Brushed DC motor noise

Thread Starter

AidanCroft

Joined Jan 7, 2015
24
Hello all,

At work we have large 277kW brushed DC motors for traction purpose (four per vehicle).

Under powering and braking (regenerative braking is used) the tone of the motor ascends and descends respectively but is largely silent during coasting. I assumed that the noise came from brush/commutator interaction but I would still expect mechanical interaction, at least, during coasting.

Can anyone suggest where the noise is coming from?

Kind regards,

Aidan.

Motor brushes (1).JPG Motor gear interface (1).JPG
 

MaxHeadRoom

Joined Jul 18, 2013
20,925
I suspect that they are driven from an AC supply that has a full wave SCR controller, this would account for the switching noise that is common, even in small T.M. motors that use this type of drive.
Max.
 

Thread Starter

AidanCroft

Joined Jan 7, 2015
24
The GTOs chop on and off at a fixed frequency (250Hz) but altering the width of the pulse. This is smoothed by various devices such as capacitors etc.

From a standing start the motor makes a very deep rumbling noise that of course increases in tone. At any speed, the noise stops during coasting.

Thanks,

Aidan.
 

Thread Starter

AidanCroft

Joined Jan 7, 2015
24
That would make sense as the Thyristor switching only takes place during accel and braking.
Max.
Would this be the case even though the GTO chopping frequency stays the same for the whole Voltage range? Only the width of the pulse itself changes.

Since my last post, I was also wondering if it might be due to arcing on each commutator bar and/or magnetisation of individual portions of the rotor coils?

Aidan.
 

RRITESH KAKKAR

Joined Jun 29, 2010
2,829
The overhead is 750V DC using GTO thyristors to supply DC to the motor via brushes.
I suspect that they are driven from an AC supply that has a full wave SCR controller
Hello,
Motor is DC Brushed then from where AC being used?
 

BillB3857

Joined Feb 28, 2009
2,533
DC supply goes to GTO chopping circuit to create PWM to drive motor. Noise can be the result of pulsating torque. During ACCEL and DECELL, current limit may be causing the PWM percentage to change at a non-linear rate and creating a beat frequency with the 250Hz chop rate.
 

Thread Starter

AidanCroft

Joined Jan 7, 2015
24
Hello,
Motor is DC Brushed then from where AC being used?
AC is not present anywhere. This is purely a DC arrangement.

DC supply goes to GTO chopping circuit to create PWM to drive motor. Noise can be the result of pulsating torque. During ACCEL and DECELL, current limit may be causing the PWM percentage to change at a non-linear rate and creating a beat frequency with the 250Hz chop rate.
That makes sense. What is causing the pitch to rise during acceleration? It really does start with quite a low rumble and it gets progressively higher. As soon as power is taken off the noises cuts out and when power is applied again the tone starts again at the pitch that it last left off from.

Aidan.
 

GopherT

Joined Nov 23, 2012
8,012
AC is not present anywhere. This is purely a DC arrangement.



That makes sense. What is causing the pitch to rise during acceleration? It really does start with quite a low rumble and it gets progressively higher. As soon as power is taken off the noises cuts out and when power is applied again the tone starts again at the pitch that it last left off from.

Aidan.

Google magnetostriction

It is the same electromechanical effect that makes a transformer Hum. The higher the current, the more noise. You say pure DC but most likely Pulse Width Modulated to avoid abrupt starts/stops and passengers flying ass over tea kettle. PwM can be argued as an AC signal. All in the semantics.
 

BillB3857

Joined Feb 28, 2009
2,533
Here is a current plot for Acceleration, up to speed, and Deceleration based upon a 3 phase full bridge SCR drive. The main difference between the SCR drive and the OPs drive is the GTO drive will provide the effect of commutation that the 3 phase AC accomplishes in the SCR drive
 

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