Acoustics & Generator Ratings

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A presentation to discuss Acoustics and Generator Power Ratings.

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Acoustics & Generator Ratings

  1. 1. GENERATING SET SELECTION & RATINGS Jonny Rodgers CEng MIMechE MIDGTE Senior Sales Support Engineer FG Wilson Power Solutions
  2. 2. Overview <ul><li>In recent years the loads required to be handled by generating sets have become much more complex. </li></ul><ul><li>Consequently more care has to be exercised in selecting the generating set to ensure satisfactory performance. </li></ul>
  3. 3. Basic Steps for Genset Selection <ul><li>Define the duty and site parameters. </li></ul><ul><li>Analyse the load transient and running requirement profiles. </li></ul><ul><li>Match the Generating set performance to the load requirements. </li></ul>
  4. 4. Definition of Site Parameters <ul><li>System Voltage </li></ul><ul><li>The genset output voltage, phase and frequency must match that of the equipment to which it is to be connected </li></ul><ul><li>Site Conditions </li></ul><ul><li>High ambient temperatures and/or high altitudes both effect genset output and transient performance. </li></ul>
  5. 5. Generating Set Duty <ul><li>Continuous Power- Base load applications </li></ul><ul><li>Prime Power – The generating set is the sole electrical power source. </li></ul><ul><li>Standby – The generating set is the Emergency power source. </li></ul>
  6. 6. Continuous Power (COP) <ul><ul><li>Average Power Output = 70% of continuous power rating </li></ul></ul><ul><ul><li>Load = Non-Varying </li></ul></ul><ul><ul><li>Typical Hours/Year = Unlimited </li></ul></ul><ul><ul><li>Typical Peak Demand = 100% of continuous rated kW for 100% of operating hours </li></ul></ul><ul><ul><li>Typical Application = Baseload, Utility, or Co-Generation </li></ul></ul>
  7. 7. Prime Power (PRP) <ul><ul><li>Average Power Output = 70% of prime power rating over 24hr period </li></ul></ul><ul><ul><li>Load = Varying </li></ul></ul><ul><ul><li>Typical Hours/Year = Unlimited </li></ul></ul><ul><ul><li>Typical Peak Demand = 100% of prime kW rating with 10% overload capability for emergency use for a maximum of 1 hour in 12. </li></ul></ul><ul><ul><li>Typical Application = Industrial, Pumping, Construction, Rental, and Co-Gen </li></ul></ul>
  8. 8. <ul><ul><li>Power is available for the duration of the emergency outage </li></ul></ul><ul><ul><li>Average Power Output = 70% of standby power rating </li></ul></ul><ul><ul><li>Load = Varying </li></ul></ul><ul><ul><li>Typical Hours/Year = 200 hours </li></ul></ul><ul><ul><li>Maximum Expected Usage = 500 hours/year </li></ul></ul><ul><ul><li>Typical Application = Standby </li></ul></ul>Standby Power Rating
  9. 9. Limited-Time running Power (LTP) Limited-time running power is defined as the maximum power available, under the agreed operating conditions, for which the generating set is capable of delivering for up to 500 h of operation per year with the maintenance intervals and procedures being carried out as prescribed by the manufacturers
  10. 10. <ul><ul><li>Power is available for the duration of the emergency outage </li></ul></ul><ul><ul><li>Average Power Output = 70% of standby power rating in 24hr period </li></ul></ul><ul><ul><li>Load = Varying </li></ul></ul><ul><ul><li>Typical Hours/Year = 50 hours </li></ul></ul><ul><ul><li>Maximum Expected Usage = 200 hours/year </li></ul></ul><ul><ul><li>Typical Application = Building Service Standby </li></ul></ul>Emergency Standby Power (ESP)
  11. 11. Load Acceptance based on ISO8528-5
  12. 12. Determining ISO 8528 Load Step levels <ul><li>The ISO8528 standard defines the load step levels on the basis of the Brake Mean Effective Pressure (BMEP) of the engine. </li></ul>
  13. 13. Determining ISO 8528 Load Step levels
  14. 14. Determining ISO 8528 Load Step levels 4016 TAG2A -2000kVA Prime rated BMEP2310kPa According to ISO8258 this generator is only required to take 36% initial load step to meet the standard. In fact this generator will do 57% initial load step to G2 classification
  15. 15. Transient response <ul><li>When significant load is applied, frequency and voltage will dip then returns to a steady state condition. </li></ul><ul><ul><li>This temporary change is called transient response. </li></ul></ul><ul><li>The size of this dip depends on; </li></ul><ul><ul><li>Amount of real and reactive power change. </li></ul></ul><ul><ul><li>Total capacity and dynamic characteristics of the genset, and the response of other loads in the system. </li></ul></ul><ul><li>On removal of load, engine speed increases momentarily (overshoot), then returns to a steady-state condition. </li></ul><ul><ul><li>The time required for the genset to return to steady-state condition is called recovery time. </li></ul></ul><ul><li>Sizing Criterion </li></ul><ul><li>3 primary criteria need to be provided to accurately size a generator set: </li></ul><ul><ul><li>Acceptable percent of voltage & frequency dip </li></ul></ul><ul><ul><li>Acceptable duration of the voltage & frequency dip recovery </li></ul></ul><ul><ul><li>Percent of each load step and type of load </li></ul></ul>Cover
  16. 16. Four performance classes are defined in order to cover the various requirements of the supplied electrical systems as follows: Class G1 This applies to generating set applications where the connected loads are such that only basic parameters of voltage and frequency need to be specified. EXAMPLE General-purpose applications (lighting and other simple electrical loads). Class G2 This applies to generating set applications where its voltage characteristics are very similar to those for the commercial public utility electrical power system with which it operates. When load changes occur, there may be temporary but acceptable deviations of voltage and frequency. EXAMPLE Lighting systems, pumps, fans and hoists. Performance classes
  17. 17. Class G3 This applies to applications where the connected equipment makes severe demands on the stability and level of the frequency, voltage and waveform characteristics of the electrical power supplied by the generating set. EXAMPLE Telecommunications and thyristor-controlled loads. It should be remembered that both rectifier and thyristor-controlled loads may need special consideration with respect to their effect on generator-voltage waveform. Class G4 This applies to applications where the demands made on the stability and level of the frequency, voltage and waveform characteristics of the electrical power supplied by the generating set are exceptionally severe. EXAMPLE Data-processing equipment or computer systems. Performance classes
  18. 18. Frequency Transient Performance
  19. 19. Voltage Transient Performance
  20. 20. Load Profile Analysis <ul><li>In certain types of load,and for some motor starting methods, the highest transient loading may not occur at the moment of switch on. </li></ul><ul><li>It is, therefore, necessary to consider how the transient varies until the normal operating load point is reached. </li></ul>
  21. 21. Direct-On-Line Load Requirement
  22. 22. Star/Delta Starting Load Requirement
  23. 23. Electronic Soft Start Load Requirement
  24. 24. Non-Linear Load Examples <ul><li>Battery chargers </li></ul><ul><li>Medical imaging loads </li></ul><ul><li>Motors used with electronic soft starters (only non-linear during starting) </li></ul><ul><li>Office equipment </li></ul><ul><li>Some types of lighting </li></ul><ul><li>Telecommunications equipment </li></ul><ul><li>Uninterruptible power supplies </li></ul><ul><li>Variable speed motor drives </li></ul>
  25. 25. Overview of UPS If the supply fails, the energy stored in the batteries continues to feed the inverter section . Input Voltage Window Typically +/- 15%, although some UPS require +/- 10%. Input Frequency Window Typically +/- 5%.
  26. 26. UPS Without Walk-in Facility
  27. 27. UPS With Walk-in Facility
  28. 28. Managing UPS <ul><li>Allowing UPS to revert to its battery during subsequent transients can reduce the size of the generating set by relaxing the voltage and frequency tolerances to those of the added load. </li></ul><ul><li>In some circumstances, however, it may not be suitable for the UPS to revert to its batteries, for example where the UPS is a significant percentage of the total loading. </li></ul>
  29. 29. Matching Genset Performance to Load <ul><li>When matching generating set performance to the </li></ul><ul><li>intended load, the following must be considered: </li></ul><ul><li>Capability in excess of load requirement. </li></ul><ul><li>Transient voltage and frequency excursions within specified tolerances. </li></ul><ul><li>Consider non-linear loads – oversize alternator if necessary. </li></ul><ul><li>Upgrade of excitation type may be necessary. </li></ul>
  30. 30. Matching Genset Performance to Load
  31. 31. Summary <ul><li>Define the duty and site parameters. </li></ul><ul><li>Analyse the load transient and running requirement profiles. </li></ul><ul><li>Match the Generating set performance to the load requirements. </li></ul>
  32. 32. Acoustics Introduction to Genset Noise Power Solutions Sales Support
  33. 33. Basics of Noise <ul><li>What is noise? </li></ul><ul><ul><li>Noise (sound) consists of travelling waves in an elastic medium (air) that are generated by some vibrating object (genset). </li></ul></ul>
  34. 34. Definitions <ul><li>Sound Power </li></ul><ul><li>A sound source transfers energy to the surrounding medium at a certain rate. The average amount of energy radiated per unit time is called the Sound Power of the source. (unit: watt) </li></ul><ul><li>Because it is a characteristic of the source its value does not depend on where an observer or measurement instrument is located relative to the source. </li></ul>
  35. 35. Definitions - cont’d <ul><li>Sound Pressure </li></ul><ul><li>The small alternating incremental change in pressure from ambient pressure that results from the production of sound. </li></ul><ul><li>Unlike Sound Power, Sound Pressure varies with distance from source and the medium through which the sound is being transmitted. (Unit: Pascal) </li></ul>
  36. 36. Sound Intensity & Sound Power <ul><li>Source radiates equally in all directions </li></ul><ul><li>Intensity of waves = I </li></ul><ul><li>I is amount of energy passing through unit area per unit time </li></ul><ul><li>I = P 2 /  c (Power) </li></ul><ul><li>Total Power = 4  r 2 P 2 /  c </li></ul>Sound Pressure P On area dA Sphere of radius r Source r dA
  37. 37. Analogy - SWL vs SPL Electric Power Sound Pressure Temperature Sound Power
  38. 38. How Noise is Perceived at a Point <ul><li>The sound intensity from a point source of sound, will obey the inverse square law, if there are no reflections or reverberation. A plot of this intensity drop shows that it drops off rapidly. </li></ul>
  39. 39. Source Location - Directivity <ul><li>Directivity Factor Q </li></ul><ul><li>Each plane causes a doubling of the amount of energy being radiated the remaining “free” directions away from the source </li></ul><ul><li>+3dB </li></ul>Directivity factor 1 Directivity factor 2 +3 dB Directivity factor 8 +9dB Directivity factor 4 +6dB
  40. 40. The Decibel Scale <ul><ul><li>Sound Power Level and Sound Pressure Level are different physical quantities that are both commonly expressed in decibels (dB). </li></ul></ul><ul><ul><li>Decibels are dimensionless units used to express the logarithmic ratio between a given value and a reference value. </li></ul></ul>
  41. 41. Why Use the Decibel Scale? <ul><li>On their own SWL and SPL are “meaningless” - we need something to relate these values. </li></ul><ul><li>Decibel scale does this - ratio of given level to that of the lowest intensity that can be heard by the human ear :(10 -12 Watts SWL/2x10 -5 Pa SPL) </li></ul><ul><li>Values that commonly occur in acoustics span huge numerical ranges e.g. </li></ul><ul><ul><li>0.000000001 Watt for whispering voice </li></ul></ul><ul><ul><li>40,000,000 Watts for Concorde @ Take-Off </li></ul></ul>
  42. 42. The Frequency Spectrum <ul><li>Sound heard by the human ear is made up of sound waves of many different frequencies. </li></ul><ul><li>In noise analysis the overall noise level is broken down into a number of different octaves. </li></ul><ul><li>An Octave is a range of frequencies whose upper value is twice the lower value. The middle value is the one quoted. </li></ul><ul><li>e.g. 63Hz 125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz 8000Hz </li></ul>
  43. 43. Some Detail – Octave Analysis
  44. 44. More Detail – 1/3 Octave Analysis
  45. 45. Lots of Detail – Narrow Band Analysis
  46. 46. A-Weighting <ul><li>Numerical weighting applied to each frequency to align measured noise to the characteristics of the human ear. </li></ul><ul><li>Most installation noise requirements refer to A-Weighted spectra. </li></ul><ul><li>Measured noise data is unweighted (linear) </li></ul>
  47. 47. Example of A-Weighting 63Hz 125Hz 250Hz 500Hz 1000Hz 2000Hz 4000Hz 8000Hz 102 99 105 104 105 108 106 109 - Linear -26 -16 -9 -3 0 1 1 -1 - Weighting 76 83 96 101 105 109 107 108 - A-Weighted Overall SPL is logarithmic sum of the frequency SPLs =10 x log 10 (10 7.6 + 10 8.3 + 10 9.6 + 10 10.1 + 10 10.5 + 10 10.9 + 10 10.7 + 10 10.8 ) = 114dBA
  48. 48. Effects of Distance from Source <ul><li>SPL decreases as distance from the noise source increases. </li></ul><ul><li>“ Rule of Thumb” can be applied to ascertain SPL at some distance from the noise source (there are certain circumstances when this rule is not applicable – i.e. when large distances are involved) </li></ul><ul><li> SPL 0 - SPL 1 =10log(R 1 /R 0 ) </li></ul>
  49. 49. Example: Genset Enclosure is designed for 85dBA @ 1m. What is SPL at 7m? SPL 0 = 85dBA R 0 = 1m SPL 1 = ? dBA R 1 = 7m SPL 1 = 85 - 10log(7/1) = 77dBA
  50. 50. Noise @ Distance <ul><li>For a True Calculation of Noise due to Distance we must base the calculation on the Change in Distance from the Conformal Surface Area of the object. </li></ul><ul><li>This calculation should be based on ISO3744: 1994 (E) & BS EN ISO 3746:1996. </li></ul>
  51. 51. Example of Calculation
  52. 52. Multiple Noise Sources <ul><li>Table below takes into account the possibility that two or more noise sources may be present. </li></ul><ul><li>Useful for multiple genset installations. </li></ul>
  53. 53. Calculating Overall Noise Level <ul><li>Earlier overall noise level was calculated using the logarithmic sum. </li></ul><ul><li>63Hz 125Hz 250Hz 500Hz 1 kHz 2 kHz 4 kHz 8 kHz </li></ul><ul><li>76 83 96 101 105 109 107 108 </li></ul><ul><li>Overall noise level =10 x log 10 (10 7.6 + 10 8.3 + 10 9.6 + 10 10.1 + 10 10.5 + 10 10.9 + 10 10.7 + 10 10.8 ) = 114dBA </li></ul><ul><li>Using the previous table we can also calculate the overall noise level. </li></ul>
  54. 54. Calculating Overall Noise Level <ul><li>The overall noise level is therefore calculated as; </li></ul><ul><li>76 83 96 101 105 109 107 108 </li></ul>102 113.5 84 102 110.5 110.5 114 dBA
  55. 55. Common Noise Requirements <ul><li>x dBA @ y metres </li></ul><ul><li>NR </li></ul><ul><li>NC </li></ul><ul><li>L aeq,t </li></ul>
  56. 56. <ul><li>Most commonly used requirement </li></ul><ul><li>Stipulates a SPL at a given distance from enclosure </li></ul><ul><li>Average or Maximum? </li></ul>X dBA @ y metres
  57. 57. <ul><li>Developed by ISO </li></ul><ul><li>Curves plotted of SPL vs Frequency </li></ul><ul><li>SPL @ each octave must be met </li></ul><ul><li>Do NOT equate to an overall SPL </li></ul>NR Curves
  58. 58. <ul><li>Predecessor of NR Curves - still used </li></ul><ul><li>Curves plotted of SPL vs Frequency </li></ul><ul><li>SPL @ each octave must be met </li></ul><ul><li>Do NOT equate to an overall SPL </li></ul>NC Curves
  59. 59. L Aeq,T The equivalent continuous A-Weighted sound pressure level measured over time T
  60. 60. Example of L Aeq,T - BP1 Canary Wharf 6 x 2.5MVA Gensets Requirement: L Aeq,5 min = 62dBA@1m
  61. 61. Background Noise Levels <ul><li>Background Noise Levels are typically in the region of: </li></ul><ul><ul><li>City of London day time - 51dBA </li></ul></ul><ul><ul><li>City of London night time - 45dBA </li></ul></ul><ul><ul><li>Rural Land day time - 43dBA </li></ul></ul><ul><ul><li>Rural Land night time - 39dBA </li></ul></ul><ul><ul><li>These are typical levels which would be measured over a 5 minute period. </li></ul></ul><ul><li>For True Background Noise Survey, the measurement should be L A90,24hr </li></ul>
  62. 62. L A90,24hr <ul><li>This is the noise level in dB(A) which during the sampling interval 24 hours, was exceeded for 90% of the time. </li></ul>
  63. 63. Average Outdoor Noise Levels <ul><li>The World Health Organization has suggested a standard guideline value for average outdoor noise levels of 55dB, applied during normal daytime to prevent significant interference with the normal activities of local communities. </li></ul>
  64. 64. Effects of Noise in a Room / Enclosure <ul><li>Noise within any Enclosure / Room (Box) is dependant on the characteristics of both the Noise Source and the Box, & any additional items therein. </li></ul><ul><li>This is due to: </li></ul><ul><ul><li>Noise being Generated. </li></ul></ul><ul><ul><li>Noise being Reflected. </li></ul></ul><ul><ul><li>Noise being Absorbed. </li></ul></ul>
  65. 65. Reverberation <ul><li>Reverberation is the combined effect of Reflection & Absorbtion on the initial Sound Source. </li></ul><ul><ul><li>Main contributing factors are: </li></ul></ul><ul><ul><ul><li>The characteristics of the surfaces within the room. </li></ul></ul></ul><ul><ul><ul><li>The size of the room. </li></ul></ul></ul><ul><ul><ul><li>The size of the Sound Source. </li></ul></ul></ul>
  66. 66. Reverberation <ul><li>• Reverberation is the collection of reflected sounds from the surfaces in an enclosure. </li></ul>
  67. 67. Reverberant Sound Field <ul><li>The sketch below depicts the sound received by a single listener as a function of time as a result of a sharp sound pulse some distance away. The direct sound received is followed by distinct reflected sounds and then a collection of many reflected sounds which blend and overlap into what is called reverberation.   </li></ul>
  68. 68. Room Charteristic <ul><li>The main contributing factors of a rooms characteristics are: </li></ul><ul><ul><li>The Absorbtion Co-efficients of the surfaces within the room. </li></ul></ul><ul><ul><li>The Conformal surface area of these surfaces. </li></ul></ul><ul><ul><li>The Transmission Loss through a surface. </li></ul></ul><ul><ul><li>Location of the source relative to the walls, floor or ceiling. </li></ul></ul>
  69. 69. Effect of increased Absorption Coeff on Reverberant SPL
  70. 70. Reverb. Calc. Example
  71. 71. Attenuation <ul><li>Reducing the amount of noise produced from a genset installation. </li></ul><ul><li>2 Basic Methods Employed - Sound Absorption and Vibration Isolation. </li></ul>
  72. 72. Methods Employed Absorption Absorption Vibration Isolation - AVMs
  73. 73. Sound Absorption <ul><li>Solid barrier </li></ul><ul><li>Splitters </li></ul><ul><li>Ducts </li></ul><ul><li>Bends </li></ul>
  74. 74. Sound Absorption <ul><li>Solid barrier - wall of enclosure/plantroom. </li></ul><ul><li>Construction of barrier important. </li></ul><ul><li>Test Bay Walls - Good for Absorption </li></ul><ul><li>Concrete - Very Poor </li></ul><ul><li>Cavity Wall - Excellent </li></ul>
  75. 75. Sound Absorption <ul><li>Splitters - used for air intake and discharge </li></ul><ul><li>Attenuation properties based on 3 parameters: </li></ul><ul><ul><li>Element Width </li></ul></ul><ul><ul><li>Gap Width </li></ul></ul><ul><ul><li>Length </li></ul></ul>
  76. 76. Sound Absorption <ul><li>Ducts - used for air intake and discharge </li></ul><ul><li>Attenuation limited to lined ducts. </li></ul><ul><li>Attenuation properties based on cross sectional area and length of duct. </li></ul>
  77. 77. Sound Absorption <ul><li>Bends - used in conjunction with splitters & ducts </li></ul><ul><li>Attenuation limited to lined bends. </li></ul><ul><li>Can provide useful additional attenuation to above attenuation techniques </li></ul>
  78. 78. Important Considerations <ul><li>Each method of attenuation has its own associated restriction to airflow. </li></ul><ul><li>Must ensure that this restriction does not exceed that which the cooling system is capable of overcoming </li></ul><ul><li>Must be careful not to generate “flow noise”. </li></ul>
  79. 79. Vibration Isolation <ul><li>Minimising amount of vibrational energy transmitted to building or enclosure structure. </li></ul><ul><li>Rubber or Spring Type Anti-Vibration Mounts </li></ul><ul><li>Degree of Isolation required often quoted as a percentage. </li></ul><ul><li>Sometimes quoted as deflection in mm - meaningless unless AVM type is specified. </li></ul>
  80. 80. Thank you for your attention. Questions & Answers

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