SCR Noise - : LUSENET : Elevator Problem Discussion : One Thread

I was recently in a very tall building, and many floors down from the machine room, I could hear the distinct noise of an SCR drive. As the elevators were the only SCR driven devices in the building I assume that the noise comes from one or more of the drives. I assumed the noise was transmitted as either vibration or was airborne. The building engineer swears the noise comes from the three phase power lines running up to the machine room. Is this possible? Which is most likely? gelectrical teith

-- A McGregorI (, September 07, 1997


I have had a job where there was building noise from three phase power lines going up drawing too much current on an across the line start. We rewired for a wye-delta start and the noise went away. I bet on this job you have no chokes or isolation transformers or they are undersized for the job.

-- Rudy Boyance (, September 11, 1997.

SCR Noise

The unfiltered output from scr drives is very closely controlled without overlap otherwise you would have short circuits. The noise is loudest when the elevator is changing velocities or leveling. The noise is the motor armature " Drumming ". The current practice is to use chokes in series with the motor for a filter. On a large Gearless machine could be 70-100 henrys and weigh from 400 to 600 lbs. These are not sized right on a lot of jobs if they are, the most you will hear in the machine room is a slight hum and nothing in the rest of the building. These drives were first used in an industrial environment and chokes were to keep the motor from beating itself to death. Noise was not a concern because the noise level was fairly high anyway.

-- Fred Baltes (, September 14, 1997.


If chokes are present they generally eliminate any large drive current noise {but don't be suprised to find a choke bypassed, all leads on one terminal ????}. I worked for a major elevator company that was installing state of the art equipment for conversions in the late 80's and early 90's and they could not elliminate the noise from the drive to the cab on a certain type hoist motor.The type motor was manufactured by Haughton Elevator and their motor field pole pieces were set at angles instead of square to the armature.I guess this created physisics problems compared to conventional motors??? The electrical noise would travel down the cables to the cab like a tin can at the end of a wire.This problem occured in many, or all, of the Haughton motor conversions and double series chokes were installed but did not elliminate the noise.It may have lowered the audible noise level, but not enough...These jobs were all part of a 'city' buildings conversion and may have not been complained about since these were all city employees in these buildings and not tennants and they were just very happy to have new elevators.I don't know since I work for a different elevator company now, but now I am very curious to know if I went into one of these jobs now would the drive noise still be present????

-- Joe McLoone (JMclo30547), September 24, 1997.

Is anyone still interested in this topic?

-- Don Vollrath (, April 27, 2000.

SCR drives draw harmonic currents from utility lines. These currents will flow in both primary and secondary wires of the drive isolation transformer. Long feeder lines laid in a tray, or pulled through steel conduit, or run through steel buss-duct, or 3-phase buss-bars open or enclosed in metal duct, allows magnetic attraction and magneto-striction effects to cause the enclosures to vibrate at one or more of these frequencies, producing acoustic noise. The vibration noise may occur only when high currents are drawn during elevator accel/decel. Loose screw/nut/bolt/washer hardware and poorly fitted sheet metal panels are usually the parts that actually vibrate.

Cures: Tighten loose hardware. Provide dampening for vibrating panels. Provide a harmonic trap filter close to the SCR motor drive.

-- Don Vollrath (, April 28, 2000.

Some DC drive units use non-polarized capacitors in the armature circuit as well as choke coils. Due to the possibility of shorted caps and the damage that these would do, fuses and resistors are usually installed in series with the caps. If the filter cap fuse blows, you will notice an increase of harmonic noise. Addition of this R-C circuit when it is missing can sometimes reduce noise.

-- Tom Saugey (, July 23, 2003.

Tom is right. An armature current ripple filter is typically used to reduce acoustic noise generation from the DC motor. This noise would be airborn and at 300/360 Hz for 50/60 Hz operation. Fuses are used internal to the filter to isolate a faulty capacitor. If the fuse is blown or pulled, there will be more acoustic noise from the motor.

Of course it is certainly possible that the noise comes from a poorly built (or aging) choke or transformer, or enslosure panels, or feeder wire ducts. You have to determine for yourself where the noise is coming from.

For more information on ripple filters see Magnetek DSD412 DC Drive application notes at DonV

-- Don Vollrath (, July 25, 2003.

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