a 3-pin plug. This is the phase sequence.
The phase angle speaks to the position of the oscillation at any single point in time. Think of it this way. You have 2 wheels. One has a groove and the other has a bump. This groove and bump match very well such that if they are put together they fit in perfectly. If we want these 2 wheels to spin together smoothly it’s not enough to just spin them at the exact same speed (frequency). They have to be aligned in their rotation (phase angle) such that the groove and the bump are meeting perfectly. This will give us a smooth spin of both wheels similar to what we would get if there were no groove or bump. This means what we are about to feed onto the bus bar matches what’s already on the bus bar.
Then we have the voltage magnitude. The voltage we are feeding onto the bus bar must match the voltage already on the bus bar. So if the voltage of our new unit is higher than the voltage on the bus bar, you can overload the grid. And if the voltage of the new unit is lower than the voltage on the bus bar, it can damage this shiny new unit.
Why Unit 7 is not pumping out 300MW yet
Remember, when unit 7 at Hwange was synchronized, they said it will not initially be pumping out the full 300MW it’s rated for but instead would start at a much lower output and gradually be increased to the full 300MW around June. Well. The Hwange power station at the time was producing far less than 300MW. So to avoid frying the grid, the output of Unit 7 starts off idling to match the voltage on the bus bar. Then it’s gradually revved up in a controlled manner with the grid absorbing the load till it operates at its rated capacity.
This is a simple but nerdy look at how a new power generator unit is connected to the grid. So that is why you cannot just plug your home generator or personal solar system into the grid. There is some hardware you need to have between your power generating system and the grid so that the power you produce is correctly and safely fed into the grid for purposes of net metering.