Bsi bs en 60034 2 1999 (2000)

BRITISH STANDARD Rotating electrical machines — Part 2: Methods for determining losses and efficiency of rotating electrical machinery from tests (excluding machines for traction vehicles) The European Standard EN 60034-2:1996 together with amendments A1:1996 and A2:1996 has the status of a British Standard ICS 29.160.01 BS EN 60034-2:1999 BS EN 60034-2:1999 National foreword This British Standard is the English language version of EN 60034-2:1996, including amendments A1:1996 and A2:1996 It is identical with IEC 34-2:1972 plus IEC 34-2A:1974, including amendment 1995 and amendment 1996 It supersedes BS 4999-102:1987, which is withdrawn NOTE IEC 34-2A:1974 (first supplement to IEC 34-2:1972) is given in Annex B of EN 60034-2:1996 Text introduced by amendments A1 and A2 is indicated by a sideline The UK participation in its preparation was entrusted to Technical Committee PEL/2, Rotating electrical machinery, which has the responsibility to: — aid enquirers to understand the text; — present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; — monitor related international and European developments and promulgate them in the UK A list of organizations represented on this committee can be obtained on request to its secretary From January 1997, all IEC publications have the number 60000 added to the old number For instance, IEC 27-1 has been renumbered as IEC 60027-1 For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems Cross-references The British Standards which implement these international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages to 47 and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards Board and comes into effect on 15 October 1999 © BSI 04-2000 ISBN 580 30737 Amendments issued since publication Amd No Date Comments BS EN 60034-2:1999 Contents National foreword Foreword Text of EN 60034-2 © BSI 04-2000 Page Inside front cover i ii blank EUROPEAN STANDARD EN 60034-2 NORME EUROPÉENNE November 1996 EUROPÄISCHE NORM November 1996 + A1 + A2 November 1996 UDC 621.313.017.2/.6.017.8.083.001.4 Supersedes HD 53.2 S1:1974 ICS 29.160.00 Descriptors: Rotating electrical machines, power losses, efficiency, determination, tests, power measurements English version Rotating electrical machines Part 2: Methods for determining losses and efficiency of rotating electrical machinery from tests (excluding machines for traction vehicles) (includes amendments A1:1996 and A2:1996) (IEC 34-2:1972 + IEC 34-2A:1974 + A1:1995 + A2:1996) Machines électriques tournantes Partie 2: Méthodes pour la détermination des pertes et du rendement des machines électriques tournantes partir d’essais (à l’exclusion des machines pour véhicules de traction) (inclut les amendements A1:1996 et A2:1996) (CEI 34-2:1972 + IEC 34-2A:1974 + A1:1995 + A2:1996) 网 享 分 m o c Drehende elektrische Maschinen Teil 2: Verfahren zur Bestimmung der Verluste und des Wirkungsgrades von drehenden elektrischen Maschinen aus Prüfungen (ausgenommen Maschinen für Schienen- und Straßenfahrzeuge) (enthält Änderungen A1:1996 und A2:1996) (IEC 34-2:1972 + IEC 34-2A:1974 + A1:1995 + A2:1996) f z b w x w ww This European Standard was approved by CENELEC on 1996-07-02 CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions CENELEC members are the national electrotechnical committees of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom 标准 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B-1050 Brussels © 1996 Copyright reserved to CENELEC members Ref No EN 60034-2:1996 + A1:1996 + A2:1996 E EN 60034-2:1996 Foreword The text of the International Standard IEC 34-2:1972 + IEC 34-2A:1974, prepared by SC 2G, Test methods and procedures, of IEC TC 2, Rotating machinery, was approved by CENELEC as HD 53.2 S1 on 1974-12-11 This Harmonization Document was submitted to the formal vote for conversion into a European Standard and was approved by CENELEC as EN 60034-2 on 1996-07-02 The following date was fixed: — latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 1997-06-01 Foreword to amendment A1 The text of amendment 1:1995 to the International Standard IEC 34-2:1972, prepared by SC 2G, Test methods and procedures, of IEC TC 2, Rotating machinery, was submitted to the formal vote and was approved by CENELEC as amendment A1 to EN 60034-2 on 1996-07-02 without any modification The following dates were fixed: NOTE Amendment to IEC 34-2, published in November 1996, contains both documents 2/939/FDIS and 2G/73/FDIS The following dates were fixed: — latest date by which the amendment has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 1997-06-01 — latest date by which the national standards conflicting with the amendment have to be withdrawn (dow) 1997-06-01 For products which have complied with HD 53.2 S1:1974 (converted into EN 60034-2) before 1997-06-01, as shown by the manufacturer or by a certification body, this previous standard may continue to apply for production until 2002-06-01 m o c f z b w x w ww — latest date by which the amendment has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 1997-06-01 — latest date by which the national standards conflicting with the amendment have to be withdrawn (dow) 1997-06-01 网 享 分 标准 For products which have complied with HD 53.2 S1:1974 (converted into EN 60034-2) before 1997-06-01, as shown by the manufacturer or by a certification body, this previous standard may continue to apply for production until 2002-06-01 Foreword to amendment A2 The text of document 2/939/FDIS, prepared by IEC TC 2, Rotating machinery, was submitted to the formal vote and was approved by CENELEC as amendment A2 to EN 60034-2 on 1996-07-02 The text of document 2G/73/FDIS, prepared by SC 2G, Test methods and procedures, of IEC TC 2, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC for inclusion into amendment A2 to EN 60034-2 on 1996-10-01 © BSI 04-2000 EN 60034-2:1996 Contents Foreword Section General Scope Object General 3.1 List of symbols Definitions 4.1 Efficiency 4.2 Total loss 4.3 Breaking test 4.4 Calibrated driving machine test 4.5 Mechanical back-to-back test 4.6 Electrical back-to-back test 4.7 Retardation test 4.8 Calorimetric test 4.9 No-load test 4.10 Open-circuit test 4.11 Sustained short-circuit test 4.12 Zero power factor-test Reference temperature Section D.C Machines Losses to be included 6.1 Excitation circuit losses 6.2 Constant losses 6.3 Load losses 6.4 Additional load losses Determination of efficiency 7.1 Summation of losses 7.2 Total loss measurement 7.3 Direct measurement of efficiency Section Polyphase induction machines Losses to be included 8.2 Load losses 8.3 Additional load losses Determination of efficiency 9.1 Summation of losses 9.2 Total loss measurement 9.3 Direct measurement of efficiency Section Synchronous machines 10 Losses to be included 10.1 Constant losses 10.2 Load losses 10.3 Excitation circuit losses 网 享 分 标准 © BSI 04-2000 Page 5 5 6 6 6 6 6 7 10.4 Additional load losses 11 Determination of efficiency 11.1 Summation of losses 11.2 Total loss measurement 11.3 Direct measurement of efficiency Section Methods of test 12 General 13 Calibrated machine test 14 Zero power factor test 15 Retardation method 16 Electrical back-to-back test 17 Calorimetric test 18 Schedule of preferred tests 18.1 D.C machines 18.2 Polyphase induction machines 18.3 Synchronous machines Figure — Mechanical back-to-back test Figure — Electrical back-to-back test Figure — Vector diagram for obtaining vector of load current I1 at rated voltage Figure — Method of the chord Figure — Method of the limiting secant Figure A.1 — Maximum permissible relative error (%P/Pin)max of input as well as output measurement Figure A.2 — Schematic diagram of a test set-up for the calorimetric calibration method Figure A.3 — Power and losses diagram Figure A.4 — Typical voltage and current waveform Annex A (informative) Provisional methods for determining losses and efficiency of converter-fed cage induction machines Annex B IEC 34-2A Measurement of losses by the calorimetric method Introduction Section General General Determination of losses P1 by measurement of the volume rate of flow and rise in temperature of the cooling medium Losses Pi measured electrically using the calorimetric calibration method Stable conditions Losses P2 not transmitted to the cooling medium m o c w ww f z b 7 7 8 10 10 10 10 10 11 11 12 12 13 13 13 13 w x Page 13 13 13 15 15 15 16 16 17 21 22 22 22 22 22 22 22 23 23 24 25 26 29 30 25 31 31 32 32 32 33 33 EN 60034-2:1996 Page Losses external to the reference surface Pe 33 Section Water as the cooling medium Application and basic relationship 34 Measurement of water flow 34 Measurement of the temperature rise of the water 35 10 Measuring accuracy 35 Section Air as the cooling medium 11 Application and basic relationship 36 12 Determination of the mass rate of flow 36 13 Measurement of the temperature rise of the air 38 14 Determination of the specific heat capacity of the air 38 15 Measuring accuracy 38 Section Practical considerations 16 Preparations for calorimetric measurements with liquid coolants 39 17 Connections and equipment for calorimetric measurements with liquid coolants 39 Figure — Reference surface 41 Figure — Parallel coolers 42 Figure — Series coolers 42 Figure — Characteristic values of pure water as a function of temperature 43 Figure — Position of thermometer pockets in the water conduit 44 Figure — Measuring throttles placed in the cooling circuit on site 44 Figure — Air density depending on temperature and humidity 45 Figure — Specific heat capacity cp of air for different values of humidity and temperature 46 Figure 47 Figure 10 47 Figure 11 47 Table I — Measurement error in calorimetry by water 36 Table II — Measurement error in calorimetry by air 38 网 享 分 m o c f z b w x w ww 标准 © BSI 04-2000 EN 60034-2:1996 Section General 3.1 List of symbols Scope A list of symbols used in the draft, with the general meanings attributed to each one, is given below: This Recommendation applies to d.c machines and to a.c synchronous and induction machines of all sizes within the scope of IEC Publication 34-1 The principles can, however, be applied to other types of machines such as rotary convertors, a.c commutator motors and single- phase induction motors for which other methods of determining losses are generally use C = retardation constant I = current I1 = load current at rated voltage I1r = main primary current at reduced voltage Io = no-load current at rated voltage Ior = no-load current at reduced voltage Object J = moment of inertia This Recommendation is intended to establish methods of determining efficiencies from tests, and also to specify methods of obtaining particular losses when these are required for other purposes n = speed of rotation in revolutions per minute nN = rated speed N = number of full revolutions of the shaft P = losses which can be directly measured P1 = power absorbed at rated voltage P1r = power absorbed by main primary winding at reduced voltage General Tests shall be conducted on a completely sound machine with all covers fitted in the manner required for normal service, with any devices for automatic voltage regulation not a composite part of the machine itself being made inoperative, unless otherwise agreed Unless otherwise agreed, measuring instruments and their accessories, such as measuring transformers, shunts and bridges used during the test shall have an accuracy of 0,5 or better (IEC 51) excluding three-phase wattmeters and wattmeters for low power factor, for which an accuracy class shall be 1,0 or better Instruments shall be selected to give readings over the effective range such that a fraction of a division is a small percentage of the actual reading and can be easily estimated On machines with adjustable brushes, the brushes shall be placed in the position corresponding to the specified rating For measurements on no-load, the brushes may be placed on the neutral axis Speed of rotation may be measured by a stroboscopic method, digital counter or tachometer When measuring slip, the synchronous speed should be determined from the supply frequency during the test When the over-all efficiency or the absorbed power is measured for a group of machines comprising two electrical machines, or a machine and a transformer, or a generator and its driving machine, or a motor and its driven machine, there is no need to indicate the individual efficiencies If, however, these are given separately, they should be regarded as approximate 网 享 分 标准 © BSI 04-2000 m o c f z b PFe w ww w x = iron losses defined in accordance with 6.2 a), 8.1 a) and 10.1 a) Pf = friction and windage losses (“mechanical losses”) defined in accordance with 6.2 b), 6.2 c), 8.1 b), 8.1 c), 10.1 b) and 10.1 c) Pk = short-circuit losses representing the sum of the I2R losses in operating windings on load in accordance with 10.2 and additional load losses in accordance with 10.4 Pt = total of the losses during the retardation test S = angular displacement of the machine shaft s = slip U = excitation voltage across terminals of main rheostat Ue = total excitation voltage Un = rated voltage Ur = reduced voltage for load test $ = per unit deviation of rotational speed from rated speed : = load phase angle at rated voltage :r = load phase angle at reduced voltage :o = no-load phase angle at rated voltage :or = no-load phase angle at reduced voltage EN 60034-2:1996 4.3 braking test Pi = losses inside reference surface Pe = losses outside reference surface P1 = losses which are dissipated by the cooling circuits in the form of heat and which can be measured calorimetrically P2 = losses not transmitted to the cooling medium but which are dissipated through the reference surface by conduction, convection, radiation, leakage, etc cp = specific heat capacity of the cooling medium Q = volume rate of flow of the cooling medium Õ = density of the cooling medium %t = rise in temperature of the cooling medium or temperature difference between the machine reference surface and the external ambient temperature É = exit velocity of cooling medium ! = discharge coefficient e = error in measurement of losses, P1 and P2 h = coefficient of heat transfer t 网 享 分 = temperature 4.4 calibrated driving machine test a test in which the mechanical input or output of an electrical machine is calculated from the electrical output or input of a calibrated machine mechanically coupled to the machine on test 4.5 mechanical back-to-back test m o c a test in which two identical machines are mechanically coupled together, and the total losses of both machines are calculated from the difference between the electrical input to one machine and the electrical output of the other machine (see Figure 1, page 22) f z b t1 = inlet temperature of the cooling medium 4.6 electrical back-to-back test a test in which two identical machines are mechanically coupled together, and they are both connected electrically to a power system The total losses of both machines are taken as the power input drawn from the system (see Figure 2, page 22) 标准 4.7 retardation test For definitions of general terms used in this Recommendation, reference should be made to the International Electrotechnical Vocabulary [IEC Publication 50] For the purpose of this Recommendation, the following definitions apply: 4.8 calorimetric test t2 = outlet temperature of the cooling medium b = barometric pressure Definitions 4.1 efficiency the ratio of output to input expressed in the same units and usually given as a percentage 4.2 total loss the difference between the input and the output w x w ww %p = difference between the static pressure in the intake nozzle and ambient pressure A = cross-sectional area of the intake nozzle a test in which the mechanical power output of a machine acting as a motor is determined by the measurement of the shaft torque, by means of a brake or dynamometer, together with the rotational speed Alternatively, a test performed on a machine acting as a generator, by means of a dynamometer to determine the mechanical power input a test in which the losses in a machine are deduced from the rate of deceleration of the machine when only these losses are present a test in which the losses in a machine are deduced from the heat produced by them The losses are calculated from the product of the amount of coolant and its temperature rise, and the heat dissipated in the surrounding media 4.9 no-load test a test in which the machine is run as a motor providing no useful mechanical output from the shaft 4.10 open-circuit test a test in which a machine is run as a generator with its terminals open-circuited © BSI 04-2000 EN 60034-2:1996 — losses by friction in the bearings, either wholly or partially depending on whether they are wholly or partly outside the reference surface The above losses, evaluated separately, shall be added to the internal losses Pi Section Water as the cooling medium Application and basic relationship This method is applicable only to machines provided with a closed primary cooling system and using water as a secondary coolant, but it gives a very practical and accurate method of measurement Typical connection diagrams for parallel and series connected coolers are given in Figure and Figure 3, page 42 The losses dissipated by the water are given in the following formula: P1 = cp · Õ · Q · %t kW where: cp = specific heat capacity of the water in kJ/(kg K) (at constant pressure p = 0.1 MN/m2) determined from Figure 4, page 43, as the integrated mean value of cp, between inlet temperature t1 and outlet temperature t2 of the water Õ = density of water (kg/m3) shown on the curve in Figure at the point where the rate of flow Q (m3/s) is measured %t = t2 – t1, the temperature rise of the water in K Where there is any doubt as to the accuracy of the factors employed for cp and Õ, particularly if the cooling water contains salts, it will be necessary for cp and ½ to be measured The care with which the measurements are made, together with the calibration of the measuring instruments, is a decisive factor in obtaining accurate results Measurement of water flow To obtain an easily measurable rise in temperature, the flow of water should be controlled by a valve placed downstream from the flowmeter The volume rate of flow of water can be measured by the following methods: — calibrated tanks, — weirs and weirs with standardized gates, — accurately calibrated volume counters, — electromagnetic or vane type flowmeters, — orifice plate, venturi meter or nozzles in accordance with ISO Recommendation R541 34 8.1 Recommendations for measurement of quantity of water 8.1.1 Measurement by calibrated tanks The volume of the tank should be such that the filling time is at least one minute The dimensions of the tank when its volume is determined by calculation only should be such that the variations in volume due to water pressure are less than 0.02 % The volume rate of flow of water through the cooling system should not be affected during measurement The time should be measured by using either two stop-watches simultaneously or an electrical timing device 8.1.2 Measurements using volumetric or velocity type flowmeters The installation of volumetric or velocity type flowmeters in pipes should be in accordance with manufacturer’s instructions (straight sections up and downstream, position, etc.) and care should be taken that no air bubbles are present in the water It is recommended that the measuring instruments should be calibrated before and after the measurements in conditions similar to those prevailing during the measurements, particularly if it is not possible to comply with the method of installation recommended by the manufacturer of the instrument In the case of volumetric measurements, the time should be measured with two stop-watches simultaneously or by means of an electrical timing device The measuring time should be long enough to ensure sufficient accuracy and should be not less than If the measurement is made with a direct reading flowmeter, about 20 readings should be made and an average value taken NOTE It is advisable to determine, by agreement between manufacturer and purchaser, the different points of measurement when establishing the layout of power plant Under certain conditions, it may even be advisable to include means to install and remove the measuring apparatus without interrupting the operation of the machine (see Figure 9, page 47) © BSI 04-2000 EN 60034-2:1996 Measurement of the temperature rise of the water The measurement can be made by means of one of the following: — thermocouples or resistance temperature detectors, preferably platinum, placed directly in the water or in oil-filled thermometer pockets, and positioned opposite each other so as to obtain direct readings of the temperature rise of the water Greater accuracy is obtainable with the use of platinum resistance temperature detectors, — precision thermometers placed in oil-filled thermometer pockets In order to reduce error, the thermometers should be interchanged after each reading and the oil should be maintained at the correct level The measuring instruments should be calibrated before and after the tests The temperature measurement includes the difference in temperature due to losses in the coolers and associated pipework between measuring points and is assumed to be deg C for a pressure drop of 4.2 MN/m2 The loss corresponding to the pressure drop should be subtracted from the total losses measured using this method It is recommended that a recording instrument be used when the measuring method permits 9.1 Positioning of thermometer pockets (see Figure 5, page 44) The thermometer pockets should be as close as possible to, and outside, the generator pit, but at such a distance from the pit that the equalizing baffle referred to below can be installed Where necessary, the water pipes should be lagged to avoid heat transfer to the outside The water temperature at the location of the thermometer pockets should be homogeneous An equalizing baffle should be installed in order to obtain homogeneous flow It should have one (or two) 90° elbows together with a pipe of length of about 20 time the diameter With more than one cooler, the water flow from each cooler should be regulated to give the same outlet temperature; alternatively the coolers can be measured separately The depth of the thermometer pocket should be between 0.6 and 0.8 times the diameter of the pipe The walls should be as thin as possible and of a material having high thermal conductivity © BSI 04-2000 9.2 Installation of the measuring device inside the thermometer pocket The measuring instrument should be positioned as close as possible to the wall of the pocket, which should be partly filled with oil to improve thermal contact To avoid heat exchange with the air, the pocket should be provided with a plug When the temperature is measured by means of thermocouples or resistance temperature detectors, the leads should be placed in contact with the outer surface of the pipe for a distance of 25 cm and thermally insulated (see Figure 5) 10 Measuring accuracy Accuracy in the determination of losses by the calorimetric method depends upon the method of measurement employed, the type of instruments used and any error in estimating losses P2 Two categories of measurement error are therefore given below in Table I: — Category A being appropriate to the highest accuracy obtainable, — Category B being appropriate to an acceptable order of accuracy suitable for the majority of cases If the relative error in Pi caused by an error in P2 is likely to be greater than 1.5 % in the case of Category A, or greater than % for Category B, the calorimetric method is not recommended Some inaccuracies are common to all measuring methods, for example, the relative dimensions in measurement of speed, voltage, intensity, etc NOTE Measurements made by water calorimetry generally give more accurate results than those made with air Also, if gas bubbles are present in the water (these can be detected through an observation window), it is preferable to eliminate them in order to use the water calorimetric method rather than to use the calorimetric method with air 35 EN 60034-2:1996 Table I — Measurement error in calorimetry by water Clause Effect of error e as a percentage of Pi Quantity Category A Thermal equilibrium Specific heat capacity × water density Volume rate of flow Temperature rise Estimation of P2 lossesb a Losses Pi: 95 % confidence Limits of error = Ce a If thermal equilibrium has not been achieved, the error can be appreciable b The lower figure is valid if all precautions described in Clause are taken The P2 is less than % of Pi Section Air as the cooling medium MEASUREMENTS MADE IN THE PRIMARY CIRCUIT 11 Application and basic relationship Measurement in the primary circuit requires experience in applied aerodynamics The method of measurement to be used will vary according to the size of the plant and the type of ventilation adopted Air calorimetry has the advantage of being applicable to all ventilating systems, whether open or closed circuit No special measuring instrument has to be incorporated into the machine during assembly For this reason, measurements made by air calorimetry can also be taken on machines already installed on site and which have not been specially designed for this type of measurement It is, however, pointed out that certain difficulties in measurement might arise because of uneven air velocities through the measuring section or because of uneven temperatures The calorimetric method using air should be used: — if the machine is completely open, circuit cooled and, as a consequence, a secondary water circuit is not available, — if the secondary circuit water contains bubbles or gases making accurate measurement of the water flow impossible, and no method of measuring water flow is applicable, — if no device has been fitted in the secondary water circuit for measuring the water quantity and temperature, and if the subsequent installation of such an instrument would be impossible As with water calorimetry, it is necessary for thermal equilibrium to be attained 36    k1 k1 k1 k1 k 0.5 k 1.5 k 2.5 Category B k3 k5 higher figure for Category A is valid provided that Air currents in the primary circuit between the hot and the cold air not affect the calorimetric measurement provided the interchange of air takes place entirely inside the reference surface The purpose of air calorimetry is to measure the loss P1 (Section 1) To achieve this, it is necessary to determine: — the mass rate of flow A Q, — temperature rise of the air %t, — the specific thermal capacity cp of the air at constant pressure 12 Determination of the mass rate of flow To determine the mass rate of flow, the volumetric air flow Q should be measured and the air density A should be read from the chart in Figure 7, page 45, at the point where the air flow measurement is made 12.1 Measurement of the air flow The air flow Q can be determined by introducing into the air circuit a calibrated aerodynamic resistance, for example, a calibrated throttle screen (Sub-clause 12.1.1), measuring the air velocity in a section through which the total air flow passes, or by using a comparison method 12.1.1 Principle of measurement by calibrated aerodynamic resistance To apply this principle, a throttle screen is placed in the primary circuit and the drop in pressure determined By means of calibration, relating the volumetric air flow to the pressure difference, the reading of the pressure drop permits the determination of the rate of flow The calibration is only valid for a given air density Therefore, it is necessary for the rate of flow obtained by extrapolation from the calibration curve to be corrected and calculated for the air density prevailing at the time of measurement © BSI 04-2000 EN 60034-2:1996 A screen consisting of a perforated sheet is used as a measuring throttle (see Figure 6, page 44) The sheets, which should be of equal dimensions and calibrated, shall be suitably sited perpendicular to the air flow and used in sufficient numbers so that the pressure drop at rated air flow is of a measurable magnitude (100 N/m2 = 10.2 kg/m2 = 10.2 mm H2O) In order to avoid excessive reduction in the ventilation of the machine, the pressure drop should be not greater than the values given above This method is particularly suitable for machines with open-circuit ventilation To enable the air flow Q to be calculated for other values of air density, the following formula should be used: Q = Q Õ1 /Õ The principle of introducing an aerodynamic resistance into the air circuit requires measurement of the pressure drop For this purpose, a manometer with an inclined tube should be used or a manometer graduated in N/m2 with a sufficiently extended scale (± N/m2) In a closed circuit, heat exchangers are suitable for this purpose, but they are difficult to calibrate 12.1.2 Measurement with an intake nozzle For air-cooled machines, the air flow can also be measured at the air inlet by means of an intake nozzle For this measurement, the following formula applies: where: A = cross section of intake nozzle (m2) Õ = local air density (kg/m3) %p = difference between the static pressure in the intake nozzle and the ambient pressure (N/m2) The coefficient µ = 0.98 with a standard intake nozzle and is independent of the airflow © BSI 04-2000 The cross-sectional area of the nozzle and the number of standard nozzles required depends upon the pressure drop to be measured, the optimum value of which is in the region of 100 N/m2 12.1.3 Comparison method In this method, a device is placed in the cooling circuit of the machine to permit the introduction of known losses P (kW) which corresponds to a measurable temperature rise %t (K) of the cooling medium When the specific heat capacity, cp (kJ/kg K) at the position of measurement is known, the air mass flow can be obtained from the formula: 12.2 Measurement of air density The air density Õ is a function of the actual barometric pressure b, the temperature t and the relative humidity of the air in the location at which the mass flow measurement is made The atmospheric pressure at the location of the mass flow measurement does not differ significantly from the atmospheric pressure in the vicinity of the installation which can either be measured by a barometer, or obtained from the local meteorological station The barometric pressure should be the actual value and not the value corrected to sea level conditions The temperature at the location of the mass flow measurement can be determined sufficiently accurately by means of a bulb thermometer To determine the air density when coolers are used for measurement of the flow, it is necessary to take the arithmetical mean value between the inlet and outlet temperature of the cooler A special hygrometer should be used for the humidity measurement Figure 7, page 45, shows the dry air and humid air densities in relation to temperature The influence of barometric pressure can be calculated from the following formula: where: b0 = 1.013 × 105 N/m2 37 EN 60034-2:1996 13 Measurement of the temperature rise of the air Measurement of the temperature can be made by means of electrical measuring detectors (resistance thermometers, thermocouples or thermistors) If the difference in temperature is in the region of 10 deg C, sufficient accuracy is obtained with mercury thermometers graduated in tenths of a degree 13.1 Measurement with open-circuit ventilation For machines cooled with ambient air, the inlet and outlet air temperatures shall be measured The temperature distribution may vary considerably For greater accuracy, the outlet aperture should be subdivided by, for example, a wire mesh, into sections of approximately 0.1 m × 0.1 m The air temperature should be measured in each section in the manner indicated in Clause 13 Care should be taken to ensure that the air velocity in the measurement section is constant When the air velocity is not constant, a screen should be fitted so as to equalize the air velocities; measurements should then be taken and the mean value determined The screen can be considered as a thermal-mean-value screen and it should be fixed by means of thermally insulated supports 13.2 Measurement with closed-circuit ventilation For machines with closed-circuit ventilation, the losses absorbed by the cooler are determined by the difference between the temperature of the warm air and the temperature of the cold air at the outlet of the heat exchanger When the warm air side of the cooler is accessible, the temperature may be measured by mercury thermometers The outlet temperature should be measured at several points as the air temperature may vary at different sections because of the temperature rise of the water When the warm air side of the cooler is not accessible, the warm air temperature should be measured by means of electrical temperature detectors placed between the cooling fins of the heat exchanger, but not in contact with it 14 Determination of the specific heat capacity of the air The specific heat capacity of the air cp at constant pressure is practically constant for the pressure and temperature ranges concerned (7 °C to 70 °C), and for dry air has the following value: cp = 1.01 kJ/(kg K) The values are higher for humid air (see Figure 8, page 46) 15 Measuring accuracy Accuracy in the determination of losses by the calorimetric method depends upon the method of measurement employed The measurement error for each category of measuring method, depending on the method used and the value of the temperature difference, is given in the following table Table II — Measurement error in calorimetry by air Measured quantity and method of measurement Percentage of error Specific heat capacity cp ± 0.5 Air density A ± 0.5 Flow of air — throttle screen — anemometer or electrical apparatus — Pitot tube — intake nozzle ± 2.5 ± 3.0 ± 3.0 ± 1.5 Temperature rise %t by mercury thermometer or electrically 38      within the range of: °C < %t < 10 °C 10 °C < %t < 20 °C 20 °C < %t ± 2.0 ± 1.0 ± 0.8 © BSI 04-2000 EN 60034-2:1996 The method to be selected for test purposes shall enable an accuracy of measurement of within 2.5 % to be attained or Category A and within % for Category B (see Clause 10) unless otherwise agreed Section Practical considerations 16 Preparations for calorimetric measurements with liquid coolants Calorimetric measurements should be performed separately on every cooling circuit With a single-medium coolant, one or more calorimeters are needed for the bearing oil, and one calorimeter for the cooling water of air- or gas-coolers (see Figure 2, page 42) The use of two primary coolants, for example, hydrogen and pure water, requires one or several calorimeters depending upon the connection of the coolers and the scope of measurement (see Figure 3, page 42) It is advisable to establish the measuring paths for oil and water flow measurements, and the temperature measuring points, when planning the pipe layout, as additions or changes to the installation at a later date are not only costly but can also result in contamination of the bearing oil and high-purity water circuits Since flow-metering devices, for example, turbine meters or throttling devices in the raw-water circuit rapidly lose accuracy because of dirt deposits or corrosion, they should be installed for the period of measurement only To permit installation and removal without interrupting operation, two parallel pipes as shown in Figure 9, page 47, are used which may be shut off at both ends These should allow for the free lengths l between slide valve and flowmeter having minimum values as follows: — in the inlet S 1: l W 10 times the nominal width, — in the outlet S 2: l W times the nominal width The small valve S is required to verify that no cooling water bypasses the flowmeter (Q), i.e that the slide valves S and S are tightly closed It is necessary for the flowmetering devices, including the adjacent flow disturbing fittings and the associated pulse transmitters, amplifiers and meters, if any, to be calibrated before the test Pipe lengths between the temperature measuring points for determining the coolant temperature rise should be provided with heat insulation Inadequate thermal insulation may result in errors in both directions © BSI 04-2000 If the coolers are external to the machine casing, a calorimetric measurement of the primary coolant may be made if the air ducts permit the accommodation of instruments suitable for correct measurement Otherwise, a satisfactory thermal insulation of the air ducts between machine and coolers should be provided to obtain a useful measurement in the secondary cooling circuit Ducts and casing should be carefully sealed against air leakage 17 Connections and equipment for calorimetric measurements with liquid coolants Figure 2, page 42, shows four gas-to-water coolers connected in parallel on the water side The total power losses dissipated by the cooling water are obtained from the measurement of the volume rate of flow of water Q and the temperature rise %t The result is independent of the distribution of water in the paralleled coolers, of the gas distribution, and of the distribution of losses in the partial gas flows to Thermal insulation of water pipes between the temperature measuring points is necessary (see also Sub-clause 9.1) Figure 3, page 42, shows the series connection of coolers for use with two-media cooling The total of the dissipated losses may be determined from the measurement of the volume rate of flow of the cooling water and the total temperature rise Thermal insulation of water pipes is necessary If the provision of thermal insulation is uneconomic, it may be dispensed with in the series connection of coolers by measuring the actual volume rate of flow of cooling water Q, but determining the partial temperature rises %t1 and %t2 individually, or by measuring directly the loss of power dissipated by the high-purity water in the cooling circuit Similar considerations apply for coolers connected in parallel To increase the accuracy of measurement of the coolant temperature rise, the test should be made with a temperature rise as high as possible For this purpose, the coolant flow may be reduced as far as is possible without exceeding the permissible temperature limits This is more practicable with cold cooling water than with the use of condensate as a coolant 39 EN 60034-2:1996 When the temperature rise of the cooling medium is too low and it is not permissible to change the volume rate of flow (for example bearing oil), it is advantageous, when measuring, to extract the losses within the bypass over a fraction of the circulating liquid flow in accordance with Figure 10, page 47, and to re-admit to the coolant the partial flow cooled down to the lower temperature tu This presupposes a sufficiently low temperature of the secondary coolant This bypass calorimetry makes possible a larger temperature difference %t, and hence an increased measuring accuracy A throttling device permits a convenient flow distribution on the parallel lines Should the physically correct connection, as indicated in Figure 2, be impracticable because of the local pipe layout and thermal insulation, combined calorimetry may be employed in which the measured total flow is multiplied by the mean value of the measured individual temperature rises of each cooler (see Figure 11, page 47) In this case, it is necessary for the partial flows to be adjusted prior to the measurement, by means of the down-stream valves so that the temperature rises %t1 to %t4 are almost equal The greater the accuracy with which this is accomplished, the smaller the error in evaluating the losses by means of the average temperature rise The maximum permitted difference between %t values shall be the subject of agreement Pipe lagging can be dispensed with 40 © BSI 04-2000 © BSI 04-2000 41 EN 60034-2:1996 Figure — Reference surface EN 60034-2:1996 Figure — Parallel coolers Figure — Series coolers 42 © BSI 04-2000 EN 60034-2:1996 Figure — Characteristic values of pure water as a function of temperature © BSI 04-2000 43 EN 60034-2:1996 Figure — Position of thermometer pockets in the water conduit Figure — Measuring throttles placed in the cooling circuit on site 44 © BSI 04-2000 EN 60034-2:1996 Figure — Air density depending on temperature and humidity © BSI 04-2000 45 EN 60034-2:1996 Figure — Specific heat capacity cp of air for different values of humidity and temperature 46 © BSI 04-2000 EN 60034-2:1996 Figure Q = Flowmeter tw = Temperature of hot coolant tu = Temperature to which the partial coolant flow within the bypass is cooled down tk = Mixed temperature of tu and tw Figure 10 Figure 11 © BSI 04-2000 47 BS EN 60034-2:1999 BSI — British Standards Institution BSI is the independent national body responsible for preparing British Standards It presents the UK view on standards in Europe and at the international level It is incorporated by Royal Charter Revisions British Standards are updated by amendment or revision Users of British Standards should make sure that they possess the latest amendments or editions It is the constant aim of BSI to improve the quality of our products and services We would be grateful if anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary of the technical committee responsible, the identity of which can be found on the inside front cover Tel: 020 8996 9000 Fax: 020 8996 7400 BSI offers members an individual updating service called 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