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Associate

Join Date: Sep 2013
Posts: 31

Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/16/2017 12:53 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 coils 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.

The more important point is the coils of power contactor 3TF57 are failing very much.Kindly suggest us how to eliminate the coils burning problem .The coil is 3TY7 573-0C .The power supply to coil is AC 220 Volts.

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

Best Regards
NVRSrinivas
GM (E & I)
Bhavya cements LTD
9491044143

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Pathfinder Tags: Coil burning of contactors
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Guru
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Join Date: Feb 2008
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#1

Re: burning of 3TF 57 siemens contactors coils 3TY7573-0C

10/16/2017 6:36 AM

Hello,

I would not follow the steps as you have suggested. Some of those transitions have more than one relay changing at the same time. I do not know what this would mean as far as motor field decays and so on. You might get VERY big sparks, or maybe not.

If this is possible, then I'd look for a series of transitions that only changed one circuit at a time.

Also note that while it may have been set-up to provide a high range of speed selection, it may also have been set up so that motor torque and currents were within expected range for each small step change. These larger transitions might cause longer term reliability issues.

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Guru

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#2

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/16/2017 8:39 AM

According to Siemens India document I just searched, 220-240VAC 50Hz coil for £TF57 is....

3TF57 02-0C-M7

Have you checked you have the right coil???

Compare energised current taken by all your contactor coils & check voltage at coils.

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Guru

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#4
In reply to #2

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/16/2017 6:17 PM

The VA for the coil I listed in post #2 is given as...

1136 closing, 16 closed @ 220V AC = 0.07 amp

1900 closing, 45 closed @ 240V AC = 0.19 amp

If you get much above these values, e.g. 0.19 amp at 240VAC, then the coil will overheat & fail.

The coil current will be excessive if the magnetic circuit air gap does not fall to expected value. Note closed current is 1/40 to 1/70 of closing current.

This could be due to dirt or rusted iron or contacts so worn or bent that mechanism cannot reach full travel. You do not know what neglect or meddling others have achieved before you.

Check the coil currents(closed) and, if high, confirm over-temperature by measuring coil resistance cold and hot.

How do failed coils look compared to a new one?

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Guru

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#8
In reply to #4

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/19/2017 10:51 AM

My guess is that cement dust has got inside the contactors, set due to damp and stopped the mechanism moving to close the the "air" gap to design values.

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Guru
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#3

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/16/2017 2:59 PM

If you are changing speeds that often, I would discard that Wound Rotor Control System and install a VFD ...

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Power-User

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#5

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/17/2017 10:48 PM

The inertia or Wk2 of the fan will be needed to calculate the acceleration time of the motor, which will then tell you whether the windings or resistors will be excessively overheated for a start cycle at a higher speed. Also the BHP curve of the fan at the starting conditions (air density, temperature, pressure) will tell you if you have enough reserve acceleration torque to get the fan up to speed in a suitable time.

You probably can start it at full speed, 90%, since it is a variable torque machine (centrifugal fan). Your wound rotor motor is the best design to apply for what is probably a high inertial load, because as you add resistance, the starting/breakdown torque is increased. If your resistance is too low, you may not have enough accelerating torque to spin the fan up. If the air is cold, and the fan must first run to pull warm air into the fan, you may get into trouble with not having enough motor capacity to spin the fan up to speed in one or two steps.

The multiple steps were intended to allow you to balance the process, but a secondary function could have been to allow the original installer to apply a less expensive motor, with less reserve acceleration torque. The smaller speed steps would allow you to distribute the acceleration heat over a longer time, for instance.

See this for further explanation of how your motor works:https://www.allaboutcircuits.com/textbook/alternating-current/chpt-13/wound-rotor-induction-motors/

If the motor is severely undersized, and considering you run at top speed most of the time, a different starting method might be easier to maintain, depending on your local technical skill level, like a hydraulic clutch/fluid coupling between the motor and the fan, and just start the motor across the line. Short out the resistors, the motor will then get up to speed in a reasonable time, and have full breakdown torque available to accelerate the fan. The fluid coupling then passes this torque to the fan shaft smoothly, accelerating the machine at a rate as determined by the coupling design.

https://www.ktr.com/us/products/power-transmission-technology/couplings/fluid-couplings/

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Active Contributor

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Posts: 20
#6

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/18/2017 9:07 AM

Your motor is being abused out of design control as rwilliams is explaining the most possible cause of issue. Install a VFD to make smooth start. In general, the motor are designed to operate at 100% and some percentage over (read manufacturer information).

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Power-User

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#7
In reply to #6

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/18/2017 1:46 PM

Not all (especially older) motor windings can handle the high voltages and distorted waveform that modern IBGT inverters (VFD) produce, there is considerable experience with stator end turn winding failure due to high voltages. Rockwell claims to have overcome this with at least one of their inverter control designs, Powerflex.

The cost of an inverter hardly seems justified, there are thousands of wound rotor motors still in service, and some proper maintenance on the resistors and associated equipment is all that appears necessary.

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Guru

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#9

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/21/2017 2:19 AM

In order to reduce the number of steps see also your post :

GRR for VRM CA Fan 07/15/2017 8:56 AM

If you reduced already the number of steps the connector coil could be energized for a longer time in order to reach the next step velocity and the coil may be overheated due to this new long duration.

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#10

Re: Burning of 3TF 57 Siemens Contactors Coils 3TY7573-0C

10/21/2017 6:55 AM

Sorry. It is not so clear what I said. In fact if the motor current will be elevated for a long time the control voltage will be low [due to high voltage drop] and the contactor will be not quite close and so the coil current will be elevated for a long time.

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