Thursday, August 13, 2009

Reverser repaired

Over the previous week, the 1005's reverser drum was repaired, tested and reinstalled. The reverser's job is to reverse field connections on each of the traction motors. On a series-wound traction motor, the field is in series with the armature. That means every field must take full traction motor current, and thus, so must the reverser. It must have a circuit for each motor, i.e. four, and at least four contact blades per circuit.

This makes for a very big switch, and it's built as a multi-pole drum switch. Because of its size, it takes a lot of force to throw. The muscle actually comes from air. Electrical signals operate a "magnet valve" which applies air to a piston, which throws the drum switch over. There are two magnet valves, one for each direction. The electrical signal to each magnet valve goes through an interlock on the drum itself, which cuts power to the magnet valve (and thus air to the piston) once the drum reaches the desired position.

You may recall two articles (1) (2, photos) about the third rail changeover switch. This switches even more current, but only one circuit. They were usually reversers with their many contacts ganged together to increase current capacity.

The Westinghouse HL equipment also has switch groups, which is a footlocker-sized cabinet with 6-8 large contactors in it. 1005 in fact has two complete sets of switch groups; that's because the additional complexity of the 600/1500V changeover required more switches than one group contained. Al has been overhauling some of the switch groups. Here you see him working on some interlock fingers. These don't carry full traction current, but signaling current. Their job is to interlock other contactors which should never be closed at the same time, such as series/parallel transitions.

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