Each day, the UK rail network transports over 3.5 million passengers.
Rail is statistically the UK’s safest form of transport, largely because of the high safety standards of the network’s trains, infrastructure and operations.
With around 74% of UK rail journeys being made on electrified trains, electrical safety plays a very significant role.
Electrical components and systems can produce interference which may affect other equipment, so these risks have to be understood and minimised before a product can be used on the rail network.
This makes EMC testing a critical part of the approval process for products used on UK railways.
What is electromagnetic compatibility (EMC) testing?
Anything electrical produces an electromagnetic field which can result in electromagnetic interference (EMI).
This interference can pose a risk to other electrical equipment or systems, potentially rendering them inoperable or unsafe.
As such, any equipment or technology used within rail – whether that be on trains, infrastructure or units installed at stations – must undergo careful electromagnetic compatibility (EMC) testing and approval.
EMC testing ensures a device, component or system is immune to external electromagnetic disturbances – continuous or intermittent, airborne or conducted.
In addition, EMC testing ensures a component will not negatively impact other components.
Within rail, EMC testing primarily focuses on ensuring electronic, electrical and rolling-stock apparatus do not interfere with signalling or other safety-critical infrastructure.
What EMC standards does rail equipment need to meet?
EMC testing for rail is subject to a number of standards.
The primary standard for rail EMC testing is EN 50121. It regulates emissions and immunity across different areas of the rail network:
- EN50121-1 – Part 1 General
- EN 50121-2 – Emissions of the whole railway system to the outside world
- EN 50121-3-1 – Rolling stock (train and complete vehicle)
- EN 50121-3-2 – Rolling stock (apparatus)
- EN 50121-4 – Signalling and telecommunications apparatus
- EN 50121-5 – Fixed power supply installations and apparatus
As rail applications are safety-critical, compliance must be verified by an EMC testing laboratory – like ETS.
How is rail EMC tested?
As mentioned, EMC testing looks at two elements – emissions and immunity. These can be either radiated or conducted.
Radiated Emissions (RE)
Radiated emissions (RE) are the unintended electromagnetic fields generated by electrical systems or components.
In the case of individual devices or systems used within rail, they are typically tested in a controlled environment called a semi-anechoic chamber – a special environment shielded from external electromagnetic interference.
Whilst operating, antennas at fixed distances record the level of electromagnetic emissions produced by the device or system to ensure they do not exceed safe levels.
In the case of larger items or entire units (such as locomotives, carriages or power lines) these tests must be conducted in the field, with background emissions accounted for.
In order to meet the EMC requirements for rail, the device or vehicle cannot exceed the regulatory limits for electromagnetic emissions as defined in the relevant sub-section of EN 50121.
Radiated Immunity (RI)
Radiated immunity tests the resistance of components or systems against external electromagnetic fields.
The item under test is subjected to differing frequencies and amplitudes of electromagnetic field. The device’s full range of operation is tested to ensure the interference does not cause dangerous or unacceptable behaviour.
However, for whole vehicles being tested in the field, this is not a requirement.
Conducted Emissions (CE) and Immunity (CI)
As well as radiated or ‘airborne’ emissions, components are also tested for conducted emissions and immunity.
Conducted emissions are unwanted electrical ‘noise’ that an electronic device generates and passes to other devices via power or signal cables.
Emissions are evaluated using a Line Impedance Stabilisation Network (LISN). The LISN provides a defined impedance to the power line and isolates the device under test from ambient grid noise to accurately measure the radio frequency energy it emits.
Common causes of conducted emissions in rail applications include high-frequency switching transients (from power supplies) and common- or differential-mode currents which flow along the live and neutral wires in equal magnitude or opposite directions, creating electromagnetic interference.
In addition, conducted immunity tests a component’s ability to resist external electromagnetic interference (EMI) entering via power or signal lines.
In this case, the test simulates radio frequency noise from nearby sources which can induce common-mode disturbances within the device’s wiring. A full range of operations is tested and evaluated.
Additional immunity test
In addition to the aforementioned testing, there are further tests required:
- Fast transients
- Voltage dips
- Surges
- Magnetic Immunity
- ESD
UK Approval
To achieve approval against EN 50121, testing must be conducted by a UKCA-designated technical service within a suitably-controlled environment.
Here at ETS, we have UKAS accreditation for testing rail devices and systems. We test railway apparatus in our UKCA-approved laboratory.
And, whilst not UKAS accredited, we also have capability to test whole railway systems and assess radiated emissions at customer-designated sites.
Looking for EMC testing for rail?
Part of the NMi Group, ETS is an independent UKAS-accredited and award-winning provider of EMC testing, certification, advice and troubleshooting for the majority of product types.
With over 25 years’ experience, we’ve played a critical role in the testing and approval of many devices and systems used across the UK rail network – and railways across the world.
Enquire about ETS EMC testing.
Back