Motor and gearbox matter

Discussion in 'The Projects Forum' started by EzerElectrical, Sep 30, 2011.

  1. EzerElectrical

    Thread Starter New Member

    Sep 30, 2011
    7
    0
    Dear all,

    Please advise me...
    Motor 250kW connect to gearbox 150kW (ratio 8.412, rpm 1480) to roll Roller-1, and Roller-1 to Roller-2 is connected by gearbox 250 kW. When this crushing machine is start with no load is no problem. But the problem is: when the machine runs with load and interrupted-with materials on Rollers-the machines can reset to run. What is wrong? For information, motor connection is delta, cable 4x1cx400mm2.
    Thank you.

    EzerElectrical
     
  2. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    just to create a picture of this:

    about a 340 hp motor?
    Is it running at 208 volts or 480?
    208 volts is 1201 amps and 480 volts will be about 520 amps.

    Have you measured the phase voltage and line voltage on each of the lines?
     
  3. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    high torque drives often start with a wye / delta, and possibly a fluid clutch? Does the equipment employ feed control via drive current sensing?
     
  4. EzerElectrical

    Thread Starter New Member

    Sep 30, 2011
    7
    0
    Please advise me...
    Motor 250kW connect to gearbox 150kW (ratio 8.412, rpm 1480) to roll Roller-1, and Roller-1 to Roller-2 is connected by gearbox 250 kW. When this crushing machine is start with no load, it's no problem. But the problem is: when the machine runs with load and then interrupted (with materials on Rollers), the machine CAN NOT reset to run. What is wrong? For information, motor connection is delta, cable 4xNYY1cx400mm2.
    Thank you.

    Machine uses 380V. I think V-line is equal to V-phase = 380 V. Please advise..
     
  5. EzerElectrical

    Thread Starter New Member

    Sep 30, 2011
    7
    0
    The machine is crushing machine in coal mining. It uses delta connection and does not use any drive current sensing.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It sounds like you do not have a clutch between the motor and the gearbox.

    The motor does not produce as much power when it is at 0 RPM as it does when it is near full speed, but it will draw maximum current when the rotor is locked.

    You will either need a clutch/fluid coupling, or a gearbox with a greater mechanical advantage to enable starting the machine under load. Changing the gearbox will be expensive and will result in a decrease in output during normal operation.
     
  7. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    you might want to expand on this as the phrase is not communicating much, and we are left guessing at what your actually saying.

    With an across the line starter and the equipment loaded, you may be simply tripping the overloads and a cool down period is required before you can reset. If you are underdesigned in regards to a starting strategy, the danger is repeated resets which increase the chance of heat damage to the circuit and it's components. Typically, you would start the equipment unloaded, then apply load within the prime movers ratings. Trying to start under full load will put large strains on the drive train.

    Describe your equipment;
    - is it across the line start / soft start / ?
    - is it a new implementation, or a breakdown of a once working configuration.
    - is the interruption due to motor trip, or controlled shutdown?
    - has an analysis of torque requirements been performed for a loaded start?
    - are multiple motors starting at the same time from the same source.

    Lot's of more questions, but one needs some basics where to start.

    I haven't worked on coal crushers, but other mills/chippers, where typically the reducing (mill) motor is current sensed, which resolves to the feed section command. As the mill load increases, feed reduces.
     
    Last edited: Oct 1, 2011
  8. VoodooMojo

    Active Member

    Nov 28, 2009
    503
    53
    yes, the locked rotor amperage can be many times the full loaded amperage rating of the motor.

    It is very important to safely read the voltages as close to this loaded motor as possible to verify the applied voltages at all lines are even and the unbalance does not exceed 5% of the line voltage.
    With a 380 volt motor that would be a 19 volt variance line to line.

    Any voltage unbalance will result in a significant decrease in motor output capacity.

    If the voltages are within the 5% tolerance, check to see if there is a current imbalance of over 10%. if so, a shorted winding is present.

    check to see what the current is while motor is not loaded.

    @1480 rpm expect to see approximately 40% to 50% of the Full Load Amps
    If the not loaded currents are balanced within their limits then the motor is more than likely being overloaded.
    Too much coal/shale loaded or too high of moisture content.

    If the not loaded currents are higher than the 40 or 50% then it probably has
    shorted windings and will need repairing.


    I am under the assumption that this was a functioning unit and now will not perform as it once did.


    edit:
    not to overlook the obvious, inspect to verify the driven components are mechanically sound and not adding to the load on the motor.
     
    Last edited: Oct 1, 2011
  9. EzerElectrical

    Thread Starter New Member

    Sep 30, 2011
    7
    0
    But the problem is: when the machine runs with load and then interrupted, the machine CAN NOT run again. The motor sounds to prove it tries to run, but the Rollers doesn't roll. FYI: when the machine interrupted, there are some coals--to be crushed--above Rollers. Roller 1 rolls counterclockwise, Roller 2 rolls clockwise. Roller 1 and Roller 2 connected by gearbox 250 kW. Roller 1 connected to motor 250kW by gearbox 150kW.

    - Right, the motor does not produce as much power when it is at 0 RPM.
    - Clutch is no need since motor connects to gearbox.
    - Cooling down isn't useful.
    - When we try to moved coals above Rollers, the machine can run again. But, should we do this thing for every interrupted incident?
    - Now we still install delta connection--as manufacturer's nameplate. There is a suggestion to install soft starter, but the question is: Can soft starter resolve the problem? If can, could you give me the calculation or information to prove it?
    - We just give information to vendor, and vendor designs and supplies this crusher.
    - Because this crusher machine connected to the system, so that interruption can be from any faults or crusher itself fault. If faults recovered, crusher should be automatically run again.
    - OK, we will ask vendor to submit Analysis of torque requirements.
    - The system consists of many big conveyors (of course many big motors, such as 90 kW, 110 kW). The system supplied from MCC Panel. The crusher uses MCCB 3-phase 800A.
    - OK, I will inspect the voltage and current.
     
  10. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Softstart is a voltage reduction technique, often used with high inertial loads, which I doubt you have.

    with your crusher running at load, measure your currents and compare to nameplate. Who specified the motor rating? Ask them if it can be started under full load.
     
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