4 minute read
Key Issue
from ECN July 2021
QinetiQ looks at how electromagnetic interference can affect an electrical installation.
In 2020, pilots flying in and out of Glasgow airport reported loss of communication with air traffic control between 6,000 and 10,000 feet. Communications regulator Ofcom launched an investigation to locate the source of the interference, which it described as “like looking for a needle in a haystack”.
Eventually, the interference was traced to a single household directly under the flight path. The homeowner had recently installed four vintage-style lightbulbs, found to emit electromagnetic noise affecting the frequencies used by air traffic control. The bulbs were removed without incident, but it’s easy to imagine how events could have played out very differently.
This isn’t an isolated example. In September 2020, an old television was found to be knocking out wireless internet across the Welsh village of Aberhosan; and in 2017, residents in a Northern Irish street were prevented from locking or unlocking their car doors due to a faulty wireless doorbell blocking their electronic key fobs.
As more technologies operate wirelessly, the electromagnetic spectrum becomes increasingly congested, demanding greater care when performing installations to avoid introducing electromagnetic interference (EMI).
As more technologies operate wirelessly, the electromagnetic spectrum becomes increasingly congested, demanding greater care
When it comes to EV charging, it pays to work with the experts.
Your installation as a source of EMI
All electrical devices produce electromagnetic signals, which can result in EMI that radiates through fields in the air, or is conducted along cables. Installations that don’t address electromagnetic compatibility – through techniques such as grounding, bonding, shielding, routing and segregation – will ‘collect’ EMI and carry it to sensitive electronic modules. They will also radiate EMI, which can affect nearby electronic systems.
As discussed, the source of EMI may be difficult to pinpoint. A client may link a failure in their systems with work you complete for them – such as wireless internet blackouts in an office following the installation of new lighting. The ability to quickly and correctly attribute the interference to its true source could save countless hours of investigation. If the lighting is indeed to blame, the fault can be promptly identified and rectified. But the interference could equally be caused by the microwave oven in the staff kitchen – in which case you must be able to prove that your work is not the source of the interference.
These principles are even more relevant in high-risk and high-security environments, like airports, hospitals, financial institutions and critical infrastructure. Here, lives and livelihoods could be at stake.
A fictional (but plausible) scenario
A newly commissioned Forex trading platform enters use. However, in its brand new data centre, servers begin failing in an apparently random pattern, at unpredictable times. The owner suspects a faulty electrical installation, bringing the installer in to carry out remedial works at the installer’s cost. After a total power and data cabling replacement, faults persist. Earth loops and earth leakage issues are then suspected, or even a cyber attack; but no cause is identified. Trading slows, share prices fall, and contractual disputes arise as businesses look for someone to blame.
Unexpectedly, the source of the interference is a collection of thermostats mounted in the main service corridor, running alongside the data centre. This installation introduced several minor breaches in the Faraday shield built into the data centre’s wall. When a thermostat opens its contacts, minor arcing occurs. The EMI caused by these arcs passes into the shielded area of the data centre hall and is enhanced by the shielding. The transient disturbance causes servers to ‘latch’, requiring a manual reset of each server.
If an EMI detection system had been installed in the data centre, the first switching cycles on the new thermostats would have triggered alerts. Proximity data from the EMI detectors would narrow the search to the service area, enabling discovery of the problematic thermostats within hours. These could then be removed and replaced, with no lasting damage.
When EMI disrupts your installation
When working on an installation, it’s not just the effect of your work on nearby systems that you must consider, but the effect those systems may have on your work. If assigned to an installation in Aberhosan in the summer of 2020, you could have been driven to despair trying to figure out why wireless systems kept failing – until the ancient television was finally discovered.
Electromagnetic awareness
Awareness of the local electromagnetic environment is an increasingly vital part of planning, installing, troubleshooting and maintaining electrical equipment. The ability to attribute EMI to its source – whether your activity, that of a contractor, or an unrelated third party – could keep rectification costs to a minimum, prevent project delays, and even protect against legal action in the event of a serious incident.
Detecting transient EMI is notoriously difficult – but not impossible. With EMI detection in place, organisations are equipped to attribute or eliminate EMI as the cause of issues – reducing the time and resources needed to restore systems. As always, it’s better for everyone to get the job done right first time.
QinetiQ, qinetiq.com
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