ACTA TECHNICA CORVINIENSIS - Bulletin of Engineering

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ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERINGAuthority for Scientific Research in the NucleuProgram.TESTS FOR THERMAL ENDURANCETO HEAT AND COLDThe thermal endurance to heat shall bedetermined by submitting the enclosures orparts of enclosures in non-metallic materials, onwhich the integrity of the type of protectiondepends, to continuous storage for four weeks at(90 ± 5) % relative humidity at a temperature of(20 ± 2) K above the maximum servicetemperature, but at least 80 °C.In case of a maximum service temperatureabove 75 °C, the period of four weeks specifiedabove shall be replaced by a period of twoweeks at (95 ± 2) °C and (90 ± 5) % relativehumidity followed by a period of two weeks inan air oven at a temperature of (20 ± 2) K higherthan the maximum service temperature.The thermal endurance to cold shall bedetermined by submitting the enclosures andparts of enclosures of non-metallic materials, onwhich the type of protection depends, to storagefor 24 h in an ambient temperaturecorresponding to the minimum servicetemperature reduced by at least 5 K but at most10 K.Figure1. Control and monitoring panel for climaticchamber Vötsch, type VC 7060The test rig designed for these tests consists in aclimatic chamber Votsch type VC 7060, having acapacity of 0,6 m 3 , and the temperature can beadjusted in the range -70 ÷ +180 ˚C. The resultof test is considered positive if the exposedapparatus shows no deteriorations that affectthe type of protection.TEST OF ROTATING ELECTRICAL MACHINES.DETERMINATION OF TIME, t ETime t E represents the time taken for an a.c.rotor or stator winding, when carrying the initialstarting current IA, to be heated up to thelimiting temperature from the temperaturereached in rated service at the maximumambient temperature.The diagram illustrating determination of time t Eis given in figure 2.Figure 2 – Diagram illustratingthe determination of time t EKey: A Highest permissible ambient temperatureB Temperature in rated service; C Limiting temperature;t Time; θ Temperature; 1 Temperature rise in ratedservice; 2 Temperature rise during stalled rotor testThe temperature rise in stalled motors shall bedetermined experimentally as follows:With the stalled motor initially at ambienttemperature, rated voltage and ratedfrequency shall be applied.The stator current measured 5 s afterswitching on shall be considered to be thestarting current I A .The temperature rise in the rotor cage (barsand rings) shall be measured bythermocouples and measuring instrumentshaving a small time constant compared withthe rate of temperature rise, or bytemperature detectors or other means. Thehighest of the temperatures obtained duringthese measurements is the one to beconsidered.The average temperature rise of the stator,determined from resistance measurements,is taken as the temperature rise of thewinding.When the stalled motor test is made at a voltageless than rated voltage, the measured valuesshall be increased proportionally to the ratio ofthose voltages, directly for the starting current582010/Fascicule 2/AprilJune /Tome III
ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERINGand according to the square of the temperaturerise. Saturation effects, if any, shall be taken intoaccount.The block diagram for the test rig used todetermine time t E is given in figure 3. To fulfil thetest rig the following apparatus was acquired:power analyzer Fluke 435, milliohmmeterCropico DO5001, data acquisition system Agilent34970A with thermocouples, laptop Dell LatitudeD830.Figure 4. Test rig to determine maximum surfacetemperature for electrical rotating machinesFigure 3. Block diagram of the test rig used todetermine time t EThe role of Fluke 435 power analyzer is tomeasure and record the important parameters(voltage, current, frequency, power factor, etc.)during the test.The Cropico DO5001 milliommmeter measureand record the values for the stator windingresistance in cold state and after the test..The data acquisition system Agilent 34970A withthermocouples is used to measure and monitortemperature during test.DETERMINATION OF MAXIMUM SURFACETEMPERATURE FOR ELECTRICAL ROTATINGMACHINESIn order to determine the maximum surfacetemperature the following apparatus is used:power analyzer Fluke 435, milliohmmeterCropico DO5001, data acquisition system Agilent34970A with thermocouples, tachometer LutronL1236L, laptop Dell Latitude D830.To determine the maximumsurfacetemperature the following steps should becovered:build-up experimental mounting accordingblock diagram from figure 4, and connectthe electric motor to adjustable load test rig;the stator winding resistance is measuredand recorded, in „cold” state, with the helpof Cropico DO 5001 microohmmeter;the thermocouples connected to Agilent34970A data acquisition system are placed inpoints considered to be the hottest pointsduring motor running;the adjustable load test rig is powered-onand the electric motor is driven on lowspeed;the electric motor is powered-on through a3-phase contactor;the load is adjusted until the motor speedreaches nominal speed (rotation speed ismeasured with the help of Lutron 1236Ltachometer);in this configuration, the system will functionuntil the maximum temperature in normalfunctioning is reached, according SR EN60079-0 and SR EN 60079-7 (temperaturerising is lower than 2 K/ hour);after reaching the maximum surfacetemperature, the motor is powered-off andthe adjustable load rig is driven so as to givea quick stop of the motor.the stator winding resistance is measuredand recorded, with the help of Cropico DO5001 microohmmeter;The rotor temperature is measured withthermocouples placed on the rotor throughsome holes affected in the drive-part shield.Delay time after power-off to determineovertemperature in rated service is presented intable 1.2010/Fascicule 2/AprilJune /Tome III 59
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ACTA TECHNICA CORVINIENSIS - Bulletin of Engineering

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