Can some one please explaine to me if possible how a static balancer works? I've seen a couple of these things installed at the end of long LV distributors but never been able to find how they work as far as I can tell they are just 3 windings connected in star but I've got no clue how they balance voltage.
It is not 3 separate windings magnetically. It is one core with 3 legs and windings on each leg
(and all our normal 3 phase transformers are like this, so to a degree automatically balance, unlike the US where they put 3 single phase devices on a pole and call it a 'phase bank' )
EDIT
Sidetrack into American practice..
They do not even seem to have used 3 transformers from the same batch in this example, so here the 3 phases will never balance well at any load level.
So back to that 3 limbed core, when one winding is magnetised, the magnetic field returns via the other two limbs of the core, inducing a voltage in those windings if it is not already there that must sum, transformer-like to the same voltage. (much as if there were only 2 limbs so it was more like a squared- off toroid the magnetism would be the same all round, and we'd not be surprised to see the same volts/turn on both sides ).
This is a bit simplified, but is the basic concept.
EDIT
(Here is a very nice if quite slow colour animation of all the little magnetic domains in the cores swinging round as full cycle of 3 phase passes. Note how each leg energises the flux lines it creates loop round by the other 2 legs in a mixture that changes over time. )
So, I hope it is now also obvious why this does not work as well,and why 3 phase transformers are not made this way..
It is a type of transformer, so designed that if one phase has a higher voltage than the others, that power is "sucked" out of the higher voltage phase and "pushed back into" the lower voltage phases.
In years gone by, "rotary balancers" were used, a form of induction motor that achieved a similar purpose.
Rotary balancers were also used on 3 wire DC mains to draw power from the higher voltage side and generate to feed back into the lower voltage side.
Also used to derive a 3 wire system from a 2 wire DC supply.
Broadgage is the closest with the first part of his post. What you are describing is a six winding zigzag transformer, connected across the three LV phases and neutral. If the phase to neutral voltages are out of balance, it will draw current from the higher voltage phases, transferring the power to the lower voltage phase, to equalise all three phase to neutral voltages.
Using Mike’s first sketch, and assuming two windings per pole (or limb) of the transformer. If you call the windings R1, R2, Y1, Y2, B1 and B2, the connections between the phase connections and Neutral would be:
Red Phase R1 -Y2 Neutral
Yellow Phase Y1 -B2 Neutral
Blue Phase B1 -R2 Neutral.
I have used the minus sign to denote the second winding is connected anti-phase, such that it subtracts from the vector sum.
it is usual practice to place a fuse between the neutral of the balancer and the system neutral - if you lose a phase, perhaps through a blown fuse, it will present a near short on the remaining two phases, attempting to equalise the voltages, taking the remaining two fuses. I can’t do the maths from first principles anymore. When I catch up with the text book on my office desk, I will post some more information.
I suspect my explanation is “clear as mud”. I find it difficult to explain through a text interface!
The only thing worse to explain than an LV balancer, is a Quadrature Booster, used to control reactive power on the super grid, but I am not going to start that now!
Thanks all of you that makes it clear how they do there thing. There was one up a pole near a customers house that used to hum and buzz like crazy think the DNO changed it out in the end. So to sum up it sounds like it uses the lightest loaded phase to boost the more heavily loaded makes sense to me
Effectively yes. We have removed most of hours in favour of using a larger conductor. When removing fuses, you have to remember to take the neutral fuse from the balancer first, or you can cause more problems than you started with!
Broadgage is the closest with the first part of his post. What you are describing is a six winding zigzag transformer, connected across the three LV phases and neutral. If the phase to neutral voltages are out of balance, it will draw current from the higher voltage phases, transferring the power to the lower voltage phase, to equalise all three phase to neutral voltages.
Using Mike’s first sketch, and assuming two windings per pole (or limb) of the transformer. If you call the windings R1, R2, Y1, Y2, B1 and B2, the connections between the phase connections and Neutral would be:
Red Phase R1 -Y2 Neutral
Yellow Phase Y1 -B2 Neutral
Blue Phase B1 -R2 Neutral.
I have used the minus sign to denote the second winding is connected anti-phase, such that it subtracts from the vector sum.
it is usual practice to place a fuse between the neutral of the balancer and the system neutral - if you lose a phase, perhaps through a blown fuse, it will present a near short on the remaining two phases, attempting to equalise the voltages, taking the remaining two fuses. I can’t do the maths from first principles anymore. When I catch up with the text book on my office desk, I will post some more information.
I suspect my explanation is “clear as mud”. I find it difficult to explain through a text interface!
Regards,
Alan.
I know about using a zig-zag transformer to derive a neutral/earth reference when a transformer winding doesnt have a star point (eg. a delta winding) but I'd never thought about connecting it to an existing system neutral in order to allow zero sequence currents to flow and equalise the voltages.
The HV neutral isn't normally distributed, so this must be for use on the LV network?
Yes, for the LV network, often at the end of a long line. You are correct with thoughts of zero sequence currents too. On HV networks, they are frequently used as an earthing transformer where the supplying transformer has a delta secondary winding.
The zig-zag winding secondary makes it a better balancer, and is less reliant on the magnetic paths being in perfect balance , but a simple 3 limb core will get you a good way just to begin with, and is far easier to describe.
They do both draw current off the highest voltage phase and stuff it back out in the right phase and power split to prop up the other two phases in proportion to their relative depression. (and as an aside to Alan's comment, sometimes it really is better if the other 2 fuses blow at the same time when one phase drops, depends on the sort of load.)
In the Isle of Man diagram, it makes it clearer once you realise the angles of the windings show the core limb they are on, so
the a to a' winding is wound over the N to b' one, and
the b to b' winding is over the N to c' one and
the c to c' is over the N to a'
the 3 limbs see a magnetisation pattern moved by 60 degrees but still do the 3 phase thing in terms of the total flux.
Hi Mike, yes thanks, those are the diagrams I was trying to figure out how to post! The views from the electricity supply industry, is that the zigzag option is preferred, although the description / maths is harder.
