Increasing DC Motor RPM

Reduce the amount of material in the kiln.

Put some grease or lubricants....My kiln is pefect after that, faced a same problem.

I would check the motor voltages and line currents right at the motor to see if they are correct. A low armature voltage will cause the motor to run slow and a high field voltage can do the same.

Next I would inspect the motor itself to see if any brushes are burned out or stuck. After that I would check the speed controlling system over to see if its damages, worn out or simply miss adjusted.

Thanks for the nice reply. We are checking on the points. However, request you to please sent what checks we can make in the drive panel.

If the motor kw is sufficient, are there any sprocket or pulley ratios in the drive system that can be changed easily?

"tcmtec" gave very good points regarding this problem.

Check the armature voltage as it is much responsible for speed.

0.7 to 0.9 is not a small variation. Check the mechanical side i-e Gear unit. Check the variation in current.

(It seems that 75 KW motor is for Barring device but for barring pupose 1.2 RPM are very high. Normally in modern Plant it is done at 0.2 RPM).

What is the nominal speed of the Kiln (At rated Feed)?

Send us your kiln design and let us see perhaps we can see what is the problem.

It may seem a basic point, but no one has written "Multiply the (normal kiln operation) motor ampere reading at the starter panel by the supply voltage reading at the starter panel. If it much exceeds 75000 x 1.1 = 82500 watts we may be talking motor overload here (particularly if the rated rpm is 1.35 at the kiln and you only get 0.9). You may have to tell the production department that overloading the kiln to increase production, leading to motor failure, ends up with zero production - until the motor is repaired. If the power is well below 75000 watts, the shunt field may be getting full volts which gives minimum motor speed, lowest mechanical load on the motor and so reduced electrical input.

Measuring voltage at the motor itself , comparing with supply voltage, will indicate if resistors in the panel are limiting its current.

Problem Does't seems to look on the motor side

Actually there will be coating inside the Kiln which makes the speed variation. In drives using DTC(Induction motors) this problem can easily noticed by noticing the torque variation for one revolution on the display of the drive.

As there is coating in the kiln, more power is required to move the kiln as one weight of material (Feed )and second weight (coating in the Kiln)