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Voltage fluctuations and motor tripping

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Voltage fluctuations and hence motor tripping is a serious problem particularly during rainy season. This presentation is just a small initiative to think and explore what can we do to reduce the problem.

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Voltage fluctuations and motor tripping

  1. 1. VOLTAGE FLUCTUATIONS & MOTOR TRIPPINGMOTOR TRIPPING By: D K Singhal deveshksinghal@gmail.com Digitally signed by D K Singhal Date: 2018.07.27 '12:32:13 +05'30
  2. 2. Voltage Fluctuations Voltage fluctuations create unnecessary and unwanted problems. Sudden change inunwanted problems. Sudden change in voltage for a moment and hence tripping of electrical appliances is a major cause for production loss in several industries. In addition, electrical motor and other items failure rate is increased due to fluctuations.failure rate is increased due to fluctuations. 2Voltage Fluctuation & Tripping, D K Singhal, July 2018
  3. 3. Source Usually, the source is upstream of the supply system.The power supply station cateringsystem.The power supply station catering several feeders may generate fluctuation when any one feeder is switched on or off; particularly if that switchgear is too old. Improper wiring, cabling, loose connections particularly in OLTC or bushing in servo mayparticularly in OLTC or bushing in servo may also create voltage fluctuations. Weak neutral can also result in voltage fluctuations. 3Voltage Fluctuation & Tripping, D K Singhal, July 2018
  4. 4. Critical Areas As obvious, the problem of voltage fluctuation is more if the supply is from afluctuation is more if the supply is from a substation having old switchgears, in an old unit, or with staggered growth of unit where new equipment are added with time, thus leaving possibility for some error and making the whole system sensitive.the whole system sensitive. Many of the grid supplied units observe voltage fluctuation several times a year. 4Voltage Fluctuation & Tripping, D K Singhal, July 2018
  5. 5. Seriousness of the Issue A fluctuation may create sudden change in process parameters, through momentarily. Inprocess parameters, through momentarily. In several instances, this may lead to quality problems. But, in case any of the equipments trips, this may cause a production loss, and becomesmay cause a production loss, and becomes more serious issue. Obviously, nobody wants a production loss. 5Voltage Fluctuation & Tripping, D K Singhal, July 2018
  6. 6. Objectives Anybody concerned with the problem would like to-like to- Identify the source of the problem Reduce the magnitude of fluctuations Try to survive with fluctuation without production and quality loss. 6Voltage Fluctuation & Tripping, D K Singhal, July 2018
  7. 7. Problem Unfortunately, many process-electrical engineers consider fluctuation beyond theirengineers consider fluctuation beyond their control, and just shrug off. Sufficient information is not available even on internet to quantify the magnitude and impact of fluctuations.impact of fluctuations. No low cost test equipment or device is available to monitor fluctuations. 7Voltage Fluctuation & Tripping, D K Singhal, July 2018
  8. 8. Initial Approach In a typical mill having more than 300 electrical motors, it was noted that duringelectrical motors, it was noted that during rainy season, voltage fluctuation was the major electrical problem. Well, with direct feeder through open supply lines (33kV) from a 132kV sub-station, with several trees near the line, fluctuationsseveral trees near the line, fluctuations cannot be avoided. The approach was to study and gather preliminary information about the same. 8Voltage Fluctuation & Tripping, D K Singhal, July 2018
  9. 9. The Cabling Generally, several systems are used for neutral-earth to supply power to variousneutral-earth to supply power to various equipments.An overview of the same is given on the next slides. Please note that all images have been taken with thanks from…with thanks from… http://miorzaini.blogspot.com/2014/06/types- of-earthing-system.html 9Voltage Fluctuation & Tripping, D K Singhal, July 2018
  10. 10. TN-C System 10Voltage Fluctuation & Tripping, D K Singhal, July 2018
  11. 11. TN-S System 11Voltage Fluctuation & Tripping, D K Singhal, July 2018
  12. 12. TN-C-S System 12Voltage Fluctuation & Tripping, D K Singhal, July 2018
  13. 13. TT System 13Voltage Fluctuation & Tripping, D K Singhal, July 2018
  14. 14. IT System 14Voltage Fluctuation & Tripping, D K Singhal, July 2018
  15. 15. Installation of VFDs With most of the systems, the diagrams show supply and the consumer as the main pointssupply and the consumer as the main points to connect the neutral. WithVFDs, some suppliers prefer that the neutral should NOT be connected toVFD, while some other demand so. In severalVFD panels, the neutral and earthIn severalVFD panels, the neutral and earth junctions are not clearly mentioned, and electrical engineers join these two, resulting in poor signal quality issues. 15Voltage Fluctuation & Tripping, D K Singhal, July 2018
  16. 16. Other Loads Furthermore, single phase loads also play their role in the whole system.their role in the whole system. To achieve higher PF, many mills have installed capacitor directly connected to feeder cables, instead of installing these near motors.motors. Thus, the overall system becomes too complicated. 16Voltage Fluctuation & Tripping, D K Singhal, July 2018
  17. 17. So, What should be done? The approach includes the following points- 1. Identify if there is a weak neutral 2.Try to quantify the magnitude of fluctuation 3. Identify the possible solutions to minimize tripping 4. Discuss with experts4. Discuss with experts 17Voltage Fluctuation & Tripping, D K Singhal, July 2018
  18. 18. Weak Neutral Weak neutral reduces the possibility of current impulse to go to supply neutral andcurrent impulse to go to supply neutral and hence the tripping of motor may be high. However, a weak neutral is generally difficult to identify in most cases. The proposed system indicates how the weakThe proposed system indicates how the weak neutral can be identified. 18Voltage Fluctuation & Tripping, D K Singhal, July 2018
  19. 19. Supervisory Neutral Bus As the name implies, this is an insulated cable, connected to transformer neutral atcable, connected to transformer neutral at one end, and having separate branches, each connected to the neutral of every motor through an MCB of say 1-2 Amps. The cable size should not be too heavy toThe cable size should not be too heavy to suppress the main earth. For connecting individual motors (branches), just a single core cable size of 0.75 or 1.0mm2 is sufficient. 19Voltage Fluctuation & Tripping, D K Singhal, July 2018
  20. 20. Supervisory Natural Bus So, what’s next. Ideally, the neutral being in place and working well, all of the MCBs shallplace and working well, all of the MCBs shall be ON as the current passing through these would always be less than 1 ampere or so. But, in case there is any problem of voltage fluctuation, or sudden problem with motor, and that particular neutral is not able to do itsand that particular neutral is not able to do its duty, the current will pass through this network, and in case this fault current is more than MCB rating, the MCB will trip. 20Voltage Fluctuation & Tripping, D K Singhal, July 2018
  21. 21. Supervisory Neutral Bus On tripping of the MCB, you know that there had been some problem with that particularhad been some problem with that particular motor, and the conventional neutral might be weak or broken! You can, then, take corrective actions as required.required. 21Voltage Fluctuation & Tripping, D K Singhal, July 2018
  22. 22. Supervisory Natural Bus In case you are not willing to install MCB, as an alternate you may consider using LEDan alternate you may consider using LED indicators of suitable rating.A glowing indicator indicates that the current is passing through that circuit, and neutral cabling is needed to be evaluated properly. 22Voltage Fluctuation & Tripping, D K Singhal, July 2018
  23. 23. Magnitude of Fluctuation Whenever we face a voltage fluctuation, we may be interested in knowing the magnitudemay be interested in knowing the magnitude of the same. A fluctuation may be quantified by the amplitude of the change in voltage and as time duration of persistence of fluctuation.time duration of persistence of fluctuation. For most practical cases, time is practically small, so change in voltage is of main concern over here. 23Voltage Fluctuation & Tripping, D K Singhal, July 2018
  24. 24. Magnitude Measurement The proposed scheme of measurement of voltage fluctuation measurement involvesvoltage fluctuation measurement involves having a set of three purely resistive loads, connected in star to each of three phases. The star junction voltage is measured with reference to transformer (or supply) ground.reference to transformer (or supply) ground. Theoretically, under normal operating condition, it should be zero. 24Voltage Fluctuation & Tripping, D K Singhal, July 2018
  25. 25. Magnitude Measurement Voltage Fluctuation & Tripping, D K Singhal, July 2018 25 Image Courtesy: https://electronics.stackexchange.com/questions/286419/controlling-three-phase-heating-element
  26. 26. Magnitude Measurement If all three resistances R1, R2 & R3 are equal, measurement of voltage at point N with 1 2 3 measurement of voltage at point N with reference to PE, should be near zero in an ideal case. Voltage Fluctuation & Tripping, D K Singhal, July 2018 26
  27. 27. Magnitude Measurement However, in practical cases where, there exists a little imbalance amongst threeexists a little imbalance amongst three phases, this may be of some small value. It is now possible to install a voltage sensing relay connected with a counter to display number of counts when the fluctuationnumber of counts when the fluctuation exceeded a predefined value. 27Voltage Fluctuation & Tripping, D K Singhal, July 2018
  28. 28. Magnitude Measurement In many cases, shop floor people know about a voltage fluctuation whenever the glow ofa voltage fluctuation whenever the glow of conventional incandescent bulb alters for a fraction of second. By the proposed arrangement, having different units at supply side as well as in thedifferent units at supply side as well as in the plant, one can know if the fluctuation was from the supply side or it was just appeared due to floating neutral. 28Voltage Fluctuation & Tripping, D K Singhal, July 2018
  29. 29. Correcting the Problem In case the fluctuation appears from the supply side, practically little can be done.supply side, practically little can be done. However, if the fluctuation is being caused by the floating neutral, one need to look into the issue within the installation. 29Voltage Fluctuation & Tripping, D K Singhal, July 2018
  30. 30. Floating Neutral Checking voltage difference between neutral and ground points at different 3-pin socketsand ground points at different 3-pin sockets can easily give a very good indication of floating neutral. A voltage difference beyond 5V suggests that the neutral is floating and a thoroughthe neutral is floating and a thorough inspection of the wiring/cabling must be done at priority. 30Voltage Fluctuation & Tripping, D K Singhal, July 2018
  31. 31. Stabilizer Imbalance Almost all mills install servo voltage stabilizers to save costly electrical machinesstabilizers to save costly electrical machines from over and under voltages. In some cases, when each phase is separately governed, there might be occasional issues when an imbalance appears momentarily,when an imbalance appears momentarily, resulting in tripping of machines. 31Voltage Fluctuation & Tripping, D K Singhal, July 2018
  32. 32. Stabilizer Monitoring As indicated earlier, star junction voltage measurement immediately after each servomeasurement immediately after each servo voltage stabilizer may be a good approach. In case you observe that there were no fluctuation from supply side, but fluctuation is recorded after servo, that means there isis recorded after servo, that means there is some issue with servo. 32Voltage Fluctuation & Tripping, D K Singhal, July 2018
  33. 33. Tripping Management Electrical machines are not only costly, but their failure can also cause heavy productiontheir failure can also cause heavy production and other losses. That is why protective switchgear are must to protect these by tripping in case of any problem.problem. However, in some cases, when tripping system gets activated at not so significant issues, one may need to look into the same. 33Voltage Fluctuation & Tripping, D K Singhal, July 2018
  34. 34. Tripping Management In some cases, where just a few motors were getting tripped during voltage fluctuations,getting tripped during voltage fluctuations, the following approaches were tried and found useful. 34Voltage Fluctuation & Tripping, D K Singhal, July 2018
  35. 35. Control Supply Change In a particular case, the control supply was being given from Red phase.The motor wasbeing given from Red phase.The motor was 110kW, operating with 3∅ 415V supply. After changing control supply from Red to Yellow, the problem got reduced by more than 90%.than 90%. Probably the fluctuation was appearing in Red phase (voltage reduction), and hence contactors were getting released. 35Voltage Fluctuation & Tripping, D K Singhal, July 2018
  36. 36. Replacement of Contactor Frequent tripping in one case, without any noticeable fluctuation was creating problem.noticeable fluctuation was creating problem. Just to clear doubts, the contactor of this motor was replaced with a new one. The problem was solved completely; maybe the contactor coil was weak. Maybe this contactor was not genuine.contactor was not genuine. After the same, that mill made a policy to procure electrical switchgears from authorized dealers only. Voltage Fluctuation & Tripping, D K Singhal, July 2018 36
  37. 37. Neutral Restoration In some cases, the motors were tripping, and on thorough inspection, it was observed that thethorough inspection, it was observed that the cabling was replaced due to some problem long back.While replacing the cables, the neutral was kept loose at one end (electrician negligence). When everything is OK, the neutral does no significant useful work, so it remained unnoticedsignificant useful work, so it remained unnoticed for long. Later, while the same was connected again, the problem reduced significantly. 37Voltage Fluctuation & Tripping, D K Singhal, July 2018
  38. 38. A Request The author is NOT an electrical engineer, but has tried to understand and reduce problemshas tried to understand and reduce problems after discussing several electrical engineer friends, suppliers, referring to internet etc. I humbly request you to please correct me wherever needed, either by updating thiswherever needed, either by updating this presentation, or by sharing some useful information. Voltage Fluctuation & Tripping, D K Singhal, July 2018 38
  39. 39. ThankYouThankYou D K Singhal deveshksinghal@gmail.com Voltage Fluctuation & Tripping, D K Singhal, July 2018 39

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