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ELECTRIFICATION & ELECTRONICS


EMC expert Chris Marshman discusses the causes of electro-magnetic interference on the railway, and what can be done about it.


E


MC is something we all experience in our daily lives, but is a particular con-


cern on the rail network, where the safety implications are enormous.


Much has been done on a UK and Euro- pean level to try to ensure electro-magnetic interference is kept safe and to a minimum, but it also depends on engineers and de- signers doing their job well.


Among the country’s leading experts on EMC is Chris Marshman, who said there is no need for the misunderstandings that occur.


He said: “Electro-magnetic compatibility – is it a black art? Is it something we can do without? Why do we need to spend money on it?


“EMC is the ability of one or more pieces of electrical or electronic equipment to work together in the same operating environ- ment. Our railway is a classic example of having lots of electric equipment working together; it’s a very harsh environment, be- cause of traction equipment, and we need to make sure our rolling stock doesn’t pro- duce interference that will cause a red sig- nal to turn to green. That’s what it’s really all about: safety.


“There are two aspects to EMC: emissions, the unwanted result of electrical interac- tion between equipment; and immunity, or the ability of a piece of equipment to withstand what’s thrown at it. We all carry a mobile phone with us these days, for ex- ample; it’s a transmitter, and if you hear it interfering with your laptop, you know it’s not got enough immunity built into it.


“The biggest source of interference is with propulsion systems, where we have invert- ers, chopper drives, lots of power, lots of harmonics, which can cause interference to signalling circuits. That can be a fairly con- tinuous problem.


“We also have transient problems – you get ‘arcing and sparking’, or transient distur- bances, which most of the existing stand- ards ignore in many ways.


“We’ve also got broadband noise due to things like commutators; there are still plenty of those around, producing broad-


88 | rail technology magazine Jun/Jul 11


Electro-magnetic interference


causes problems on the railways - and at home.


band noise up to about 33Mhz.


“Then there are a whole range of auxilia- ries: lighting inverters, wiper motors, air conditioning fans and the drives associated with those, and auxiliary inverters. We’re getting bigger as people, we’re cramming more people into trains – we need air con- ditioning.


“Then there’s infrastructure – you’ve got signalling equipment; digital electron- ics; equipment cabinets; visual display units. Increasingly we’re looking at using GSM-R; track-to-train communication like TASS; substations; rectifi ers; switchgear; SCADA and other telemetry systems – a whole range of things that can be interfered with and cause interference.


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