Parry People Movers

Parry People Movers (PPM) is a British company manufacturing lightweight railbuses that use Flywheel energy storage (FES) to store energy for traction.

Usage
Although it is not the only place where such tests have been carried out, the flywheel technology was tested on the Stourbridge Town Branch Line in the West Midlands during 2006. Since Central Trains had no plans to introduce a Sunday service for the branch, the initiative was brought to test a PPM50 model on the branch on Sundays.

The trial was intended to be for one year only and, indeed, the winter timetable introduced for 2007 did not include any Sunday services on the Branch Line.

The initiative is being looked at as a serious option for replacement of the Class 153 single-car DMU that currently works the Branch. The more environmentally-friendly and far more efficient PPM 50 would increase profit on this line, through minimal fuel use.

London Midland, the operator of the new West Midlands franchise, have decided to use the PPMs on the Stourbridge line. Two PPM60 units, which have been classified as Class 139, will be purchased to operate the service, replacing the single car Class 153 DMUs.

Technology
PPMs utilise rotating flywheels as a store of kinetic energy which is then used to power the vehicle. A typical PPM flywheel is made from steel laminates, 3 feet in diameter and 1120 lbs in mass, rotating at a maximum speed of 2,500rpm. The flywheel is mounted horizontally at the centre of the unit, beneath the seating area.

The flywheel allows the direct capture of brake energy (when slowing down or descending gradients) and its re-use for acceleration. Since the short-term power demand for acceleration is provided by the energy stored in the flywheel, there is no need for a large engine. A variety of small engine types can be used including LPG, diesel or electric.

On a route with stations a short distance apart it is theoretically possible to use the unit as a streetcar without any engine or overhead electrification at all. Instead the flywheel could be reenergised at each station storing enough power to carry it on to the next one.