Temporary HV
Last week I was surprisingly involved in the installation of temporary electrics. I say surprisingly, because at the start of the week I didn’t think I’d have any involvement in this area of the project. Before I go on any further I’ll explain what the current temporary electrics plan is and how it was / is planned to develop.
The temporary electrics subcontractor is Wyse power. There are currently two temporary substations (TSS) set up in a radial to provide power to the site, with a third that and has now been delivered to site and is due to be energised shortly in order to allow a ring main to be established. The HV power comes onto site through an intake substation just off phase 1 and runs under the road on the western boundary before coming into the basement at TSS 1. From here TSS1 is connected to TSS2 via an internal cable. Another cable was pulled at the weekend which will eventually be connected to TSS 3. TSS3 will subsequently be connected to TSS2 via an internal cable allowing the ringmain to be completed. (Please refer to single line diagram).
Single line diagram showing the temporary HV set up.
This blog will deal with the delivery to site of TSS3 and the pulling of the cable that will eventually be connected to the ISS and TSS3.
My involvement in the delivery of TSS3 and the pulling of the cable came about because someone was on holiday and I was apparently best placed / willing to get involved. This is despite being only aware of what was happening and not read into the detail.
The delivery of TSS3
The delivery of TSS3 should have occurred last Wednesday. The plan was simple, use a tower crane to pick the TSS up from the delivery vehicle and drop it directly into its final resting place.
Problem 1? The substation didn’t arrive on Wednesday and the concrete subcontractors were due to be placing falsework in the area where the substation needed to go. Once the falsework was in position there would be no opportunity to directly drop TSS3 in with the crane as the falsework was for a slab pour. Unfortunately for me the Carillion construction team had been told in no uncertain terms that any delay to the concrete contractor was not acceptable. This led to the area I needed the TSS to go being filled with false work and covered over in preparation for a pour.
Solution 1: Placing the TSS as close as possible to where we wanted it to end up and then sliding it into position once the pour had been completed and the falsework had been removed (the TSS isn’t due to be energised for another few weeks, so curing time wouldn’t be a problem).
Problem 2: Wyse power were telling me that the TSS was going to be approximately 2.5 x 2.5m and weight in at around 5 tonnes. This meant that there wasn’t physically a route to get the TSS into its final position from the available intermediate positions.
Solution 2: When pulling the HV cable that would link up to TSS3, pull as much cable as possible into the basement in order to maximise the chance of being able to reach the TSS without having to pay for a cable joiner to come out.
Final solution: In the end the TSS arrived on site and measured only 1.8 x 1.6m and only 3 tonnes. Therefore, more by luck than judgement, we were able to place the TSS into a position that would allow it to slide into its final position at a later date.
Cable pull:
At the weekend that has just gone the cable that will eventually connect the ISS to TSS3 was pulled. This required the power to site to be switched off due the cable being pulled being in a duct parallel to the existing temporary HV power. Getting the HV power turned off is a relatively big deal involving having APs on site as well as the DNO – everything needs to run smoothly! The weekend prior to the cable being pulled preparatory works were conducted (cable pulling pits established) in order to allow the cable pull to proceed smoothly. The back brief everyone in Carillion had received was that these preparatory works had gone smoothly and that we were ready for the cable pull. However a quick chat between the groundworks supervisor and myself highlighted that everything wasn’t quite so squared away. In order to get the cable into the basement there needed to be a hole in the kingpost and sheet pile walls for the cable to pass through – there wasn’t. Fortunately this conversation happened at the start of the week, so it was fairly simple task to get the sheet pile wall cut down (the capping beam has yet to be put in position and will be formed around the cable duct), and a hole cut in the king post wall.
Comments / reflection:
My involvement in the temporary electrics came about because someone was on holiday. In future I need to do a bit more of an estimate as to what might come my way when people are away so that I can better prepare myself.
Everyone knew when TSS3 was supposed to be being delivered, but nobody had highlighted the critical nature of the delivery window – communication is key. A 5 minute conversation between the MEP team and the package manager for this part of the building would have highlighted that the falsework was going in imminently and could have led to the delivery date being brought forward to allow for unforeseen delays, or additional pressure being placed on Wyse power to ensure the delivery date was met.
Wyse power didn’t know the specs of their own transformer – everyone is a middleman. This detail should have been known in advance. In addition I should have questioned Wyse Power’s dimensions more. I could have looked at the dimensions of similar MVa transformers as a reality check on what Wyse Power were telling which would have simplified the issue of getting the transformer in position.
The groundworks contractor knew that the HV cable had to run into the building and that there weren’t any penetrations in the basement wall. Why didn’t they report this first thing on Monday morning? Why did it take a chance conversation to highlight the problem? Talking to people when you’re walking about on site it key to finding out and confirming what is actually going on. Also don’t take what you’re told at face value, question it and check for yourself.
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De ja vu!!! Exactly the same happened with TS 1 and 2! The story doesn’t seem to have changed, everyone wants power but nobody wants to facilitate getting it, Wyse power are useless and O’Keefe don’t know what they built and where. Richard and I found that you actually have to hold everyone’s hand, tell them in person and email them to stand half a chance in co-ordinating something. Have they decided where to put the permanent power yet? That’s also going to be fun finding the ends of cables and holes in the capping beam to pull it!
Angela,
We’ve got holes drilled in the capping beam for the permanent supply and the ducts laid, the cable was supposed to be pulled at the same time as the cable for TSS3…but the client changed their mind. It turns out that since you installed the services the basement for phase 3 has been redesigned and there is now a clash.This means the services along the western boundry need to be moved and there may well be a need to get the micro bore on site again.
Oh dear! I’m glad they have a spare £1m floating around. At this rate the whole phase 3 basement will become a giant foul pump station!
Do you think your man from Wyse was just working on the principle of better to go worst case? It appears to me that people don’t really check where their data is coming from much.
Henry,
That’s what he was definetely doing, but worse case was causing quite a few headaches.
Angela,
I think the client would be quite happy if they got away with £1m for this variation.
Rich,
As these transformers are only temporary I take it the fixed ones will all be of the same kVA value? How long is temporary? We have 3 separate substations on our site each with 3 x 2000kVA transformers arranged in an N+1 confg. My point being all 9 transformers are the same kVA rating for ease of switching loads across transformers for maintenance or failure reasons. I’d post a line diagram but doesn’t look like the comments feature allows it…
Fran,
Temporary is until our permanent transformers come online (over a year from being delivered) which may be about to be delayed due to issues with the services being changed. Our permanent transformers will not be exactly the same size, but they will be in the region of 1 MVA. Our system doesn’t have anywhere near the redundancy yours has. We’re on an open ring. If an individual transformer goes down then the load supplied by it looses power. There’s a life support generator which kick in to provide power on the LV side to critical systems, but that’s it. Part of the FM package is that a replacement transformer can be sources within 4 hours.
Wow that’s some FM package – sourced in 4hrs is pretty rapid but surely that’s not connected up and ready to take over as well? Is the new trans just going to sit outside somewhere or will it be an actually replacement? (granted dependant on why it has failed in the first place but seems a little bit like they’re wishing none of them break).
Fran,
I’m sure the client is hoping that none of the transformers break, but at the same time we’re supplying a residential building, not a hospital and the client needs to make money. There are already 10 transformers in the basement roughly clustered in two locations. To get the same n+1 redundnacy as you we’d probably need another 2 transformers or have to increase the size of each transformer to achieve the additional capacity with the same number of transformers. Either approach would require more floor space which would mean less carpark space, or storage space to sell and less money coming in, pluss the additional cost of buying more capacity. Why exactly would a transformer break? They’re inherintely relaible and the most likely cause of failure will be something tripping which can be resolved in by the FM package in under 4 hours. Worst case would be a transformer fire / explosion in which case there may be a few more issues than getting power back to one part of the building.
Rich, agreed. I have heard of transformer trailers that can rock up be left outside and connected into a special terminal junction box which bypasses the failed one. Just think 4hrs from failure to power restored especially with an AP nodoubt required quite a tall order. Interesting client perspective but understandable.