A Top Drive is a device that is used in drilling to turn the drillstring and allow the drilling of the well bore. It is a powerful device that is made up of one of more motors typically powered by hydraulics.
Unlike a Rotary Table, the Topdrive is suspended above the drillstring inside the drilling derrick, raised and lowered whilst attached to the drillstring by the draw works along the dolly track.
Top Dive Offshore Drilling
Today, a TopDrive is more commonly used in offshore drilling than a Rotary Table. This is due to the ability to quickly and easily swap them out for servicing and maintenance, causing less downtime.
Video Of A Top Drive During Drilling
Image courtesy of NOV. Video courtesy of BenTEC