Summarization request:
Please summarize the process of how an electric locomotive draws power and converts it to mechanical energy, as well as the equipment used to control its speed.

Source text:
The electric locomotive draws power from the over head equipment (OHE) with the help of Pantograph and converts this electrical energy to mechanical energy, in controlled manner, through Traction Motors which drive the axles.
To enable the locomotive to perform this task, it is equipped with suitable equipment, which enable loco pilot to control the speed of the train as per requirement by controlling the applied voltage to traction motors.
In conventional locomotives, 25KV, Single phase, AC supply is collected by a roof-mounted pantograph from the OHE and is stepped down by a transformer inside the locomotive.
This supply is then converted to DC supply by a full wave silicon rectifier and associated smoothing filter before being fed to the traction motors.
Torque / speed control is achieved by variation of the AC input voltage to the rectifier through an on-load tap changing arrangement on the primary winding of the loco transformer.
The equipment on electric locomotive, depending up on where it is located, can be classified in three different categories viz.
1. Roof equipment,
2. Inside equipment and
3. Under Frame equipment
Both the roof and the under frame equipment are subjected to lot of dust and atmospheric pollution and are therefore designed to withstand these severe working conditions.
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