Embassy Gardens is a premier construction site in London being constructed by the Ballymore Property Group. Typically, large construction sites at the start of a new project are not connected to the main grid. A temporary electrical supply, in this case provided by Electro & Mechanical Systems UK, a company specialising in providing temporary supplies for building sites, is provided so that the site can commence operations. This development has a number of tower cranes, each one operating at up to 75kVA when lifting loads and, five hoists drawing up to 60kVA each. In the early stages of a building project the load is fairly low, but as more tower cranes are installed, the load can rise dramatically.
EDF supplies the power from the HV network provided by UK Power Networks. The supply is drawn from a local HV substation from an MCB rated at 800Amps. If the current drawn rises above this figure the Air Circuit Beaker controlling the electricity supply will tripped by a Schneider Micrologic 5 control unit in the HV substation. This has dramatic effects on the site machinery, cranes will stop and hoists will come to a halt. This is the last thing that is wanted on a busy and critical building operation. If all loads are switched on together Ballymore was anxious that the current could rise above the threshold level and cut supply to the site.
This is where SHM Metering’s special services have come into play. SHM has installed an Iskra MT382 meter with integral 3G mobile data communications on the incoming supply. The meter records two sets of consumption data, one at 5-minute intervals and the other at 1-minute intervals. The 1-minute data is downloaded over the mobile internet by the SHM Metering server every night after midnight and sent as an Excel file to the client. This gives the client his consumption pattern minute by minute throughout the day, and ties consumption peaks to the exact times of day when the load is high.
The second 5-minute load profile is continuously downloaded to create a Metering Dashboard. The SHMMetering Server presents the data with a maximum delay of 15 minutes, and at a resolution of 5minutes so the client can see almost in real time his kVA consumption. The dashboard also graphs the individual phase currents. The kVA and current demand is calculated as the average over each 5min period. The customer gets a detailed almost real time picture of the site’s kVA loading. This is much more useful than the retrospective half-hour kW demand load profile provided by the electricity supplier on the next working day.
At Embassy gardens the load measured has never been above 115kVA on the 5 minute demand curve or above 230kVA on the 1 minute kVA curves. Current has never exceeded 400 Amps on the 1 minute curve. So the power taken is well within the 600kVA /800Amps load contracted supply at Embassy gardens and the client can relax.
On other sites the demand and the maximum current may be much more critically close and it is important to know when power is close to its limit before any damaging supply interruption is caused. In other cases the requirement is to avoid high tariff charge penalties for exceeding the contracted kVA power availability.
SHM will supply similar power demand monitoring at any site. The key feature of the Embassy Gardens Project is that data is being collected at frequent intervals even where this is no fixed internet connection. This is often the case on temporary supplies, so that mobile telephone network internet can provide a totally independent way of providing up-to-the-minute power monitoring.
The installation of temporary building site monitoring is quick and easy, and once the meter is installed the flow of data can start immediately.
Peter Hutt, C Eng MIET MA Cantab DIC BSi Lead Auditor ISO5001, Managing Director, SHM Communications Ltd, Valley House, 6 Winnall Valley Road, Winchester SO23 0LD UK
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