How to decommission and demolish a substation or small power station safely in Australia

Substations and small power stations are a different kind of demolition job. The structures are usually modest. The hazards are not. The thing that will kill you is invisible, the waste streams are some of the most tightly controlled in the country, and the asset next door is very often still live.

This covers zone and distribution substations, switchyards, and small generating plant, the diesel and gas generator stations, small thermal units and standby plants that sit behind hospitals, mines, data centres and remote towns. It is written for asset owners, network engineers and the consultants advising them.

Rule one: you do not prove it dead. The network does.

A demolition contractor never decides that a substation is de-energised. The network operator or the asset owner's authorised person isolates it, earths it, proves it dead, issues an access permit and hands the site over under their own switching and access procedures. Until that permit is in your hand, every conductor on the site is live and you plan on that basis.

Two things people forget. Adjacent assets often stay live, so the boundary between the isolated plant and the operating plant has to be marked physically and briefed daily. And nearby transmission lines can induce voltage in conductors that are isolated and earthed at one end only. Earthing arrangements are set by the network, not improvised by the crew.

What is on a substation site

• Power transformers. Large, heavy, and full of insulating oil. Older units may contain polychlorinated biphenyls in that oil or in the gaskets and paper.
• Switchgear. Air insulated outdoors, or gas insulated using sulphur hexafluoride, which is one of the most potent greenhouse gases in use anywhere.
• Circuit breakers, capacitors, reactors and instrument transformers. Capacitors in older installations are a second common home for PCBs.
• Cables. Paper insulated lead sheathed cable in older sites, with the lead a waste stream in its own right, and cable joints that may contain compounds you do not want to breathe.
• The earth grid. A buried copper mesh under the whole yard, worth a great deal to a scrap thief and critical to the safety of anything still live nearby.
• Batteries and chargers. Lead acid or nickel cadmium banks for protection and control.
• Control building and switchroom. Asbestos in arc chutes, panel linings, cable boxes, fuse carriers, roof and wall sheeting on anything of age.
• Bunds and oil containment. The ground under and around every transformer bund has usually seen oil at some point.
• Steel and concrete. Gantries, structures, foundations and cable trenches.

What a small power station adds

• Fuel. Diesel or gas supply, bulk tanks, day tanks, pipework, and on older sites an underground tank nobody has a drawing of.
• Engines, turbines and alternators. Heavy, oily, and often worth relocating rather than scrapping.
• Exhaust systems and stacks. Asbestos lagging on older exhausts, and a stack that may be licensed demolition work on height alone.
• Boilers and refractory on small thermal plant, with the same asbestos and refractory issues as any furnace.
• Cooling towers and water treatment. Legionella risk in anything that has held water, asbestos in older tower fill and cement sheeting, and treatment chemicals in the store.
• Grid connection. A generator that is connected to the network cannot simply be switched off and cut out. Disconnection is arranged with the network operator and, for larger units, with the market operator.

Step one: investigate before anything is isolated

Asset register and drawings. Every transformer, breaker, capacitor and cable, with age and manufacturer. Age tells you where the PCBs and the asbestos are likely to be.

Hazardous material survey. Asbestos, lead, SMF insulation and refractory. On a substation this is inside the switchgear and the cable boxes as much as in the building fabric, so the survey has to go where the electrician goes, under an access permit.

Oil sampling. Every oil filled item is sampled and tested for PCBs before a drop is drained. The result decides whether the oil and the carcass are ordinary trackable waste or scheduled waste with its own destruction pathway, and it changes the price of the job.

SF6 inventory. Which switchgear is gas insulated, how much gas is in it, and who is licensed to recover it.

Contamination assessment. Soil under and around every bund, the oil store, the fuel tanks and the generator hall. Hydrocarbons are near certain. PCBs in the ground are possible on older sites and change everything.

Underground services and tanks. Cable trenches, the earth grid, and any fuel tank the drawings forgot.

Step two: isolation, permits and the handover

The network isolates, earths and proves dead, then issues the permit. Fuel and gas are isolated at the supply and locked. Batteries are disconnected and removed early, because a battery bank is a live source that survives every other isolation on the site. Fire systems and their gas suppression bottles are dealt with before they can discharge on a crew.

Then the boundary. Where any part of the site or any neighbouring asset remains live, the demarcation is physical, marked, and walked with the crew at the start of every shift.

Step three: decontaminate and remove the regulated items first

Transformer oil. Drained by people set up to do it, into sealed containers, with the PCB result governing where it goes. Oil is trackable waste and travels with the paperwork. Transformer carcasses are cleaned before they are cut, and a carcass with PCB history follows the scheduled waste route regardless of how clean it looks.

SF6. Recovered by a licensed technician into approved cylinders. It is never vented. Not a little, not to speed things up, not because the breaker is "nearly empty". The environmental consequence is severe and so is the regulatory one.

Capacitors and instrument transformers. Treated as PCB suspect until tested, and removed intact.

Batteries. Removed whole to a licensed recycler. Lead acid and nickel cadmium each have their own route.

Asbestos. Licensed removal, regulator notified before it starts, licensed supervisor on site for friable material, clearance before the area is released. Perfect Contracting holds a Class A friable asbestos licence and an EPA waste transport licence, so the removal, the transport and the paperwork stay with one contractor.

Fuel systems. Drained, purged, gas freed and certified before any cutting. Fuel tanks are treated exactly like any other tank that has held hydrocarbons, which means nobody cuts one until it is proven safe for hot work.

Cooling towers. Drained and treated for legionella before they are opened up, then surveyed for asbestos fill before they are broken.

Step four: the demolition

• Switchgear and plant out first, largely intact, because most of it is either regulated waste or worth money whole.
• Cables. Cut only after the permit, only with the earth grid arrangements confirmed, and with lead sheathed cable separated for recovery.
• Structures, gantries and buildings. Conventional controlled demolition. Stacks and anything above fifteen metres are licensed demolition work in New South Wales.
• Engines and alternators. Lifted out to a plan. Many are resold or relocated, which is a decision to make before the crane is booked.
• The earth grid. Removed last, and only when the network confirms nothing nearby depends on it. Where an adjacent site is still live, part of the grid may have to stay.
• Steel and copper. Separated and recovered. Copper is the reason these sites need security from the day the permit is issued.

Step five: the ground

Bunds and foundations come out. Hydrocarbon affected soil is excavated, classified and removed. If PCBs are found in the ground, the site becomes a contaminated land matter with its own approvals and a much longer programme. Cable trenches are cleared, underground tanks are removed, and the site is validated by sampling before anyone signs it off for its next use.

What not to do

• Do not let anyone but the network operator decide it is dead. A demolition crew's meter is not a proving process.
• Do not drain a transformer, capacitor or breaker without a PCB result. One untested drum in a general oil load reclassifies the lot.
• Do not vent SF6. Ever.
• Do not sell a transformer for scrap with the oil still in it. The liability for what is inside stays with the site owner.
• Do not cut cable or lift earth grid near anything live. Induced voltage and step and touch potentials do not care that your part of the site is isolated.
• Do not cut a fuel tank that has not been gas freed and certified.
• Do not skip the soil under the bunds. That is where the cost is hiding.
• Do not treat a small generator station as a shed with an engine in it. It has fuel, oil, batteries, asbestos and a grid connection, and each one is a job.

Approvals and notifications

Network operator isolation and access permits before anything. Local consent for the demolition. Regulator notification for licensed asbestos removal and for licensed demolition work. Waste tracking for oil, PCB material, batteries and asbestos. Contaminated land approvals where the ground is affected. Disconnection arrangements with the network and, for connected generation, the market operator. Start these with the investigation, because the permits are what set the programme.

Who should be doing this

A contractor who is comfortable working under a network's access and permit system rather than around it, who holds the asbestos and waste transport licences in their own name, and who has taken apart oil filled and gas insulated plant before. The demolition is the easy part. The permits, the oil, the gas and the ground are the job.

Perfect Contracting works on plant decommissioning and industrial demolition across New South Wales and Queensland, including energy and renewable assets, and travels for the right project. If you have a substation or a generating site coming to the end of its life, the earliest conversation is the cheapest one. Call 02 8015 6345 or read more about our plant decommissioning and energy decommissioning work.