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Case Study – Airport Critical Services switch room load metering checks
Energyworks
Case Study – Airport Critical Services switch room load metering checks
"They asked a simple question: could the existing airport sub-electricity meters be relied upon before a new multi-million pound investment in high-energy demand high-tech aircraft loading baggage system could be specified by the design team"
Author: Percy Albuquerque, Technical Director
Case Study – Airport Critical Services switch room load metering checks
1. Overview
Critical services exceeding 1MVA load such as ports, airports, data centres and 24/7 industrial sites will be supplied by transformers from the Grid supply take-off and the maximum supply capacity must not be exceeded for technical and contractual reasons.
This case study discusses how to verify that energy demand metering information is accurate; especially prior to investment in new plant and machinery that may exceed energy capacity limitations of your site.
This case study shows how one major airport in the UK was evaluating the potential energy demand effect on site transformer load for proposed new airport baggage system and requiring verification of existing electricity meter accuracy. An international building engineering consultancy appointed PA Energy for the task of meter verification.
PA Energy’s Percy Albuquerque, Technical Director commented “we will typically be given a minimal briefing by the client ahead of the project.
Every significant site attendance by engineers for metering installation work will be preceded by inspection of the site; this will include understanding the location of the switch rooms, switchgear metering and the client’s objectives”.
In airport case; there were several switch rooms each serving specific purposes and the maximum aggregated design load would be a set percentage (% ) of the total active transformer capacity; which in large sites can be up to 2MVA+ with a spare standby supply. The client’s electrical design team will specify that any new equipment must not exceed the buffer limit of total transformer capacity, allowing a significant contingency. Typically the site transformer will be 11kV or 33kV from grid input with a site wide step down to 415V for the local distribution boards.
This means that existing metering must be verified thereby ensuring that the measurements are indeed accurate and dependable. Often it is impractical to shutdown the site or even circuit switch to install metering and therefore specific techniques must be utilised to allow for fitting of metering without shutdown. This method enables PA Energy to safely access switchgear chambers to allow the fitting of the check meter equipment and if necessary automated metering reading equipment with 3G communications pushing raw metering data into the cloud.
RED STS Visualisation generated by Fuse Insight, shows a weekly energy profile of a switch room at a disused power station undergoing decommission.
2. The Concept of electricity meter verification check process
The methodology will be to supply and fit temporary electricity meters in series with the existing metering and verify that energy readings such as instantaneous power kW/MW, total energy kWh/MWh and current Amps are the same between the primary meter and the check meter.
The meter will be essentially measuring the Active Power
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Active Power kW, P = √3 VI Cos Ф
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kVA = kW x Power Factor
The higher system voltages are used in power transmission, hence the Grid starting at 400KV and stepping down to 132kV
Once installed an opening read will be made directly and noted. If an automated meter reading device is fitted, then an opening read is configured into the system. Once the check meter is installed and energised then the consumption of energy recorded over time will be the same across the two meters (i.e. primary and check meters).
3–Phase (TP) energy often described in schematics as TP&N . N is neutral line. Meters are either current transformer sensing or whole current meters; the former is easier to install, less invasive but more costly than whole current meters; notwithstanding that the latter for installation will require a power shutdown of the circuits in question. The electricity meter will also require reference voltage (VRef) connected to each the three phases.
3. Considerations when installing a check meter
The key factors when selecting a suitable electricity meter is determining the voltage of the supply line to be measured (Vmax), number of phases (VRef - typically 3-Phase) and the current transformer ratio; in a high power switch room this could be a maximum of 3200A. The metering arrangement must therefore be configured to accept those inputs levels.
Schematic line drawing of a 3 Phase metering arrangement using current transformers (CT)
Prior to installation a health and safety risk assessment will be made, in the case of PA Energy, it will use methods that have been accredited by Safe Contractor, the health and safety scheme.
The existing meter related terminal blocks will often have shorting blocks, allowing the voltage to be neutralised and with fuses to the VRefs disconnected, it allowed the check meter to be installed in series with the existing meter CT’s and parallel connection of the VRefs.
4. Example of a electricity check metering application
The airport design engineers who are a major international M&E design house contracted with PA Energy to verify if the existing airport electricity metering was accurate and there were several switch rooms with existing high power electricity meters in-situ. They asked a simple question: could the existing airport meters relied upon before a new multi million pound investment in high-energy demand aircraft loading baggage system could be specified by the design team.
It was also decided that it would beneficial if PA Energy remote monitoring devices were fitted to allow the parties to observe the energy operation of the switch room concerned. PA Energy fitted the IP (internet protocol) metering data devices with a 3G router; this meant that any data convergence on the airports IT data network was unnecessary. PA Energy uses a cloud base web service Resilient Energy Data which is a Amazon WS cloud platform powered by Fuze Insight; this store and forward capability with visualisations allows access to meter data and benchmarking of other specific meter points in the form of graphs, tabular or raw data download in Excel or CSV data.
5. Conclusion on the critical services meter verification
Following the pre-determined methodology agreed with the client PA Energy with the data it had gathered on-site and also remotely with the AMR system concluded the primary metering and check meter matched and that the existing metering was reliable. PA Energy helped the client ‘s client to avoid the cost of retro-fitting new electricity metering that would have otherwise amounted to £30,000. The cost of engaging PA Energy for consulting, equipment, engineers and data services was less than £3,000 less than 10% of the cost of a new metering system. It would allow the airport M&E design team to use the existing meter consumption information with confidence to factor in the new energy demands and establish a strategy to determine if the proposed new airport baggage equipment would operate within the airport’s overall transformer capacity and contingency envelope.