Monday, June 27, 2011

Analysis; Damage to a power network from multiple major earthquakes.

Christchurch has had 3 major, 10 moderate, and around 7000 minor earthquakes and aftershocks at this point in time. The following is a personal account of the damage based on my personal experiences and the different side-effects of earthquakes. 

I need to stress at this point in time, I am NO geologist, seismologist, or network analyst. So some of this information may not be accurate, it's simply based on my logic as an Electrical Tutor! I apologize in advance if I say anything incorrect, and feel free to post anonymous comments (this has been done, already, thank you!) and correct me.

In my opinion there have been four major side-effects of a quake (in Christchurch's case): 
  • Ground shaking 
  • Liquefaction
  • Lateral spread
  • Landslides/building collapse/rockfalls. 
Christchurch did not experience tsunami related to our own quakes at any stage. I will cover each category for some systems in the Christchurch distribution network that were affected, namely:
  • Substations 
  • Overhead lines 
  • Underground cables


Substations:

Ground shaking:
Large cast-iron circuit breakers and large transformers were affected by the shaking. Nothing is exempt from the ground acceleration and the following effects occurred:

Masonry bolts were removed from the concrete foundations by the ground shaking, which affected both circuit breakers and transformers. Also on multiple occasions, oil-filled transformers 'tripped out' due to the 'sloshing' of the internal insulating oil, making the float
switches think the transformer had developed a leak, which causes outages. I am not aware of any circuit breakers 'tripping' due to ground shaking, but it is a possibility.

Seismic bracing behind circuit breakers at Bromley substation 

Seismic bracing at Bromley substation 
During the last two decades, Christchurch's Network owner invested a significant amount of money in seismic strengthening their 270 brick substations which resulted in few sustaining serious damage. See HERE for more information.


Liquefaction:
Christchurch is effectively built on an existing swamp, particularly the eastern areas. The worst-hit example of a substation affected by liquefaction was New Brighton substation, which is approximately 200m from the Avon River. Lateral spread and a high water table were factors here also.


New Brighton substation sunk due to liquefaction


The February magnitude 6.3 quake caused the New Brighton substation to sink approximately 2m into the ground, damaging incoming and outgoing power cables. It also filled the switch room with approximately 700mm deep silt and water. This had to be cleaned out comprehensively and the two 66kV transformers were replaced with a single 66kV transformer fed from a new overhead line.

There were several smaller substation buildings that also sank and 'went out of level', but most appeared to continue operating without issue.

Lateral spread:

New Brighton substation may have been affected by lateral spread, but evidence was sparse to indicate that. As with liquefaction, lateral spread would have affected any substations that were near the Avon River. I'm not sure if that actually occurred at any stage.

Landslide/building collapse/rockfalls:
Sumner substation was hit by a massive boulder and partially disabled by this. It was built below a cliff composed of volcanic rock, some brittle, some boulders. I'm no geologist, so I couldn't describe the type of rock the cliff face was composed of, but the boulder that hit the substation was substantial and did serious damage.

The boulder that destroyed Sumner substation


Inside Sumner substation


Overhead lines:

Ground shaking:
Having seen up to 2.2G of ground acceleration from the magnitude 6.3 quake of February 22nd, Christchurch has seen unprecedented shaking due to an earthquake. Thousands of poles were heavily affected by this shaking and a large number were affected, predominantly by being left on leans, pulling barge boards off houses, straining lines, and damaging pole fittings such as cross arms and insulators. Conductors swung to within arcing distances and proceeded to do so. Also the ground acceleration caused the shafts of insulators to be bent and ties to be broken. 


Leaning poles due to a combination of shaking and liquefaction  in Kingsley St.


Video of using a helicopter to repair broken ties on an 11kV circuit that was inaccessible due to rockfall hazard in Sumner:





Liquefaction:
Many poles were affected by liquefaction, some sinking straight down, some leaning due to liquefaction coming up underneath the pole. 


Installed 3 weeks prior to the June 13 magnitude 6.3 quake, this pole was affected by liquefaction.

The same newly-installed pole.




Lateral spread:
Once again, many poles close to rivers were affected by this in a similar manner to liquefaction. Also, due to the lateral spread, the land sank, causing the water table to rise, which also caused poles to sink.


This building sank more than the pole did, ripping the termination bracket off the roof of the building.


Landslide/building collapse/rockfalls:
Poles above and below cliffs were affected by rockfalls and landsliding. Poles were hit by debris below, as well as their associated lines. This damaged poles by outright destroying the pole to breaking insulators and crossarms.


The Sumner boulder that fell on a pole.


The pole with the boulder on it.




Underground cables:


Ground shaking:
Two of the four types of dynamic force that travel underground during a large earthquake can be seen below.




A static description of waves is shown HERE.


As anybody can imagine, these massive forces can affect subterranean infrastructure systems, such as power cables, telecommunication cables, water pipes and waste pipes to name a few. In Christchurch all the aforementioned systems were affected by the quakes, power cables being in the firing line.


A minimum of four major 66kV underground cables were damaged, two beyond repair. The sheer ground acceleration ruptured the concrete the cables were embedded in in multiple locations, mostly where the liquefaction was at its worst. The other two cables had faults that were able to be repaired.



Partially completed 66kV XLPE repair joint


In the centre of the picture is a faulted 11kV PILCA cable, above is the concrete in which the one of the heavily damaged 66kV oil-filled cables can be partially seen.


3-in-a-row; three PILCA 11kV cables all bent and faulted.


Other cables were damaged also, approximately 800 underground cable faults occurred from the February quake. 11kV paper insulated lead covered armoured (PILCA) cables were bent into Z and S shapes, causing the insulation to fail on them. Other faults included previous faults pulling apart and terminations being removed from protective devices. Cables that transitioned up poles were bent by the pole swaying during the quake.


Liquefaction:
The makeup of the swampy soil in the eastern areas of Christchurch seemed to allow cables to be damaged as stated above, but the actual liquefaction process of water bubbling to the surface of soil did not affect cables as the shaking did. Liquefaction rather made travel impossible in some cases and created large potholes that vehicles fell into. The higher water table involved pumping out joint holes before work, which in some cases took hours.


An abandoned joint hole, this particular joint incomplete as several faults were found on the same cable.


Lateral spread:
Lateral spread caused cables to fault next to bridges that the cables passed under, and also caused joints to tear apart near rivers. Also cracks that appeared in land on hillside suburbs tore T-joints, other joints and terminations apart. 


Originally straight; this <still functioning> LV XLPE cable has been bent by lateral spreading.

Steve from Connetics showing the bent cable.


An 11kV XLPE joint torn apart by lateral spread.


A LV joint torn apart by lateral spread.



Landslide/building collapse/rockfalls:

I'm not aware of any faults due to these effects, however I understand many kiosks were damaged by falling buildings in the Christchurch CBD 'Red Zone' and the Lyttelton town centre.

Solutions:

Substations:
The circuit breakers inside Bromley substation were reinforced with steel braces to prevent further shaking and destabilizing. New Brighton substation was relocated to Rawhiti Domain, where there was little liquefaction and lateral spread. Sumner substation, I'm not entirely sure, but I think it was bypassed. 



Overhead lines:
Due to the ease of fault finding and maintenance, overhead lines were rapidly repaired. Severe unstable poles were immediately repaired, and ongoing pole straightening is continuing.



Underground cables:
Approximately 800 underground cable faults were repaired. Test Technicians and Cable jointers from all over New Zealand and Australia were employed to assist with the mammoth diagnosis and repair effort. Specialist 66kV jointers were bought in to repair oil-filled and XLPE insulated cables. The irreparable 66kV cables were replaced with temporary 66kV overhead lines, to keep the power supply running through winter until such time as a window of opportunity to replace the faulty cables exists.




See HERE for my blog post regarding the Bromley-Dallington 66kV overhead install.
See HERE for my blog post regarding the New Brighton-Rawhiti 66kV overhead install.




Thursday, June 23, 2011

Weeks 19 & 20 - Prebbleton Sub and major quake #3.

Another fortnight post unfortunately, sorry. Life has become busy since June 13th when we had our 3rd major earthquake. Classed as an aftershock of the Mag 7.1 quake of September 4 2010, this was a Mag 6.3 quake which struck at 2:20pm on June 13th. More damage and liquefaction occurred, and was violent where I was working with my Line crew in Akaroa. I will cover this quake in depth later.

Work log: 

Tuesday 7th June: 
Connect 11kV cables into kiosk for 4x 1MW emergency generators, QEII park.

The 4x 1MW diesel generators, QEII park

Wednesday 8th June:
Connect 11kV cables from 4x 1MW generators into 11kV network, QEII park.

'Tapped into' 11kV cable, QEII park generator supply.

Thursday 9th June:
Underground-overhead 33kV transition terminations, outside Prebbleton substation.

Me doing 33kV termination, Jeff on right.
Friday 10th June:
Underground-overhead transition terminations, outside Prebbleton substation.

The overhead guys connect the 33kV terminations from the underground cables to the overhead lines.
Monday 13th June:
11kV overhead circuit breaker oil replacement live line and M6.3 aftershock.

Oil replacement in overhead circuit breaker


Tuesday 14th June: 
Post-quake network assessment before repair start.

One of the underground Managers digging silt out of New Brighton substation (again)
Wednesday 15th June:
Re-energize domestic dwelling in Sumner after boulder destroyed pole, replace pole Lyttelton after quake caused wall to collapse and destabilize pole.

Me in front of the boulder that landed on a power pole. The boulder won..
The pole under the boulder. The cliff behind shows where the boulder came from.
Replacement pole being installed in Lyttelton. The bucket is holding the lines up temporarily.


Thursday 16th June:
Replace pole, Ripon St, Lyttelton after collapsing wall destabilized pole.

Unstable pole due to quake-related wall collapse in Ripon St, Lyttelton.

Friday 17th June:
Multiple jobs: Straighten pole Breezes Rd and reterminate conductors, straighten pole and reterminate conductors, Burwood, reenergize dairy, South Brighton, replace broken crossarm Waltham Rd, disconnect link pole Redcliffs.

Broken crossarm due to falling bricks, Waltham Rd

Broken crossarm

Analysis: Cable Jointer and Line Mechanic procedures


Due to the electrical industry in general being highly regulated, all trades within the sector have regulations and procedures all with one overarching purpose in mind: SAFETY.

Electricity can be lethal, as can falling, cutting, burning, crushing, and a host of other hazards. But with correct procedure and accurate following of that procedure, safety can be well maintained.

Connetics follow a strict procedure of using safety sheets in conjunction with job permits. All employees (and observers) must read this hazard sheet and sign it to state they are aware of the hazards and will comply with the site hazard rules. There are also job sign on/sign off sheets as well. It is not unusual to sign several safety sheets for a job, one for the job permit holder and another for the Site Traffic Management Supervisor (STMS).

One side of a hazard sheet. It has been blurred to protect privacy and copyright.
All Connetics vehicles carry an on-board safety folder which pack the latest safety regulations (the SM-EI manual is one), and lists safety procedures for Connetics staff and Orion contractors.

Lines vehicles carry several documents; examples include (see below):

The Orion Standard Construction Drawing Set <(c) Orion>. This contains instruction as to how poles and structures shall be constructed for the Christchurch and Canterbury region. 

And the Connetics Live Line Procedure Manual <(c) Connetics> . This contains in-house instructions of procedure  that must be followed when doing live line work.

Cable jointers also have such a comprehensive set of procedural rules, called the 'Underground Manual', which must be adhered to. Each jointing kit also has comprehensive instructions inside that describe how to safely and correctly complete a cable joint.



Accuracy in both jobs is crucial. Faults and mistakes can be very costly and dangerous. The ability to follow written instruction and procedure is critical in the supply industry, and unfortunately, students must develop skills in literacy to be able to perform jobs successfully and safely.

Sorry for such a short post, I'm developing a post about damage to power networks next, which should be very interesting. As always, questions and comments are welcome.

A wee link here showing how digital media can be used successfully for assignments:
http://www.stuff.co.nz/technology/digital-living/5160793/Students-give-YouTube-assignment-an-A-pass

Thursday, June 9, 2011

Week 18; The relocation of New Brighton substation to Rawhiti substation.

This week I observed the finishing of the circuit which is an extension of the original 'emergency circuit' that Orion, Connetics, Independent Lines, and Mainpower constructed to enable relivening of the New Brighton Substation after it was sunk by liquefaction from the M6.3 aftershock of the 22nd February 2011.

The extension runs to a new substation in Rawhiti Domain in New Brighton, which did not (and in future, hopefully won't) get much liquefaction. See 'Analysis' for further information.

New Brighton substation - a door even I can reach!
Work log: 

Monday 30th May: Install 66kV poles on Keyes Road.

Tuesday 31 May: Start running 66kV conductors, Baker St.

Wednesday 1 June: Run 66kV conductors from Baker St to Keyes Rd.

Thursday 2 June: JOINTING: Prebbleton substation installation.

Prebbleton substation

11 and 33kV cables underneath the Prebbleton substation

Friday 3 June: Run 66kV conductors into Rawhiti substation.



ANALYSIS: How to relocate a substation and its circuits


Footage of the quake itself


Footage of liquefaction

The 22 Feb aftershock damaged Christchurch city power (and general) infrastructure terribly. As shown earlier in this blog, not only were subterranean power cables damaged and torn apart, substations were damaged also, and some sunk. The most crucial substation was the New Brighton substation on Pages Road.

The sunken New Brighton substation
Orion, Christchurch's power distribution company, immediately swung into action to get the power back on in  the Eastern suburbs due to cable failures and the afore-mentioned substation. The underground 66kV oil-filled  cable that originally supplied New Brighton substation was broken, bent and sheared off in many locations, rendering it unrepairable.

Uppermost embedded in the concrete is a damaged section of the original 66kV oil-filled cable that supplied New Brighton  substation. Fully exposed is a damaged 11kV PILCA cable.

Orion called on some of its contractors, Connetics and Mainpower in conjunction with Transpower's contractor, Transfield, to construct an overhead 66kV circuit from the Transpower Bromley substation (which itself received damage) to the sunken New Brighton substation. This line was constructed in two weeks. In a normal situation, it would take around 18 months to get resource consent and approval to construct this kind of circuit.

Circuit map of the 66kV installed in record time inside 2 weeks after Feb 22nd.

Whilst the circuit was being constructed, the substation itself had to have tonnes of silt removed from inside to allow use of it again, and the two 66kV-11kV transformers had to be replaced by a single undamaged transformer, which I understand was obtained from Ilam substation.

The dark mark shows the level the silt was up to inside the substation.
After several 11kV underground cable faults were repaired, New Brighton substation was able to be re-energized, providing power to much of the Eastern side of Christchurch, including my own house (unfortunately it was too late for the anemones, clams, corals, tubeworms, starfish, and the Mandarin fish in our saltwater tropical fish tank, but hey, we're alive, right?).

The decision was undertaken to move the location of the New Brighton substation to a location that was not so prone to liquefaction and lateral spread, and Rawhiti Domain was deemed to be suitable.

Immediately the decision was made, preparations for construction began at the new substation site. This is another project that is being achieved in record speed.

Work beginning on Rawhiti substation site

A closer look


Good public information. All residents affected were given letterbox drops.
Once the substation was almost ready, Connetics and Independent Line Services were again contracted to do 66kV overhead lines, this time extending the original Bromley-New Brighton circuit to Rawhiti substation.

Circuit map of the New Brighton substation - Rawhiti substation run.
Pole installation began on the 25th May. The Connetics crews I was working with were on the northern side of the Avon river, Independent Lines Services doing the southern side and the river crossing.

Unfortunately I contracted a Gastronomic Virus at the start, so I was unable to see the first poles installed down Baker Street. I did, however, take a series of photos showing before, during and after..



A common misconception expressed by the public I spoke to on many an occasion was over the poles 'not all being straight'. Several poles are 'strainers', which means they are set at an angle on purpose on the outside of a bend or turn. 'Breast blocks' and 'Heel blocks' are pieces of pole underground which are actually used to keep the pole set at the angle it's set at.


Diagram of how underground blocks work.



Baker St poles


Live lines being temporarily held aloft while the existing pole is replaced with a much bigger 66kV one.

Live lines being temporarily held aloft while the existing pole is replaced with a much bigger 66kV one.
The insulated temporary crossarm, with spring loaded 'rat traps' which can be released using insulated 'hot sticks'.

Reconnecting LV crossarm and insulators

The 66kV HV line being strung above the LV crossarm

The poles were all installed, and the conductors done by 'streets', Baker St the first day, Gresham St the second day, and Keyes Rd into the substation on the third day.

As with Dallington, insulators were placed on the LV circuits below where we were running the 66kV conductors, and the conductors were fed through rollers attached to the insulators.

All rollers in place

Blair feeding conductor through a roller

Tim showing his pulling power!

Me being creative.. a view from the cable drum rollers. Winches are holding the conductors from rolling out and contacting the ground.

'Pistol grips' were used at every 90 degree pole, which is the norm. This allows the conductor to be run 'street by street'.

A 90-degree turn pole.


The substation wasn't quite ready for us, but conductors were run into place on time into the substation for connection onto onsite insulators.

Substation technicians install equipment

The transformer cooling unit arriving

Transformer and cooling unit in place. The overhead cables connect from the left of this picture.

The final run. 
Once again, I am left in awe of the commitment of the supply industry workers, flawless, methodical work being done with all safety procedures being observed to the letter. Once again I observed the Line Mechanic 'psychic' ability of knowing the procedure inside out and working as one with little communication. Observation linked to good training and a professional attitude seem to be the keys to this ability.

The three 66kV overhead circuits that have been constructed to help keep the power  on in Christchurch due to the M6.3 quake 22 February.





Next week I will cover connecting up 4x 1 Megawatt generators at QEII for bolstering the Eastern network over the winter. As seen on Queens' Birthday Monday, our shaking hasn't stopped and keeping the power network going over this winter is going to be a real task for Orion and its industry partners.

A sign that was attached to one of the new 66kV poles on Baker St. you just can't please everybody!