Abstract


Textile mill is the only industry segment where in the individual equipment motor, the prime mover is enclosed in a hood. Condition based monitoring with respect to time; and with respect to Machine to Machine points to the fact that ring frame motors dont maintain sustained efficiency over years. Hotter motors inside the mill are the symptom of mill inefficiency. Allow the motors to breathe out openly and the spinning mill will have sustained good health in the coming years.


Textile is the only industry segment where in the individual equipment motor, the prime mover is enclosed in a hood and in other industry segments the prime mover motor works comfortably in the open. In tropicalized region like India the motor works better at ambient unlike the western counterparts. In other industry segments, they keep the motor in ambient and allow the motor to vent out its internal losses which appear as heat. Mainly the long frame motor and pneumafill motor are hotter at half the loading level hence the efficiency reduces gradually by 3 to 5 % due to prolonged and sustained starved harsh ambient conditions.


Especially why we are concentrating in ring frame motor is because more than half the mill power consumption is accounted by ring frame only. The mills having KVAH, KWH meter recording in each ring frame and in the SSB level have understood the need for this frame to frame relative condition monitoring. In some cases the power consumption is differing by 10 % even in adjacent frames running at the same speed & production levels. For that matter, any power deviation above 5 % between the adjacent ring frames need to be the focus area in future. This focus point will be short cut to energy savings.


Motor-when it consumes more; then becomes a Consumable

  • Where Your Motor Efficiency Stands is that the efficiency of our motor is to be tested in the Hot Running ConditionsThis indicates the real efficiency practically at the part loaded condition after running for years.

  • Thanks to increasing Invertor drives in mill, the motors are hotter due to negative torque by the 5th harmonics and this harmonic generation must be curbed at the source of generation then and there. If this harmonics propagate to other machines like a contagious virus, then the losses are much more. So first Arrest the Harmonics at the frame or SSB itself. This has to be first step to KVA demand in each machine and later to correct at the power house to fully make use of the sanctioned demand.

  • FAN OUT THE MOTOR FINS - Cheap & Best way for Sustained Efficiency-

  • EE motor OEMs have given more fins now compared to old motors as this is the easy way to dissipate the heat & improve its working. The symptom of loss comes out as heat and is fanned out of fins by throwing away the heat all round the motor out. But what we find, when we open the motor hood in long frame, is the fluff coating on motors practically. It is like we putting a sweater and running under sunshine on a hot sunny day!

  • For your kind information, in one industry, one good running motor after routine service and painting was put back to service. In few days it failed due to over coating of paint that acted as thermal insulation on motor & retained its heat. Like wise if we focus on the fluff deposit, motors active ventilation and bearings lubrication then we can make our motors more healthy & efficient. To circum vent the problem the OEM is giving TEFC or TENV motor and here too this motor can perform better only when you have cross flow of fresh surrounding ambient air across the fins all around the motor frame.

  • Just because the motor insulation spec is Class H temperature limiting to class B levels etc. we cannot wait for the motor fins to be heated up to 80*C to take up routine maintenance and in some cases motor even boils! The higher the temperature, more the power losses as waste output. First we have to see the cause of overheating and try to reduce waste output and this will automatically enhance useful output to production.
  • The loss method of calculating boiler efficiency as an analogy, indicates any equipment with a skin temperature of 20*C above ambient, is losing more. So healthy running motor cannot have more than 20* C above ambient as fin temperature, the same measured by the Infra red gun or by thermal imaging. Higher than 60*C on skin does not mean motor must not be run. We have to infer that it is running unhealthy and loss is shown as heat symptom.

  • Hence to cool the long frame horizontally finned motors, now the fluff air washing the motor from the top & this does not serve the purpose at all and the motor fan running is waste. To duct out the fluff air from pneumafill fan and divert the same to the trench. Separately, fresh air can be provided from the side cover of hood opposite to fan cowl through Netlon filtered hood cover with chute provision inside so as to be sucked by ring frame motor fan, making it cooler & efficient.

  • This practice is being now adopted by the latest Autoconer OEM by providing mesh filter on hood cover so that the motor fan inside facing the filter sucks the ambient air from outside and blows all around its motor fins.


Motor breathes shallow or deep now?

  • TESTO Thermal Imaging of two types of Ring Frame motors in a textile mill Courtesy R.N.Agencies, Coimbatore.

  • The above images show that the heat retention is uneven on the motor skin, the top skin shows less heat and bottom skin part shows more heat. This is due to uneven air ventilation across the surrounding skin & this affects motor efficiency over years.

  • The thin hot air pushed out by the pneumafill motor along with micro dust and fluff after the filter has less cooling potential on the main motor. Moreover, the fluff gets deposited on the main motor fins etc. The normal skin temperature of any efficient running motor at optimum load is around 50 C i.e. that is 10 C above the ambient. But the motor skin temperature normally is around 60 C plus and this does not reduce by the pneumafill air which is hot, stale, dry RH, mixed with static heat from the material. In fact the localized heat on the fins is forced to stay there always. The bottom portion of the motor is still hotter due to poor circulation of the above hot air. The motor is not allowed to radiate & dissipate the heat outside.

  • Thats why we find the inside temperature at the motor hood is around 5C more than the ambient practically in many cases. Hence we find the motor for the given power input, gives only lower output due to combined effect of hotter and thinner air.The primary working of pneumafill motor is to suck the fluff with air and push it into the trench. We wanted to achieve two solutions with one impeller but it will be all the more better approach to separate motor cooling & fluff air exhausting.

  • So, now many users & OEM are thinking of over-motoring the ring frame main motor as a viable alternative. Now days, The motor OEMs also offer their motor for testing at ring frames at an optimum loading of around 50% only.
  • Hence the motor is derated and details of de-rating of motor given by ABB in their table below.

  • Ambient Temp C

    30

    40

    45

    50

    55

    60

    70

    80

    Permitted output

    % of rate output

    107

    100

    96.5

    93

    90

    86.5

    79

    70

    Height above sea level, m

    1000

    1500

    2000

    2500

    3000

    3500

    4000


    Permitted output

    % of rate output

    100

    96

    92

    88

    84

    80

    76



    The proposed Modification at the vertical finned Ring frame motor


    • The pneumafill motor instead of running with impeller at one end, it is proposed to run the same motor with both side impellers. (Now it runs with one side impeller only) Let the existing impeller do the same work of sucking the fluff and air and push out thro the pneumafill trench separately with out passing thro the main motor.

    • The new impeller to be fitted on the Non drive end will suck the air from top / side of the panel and force the air thro the vertical circular fins from top and at bottom this helps to reduce the motor skin temperature. V type filters to be provided on the top or side of the machine panel to supply air to the pneumafill motor housing.

    • This addition of non drive end impeller does not need a separate prime mover motor. But this will consume in addition say few hundred watts and the same motor of size 5.5 KW can take up this load. Again this is offset by the reduction in power due to the chute diverter duct to be fixed on pneumafill air discharge to trench.

    • What we observe in many mills is that ring frame main motors are hot but pneumafill motors hotter. Many of the mills have changed this pneumafill motor to inverter duty type and putting the inverter in automatic closed loop suction pressure control. So active & fresh air ventilation becomes mandatory for the same so as to avoid burnout later.

    • Brief Pre Cooling & Post Cooling of main motor in between Doff cycle helps to expel the heat out of motor, but now it is retained in motor. Additionally to improve the overall system efficiency and performance, we can add a Time delay to Pick up and Drop out Timer one minute for the pneumafill motor contactor. This helps to keep the main motor fan out its heat prior to starting and post stopping cycle. We have to provide built-in comfort to 24 X 7 motors so as to avoid Accelerated Ageing and sustain its energy efficiency for many years.

    • This retrofit exercise can be done in few hours and the cost will be less than Rs.10 K and more important after the above exercise is that the both main and pneumafill motors efficiency can be sustained for many more years of usage.



    Industry to Focus on Energy Losses Now


        During the correct transfer of energy - In the running equipment; if the same is perfect & smooth accepting unavoidable losses, then the productive output is more and the wasted output is less. During the incorrect transfer of energy - In the running equipment is done with more avoidable losses, then productive output reduces, and waste output increases & dissipated in the form of heat, light, sound which is a sign of visible loss in equipment operating parameters and inferred thro our Energy Audit.


        Likewise the efficient motors to be tested yearly after commissioning in each ring frame to confirm the motor is able to maintain the sustained efficiency right from the commissioning month. Any new EE motor will definitely outperform the old existing motor during trial and commissioning month. What the mill has to see is that the same % over-performance since commissioning is maintained even after one year and it has to be repeated annually for the mill sustenance.

    • The mill manager can question that this was not the problem before and the ring frame performed well all along. Before we ran sub 15 K speeds and now we are gradually increasing above 20 K speeds. So to take the best out of the ring frame, the present trend is correct but equally we have to comfort the machine to achieve sustained efficiency at higher speeds. The same can be done only first by condition monitoring with respect to frame, with respect to time for given textile parameters.

    • Considering the flexibility of operation and automation needs, now the ring frame motors need to operated by invertors from now on. When we are taking care of the harmonics dumping to incoming side by the invertor, we have not taken care of the load side of invertor that is the motor, till date. The motor becomes hotter due to invertor spikes, non linear quasi sine wave, inability to dissipate the heat outside and lack of high temperature lubrication.So we have to take steps to arrest thro load choke retrofit, switch over to high temp greasing on motor bearings and implement active ventilation process.

    S. Ashok is a BEE certified Energy Auditor; please visit Energy Measure to Save for detailed energy savings in Utilities & in the textile industry.