CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Cable Damage Reason   Next in Forum: Induction Melting Furnaces
Close
Close
Close
7 comments
Associate

Join Date: Sep 2013
Posts: 30

GRR for VRM CA Fan

07/15/2017 8:56 AM

Dear sir,

We are having following motor for our Vertical Raw Mill CA Fan in our cement plant and we are using it with a GRR for speed control. The details of the motor and GRR steps with speed are given below. As we have enhanced production, we are running CA fan at 90% or 100% speed. Hence, we don’t need to have this many steps of speed while running the motor. Hence, we are thinking of reducing contactor operations in order to minimize contactors failure in GRR and to reduce maintenance cost. We like to operate the fan in steps 1,2,4,8,9,11,14,18,22 and 26.I have given the speed of the motor at that particular steps. Kindly give your opinion. I want to know what should be the minimum speed to start the motor.The minimum speed at present is 640 RPM.Can we make the minimum speed to 800 or 850 RPM with GRR. Will it have any impact on the motor?Kindly give guidance.

1. Motor details

KW-2000, Amps-223, RPM-993, Rotor Volts-1825, Rotor Amps-650, Make-CGL

STEPS

C1

C2

C3

C4

C5

C6

Speed

Raise in speed
1OFFOFFOFFOFFONOFF640
2ONOFFOFFOFFONOFF65515
3OFFONOFFOFFONOFF670
4ONONOFFOFFONOFF68530
5OFFOFFONOFFONOFF700
6ONOFFONOFFONOFF715
7OFFONONOFFONOFF730
8ONONONOFFONOFF74560
9OFFOFFOFFONONOFF76015
10ONOFFOFFONONOFF785
11OFFOFFOFFOFFOFFON81050
12ONOFFOFFOFFOFFON820
13OFFONOFFOFFOFFON830
14ONONOFFOFFOFFON84030
15OFFOFFONOFFOFFON850
16ONOFFONOFFOFFON860
17OFFONONOFFOFFON870
18ONONONOFFOFFON88040
19OFFOFFOFFONOFFON890
20ONOFFOFFONOFFON910
21OFFONOFFONOFFON920
22ONONOFFONOFFON93555
23OFFOFFONONOFFON950
24ONOFFONONOFFON965
25OFFONONONOFFON980
26ONONONONOFFON100065

We want to understand that the speed raise of 60 , 65 RPM per step is OK for the motor or not.

We want to explore the second option also as given in the drawing.

We want to minimize the no. of contactors in GRR and go for the above mentioned scheme. I want your guidance whether this scheme can be adopted or not. I have given the original scheme for your information and understanding.

Kindly guide me with a proper scheme to minimize maintenance cost.

Thanks,

NVRsrinivas

Register to Reply
Pathfinder Tags: GRR for VRM CA Fan
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 17968
Good Answers: 1037
#1

Re: GRR for VRM CA Fan

07/15/2017 11:10 AM

You can generally exceed max voltage for motor windings 136-150% for 60 seconds, depending on motor spec...check your spec, monitor amperage draw...consider SPRS system...contact manufacturer rep for recommendations....

https://www.kuttikasi.com/assets/pdf/EM-CG/3%20Phase%20Motor%20CG%20Catalogue.pdf

https://library.e.abb.com/public/a871dbcb1293adc948257d080018579f/EN_ACS800_IGBT_SPRS_Brochure_A.pdf

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru
United States - Member - New Member Engineering Fields - Power Engineering - New Member

Join Date: Sep 2006
Location: California, USA, where the Godless live next door to God.
Posts: 4360
Good Answers: 720
#2

Re: GRR for VRM CA Fan

07/15/2017 12:12 PM

Wound rotor control does not directly affect the speed of the motor, it affects the torque, and the torque affects the speed. Reducing the amount of steps will simply increase the torque on the motor shaft between steps, and may or may not damage the shaft and/or distort the fan as a result. There is no way to tell in advance whether or not this is OK to do.

But GENERALLY, that is a lot of steps in a wound rotor control system, so someone must have determined that this was necessary, because they paid a lot of extra money to get this scheme. So the real question is, why? If the purpose is to minimize torque stress between steps because of the issues mentioned above, then I would be reluctant to make changes, other that to probably increase the size of the contactors so that they don't fail as often. But if the purpose of all of those steps was because of a process control issue, for example air flow control, then I would remove that system, short out the rotor and install a VFD.

But given that you only go from 90-100%, you might consider just running at full speed and using damper control for the flow. In that case, leave one step of resistance in place and start it with a soft starter.

__________________
** All I every really wanted to be, was... A LUMBERJACK!.**
Register to Reply Score 1 for Good Answer
Power-User

Join Date: Jul 2016
Posts: 334
Good Answers: 17
#3
In reply to #2

Re: GRR for VRM CA Fan

07/17/2017 9:42 AM

Check the current required to accelerate the fan, using the Wk2 of the fan, that may be where you find the reason for the number of steps. Also, if there is overshoot or delay in the fan acceleration, does that affect the quality of the product?

http://www.aerovent.com/docs/fan-engineering-topics/application-guide-for-selecting-ac-motors-capable-of-overcoming-fan-inertia---fe-1800.pdf

If accelerating the fan quickly exceeds the ability of the process to maintain the gas temperature, then you may find you run in overload conditions, moving cool air which could, as JRaef notes, distort the fan blading. Or perhaps your vent fan can't keep up. plugging the classifier. Your instruments may not have the accuracy over a wide range, for instance using pressure to measure flow, to allow quick changes in air flow. Maybe there is no fine trim control for air volume, like a damper, so your most efficient operation depends upon having the correct speed for your production rate.

If those all check out, then perhaps someone was covering themselves to make sure the required speed for a wide range of products was available, and you can skip those unused intermediate speeds.

Only a few select readers in your multiple postings are going to understand the operation spectrum of a vertical mill classifier supply air fan. The original design specifications would be a great source to determine the intent for the design. Once your audience knows this, your question will be easier to answer.

Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26292
Good Answers: 689
#4

Re: GRR for VRM CA Fan

07/17/2017 11:43 AM

<...what should be the minimum speed to start the motor...> The minimum speed for starting any motor is zero.

What did the motor manufacturer say in response to the telephone calls that have been made on this topic? Did it recommend a change to variable speed/voltage drive technology?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
2
Anonymous Poster #1
#5

Re: GRR for VRM CA Fan

07/17/2017 12:08 PM

GRR

CA

Kindly define TLAs before using them.

Thanks,

Anonymous Poster #1

Register to Reply Good Answer (Score 2)
Associate

Join Date: Sep 2013
Posts: 30
#6
In reply to #5

Re: GRR for VRM CA Fan

07/19/2017 1:15 AM

GRR controller ----Grid rotor resistance controller

CA Fan ---- Circulating Air Fan

Register to Reply
Guru

Join Date: Oct 2012
Location: 100 miles North from the World Center
Posts: 740
Good Answers: 29
#7

Re: GRR for VRM CA Fan

07/20/2017 9:56 AM

I presume, the rotor is Y connected and at the beginning the exterior resistance is star connected and each step the resistance decreases [5%]up to step 10 after which it goes to delta , introducing at first all the resistances and reducing gradually up to short-circuit.In my opinion R1,R2,R3,R4 have to be 5%,15%,25%,and 55% -from the total inserted resistance .In 26 steps [from 100 % to 40% in Y connection and from 33% to 13.3% in delta] the torque remains about 1 p.u.]

You intend now to reduce to 3 steps only: star and delta that means from full resistance to about 1/3 and short-circuit[100%,33%,and 0].

I think a complete calculation has to be done.

The current and the torque limits when jumping from 100% to 33% will be in the limits, I suppose, but jumping directly from 33% to zero the current and the torque will be elevated –about 3 p.u.].

Attached it is an example [of another motor!]

__________________
Julius
Register to Reply
Register to Reply 7 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

7anoter4 (1); Anonymous Poster (1); JRaef (1); nvrsrinivas (1); PWSlack (1); rwilliams (1); SolarEagle (1)

Previous in Forum: Cable Damage Reason   Next in Forum: Induction Melting Furnaces

Advertisement