Repairing rail generators to hit four year reliability target

The rail industry requires its equipment to operate on a four year period between servicing. To guarantee this service life, operators pay a fixed contract fee that will include any repairs that are required during the four year period. With such contracts, high quality repairs are essential in order to avoid additional costs outside of the expected operating period.

Improving generator reliability

From the point of view of the maintenance provider, it is very important to deliver a high quality service. The challenges involved in these maintenance projects can be demonstrated by looking at an ongoing contract to repair 70kVA generators that power traction motors in rail bogies.

Generators are quite literally the heart of every train, designed to drive all the electrical circuits, including the main drive motors, lighting, ventilation and other circuits on the trains. However, having been originally designed and built over twenty years ago, many are now seeing an increased load, especially after the trains are refurbished. Increased demand for more electrical equipment, such as outlet sockets, buffet cars and air conditioning, has increased the load on the generators and they are now required to operate close to maximum capacity.

Delivering on time refurbishment

When a train carriage is taken out of service the operator has a very short maintenance window in which to complete the repairs and return the carriage to service. Failing to achieve the turnaround in the time will result in a reduced passenger service and potentially lost operator revenue. It is therefore crucial to complete every maintenance project on time and this emphasis is passed on to every supplier involved in the servicing program.

Operators of these trains demand all repair processes to be supported by in depth documentation and to provide full traceability of all repairs and spare parts. Any replacement parts must be sourced from the original equipment manufacturer (OEM) and every sundry part, such as wire connectors or seals must meet current rail specifications, which requires the maintenance provider to keep up to date with any changes.

Turnkey generator repairs

The challenge to repair these generators for one particular operator has been taken up by Sulzer’s Nottingham Service Centre, which has become more involved in delivering repair services to the rail industry over recent years. With extensive facilities and skilled engineers, the facility has developed the capacity to deliver a turnkey repair service for the generators that includes in house repair of the controllers and load testing of the generators.

The repair program, which centres on a common 70kVA generator, is designed to match that provided by the primary maintenance contractor who is responsible for dismantling the train and returning it to service within a set timeframe.

Any obvious faults with the component are identified during an initial light load electrical test of the generator when it first enters the service centre, after which it is dismantled and carefully inspected. An initial inspection report is delivered to the main contractor highlighting any significant issues.

The in house load cell is used to simulate load conditions in service and confirm the performance of the generators before they are returned to the main repair contractor. The test cell was designed and built by engineers within the service centre, with the rig itself fitted with rail specification connectors. The connectors speed up the install for test process and ensure that all the readings recorded in the final condition report reflect those seen when the generator is reinstalled for service.

Seven days to provide four year reliability

The repair cycle for the generator has to be completed within a week in order to match the repairs being completed on the rest of the bogie assembly. In the majority of cases, the generators only require a mechanical overhaul, but in some cases, it may be necessary to rewind stators, rotors or exciters in order to complete the repair.

In these situations, the service centre is set up to still achieve the repair inside the seven-day deadline, as it has built up a limited stock of already rewound, ready to use replacement components. Sulzer’s electromechanical service centres all have the capability to rewind a variety of small and medium sized motors and generators in house, making the repair more cost effective and time efficient, which benefits the customer.

In some cases, the generator may be beyond economic repair, in which case a previously refurbished replacement generator will be installed in the train bogey to ensure that the overall project for the carriage is not delayed. The original generator will still provide useful parts that can be refurbished individually and used in the future as spares on the other generators within this repair program. By creating this in house stock of spares, Sulzer is able to streamline the repair process and ensure that the customer receives the greatest value for their investment into these repairs.

Over a four year period, the Nottingham Service Centre has serviced over 1,000 of the two most common rail specification generators and during that time only a very small percentage has been returned for repair before the four year operation cycle had been completed. Bearing in mind the arduous nature of this industry, this is a significant endorsement of the quality of refurbishment work completed by Sulzer’s engineers.