Class 331 upsetting other traction
Since Northern’s CAF Class 331 EMUs entered service there have been reports of Electro-Magnetic Compatibility (EMC) issues. The first came in October when the regenerative braking had to be switched off.
Where the Hitachi 800 Series generated Electro-Magnetic Interference which affected lineside communications, the Class 331 appears to generate spikes in the 25kV overhead line supply which upset other traction.
This power supply compatibility-related issue is limited to the Preston area, between Euxton to the south, Blackpool to the West and Catterall to the North. Within this area limitations have had to be imposed on both the Northern Class 331 and TransPennine Express’ similar Class 397 EMUs.
According to a Restriction notice published on 4 November, Class 331 and 397 units stabled in this area must have their pantographs down. Before pantographs are raised in Preston Croft Street sidings permission must be sought from Preston signal box. The signaller will then check that there are no Class 92 hauled services in the area before giving permission.
According to Informed Sources the problem is caused by resonance generated by the traction package when it is taking only power for auxiliary system.
Resonance creates spikes in the traction power supply high enough for protection systems to shut down the converters in the Class 92 electric locomotives hauling the Caledonian Sleepers. The converters can’t be reset until the Class 331 has left the electrical section supplying the Class 92.
Why should an EMU sitting around doing nothing cause problems? The best theory from my electric traction gurus is instability in the converter which provides auxiliary power.
When a train is running the auxiliary converter has plenty to do, supplying the air compressors, heating or air conditioning as well as keeping the batteries topped up. Stabled there are none of these load.
Designing a controller to cope with two such widely different demands is not easy. In some cases it is easier to have a dual mode controller with a separate mode for very light loads. This was the case on Eurostar.
A test with modified software was scheduled on 5 November, which it was hoped would resolve the problem. Given that it is ‘only’ Version 7, CAF is not yet in the Siemens or Bombardier league where any software Version not in double figures doesn’t count.