Hwange Unit 7 Synchronization. How a power generator unit is synchronized

Edwin Chabuka Avatar

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.

Alternating Current

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.

Phase Sequence

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.

Phase angle

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.

Voltage Magnitude

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.

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  1. Joe Biden


    1. Verstappen

      Shallow minded people like you shouldn’t comment on these articles,they require intellect and educated brains

      1. Joe Biden

        You can shove your intellectual brain up your ass Vertsappen because there’s nothing you can possibly say to sway my opinion nor justify your pleasure for mind numbingly boring articles.

        1. God’s love

          Learning never ends. Thank you.

      2. nhems

        The processes is to long

  2. Kulu Savvy

    Man i did Physics at A Level i never knew what this was exactly.So ndikangopinda muKariba ndobatidza magenarator nezvinhu ndotopisa fridge yekumba kwaExy wangu ? . Nice🤝😂

    1. Kamikaze

      People who wrote our syllabus didn’t want us to know too much…. this stuff should be available in high school, while other countries are teaching their young generation to make microchips and machinery we still learning stupid things that will be covered by machines in a few decades.

      1. Douche

        You are quite correct there l studied a level physics last year most of the content in the syllabus is outdated and the practical experiments are useless in this modern era imagine being asked to measure period at this level something a primary student can do

        1. Ishe Anesu

          Pendulum 🤣🤣🤣 I can relate

  3. Me

    Aaa this unit 7 tanzwira nayo haiperi process yacho handiti. But anyway tadzidza zvakawanda

    1. Anonymous


  4. Elphas Masuka

    Thank you Mr E. Chabuka, that was enlightening.

  5. Doctor Love

    So we’re going to suffer until when in ZIMBABWE?

  6. Anonymous

    Peak voltage is not 220vac, that is the rms value.

  7. Tigu

    Ehe nyaya ye synchronization ndainzwa but the bottom line is uebert angel nevamwe vake varikuba mari.kamukadzi kekubatwa negoridhe kana statement hakana kupa karikuziwa mhosva dzako

  8. Imi Vanhu Musadaro

    So, when we are importing power how come we never have to synchronise the grid. Zambia, Mozambique, South Africa and Zimbabwe power grids cannot always be in perfect sync.

    1. Edwin Chabuka

      That is the function of the SAPP (Southern Africa Power Pool) to ensure all members have grids that are in sync

      1. Imi Vanhu Musadaro

        How is that done, given that synchronising seems to be a lengthy process? Kariba units are taken offline often and seem to resume operation without any syncing required.

  9. Francov

    To be honest, there are problems with unit 7 and we are not being told the truth. Zhing zhong chete poor quality . Imagine all the time and energy supply lost in all this. A unit can trip but it does not take 10 months to snychronise it with the grid, zhing zhong basi.

  10. Tino

    I’m afraid pindula and techzim are conflating two differnt things, a week ago pindula reported that Hwange Thermal Power Station’s Unit 7 first achieved a full capacity output of 335MW at 9:27 AM on Thursday 30th March 2023.
    The Zimbabwe Power Company (ZPC) managed to synchronise the first of two generators on Unit 7 into the national grid on Monday, 20 March after failing to do so several times.

  11. Eng Francov

    It was all not true, how can you commission a thermal unit and then reduce capacity?? Its a zhing zhong unit. We were robbed.
    In engineering we do not accept this, and we define it accordingly “you think we are not stupid”

  12. Avatar Game

    This industrial zone partly reflects the similarity between industrial zones. Interesting video!

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