Is it possible to measure the current in each brush with a DC/AC mapere clamp? there is a possibility that not all brushes are needed to deliver the current under these loading conditions. This is a common problem on underloaded Ac and DC rotors.
If brushes are deligned e.g. for 10Amps / cm2 but...
i would like to mention the soft starting possibility through the generator itself.THis is an option, only when the generator is dedicated to one motor only.
So this is not our case, unless you acquire another generator only for starting the motor (or also a transfer breaker system to transfer...
maybe this will help our condsiderations
A slip ring motor was employed, 950kw, 1500rpm, with an oil cooled starter, is operating excellent for more than 3 weeks now, with a very smooth starting 30 secs(acc to the owner). As i see it, seems to me like a starting with " not closed" damper...
We are not the manufacturer, we are not the owners, nor the system designers. The manufacturers of the motor and the fan are well known. We only participate to the point we can advice regarding the nature of the failures.I strongly believe that we have the case of a large motor in respect to the...
We are not the manufacturer, we are not the owners, nor the system designers. The manufacturers of the motor and the fan are well known. We only participate to the point we can advice regarding the nature of the failures.I strongly believe that we have the case of a large motor in respect to the...
Dear Lionel
i disagree. The cange of inertia changes a little the schenery. (it is just a multiplier). On contrary, the load curve that is 80 and not 40% at nominal speed, is the dominant parameter, since the startind time is proportional to the sum(d(speed)/d(Net torque)).
steady state dumpe...
Dear Lionel
motor and fan manufacturers claim 25secs starting with closed damper.
I measured : 84amps with "closed damper" at 1500rpm (50hz)and 46secs starting time.
What i say is that what they call "closed damper" is not "no load" condition.
The motor is 22Amps at no load (uncoupled)...
Dear Petronila
if you check in the early potings, you will find the results of your formulas. For me there is only one question. We are all engineers in plants or engineering firms. Do we or do not rely on manufacturer's data? what else do we have? If i was not lucky enough to take the starting...
another maybe useful note is that acc to my calculations, the impact of a larger fan inertia (if we doubt the manufacturer data) is mch less of that of an inadequate damper.
Dear rmw
i am electrical engineer and definatelly not been in the air circuit. I will though, because, as you do, from my calculations, the only option is that the so called "closed damper" is not closed. A fan is drawing 750kw when delivers work and not when rolling.
And yes, i forgot to mention, that up to know they have opened the 1st failed motor, copper squirel cage and lifted bars..... For me 46 secs means that 150 deg Celcius are reached in stator and maybe 300 in rotor. The other 2 failed motors have aluminium rotor and i suspect aluminium decoration...
Dear All
when the customer says "damper is closed", means they even let people work on the bag filter. Therefore: damper is closed. The network is ungrounded. 3 motor failures, only one developed 3phase to ground. the other 2 were 1 phase interrupted from the other 2. My question is: In the...
exactly edison123! that is m point. 84 Amps is 750kw. the almost open damper is 110 amps (1050kw). the manufacturer claims 0,3Rated torque with closed damper. This is much more! Therefore, is it correct design for Direct on Line Starting the fan? I would certainly prefer the poor old slip ring...
Thanks for the answers.
Motor speed =fan speed. Motor inertia=33kgm2, fan inertia=413kgm2. 84 amps is steady state with still closed damper , following starting transient. Staring current is 700Ampa SCIM(6,5X In).
It was the 3rd failure in 900kw 6kV 4 pole induction motor, turning a fan in a steel plant. Originaly the closed damper starting dictates that the load starting characteristic is all below the 0.3 of nominal torque at nominal speed. Neverthless, the measured current at closed damper condition...
Dear All
quite often we see installations of VFDs without the line harmonics filters (i do not mean the line chokes), concequently meading to failures to nearby capacitor banks installations.
What would be the recommended retrofit as regarding the input "cleaning"?
