Generator power
Last week one of the small projects that I have been planning since I arrived finally finished – transferring the Emergency Department (ED) onto generator power, relocating the sub-mains cables and then transferring the power back to mains.
Figure 1: Delivery of 2x 350kVA Aggreko Generators.
Figure 2: Original location of the ED sub-mains, on the floor slab of L1 (previously this had been the roof slab of the 1 storey ED). Note, the mechanical protection has already been removed.
Figure 3: New location of ED sub-mains: Now on high level cable trays in main corridor.
Rather than detail the whole process, I will instead highlight some of the risks and difficulties and how these were overcome.
- The ED runs 24/7, therefore there is no convenient time to turn off their power. But following a week long investigation of power demand, Tuesday-Thursday was identified as the period of the lowest demand and therefore the “least busy period”.
- Sizing of generators: Both 350kVA units was sufficient for the whole department, but to maintain redundancy 2 units were connects – one to Essential and one to Non-Essential (with an automatic switch between them in case of any issues).
- The hospital’s UPS (Uninterruptible power supply) was broken, therefore if power was cut all the critical infrastructure, e.g. life support machines, would switch off. This little bombshell was dropped at 1600 on the Friday before the works was due to start. The simple solution was to postpone until the UPS was fixed.
- During commissioning of the Emergency Department (2 years ago, by a different builder), the generator manual transfer switch was not tested. The risk was the hospital’s to take, therefore they were required to conduct physical switch over – the mains power was maintained at the switch until after the hospital had confirmed that it had worked.
- Fuel: although the generators had a fuel capacity to run for 28 hours at half load, in order to appease the client the tanks were re-filled every 6 to 8 hours. At no point did the levels drop below about 75%. This was a very conservative strategy but keeping the client happy is critical.
- Diesel exhausts blowing into the ED air conditioning intakes. There was only one space that the generators could go – approx 25m from the intakes – other than extending the exhaust flue by 2m (the big pipe on the ground in figure 1), this was a question of keeping my fingers crossed that there would be no complaints.
- Over night noise – the generators were rated at 70 dBA at 7m, but with EchoBarriers installed this dropped to 55 dBA. Although this made us code compliant, at 2am in a residential area it is still pretty loud. This required some more crossed fingers that there would be no complaints.
The overall project success was due to a lot of planning with the various sub-contractor and consultation with the client.
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James,
Sub main cables; existing cables relocated or new cables installed?
Sam
Existing ones relocated. They were cut, coiled up in a plant room and then pulled into place.
The future proofing of the design was terrible. They were designed to be long enough for the relocation, but where they came up through the slab was in the middle of a new corridor. So we had to close down an area below in the ambulance bay to core a 210mm hole. It would have been easier had some one just moved a few lines on the architect’s drawing before we started building!
Looks like a fair bit of stakeholder management was needed there James; just the job for a fellow well equipped with ‘touchy feely’ people skills such as yourself.
Lots and lots of touching and feeling.