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I'm linesman and Electrical Fitter in powerline distribution in Australia AMA ?
Posted by tobyrobb on 26 Apr, 2023 02:49 -
I've worked in the Australian Power distribution industry for the last 14 years in NSW as a linesman and other roles.
I thought I would gather a few thoughts here and post after a recent episode on the amp hour around the power grid.
A lot of people have no real exposure to the distribution system other than the outlet on the wall and a basic understanding of AC.
But it's actually not that hard or that different. In fact, a lot of the layout is fairly basic compared to your average electronic circuit.
However the distribution system has its own unique challenges such as fault detection and isolation, as well as high voltage conductors and reactive power.
The high voltages also mean that special principles apply to circuit breaker design and insulation.
In NSW, generators usually producing 11 or 22KV step up to 330 or 500KV and pass this to the transmission operator (transgrid) who marshall the feeds at switching yards before transforming it down to 132KV and sending it out on long span steel towers to our local companies, essential energy, endeavor energy and ausgrid.
Distribution companies receive the 132kv and generally pass that around their own network on steel towers, although more recently vertically constructed concrete poles are available for 132.
Transmission zone subs pretty much only deal with splitting up the 132 and do not supply any customers, they will generally kick the volts from 132 down to 66kv and send this out to various distribution zone subs.
The general layout for a zone sub is one or two incoming feeders at the highest voltage sit on what we call a primary bus bar. The primary bus bars job is pretty much mechanical with some mechanical switches available. Hanging off the bar will be a couple of transformers that have a 132KV primary and a 66 KV secondary. The output of those transformers will go onto the secondary bar which also contains mechanical switches.
Each connection of a feeder or a transformer to a bar will go via a breaker. There will also be a current sensor ( CT ) and a voltage transformer (VT) which generally transforms the voltage to a standard of 110 volts.
Relays monitor a proportion of the real current via the CT and a proportion of the real voltage via the VT. Parameters can be set in the relay which has control over the breaker.
When high voltage contacts are opened an arc is formed and this can continue to exist as it ionizes the air around it creating a nice path. Arcs are not actually a dead short and therefore will not induce any further tripping as over current.
Unfortunately, an arc is hotter than the surface of the sun. In fact, the hottest thing in the universe and if it's there for too long, it's going to melt everything including your metal, which by the way is often aluminium as it is almost as good a conductor as copper but much lighter and therefore much more suitable for an aerial conductor.
High voltage breakers rely on different techniques to extinguish the arc . High speed opening, air blasts, arc chutes which are layers of metal that become magnetized during an arc and will suck the arc into them, oil or gas like SF6 sulphur hexafluoride which is an insulating gas meaning the arc has trouble passing through it.
If you look closely, you will see levers that can open mechanical connections across the tubular bar conductors. These are usually not operated under load. But you can see plenty of YouTube videos of people doing it the wrong way. That's when you see the big arcs. Generally, breakers are used to de energise the bar in a zone sub and then the mechanical switches are opened, locked off and danger tagged.
Sometimes the bar can be split into one or more sections by a breaker to allow isolating for faults or to switch between say Transformer 1 and Transformer 2 . One may be in use and the other is awaiting to step in If the first one has a fault it will automatically step in or one may be in use and the other is currently undergoing maintenance.
After leaving the secondary bar at 66 KV, via transmission breakers it often leaves on poles and wires to the distribution zone subs. These are the buildings and yards you see scattered around your neighbourhood. There is usually an incoming 66 and an outgoing 66 as the network is set up either daisy chained or in a ring configuration. When set up as a ring this means if an incoming feeder needs to go down, the network can be back fed to provide supply from the other direction.
Distributions zone subs take the 66 and split it down via 1,2 or several Transformers and put this onto the 11KV bar (sometimes 22) . Hanging off this bar are all the distribution circuit breakers. This is where the real business begins as the 3 wire 3 phase conductors leave generally on poles and wires or possibly underground out into the neighbourhood.
The three conductors travel on wooden poles with ceramic or poly insulators keeping the conductor from arcing to the pole.
In general, dry wood is a pretty good insulator and helps insulate the system from the ground.
The three phases enter a pole mounted transformer or a ground level padmount transformer primary windings and are connected in Delta. There are always fuses or a breaker on the high voltage side leading into the transformer. (Eg expulsive drop out fuses) (>11kv requires boric acid) these can also be used for isolation to allow working on the transformer.
On the secondary side, we have our four phases derived from a star configuration in the windings. The centre of the star becomes the neutral which in Australia is tied to the earth. The nominal voltage between phases in Australia is 400 volts and from phase to neutral or ground is 230 volts. (Not 240 dave!!
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There are fuses on the secondary side but they are fairly slow acting HRC. There is usually a wiring harness on the Transformer that connects to the conductors in both directions and provides fusing and blade switching options.
The lowest set of 4 wires travels from pole to pole and at each premises a single layer XLPE aerial bundle cable (service mains, private service, private mains) is tapped onto the conductors and sent to the point of attachment on the house.
From there we have the consumer mains which run from the point of attachment into the house and down into the switchboard, usually a galvanised box in Australia on the side of the house.
Inside the switchboard is a service fuse which is a HRC for each phase. This then carries through to the meter and onto the customer's main switch and hot water switch which go out to the customers light and power CBs and thence into your GPOs and lights etc.
Some things to note.
We measure our transformers in KVA. A typical pole mounted transformer may be 100 - 300 KVA. A padmount transformer would be 500 KVA. To work out power we multiply kva by power factor.
We measure our ratios beyween capacitive, inductive and resistive loads using power factor.
We would love our power factor to be 1.0 - inductive loads reduce that and adding capacitors can raise the power factor back up. In Australia, if you are a private householder you do not need to consider power factor and you will not be charged for poor power factor EG. Lots of inductive loads. However, as a large commercial customer, you are expected to have power factor correction, capacitors etc. It's not as hard as you think. In fact, most appliances have power factor correction capacitors installed.
So what is power factor? Well, let's say you have a poor power factor. This means that you will be drawing your current and voltage out of phase because a perfect power factor of one means that the current and voltage are in phase and whatever voltage and current you are taking from us is all we need to supply. However, let's imagine a load that's highly inductive. We know that power is volts times amps so If we think about a voltage sine wave then maximum power will be if both the voltage and current sine waves rise together . Anytime that they are out of sync, the actual true power delivered will be lower.
So the grid is supplying a lot of extra current that isn't really making it into true power. But that extra current still causes losses due to the I squared r rule etc
Why does inductive current lag behind voltage ?
The best way to imagine inductive power is to imagine that as soon as you apply power, the voltage will be instantly measurable on the terminals of the coil. However, due to lenzs law, the current will be restricted because as the magnetic field builds up, it will induce an opposite current to restrict current flow. Therefore the voltage will lead the current..
Why does voltage lag behind current in a capacitor ? The best way to remember this is that as you apply voltage, the current is drawn straight away to begin to fill the capacitor but The voltage only starts to rise as the capacitor fills. Therefore, the current leads the voltage.
A lot of people ask or assume that the distribution system is antiquated. The reality is that simple devices made of steel and filled with oil are robust against lightning strikes, heavy loading, faults and are forgiving and easily maintained, cleaned and repaired.
Generators have governors which adjust the speed of the generator automatically to feed in more fuel as the load makes the 50hz slow down.
Solar has ohms law, eg you need to float your solar voltage higher than the network if you wish to drive current out on to the grid.
We don't have our data and control systems like scada on internet, and the control systems mostly don't make relay decisions eg overcurrent (which is hardwired directly in to the relay) , our control systems mostly report and maybe trigger a reclose or allow the control room to switch brakers and portions of the network.
We do have load shedding, this is so that if a supply feeder is overloading we can remove feeders to reduce the load and keep the network from crashing. Eg a black start.
Most gennys are between 600 and 1000 Megwatts.
There are some strange gennys like wind turbines and gas powered converted caterpillar engines in shipping containers that can be switched in and out they are about 1mw each
There are also the odd Reactor and capacitor banks spread around, but they are usually to deal with odd feeders that mya supply am aluminium works for example they stirke HV arcs to melt crucibles! gives the network many spikes that have to be smoothed.
There are so many more features, if you have questions , ask away!!
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do you know anything about the superalloys used in switch gear etc contacts, for instance tungsten silver alloys?
This is a part of the magic of how those beastly contacts work. I think its a bit more then just arc management, its also materials choice. I imagine a piece of brass in the tip of the switch would be adios muchachos for the switch yard -
Wild question: ever envisage a future where local polemount and padmount transformers (11kV->240V) come with automatic on-load tap-changing? That'd be an interesting way to address voltage rise caused by home solar; and I don't think it'd need as much copper as some other solutions; but I don't know how reliable these mechanisms are.
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I think for breaker contacts inconel might be the material?
We try to do a lot of off-load switching and use arc suppression strategies for some of the high current interruptions. 132 is almost always SF6 gas filled. But street hv blades eg USL's often lighty coated copper.
Each substation breaker has the fault current recoded if possible and maintenance is carried out and documented, this includes contact cleaning or replacement!
I think the Arc suppresion through various means help a lot with arcing and contact pitting. And the relays try to open on the zero crossing point, eg no current.. -
Yep absolutely, we have autotapping on the HV through Zone transformers and the pole mounted three phase regulators, ie a good solution on long distance feeders where the voltage drops/fluctuates. But yeh we have may have to tap distribution transformers up in the Winter and down in the summer. Atm, requires an outage to do it. The autotappers are complicated and they have multiple coil windings in an Auto Transformer arrangement. Lots of contacts x3 and require to carry full load current.
and if its field mounted, i guess its more costly again.. High power semiconductors are just not there yet..
The mechanism is reliable, but with hard to change components, it's best to have changeover spares in situ to get the power back up and running asap, something possible in some subs, eg two transformers running in parallel but one can handle both loads of auto switched... but in the field of it could be problematic to fix, replace..
having said that, I've replaced many Transformers on the pole just takes 4-8hrs.. -
The nominal voltage between phases in Australia is 400 volts and from phase to neutral or ground is 230 volts. (Not 240 dave!!
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it is 240V in Western Australia :-) But since you are from NSW, I might as well have commented its 240W in Wales.
What a country, if you cannot even standardize on a mains voltage p)
(I know there is no national grid in Australia, the east and west coast aren't coupled. Anywhere between Kalgoorlie and Adalaide the only energy source is Kangaroo-dung.) -
Well Australia is trying to align our "nominal" voltage, although its still usually the same range 217-253 around the country ive noticed, its the plus or minus range they vary. eg 253v is plus 10% against 230v but 240v in WA or QLD its just plus 5% ?
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Thanks for the post, awesome!
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Well Australia is trying to align our "nominal" voltage, although its still usually the same range 217-253 around the country ive noticed, its the plus or minus range they vary. eg 253v is plus 10% against 230v but 240v in WA or QLD its just plus 5% ?
I had to laugh when I saw the change that came through in 2000.
Before: 240V +6% -10%
After: 230V +10% -6%
...... do the math.
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110V +131% --+96%
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Well Australia is trying to align our "nominal" voltage, although its still usually the same range 217-253 around the country ive noticed, its the plus or minus range they vary. eg 253v is plus 10% against 230v but 240v in WA or QLD its just plus 5% ?
I had to laugh when I saw the change that came through in 2000.
Before: 240V +6% -10%
After: 230V +10% -6%
...... do the math.
I know you lads like graphs so I asked our new friend (GTP, who likes to chat) to make a little chart:
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Hi Toby,
Is there much variation with how the networks operate and the equipment used between states, or are they generally quite similar in that regard?
Also, as someone that doesn't deal with anything above about 30 volts, how do you get in the mindset build up the trust in process/safety systems in order to have the confidence that the HV systems you're working on are actually safe? Is it just through training and procedure or is there more to it?
Also, Sulfur Hexafluoride, that's the "anti-helium" gas, isn't it? The one that makes your voice really deep when you inhale it. But if I recall correctly you have to take special precautions to exhale it all otherwise it takes up the space of oxygen in your lungs because it's heavier than air
I remember reading about how it was a very good insulator but didn't know what its use cases were. Now I do 
Thanks
Great Amp Hour episode.
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I really enjoyed nerding out over powerline distribution systems with Dave!
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If you're interested in this subject, there are lots of good vids on the subject from this Canadian lineman
https://www.youtube.com/@Bobsdecline
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A few comments on statements made:
Work is ongoing to phase out SF6 switch gear globally as it's a fantastic greenhouse gas. Currently the only commercial replacement is g3 gas from GE and Hitachi (https://www.gegridsolutions.com/hvmv_equipment/catalog/g3/).
Also Dave's comment on raising the voltage to turn off solar inverters is real and part of standard operating practices in South Australia during interconnecter and large transmission outages. It ensures minimum load requirements for large synchronous generators is maintained. Should load fall bellow the minimum level generators would automatically switch off causing mass blackouts. Remote control of inverters is being developed globally however only SA Power Networks, Western Power, Californian utilities, and PPL (a pennsylvanian utility, and only through a trial) currently do so. This is only a requirement on new installs and all new inverters come with capability for either direct or indirect control. The remote control is standardised internationally through IEEE1547 and has legislated adoption in the us through UL1741. Sa Power currently has trail in place using this standard to allow for flexible export export limitations allowing for larger consumer solar export connections. It was expected and trial results have confirmed that the higher limit only needs to be reduced for a few days in spring and autumn to prevent localised over voltage and thermal damage. -
I found they use tungsten/silver alloys for rotary EDM 'grinding' machines
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A great channel and very similar work to an Aussie linesman, a smart bloke and have been watching his channel for a while as well!
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If you're interested in this subject, there are lots of good vids on the subject from this Canadian lineman
https://www.youtube.com/@Bobsdecline
A great channel and very similar work to an Aussie linesman, a smart bloke and have been watching his channel for a while as well! -
Like smart metering and remote reads over the mobile network, it will take time to implement smart inverters, not just because of the wait required for new inverters to be installed, but the control infrastructure as well IMHO. We have also seen a lot of local load balancing being taken care of through batteries. Batteries seem to have the benefit of providing resilience as well as sucking up the extra volts without having to throttle the inverters..
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I wonder if the allocated supply to the average house is getting more and more.
Once upon a time a house would have a handful of 60W incandescent light bulbs, a single TV and so on. While inefficient by today's standards, they would not draw a lot of electricity. Compared to today with 100" TV's and more lights then you can poke a stick at and every gadget under the sun. Air con's everywhere and so on. -
Air-conditioning has been a source of big load increases.
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I mentioned some of the great test gear used in the power industry on the podcast, here is an example..
https://www.doble.com/product/f6150e/
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Hi Optoisolated,
When travelling around the states i can't help but look at the electrical infrastructure wherever i go
Almost all of the networks i have seen follow the same basic design of three phases of HV and three phases of LV with a neutral.
What tends to differ the most is the layout and construction methods. Although most networks also have a range of designs in their book that can work for any given situation.
For example in NSW most of the newer constructions have the HV as the top set of conductors with a single or double crossarm holding the two outer conductors and the center phase on a pin at the very top of the pole, this is called a delta construction (eg a triangle)
It can be in bare aluminium or covered conductor such as CCT.
However there are many "flat constructions" still where the centre conductor is also on the crossarm, swapping sides each alternate pole.
As for the LV circuits, they are usually similar with four conductors per xarm, some regions having the neutral on the roadside (vehicle safety?), some on the footpath side (pedestrian/property safety?) and some in the middle closest to the pole (easy access for lineworkers?)
The poles can be timber, concrete, steel or composite.
Often each state will pick and choose the pole to suit the conditions it is in or availablity and cost. Most of the switchgear, terminations and conductors are from the same big manufacturers and so are quite recognizable between states, however they often may choose one style of gear over another, eg, ceramic string insulators vs poly insulators Although most networks will have a mix of both..
Sometimes a network will have piece of unique hardware such as a center conductor riser/extension bolted to the top of the pole to increase its height etc and keep a pole in service longer, usually these are things that have been added over the years to allow a pole or something to continue to be useful or fit into a new design/augment.
As for electrical safety, its the most important thing of course and there are very rigorous procedures to be followed, but easy to to do and simple to follow. Try looking up "Electrical Safety Rules" for Endeavour Energy or Essential Energy, all the field staff will need to pass an annual test/quiz (100% required!) to be able to continue to work on the network. Any updates or incidents are always communicated to all workers.
* ISOLATE - the apparatus
* SECURE - the isolation eg locks and danger tags
* PROVE DE_ENERGISED -check the isolation through testing means, (and test the tester against a live supply!) NOTE: All the people out there using proximity detectors, they are not approved and are a bad idea!
* EARTH and SHORT CIRCUIT - all conductors. This is what a lineman will look for on a job site, big bright and hanging off the mains, these will tell you that the line must be off. Shorting ensures conductors are de-energised, and stay that way not allowing volts to rise
and ensure protection will trip ASAP if accidentally energised.
* ISSUE an ACCESS AUTHORITY - A paper/digital form ensuring that all members of the work party sign on to and the isolations are listed and you can see what is isolated. Additionally the AA cannot be surrended and re-energised until all members of the work party have
signed off.
As for working around power at home or in the workshop etc , "test before you touch" is pretty much the best method, and ALWAYS test your meter immediately after (dont change multimeter settings etc.) on a known live supply. Tag your breakers out to be the safest.
And yes SF6 is the "deep voice" gas , Its a super dense gas that can suppress arcs very well. Must be captured and contained as its a potent greenhouse gas. Not recommended to breathe is as there can be toxic products in gas exposed to arcs etc. and yep it will sit in your lungs and stay there?
Thanks for the feedback on the episode ! really enjoyed recording it with Dave.
Hi Toby,
Is there much variation with how the networks operate and the equipment used between states, or are they generally quite similar in that regard?
Also, as someone that doesn't deal with anything above about 30 volts, how do you get in the mindset build up the trust in process/safety systems in order to have the confidence that the HV systems you're working on are actually safe? Is it just through training and procedure or is there more to it?
Also, Sulfur Hexafluoride, that's the "anti-helium" gas, isn't it? The one that makes your voice really deep when you inhale it. But if I recall correctly you have to take special precautions to exhale it all otherwise it takes up the space of oxygen in your lungs because it's heavier than air I remember reading about how it was a very good insulator but didn't know what its use cases were. Now I do
Thanks Great Amp Hour episode. -
I think one of the most fascinating pieces of equipment used in electric power distribution that you never find anywhere else is the zig zag transformer, aka grounding transformer. Somewhat analogous to when you feed three *identical* 120 degree separated sinewaves into three resistors terminated to a common point, the measured voltage at that point will be zero, if you feed the same three sine waves into a zig zag transformer the nett effect will be zero. But if those sine waves start to differ from each other as regards voltage, phase separation degrees, distortion, they will fight each other in order to maintain exact balance. Much like a rigid crankshaft maintains precise relative movement in a 3 cylinder piston engine.