Elevator motor control – Generator versus motor drive

I was doing a walk through on four elevators that we needed a number of things for and I was looking at a older Virginia Controls elevator with a MG set.  This controller had one cabinet for the controller portion and one for the generator and motor control.  The other passenger elevator in the building had been modernized and had a motor drive.  It was a night and day example of how technology removed so many failure points from the elevator system on traction cars.  At one point in the elevator universe this was cutting edge technology, but technology moves on. 

Existing machine – This was a machine most likely replaced in the late 1980’s early 1990’s.  Good bones, if it where to be replaced again it would be replaced with a machine just like it. 

Existing controller – Holy smokes this has a lot of relays in it.  How many guys carry a relay tester in their car?  More relays more potential problems.

Existing Generator – This is an item that kept elevator guys busy changing brushes to keep the generator going.  There is an art and a process to replacing brushes.  If a generator is not maintained it will be a very expensive proposition to repair or replace it.  Oh yeah there is also generator dust.  The 2^nd picture is the data tags from the generator, there is an incoming AC side and an outgoing DC side.  It took me a few years to wrap my head around this when I first started in the business.

Existing motor control panel – This is a panel with resistors, relays and phase protection.  If you look you can see there still is a mercury phase monitor on this controller.  Be careful how you dispose of this, mercury does not go away and is dangerous.

New style motor control – This box which is approximately 24” x 18” replaces the giant motor control panel and generator.  There are maintenance items to perform on this device but not nearly as much as the generator.  This is a great device, it makes life a lot easier for elevator technicians.

Why did this elevator have a generator? – Back before the motor drive was invented they used DC power to allow the elevator to have better leveling accuracy.  AC power plugs into the generator and DC power is sent to the motor.  It got rid of the floor accuracy problems of single speed AC motors and two speed AC motors. Tesla Vs. Edison. Tesla won but…. Edison’s DC power was cleaner, efficient and easier to control.  But you needed generators nearby.  Tesla’s AC could but run with wires over long distances without generators nearby.  AC power also fluctuates over time, in America 60 times a second. 

Take away – For most applications you can get rid of the elevator generator and you will get rid of a lot of your headaches, or potential headaches.

As always feel free to contact us at www.colleyelevator.com, email Craigz@colleyelevator.com or call 630-766-7230.