# Physics industrial visit

Supertram

Introduction:

Sheffield’s Supertram is a vast network of tracks linking the whole city together. The Sheffield supertram is run by stagecoach. The supertrams employ many aspects of physics in there day to day running I am going to discuss two of these namely regenerative breaking and

Three Phase power supply:

The trams are supplied with electricity through the series of overhead cables which run above all the tracks. The trams then utilise a three phase power supply of 3x 380 V, 100Hz, 13kVA and a DC supply of 24 V, 5kW these originate in the 12 substations that are spread around the city at different maintenance points. The three phase power supply is an alternating current supply with 3 voltages operating at 120° out of phase (see below).  All the currents have identical wavelengths and frequencies just out of phase. Having a three phase supply means the trams are supplied constantly with maximum power. The nature of three phase supply and the great deal o detail requires means it is expensive to install as various expensive components are required namely the converters that are needed. Although the initial costs are high the system is incredible in the way it increases the efficiency as the amount of power per amp for example a standard single phase 120/240 volt supply at 100amps would provide around 18000-26000 watts whereas a three phase supply with the same supply could provide up to twice as much. So when you look into this it means that the same amount of power can be generated with a lower voltage meaning less electricity is required which will therefore reduce the running costs of the tram. (You can see this by using the formula P=IV). As stated before though not all the required power for the tram can be received and generated in this way other DC supply is required this is kept separate to the three phase supply as the DC is used elsewhere on board the tram.

Regenerative Braking:

Regenerative breaking is used on all trams as it is a great way to convert what would be wasted energy back into electricity and back into the system. It is especially useful in Sheffield supertrams as there are many trams on the track throughout the day and the sheer amount of stopping at starting they do means a great amount of energy will be fed back into the system. How this works and the way it is utilised will be discussed below.

The kinetic energy that the tram has whilst moving is converted back to ...