Editor’s Note: We regularly receive requests from readers to publish stories about real EMI/EMC problems faced by real engineers. We are pleased to bring you Banana Skins, a new monthly column in In Compliance, and a 20-year tradition that began in the pages of the EMC Journal. We hope you enjoy the column and look forward to continuing the tradition of sharing these valuable stories.
1. 10MW power converters interfere with wired telephones over 12 miles away
To cope with increased North Sea oil production, two new pumping stations with 6 MW adjustable speed induction motor drives were built and installed in Scotland, one in Netherly and one in Balbeggie. Soon after commissioning the local power utility and the telephone company received a flood of complaints. Geographically the complaints came from concentrated pockets spread over an area up to 12.5 miles away from the 33 kV overhead supply lines feeding the drives. A payphone over 4 miles away from the power line was noisy enough to be almost unusable, whereas just across the street a householder’s telephone was relatively unaffected. Other symptoms included loss of synchronisation on TV sets (rolling pictures) and ringing on the supply to fluorescent lighting circuits.
Although the drives had been designed to, and met the supply industry’s G5/3 harmonic limits, the problems turned out to be with higher order harmonics than it covered, up to the 100th in fact (i.e. 5 kHz). The problem became a public relations nightmare for all involved, and culminated in questions being raised at Government level. Remedial EMC work was urgently required and was in fact accomplished, although under extreme difficulties because the cost of any downtime of the oil pumping stations was so high.
(Taken from: “Harmonic filtering of large induction motor variable frequency drives” by M J V Wimshurst of Hill Graham Controls, High Wycombe, U.K., and Allan Ludbrook of Ludbrook and Associates, Ontario, Canada. Presented at the 7th International Conference on Harmonics and Quality of Power (IEEE) at Las Vegas, October 16-18, 1996, pages 354-359 in the Proceedings. Also presented at the “Sixth International Conference on Power Electronics and Variable Speed Drives”, Nottingham, UK, 23-25 September 1996, IEE Conference Publication No 429, pp 24-29, http://www.iee.org.uk/Library.)
2. PC proximity switches off bathroom shower
A (CE marked) portable PC carried up the stairs in a domestic household whilst operating, reliably caused the “power shower” in the bathroom to turn itself off if it was in use at the time.
(Personal communication with Editor
in 1997)
3. RF interference in ambulance causes death
Medical technicians taking a heart-attack victim to the hospital in 1992 attached her to a monitor/defibrillator. Unfortunately, the heart machine shut down every time the technicians turned on their radio transmitter to ask for advice, and as a result the woman died. Analysis showed that the monitor unit had been exposed to exceptionally high fields because the ambulance roof had been changed from metal to fibreglass and fitted with a long-range radio antenna. The reduced shielding from the vehicle combined with the strong radiated signal proved to be too much for the equipment.
(An article in the Wall Street Journal reported in Compliance Engineering Magazine’s European edition September/October 1994.)
4. Running Windows™ causes cat flaps to rattle
Computers used in a room close to a door fitted with a high-technology (magnetic) cat flap caused the latches on the cat flaps to rattle continuously whenever Windows™ was loaded or a Windows™ application run.
(From the New Scientist magazine,
7th May 1997, www.newscientist.com.)
5. Poor power connections interfere with search and rescue satellite comms over large area
The Langley (USA) Air Force Base Rescue Co-ordination Centre reported that its search and rescue satellite was receiving interference on its 121.5 and 243 MHz distress frequencies. The area over which interference was a problem was around 8 square miles, which was significant because normal emergency transmitters on these frequencies can only be detected at ground level for about one mile. The problem was eventually traced to poor connections on an overhead power line.
(From an FCC Field Operations Bureau news release, 1994, also reported in Newswatch…EMC in Compliance Engineering European Edition
January/February 1995, page 6.)
6. Desert Shield and Desert Storm suffered ‘serious and significant’ EMI problems
An advertisement for engineers for “The HERO Project” quoted Rear Admiral Roland T Guilbalt, Deputy Director, Electronic Warfare Division US Navy as saying that both Desert Shield and Desert Storm suffered from serious and significant EMI problems. We have no more information on this at present, but presume it was due to the very heavy use of high-tech civilian equipment used for the first time in a military situation.
(From EMC Technology magazine, 1993. HERO stands for Hazards of Electromagnetic Radiation to Ordnance.)
7. Mains harmonic currents increasing, causing overheating and other problems
Excessive mains harmonics in the London area, due mainly to the rapidly increasing use of personal computers, are causing overheating problem in AC power cables (including those that run under the Thames). In the offices where the computers are, it is increasingly common for the power-factor correction capacitors normally fitted to fluorescent lamps to blow (the electricians usually just remove the blown capacitors).
Damaged and overheated neutrals, and damaged electrical switchgear is increasingly seen as a result of harmonic mains pollution. In the US, fire insurance companies are being urged not to take on any new policies unless they have had the size of the neutral cables in the company concerned checked for their adequacy for the heating effects of harmonic currents.
(Personal communications with Editor, January 1998)
8. Hair dryer can be turned on spuriously by mains transients
Hartman Products of Los Angeles, California, has agreed to pay a civil penalty of $60,000 to settle allegations that it failed to file a report regarding a defect in the 1992 Hartman Pro1600 hair dryer. The CPSC (a US consumer safety agency) believes that these hair dryers can turn themselves on even when the on/off switch is in the “off” position. While the dryers’ heaters start, their fans do not, potentially causing internal components to overheat and cause fires.
(Compliance Engineering May/June 97, www.ce-mag.com.)
9. Radio-activated car keys unreliable due to EMI
The AA and RAC estimate that around 9000 breakdowns they attended in 1996 were the result of remote key fobs being blocked by RFI. An AA spokesman said: “The number of cars being produced with radio-activated keys is standard now. If we’re getting 9000 now, what will the problem be like later on?”.
(Electronics Times, 13th Oct. 1997.)
10. Desk toy wipes floppy discs and distorts monitors
We recently bought what looked like a fine new idea for an executive toy. It consisted of a very strong magnetic base with lots of ball bearings attracted to it, which it was possible to form into beautiful sculptures. What we did not realise at the time is that magnets and office desks are not cheerful companions. But we soon found this out when the discs with our accounts on them were mysteriously wiped, and the monitor screen went all the colours of the rainbow. It is now only possible to use our office desk toy when not at our desks, and well away from the office.
(Letter from Michael Fell in 29 November 97 issue of New Scientist, www.newscientist.com.)
11. Electric wheelchairs erratic due to EMI
Wheelchairs have come in for special scrutiny by the FDA (the US Food and Drug Agency). A few months ago, the agency ordered makers of wheelchairs to shield them and to educate users about the potential hazards of interference. The FDA acted after receiving “many reports of erratic unintentional powered wheelchair movements.” These included sudden starts that caused wheelchairs to drive off curbs and piers when nearby police, fire or CB transmitters were activated. Miraculously, no fatal injuries have been reported.
(But broken limbs have occurred as a result of such interference – editor.)
(Compliance Engineering – European Edition September/October 1994.)
12. Railway signaling interferes with recording studio
Around 1990 Alan Little leased a derelict arch under the railway line in Camberwell from British Rail. He borrowed money to convert it into a two-level mix of recording and rehearsal studios. The total cost was pushing £50,000. Up until November 1991 it was popular with up-and-coming bands needing somewhere to rehearse and record. Then, one fateful Saturday morning, with three bands booked for the morning and three for the afternoon, disaster struck. All the studio equipment, and the bands’ amplifiers, started warbling. The bands and studio crew thought at first that they had an equipment fault. Then other studios in other railway arches in the area began phoning each other. They all had the same problem.
Alan Little phoned British Rail and on the Monday morning a BR engineer came round, listened and said the cause was a new signalling system installed by BR.
BR controls its track lights by feeding electric current through its rails. When a train runs over the rails it provides a short-circuit between them, triggering a red light behind the train. Recently BR has begun changing to the use of alternating current. The long rails act as a highly efficient aerial, radiating a powerful AC magnetic field (this was actually around 1 Amp/metre over much of the studio – editor). The AC is at audio frequency, using tones of between 1 kHz and 4 kHz. The tones are complex warbles, to safeguard the system from outside interference.
The effect was heard through the mixing desk, with pick-up from mains and connecting leads. It was even heard through unpowered loudspeakers (even when they were disconnected from their cables and their terminals shorted – editor). It was worst when an electric guitar is plugged into an amplifier. Guitar pick-ups are designed to convert their magnetic fields, modulated by the movement of the steel guitar strings, into sound. They cannot distinguish between magnetic fields from a BR signalling system and those from vibrating strings.
(Extracted from an article by Barry Fox in Studio Sound Magazine, June 1992)
13. Magnetic airline tray tables wipe hard drives
It was reported in the Sunday Times (15/2/98) and New Scientist (7/3/98) that Sabena Belgian World Airlines had installed magnetic tray tables in its new fleet of A340 Airbuses, to prevent the nuisance of rattling trays on their flights, but that these tray tables were apt to cause loss of data on PC hard disc drives.
New Scientist of 28 March reported that the story was untrue, but that tables of this sort had been discovered on a train from Frankfurt to Berlin. The conclusion seems to be that if you intend to use your PC in any kind of vehicle you should always carry a (steel!) paper clip and use it to check for magnetised tables.
14. Electromagnetic ‘bombs’
High intensity radiated fields (HIRF) guns and electromagnetic pulse transformer (EMPT) bombs are already easy to build from off-the-shelf components. The effects of even hand-built HIRF or EMPT weapons can damage microprocessors at ranges of hundreds of metres. Possibly, in a few years, a van equipped with suitable electronics could cruise down Wall Street (or through Canary Wharf – ed.) and disrupt the information processing capability of thousands of computers without being detected by the
local police.
(Extracted from an article in the IEE’s Control and Computing Journal, April 1998 (page 52), www.theiet.org.)
15. More on radio activated key lock-out problems (Banana Skin No. 9)
Most radio activated key-entry systems have a manual override. Unlocking the door can be as simple as inserting the mechanical key into the lock and trying the lock according to the instructions printed in the car manual.
(From an Electronic Times article on 29th September 1997, www.eetuk.com. The trouble with this advice is that the manual will usually be locked inside the car – or are we supposed to carry it around with us at all times?).
16. More medical incidents
The magnetic field caused by ground currents in a water pipe system made it impossible to use sensitive electronic instruments in part of a hospital.
A patient-coupled infusion pump was damaged by an electrostatic discharge, but thankfully the alarm system was not affected and a nurse was alerted.
An operation using a plastic welding machine caused interference with a patient monitoring and control system, causing failure to detect that the circulation had stopped in a patient’s arm, which later had to be amputated.
(Taken from Compliance Engineering European Edition March/April 1998.)
17. Inadequate lightning protection led to serious explosion in oil refinery
At 1:23 pm on Sunday, 24th July 1994 there was an explosion at the Texaco Refinery, Milford Haven. Its force was equivalent to 4 tonnes of high explosive and it started fires that took over two days to put out. Shops in Milford Haven 3km away had their windows blown in. 26 people sustained minor injuries, and the fact that it was Sunday lunchtime and the site was only partially occupied meant it could have been very much worse. Damage to the plant was substantial. Rebuilding costs were estimated at £48 million. There was also a severe loss of production from the plant – enough to significantly affect UK refining capacity. The incident was initiated by an electrical storm between 7:49 and 8:30 am on the Sunday morning that caused a variety of electrical and other disturbances across the whole site.
(Taken from IEE Computing and Control Engineering Journal, April 1998, pp 57 – 60, www.theiet.org.
There is an HSE report on this incident: “The explosions and fires at Texaco Refinery, Milford Haven, 24th July 1994” HSE Books, May 1997.)
Comments by the Editor: I have not read the HSE report, but understand from private conversations with HSE experts that the large explosion was caused by the electrical storm giving rise to power surges which tripped out a number of pump motors whilst leaving others running. As there was a great deal of panic and confusion due to the information overload caused by the numerous small fires and equipment outages from the time of the storm, it was not noticed that flammable substances which should have been flared off were accumulating in pipework and vessels. After five hours something ignited the total accumulation, resulting in the large explosion.
18. CE marked 8kA DC motor drive causes severe interference with monitors
A very powerful (±8,000 Amps) DC drive was recently purchased and installed in an industrial plant. It was contractually agreed that it would meet and be declared compliant to the EMC Directive. A control room was also required (like most modern control rooms it was full of PCs and CRT-based VDUs) and the drive manufacturer said that it could be installed near their drive cabinets. When the drive was operated the images on the VDUs were squashed into 50% or less of the screen width. It was possible to tell the direction and loading of the drive directly from the movement of the VDU images, which of course were completely unreadable. The magnetic fields caused by the drive were of the order of 235µT, and most CRT-based VDUs show image movement at greater than 1µT (1µT is approximately equal to 0.8Amp/metre and to 10 milligauss).
The drive manufacturer claimed that his drive did meet the EMC Directive despite the fact that it caused interference with the control room VDUs. What they in fact meant was that it met the industrial generic standards, which do not include any limits for low frequency magnetic field emissions. They forgot that their EMC Declaration of Conformity binds them to not causing interference of any kind, and that compliance with a harmonised standard only gives a presumption of conformity.
The situation has been remedied by the use of LCD screens, which have only recently been available with a specification suitable for the SCADA system that was used. “Dog kennel” magnetic shields and active field cancellation devices were also investigated. The delay in the use of the control room was several months, and this had an impact on productivity far beyond the cost of the remedial measures.
(Submitted by an EMC Consultant who wishes to remain anonymous, May 1998.)
19. Bathroom fan triggers security lights, which then cause radio to switch on
We’ve learned to live with the condition that if we get up in the middle of the night to use the bathroom, when we turn the light on the fan timer starts. The fan will keep running for twenty minutes, and when it turns off it causes interference that turns on the outside security light (infra-red triggered 500W halogen) which then runs for its time period (15 minutes) whilst shining through the bedroom window.
Now you’ll have difficulty believing this bit… Monty Python eat your heart out… before the 500W halogen lamp we had a high pressure sodium lamp with an inductive ballast. When this switched off it would cause interference which would sometimes start the bedside radio. So the scenario was this…
Get up at 2:00 am, go to bathroom, turn on light, turn off light, go back to bed, and after twenty minutes a bright light would shine through the window and wake you up. If you slept through that (or went back to sleep), fifteen minutes later when the light switched off the radio would start, and then you would wake again.
The moral of this story? If you have bad EMC immunity make sure you use the bathroom before you go to sleep.
(From Chris Dupres via emc-pstc@ieee.org, 8th July 1998)
The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column.
The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans
of the column. All of the EMC Journal columns are available at: https://www.emcstandards.co.uk/emi-stories, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community.
We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.
