Unbalanced 3-phase power nearly killed the radio

So let’s start by stepping back a little. Our innovative partners, OMASI, have set up a number of different productive, social and community projects on their main site in the village of Terat in the Simanjiro District of Tanzania. There’s a shop, a community meeting hall, and a hostel (originally set up as somewhere for abused women in the Maasai community to stay with their children, but now the go-to place for academic researchers, NGO workers, visiting doctors or adventure tourists to stay in the area). There’s a dairy, which buys milk off Maasai women and turns it into value added products like cheese, yoghurt and ghee. But the dairy uses so much power that when it runs (when there’s lots of milk available) it runs off a separate power system. And there’s a community radio station, ORS FM, the only station broadcasting to the whole region in Maa – the Maasai language. For many Maasai who don’t understand Kiswahili or Maasai, it’s their only source of information.

Since we started work on this project in earnest, we had a little side interest in trying to make the electricity provision to these various projects on the site more sustainable than the large, old and expensive generators they were running off. One of the main issues we couldn’t understand was why the generators were so expensive to run. They seemed to be using twice the amount of diesel that they should be. They were old, they were oversized, but still – 8 litres and hour instead of 4 is a lot!

Over Christmas, we came up with some ideas for replacement systems, that should be cheaper to run. And we could still use the old generators as (expensive) backup, just in case. On our next visit, after New Year, we were sad to hear that the radio station had been forced to go off the air, as the diesel had become unaffordable. So as soon as we had an idle moment, we decided to take a look at how the existing gensets could be wired up as back-ups, to facilitate the new approach. The most critical load is the radio station – you don’t want that to ever go off the air. “Do you happen to know how it’s wired?” we asked. “Oh yes – we think it’s on the red phase.”

All of it! The whole station – transmitter, a/c, studios…

If you don’t know about three-phase power (and trust us, we learned a LOT more about it over the next few days) the super simple breakdown is this. If a 3-phase generator is putting out 36kw, that’s equivalent to 12kw per phase. Ideally, you want the loads across the phases to be balanced. On a national electricity grid, you get that by connecting different households to different phases, so over 1000s of households they balance out, even if they’re all using their kettles at different times. (Sorry, we did say this was simplified).

If the load (the equipment that’s connected) is very different across the three phases, it’s said to be “unbalanced”. That’s not too good for the equipment, but it also means you’re making more electricity than you’re using. Intrigued, we bought a jerry can of diesel and asked our partners to fire up the genset and the radio station. And then we got busy with our multimeter.

Here’s what we found (we were measuring the current in each phase circuit)

Yup, that’s right. Virtually everything was on a single phase. Presumably when it was first wired up, everything balanced out. But over the years, other loads had been disconnected, so now the system was massively unbalanced. The radio station was using a maximum of 10kw, but because it was all on one phase, the generator was having to run at up to 30kw, even though the other 20kw weren’t being used. No wonder it was guzzling fuel.

So the lessons we drew from that were 1) we shouldn’t be so quick to think that old equipment is just naturally performing suboptimally, and 2) if you have a 3-phase offgrid system, check it to make sure it’s running as balanced as possible!

Follow the next installment of this story here:

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