bvn tm elec3 rotating machines and transformers head office – department technology equipment - v0...

BVN TM ELEC3 ROTATING MACHINES AND TRANSFORMERS Head Office Department Technology Equipment - V0 December 2009

CONTENT 1 Objectives 2 Rotating machines and requirements 3 Transformers and requirements

3 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Electrical equipment THIS MODULE IS MAINLY BASED ON HO DTM/DT3 TRAINING REFERENCED SMS64

1 Objectives

5 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Electrical equipment Objectives To be familiar with Classification Rules regarding rotating machines and transformers Study of Classification Rules requirements for rotating machines and transformers

2 Rotating machines and requirements

7 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Rotating machines TYPICAL PRODUCT DESCRIPTION AND REFERENCE OF REQUIREMENTS FOR STUDY

ASYNCHRONOUS MACHINE

9 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Principle of an asynchronous machine Turning Magnetic Field in the Stator Rotor carried by inducted currents/forces Rotating machines Asynchronous machine

10 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Asynchronous motor (induction motor) Most commonly used type of motor (pumps, fans, thrusters). Simple and cheap construction. High starting current (5 to 9 times the full load current) necessity of starters to avoid damages on lines, and voltage drops on the distribution circuits. Converter or special arrangement are to be provided for speed variation or starting (ex: star/delta starting, autotransformer, etc). Low power factor (0.8) ( = active power (kW) / apparent power (kVA) ) Low air gap : less suitable to withstand harsh mechanical conditions Rotating machines Asynchronous machine

11 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Limitation of Foucault currents (heating phenomenon) Rotating machines Asynchronous machine

12 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 T sensor Rotating machines Asynchronous machine

13 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Rotating machines Asynchronous machine

14 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Asynchronous motor : stator Rotating machines Asynchronous machine

15 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Asynchronous motor : rotor Rotating machines Asynchronous machine

24 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Wound rotor motor Rotating machines Asynchronous machine

25 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Nb: this curve is to be transmitted when the overload test hasnt been done to check the capacity of withstanding a momentary excess of torque Rotating machines Asynchronous machine

26 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 N CeCe Alternator zone Motor zone NsNs g =1 g = 0 C max Working in asynchronous motor mode Working in asynchronous generator mode Rotating machines Asynchronous machine

27 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Asynchronous motor : star / delta connections 380 V 220 V 380 V Star connectionDelta connection Rotating machines Asynchronous machine

28 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Insulation class When the motor is started, his temperature starts to increase. Each insulating material has a maximum allowable temperature, depending of his class (IEC 60085 ; A : 105C, E : 120C, B : 130C, F : 155C, H : 180C). The sum of the temperature rise and the ambient temperature is not to be above the limit defined by the insulation class, minus a margin defined for each electrical device. Operating a motor above the limit of its insulation class reduces the motors life expectancy. Rotating machines Asynchronous machine

29 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Duty types S1 : Operation at a constant load maintained for a sufficient time to allow the machine to reach thermal equilibrium. S2 : Operation at a constant load maintained for a given time, less than that required to reach thermal equilibrium, followed by a time de-energized and at rest of sufficient duration to re-establish machine temperatures within 2 K of the coolant temperature. S3 : a sequence of identical duty cycles, each including a time of operation at constant load and a time de-energised and at rest. S4, S5, S6, S7, S9, S10 (less important) Nb : the Duty type is an important parameter for the choice of the motor Rotating machines Asynchronous machine

30 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Starting of asynchronous machine Star delta starting : windings of the stator are connected in star and afterwards in delta Part winding starting : a part of the stator windings is used to start the motor Transformer starting : the motor is connected to a autotransformer Soft starting : the motor is connected to a static converter Rotor resistors starting : several resistances are connected to the rotor (wound rotor) Rotating machines Asynchronous machine

31 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Motor panel Efficiency = mechanical shaft power (W) / electrical power (W) Motor speed Motor service: S1 permanent service S2 temporary service S3 periodical service IEC Ambient temperature (Nb: 45C for BV Rules) Isolation class Rotating machines Asynchronous machine

32 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Motor panel I starting Starting torque Rotating machines Asynchronous machine

33 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Wound Rotor Motor panel Rotor Voltage and Current Used for sizing of variable resistances associated Rotating machines Asynchronous machine

SYNCHRONOUS MACHINE

35 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Principle of an synchronous machine N S w S N w Stator windings supplied by AC Voltage at certain frequency creates a turning magnetic field (synchronism speed) Rotor windings supplied by a continuous current that make the rotor acting like a permanent magnet that try, at all time, to be in line with the turning field of the stator (no slip) Rotating machines Synchronous machine

36 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Principles of synchronous machine Synchronous motors are the most commonly used type of motor for electric propulsion Most of the motors have double winding Power factor can be adjusted to 1 New type of permanent magnet motors are becoming common The power factor can be adjusted to unity by using a proper field excitation current relative to the load Synchronous motors are started by a converter, as an asynchronous motor or by a pony motor (the pony motor brings the rotor at the synchronous speed where the excitation can be switched on) Synchronous machines are generally used as alternators. Rotating machines Synchronous machine

37 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Synchronous machine with slip rings Rotating machines Synchronous machine

38 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Excitation of synchronous machine Rotating machines Synchronous machine

39 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Synchronous machine without slip rings A B C ROTOR STATOR N S DC SUPPLY Rotating machines Synchronous machine

40 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Synchronous machine inside a POD Rotating machines Synchronous machine

41 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Diesel alternator Diesel engine (speed regulation) IeIe + - NSNS Exciter (voltage regulation) Synchronous machine Rotating machines Synchronous machine

42 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Synchronous alternator The active power (mechanical power) comes from the diesel engine. Reactive power comes from the exciter. Cos (phi) is defined by the network. Precautions are to be taken to connect alternators in parallel (same voltage, same frequency, same phase) Rotating machines Synchronous machine

DC MOTOR

44 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 DC machine Advantages Easy to control Good speed variation Reversal and high torque at low speed Disadvantages Power limitation (10 MW) Higher volume and mass Higher construction cost Higher maintenance cost because of the brushes Rotating machines DC machine

45 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 DC Motor Based on Laplaces forces: a conductor crossed by a current and place in a magnetic field is submitted to Laplaces forces 1 2 3 4 4 3 2 1 B B F F Rotating machines DC machine

46 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 DC machine Brushes Slip rings Rotating machines DC machine

TESTING OF ROTATING MACHINE

48 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Tests of rotating machine : procedure The manufacturer is to issue a test report giving information concerning technical data relevant to the machine. This document is to be provided to the society for machines for essential services. For other machine, the test report is to be made available upon request of BV All machines of 100 kW and over, intended for essential services, are to be surveyed by BV and if appropriate during manufacturing. Rotating machines Testing

49 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Type tests and routine tests Rotating machines Testing

50 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Overspeed test For AC machines, 1.2 times the maximum rated speed. The duration is 2 minutes. The test is satisfactory if no permanent abnormal deformation is apparent subsequently and no other weakness is detected. After the test, the rotor windings are to comply with the required dielectric test. Rotating machines Testing

51 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Withstand voltage test : Withstand voltage test shall be carried out immediately after the thermal test (when carried out) Test to be applied between the windings under test and the frame of the machine (core and windings not under test connected to the frame). Machine of less than 1 kW to be tested at 500 V + 2 x U. Machine of more than 1kW to be tested at 1000 V + 2 x U. The full voltage is to be maintained for 1 minute. In case of second test, the test voltage shall be 80 % of the voltage specified above Partially rewound windings are to be tested at 75 % of the test voltage for a new machine Rotating machines Testing

52 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Occasional excess current A current in excess of the rated current will result in increased temperature. The heating effect varies approximately as the product of the time and the square of the current. AC generators having rated outputs not exceeding 1200 MVA shall be capable of withstanding a current equal to 1.5 times the rated current for not less than 30s. Polyphase motors having rated outputs not exceeding 315 kW and rated at voltages not exceeding 1 kV shall be capable of withstanding a current equal to 1.5 times the rated current for not less than 2 minutes. For polyphase motors having rated outputs exceeding 315 kW and for all single phase motor, no occasional excess current test is specified Rotating machines Testing

53 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Momentary excess torque for motors Polyphase induction motor : it shall be capable of withstanding an excess torque of at least 60 % of the rated torque for 15 s, without stalling or abrupt change of speed (voltage and frequency at their rated value). For wound motor, the torque excess is 35 %. Polyphase synchronous motor : it shall be capable of withstanding an excess torque without falling out of the synchronism. The excess of torque depends on the technology of the rotor. Unless otherwise agreed, the excess of torque is 35 % for a cylindrical rotor and 50 % for a salient rotor (duration of 15 s) Rotating machines Testing

54 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Temperature rise test The temperature rise of a part of a machine is the difference between the temperature of that part, measured by the appropriate method and the temperature of the coolant. For propulsion motor, is necessary to consider the supplementary thermal losses induced by harmonic currents in the stator winding (to be checked during sea trials) Rotating machines Testing

55 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Methods of measurements of temperature Resistance method : the temperature of the windings is determined from the increase of resistance of the windings. Embedded temperature detector (ETD) method : the temperature is determined by means of temperature detectors (e.g. Resistance thermometers, thermocouples,...) built into the machine during construction, at point which are inaccessible after the machine is completed. Thermometer method : the temperature is determined by thermometers applied to accessible surfaces of the completed machine. Thermometers include bulb thermometers, non-embedded thermocouples, resistance thermometers. Rotating machines Testing

56 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Cooling : Cooling mediums are based on air, hydrogen, water, . Cooling systems are based on a primary coolant and (if any) a secondary coolant Primary coolant : a medium which removes heat from parts of a machine Secondary coolant : a medium which removes heat given up by the primary coolant by means of a heat exchanger or through the external surface of the machine The method of cooling can be either direct or indirect Direct cooled winding : winding cooled by coolant flowing in direct contact with the cooled part (through hollow conductors, tubes, ducts, .) Indirect cooled winding : any other winding cooling than a direct cooled winding Rotating machines Testing

57 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Ducts (direct cooled winding) Rotating machines Testing

58 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Temperature rise limits (BV rules, ambient temperature of 45C) : Rotating machines Testing

59 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Reference coolant from IEC Temperature of the ambient air is not considered Cooling through the external surface of the machine Rotating machines Testing

60 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Temperature rise limits from IEC (indirect) Rotating machines Testing

61 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Temperature rise calculation : Most of the high powered motors (thrusters, propulsion motors) are based on an air / water indirect cooling system. Example of a thruster : 1.5 Mw, class F, air / water indirect cooling system, water temperature at 37C t=105+15-(37-25)=108C Rotating machines Testing

62 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Indirect test method for synchronous machines Rotating machines Testing

63 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Verification of steady short circuit current : Under steady short circuit condition, the generator is to be capable of maintaining, without sustaining any damage, a current of at least three times the rated current for a duration of at least 2 s (or any time delay which may be fitted in a tripping device). Rotating machines Testing

64 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Load impact for alternators : According to IEC 6092-301, governors shall be such that they will maintain the speed within a momentary variation of 10 % and a permanent variation not exceeding 5 % when the rated load is suddenly thrown off and when 50 % load is suddenly thrown on, followed after a short instant by the remaining 50 % load. The application of load in more than 2 steps is permitted in some cases. The recovery time is to be less than 5 seconds. IEC 60092-301 also defines voltage variations when a load equivalent to 60 % of the rated current (or maximum load on board) is applied (85% to 120 % of the nominal voltage, with a restoration within + / - 3% in not more than 1.5 seconds). Requirements are different for emergency sets (+ / - 5 % in not more than 5 seconds). Rotating machines Testing

65 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Loads on alternators running in parallel : For a.c. generating sets operating in parallel, the governing characteristics of the prime movers are to be such that, within the limits of 20% and 100% total load, the load on any generating set will not normally differ from its proportionate share of the total load by more than 15% of the rated power in kW of the largest machine or 25% of the rated power in kW of the individual machine in question, whichever is the lesser. When a.c. generators are operated in parallel, the reactive loads of the individual generating sets are not to differ from their proportionate share of the total reactive load by more than 10% of the rated reactive power of the largest machine, or 25% of that of the smallest machine, whichever is the lesser. Rotating machines Testing

66 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Specific test for high voltage rotating machine A frequency high voltage test is to be done on the individual coils. This test is to be done on the coils after they have been inserted in the slots. The purpose is to verified that the coils have not been damaged during the insertion. Due to the various technologies involved, no general requirements can be specified for the test values Rotating machines Testing

REQUIREMENTS FOR ROTATING MACHINES

68 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Rotating machines REQUIREMENTS Classification Rules requirements to be studied

3 Transformers and requirements

Transformers principles

71 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Working principle A transformer is an electrical device that transfers energy from one electrical circuit to another one by magnetic coupling but without any moving parts. Transformer consists in two windings (or coils) with the exception of autotransformers. Primary winding is fed by alternating current which produces changing magnetic field. Secondary winding which is placed in this varying magnetic field develops alternating voltage and a current when the secondary side is connected to a load (A transformer is a voltage generator) Transformers Principles

72 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Two separate windings transformer Electric diagram V1 I1 V2 I2 V2 V1 n2 n1 I1 I2 n2 n1 Primary winding Secondary winding Magnetic circuit Transformers Principles

73 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Generalities As energy is transfer by magnetic coupling transformer provides a galvanic isolation. Ratio of voltage between primary and secondary windings is just ratio in turn of the two windings V 2 = (N 2 /N 1 )V 1 Set down and set up voltage transformer used the same principle Power delivered by a transformer cannot exceed the power fed into it. Efficiency of transformers is about 98%. Transformers Principles

74 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 V2 V1 n2 n1 I1 I2 V1 I1 V2 I2 n2 n1 Transformers, except those for motor starting, are to be double wound (two or more separate windings). Auto-transformer Common winding transformer Electric diagram Transformers Principles

75 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Current transformer Electric diagram Used for measurement of current in high voltage installation Transformers Principles

76 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 V1 I10 L1 n2n2 n1n1 n2n2 n1n1 I2 I1 I2 V2 Rf I1F I1V Rs V1 n2n2 n1n1 Ls V2 V1 n2 n1 I1 I2 Equation - Formulas Electric diagram Transformers Principles

77 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 2 B = n1 S V1 B saturation e=d /dt B or I Saturation Saturation Limit of use Saturation curve Transformers Principles

78 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Magnetic circuit - principle The lines of the magnetic field pattern run through the coil, spread out from the end and go round the outside and in at the other end (Fig 1). The purpose of the magnetic circuit is to concentrate the magnetic field, to avoid flux leakages (Fig 2). Fig. 1Fig. 2 Transformers Principles

79 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Magnetic circuit - principle As magnetic circuit is a conductor, voltage will generate induced wasteful currents (called Eddy current) causing resistive heating of the core. To limit these currents, magnetic circuit is to be poor conductor. So it is made of steel laminations made of thin insulated (varnish) iron sheets clamped together. Transformers Principles

80 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Arrangement of transformers Diagram showing windings and magnetic circuit Primary winding Secondary winding Single Phase Transformer Three Phases Transformer Magnetic circuit Phase 1 Phase 2 Phase 3 Transformers Principles

81 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturing of transformer Picture of magnetic circuit Transformers Principles

82 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturing of transformer Picture of windings Transformers Principles

83 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturing of transformer Picture of windings before impregnation Transformers Principles

84 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturing of transformer Picture of dry type transformer Transformers Principles

85 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturing of transformer Picture of connection heads of a dry type transformer Transformers Principles

Transformers main parameters

87 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Type - Dry type Pictures of dry type transformer Transformers Main parameters

88 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Type - Oil immersed Pictures of oil immersed transformer (sealed/hermetic type) -Drain valve -Drip tray for collecting oil leakages -Non-toxic oil and not supporting combustion -Gas-actuated protection device Transformers Main parameters

89 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Type - Oil immersed Oil immersed transformer (breathing type) Conservator Transformers Main parameters

90 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Type - Oil immersed Pictures of oil immersed transformer (breathing type) - Design to prevent risk of spilling liquid when inclined - Provision for breathing (suitable dehydrator) Transformer installed aboard Queen Mary 2 Transformers Main parameters

91 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Time index : phase displacement between primary side and secondary side (important for transformers working in parallel). The phase displacement is usually expressed by using a clock-hour figure. In this example low voltage vector lagging the high voltage vector by an phase angle of 30 Coupling Dy 11 coupling A B C b c a 0 11 Dy11 a bc A B C LV side HV side n 12 3 6 9 Transformers Main parameters

92 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Coupling Other possible couplings Transformers Main parameters

93 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 I 2N I 1N U %. U N12 U %. U N23 U %. U N13 Short-circuit characteristics Definition of Ucc Ucc is the percentage of the primary voltage that produces the nominal current when the secondary side of the transformer is short circuited. Short-circuit impedance of a transformer Z T = U CC. U S N U : No load phase-to-phase voltage S N : Transformer kVA rating For information : Transformer of 630 kVA U CC = 4% Transformer of 2500 kVA U CC = 6% Transformers Main parameters

94 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 V1 I1 V2 I2 Z2 E2 + n1 n2 Transformer impedance Voltage on secondary side to be adjusted when transformer is loaded (tapping points: -5%, -2.5%, 0, +2.5%, +5%). Transformers Main parameters

95 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturer plate Example 1: Transformers Main parameters

96 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Manufacturer plate Example 2: Transformers Main parameters

Transformers requirements

98 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Design of transformers (BV rules) Transformers, except those for motor starting, are to be double wound (two or more separate windings). Transformers are normally to be of the dry type. When a forced air cooling system is used, an alarm is to be activated in the event of its failure. Liquid-cooled transformers are accepted with some conditions (non toxic liquid, temperature and pressure alarm, liquid gauge,....). Transformers Requirements

99 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 System design with transformer (BV rules) Where transformers, converters or similar appliances constitute an essential part of the electrical supply system, the system is to be so arranged as to ensure a continuity of supply. This may be achieved by arranging at least two three-phase or three single-phase transformers At the secondary side: Delta connection or star connection with a spare part. Each transformer required is to be located as a separate unit with separate enclosure or equivalent, and is to be served by separate circuits on the primary and secondary sides. Suitable interlocks or a warning label are to be provided in order to prevent maintenance or repair of one single-phase transformer unless both switchgears are opened on their primary and secondary sides. Transformers Requirements

100 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 System design with transformer (BV rules) Transformers Requirements

101 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Primary side Secondary side Three single-phase transformers Arrangement diagram Transformers Requirements

102 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Transformers working in parallel The voltage ratio are to be identical. The time index are to be identical. The Ucc% are to be identical (ratio between 0.9 and 1.1) Provisions are to be provided to trip the switch on secondary winding side when the corresponding switch on the primary side is open. Transformers Requirements

103 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Transformer working in parallel 630 kVA 400V / 230V Dyn11 Ucc: 6% I 400 V 230 V 630 kVA 400V / 230V Dyn11 Ucc: 6% I Transformers Requirements

104 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Generalities The tests and, if appropriate, manufacture of transformers of 100 kVA and over (60 kVA when single phase) intended for essential services are to be attended by a Surveyor of the Society. Transformers of 5 kVA up to the limit specified above are approved on a case by case basis, at the discretion of the Society, subject to the submission of adequate documentation and routine tests. Transformers Requirements

105 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Document to be submitted For the case by case certification of power transformers, following documents are to be submitted to LPO for examination. Drawings are to be approved and all comments cleared before inspection at works. Technical data sheet General arrangement/main dimensions diagram Auxilaries connection diagram (e.g. temperature sensors, protection device for oil immersed type transformer) Test procedure For transformer with a forced cooling system Cooling circuit arrangement + BV certificate of main auxiliaries (heat exchanger, electrical motor of pump) For breathing transformers Justifications that precautions have been considered to prevent oil spillages Transformers Requirements

106 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Test of transformers On new transformers intended for essential services tests are to be carried out. The manufacturer is to issue a test report giving technical information and the results of the tests required. Such test reports are to be made available to the Society. In the case of transformers which are completely identical in rating and in all other constructional details, it will be acceptable for the temperature rise test to be performed on only one transformer. Transformers Requirements

107 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 High voltage test Transformers are to be subjected to a high voltage test. Test intended to verify the AC withstand strength of the line and neutral terminals and their connected windings to earth and other windings. The r.m.s value of the test voltage defined by BV rules is to be equal to 2 x U + 1000 (minimum 2500 V). Repeated dielectric tests are to be carried at 80% of the test voltage required for new machine. IEC 60076 requires to test the low voltage transformer at 3000 V. For high voltage transformer, BV rules refer to IEC 60076 (for a 6.6 kV transformer, the test voltage is 20 kV). Full voltage is to be maintained for 1 minute. Test is successful if no collapse of the test voltage occurs. Transformers Requirements

108 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 High voltage test Test description Repeated dielectric: For transformers which have been already been in service and have been refurbished or serviced, the dielectric test shall be repeated at test levels of 80 %. Transformers Requirements

109 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Induced voltage test Test intended to verify the insulation between windings and between phases. Weakness in dielectric design during manufacturing may cause partial discharge activity during induced voltage test. Internal insulation is to be checked by applying 2 times the rated voltage of the transformers. In order not to exceed the usual induction, this test can be made with a voltage source having a frequency of at least twice the rated frequency. The test time at full test voltage is to be 1 minute for any test frequency up to 2 x F rated. When the test frequency exceeds twice the rated frequency, the test time can be reduced to 120 x F rated / F test (but not less than 15 sec). Transformers Requirements

110 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Induced voltage test Test description VV U TEST = U N x 2 Duration of test : (at least 15 s) 120 x F N F TEST Transformers Requirements

111 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Temperature rise test Transformers are to be submitted to a test under the rated load current. This test is to last long enough for temperature stabilising (2 K per hour). The permissible limits of temperature rise with an ambient air temperature of 45C for (natural or forced) air-cooled transformers are given next page. The temperature rises shown for windings refer to measurement by the resistance method while those for the core refer to the thermometer method. Transformers Requirements

112 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 I 2N I 1N U % xU N12 U % xU N23 U % xU N13 U 12 U 23 U N13 Temperature rise test The test is to be carried out at rated power. The test can also be split in 2 parts : nominal voltage and nominal current. The temperature rise is then calculated. Transformers Requirements

113 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009 Classification Rules requirements to be studied Transformers Requirements

114 Bureau Veritas S.A. internal use only BVN TM ELEC3 V0 December 2009

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