Saggy wires halted trains

The peak-hour shutdown of trains in the Wellington region on Tuesday last week was caused by old equipment and sagging wires at Wellington Railway Station.

Some of the equipment holding up the wires is up to 70 years old, and the older fixed tension wires are not supported by a modern balance weight system.

The afternoon outage occurred when a train’s pantograph – the device that sits on top of the train and connects it to the powerlines – became entangled in wires near the entrance to Wellington Railway Station.

‘‘We don’t know the exact cause, it’s going to be one of two things,’’ KiwiRail general manager assets Dave Gordon said.

‘‘It will either be in some way the pantograph ... worked its way loose and tangled the wire, or the other way round – in which the wire got loose and sagged and entangled in the pantograph.

‘‘The more probable of the outcomes is that, with the heat of the day, the wire sagged and got caught in the pantograph.’’

The wires were significantly damaged in the incident. They have since been restored, but KiwiRail said it was looking at how to improve ‘‘robustness and ease of maintenance’’.

‘‘It reinforces the need to get on and replace the old stuff,’’ Gordon said.

The equipment supporting the wires ranged in age from the 1940s and 50s. The wires themselves have a lifespan of about 15 years, but the clips and poles that hold them are a mix of ages from 40 or more years ago.

Train lines across the network are currently made up of two systems: an old system of fixed tension wires, and newer wires that are supported by a modern balance weight system.

KiwiRail is planning a temporary solution of extra support poles and structures to reduce the risk of sagging wires. It will upgrade all older wires across the network with a modern balance weight system over the next four years, with $98 million allocated for the programme last year.

KiwiRail is about 60 per cent of the way through a major network overhaul announced in 2014, which will replace all old equipment.

Six KiwiRail staff are working to determine the cause of Tuesday’s outage. Train operator Transdev is carrying out a separate investigation.

The issue of a pantograph becoming entangled in wires also occurred less than two weeks ago, on January 19 at Linden station. There was another fault in October last year in Porirua, which was caused by a failure of the wires.

Greater Wellington Regional Council, which sets local train fares, has refused to refund or provide a free afternoon of travel to commuters affected by Tuesday’s outage.