14. starptautiskā konference 2012 - Latvijas Jūras akadēmija

Proceedings of 14th International conference „Maritime Transport and Infrastructure - 2012”TECHNICAL DIAGNOSTICS OF THE SHIP ELECTRIC COMPRESSORINSTALLATIONS ON THE BASIS OF MATHEMATICAL MODELAleksandrs Gasparjans*, Aleksandrs Terebkovs*, Anastasia Zhiravetska***Latvian Maritime Academy, 5B Flotes st, LV-1016, Latvia, E-mail: Aleksandrs.Gasparjans@latja.lv,aleksandrs.terebkovs@latja.lv.**Riga Technical University,14 Azenes st, LV-1048, Latvia. E-mail: zhiravecka@eef.rtu.lvAbstractThe system of technical diagnostics of double-stage electric compressor installation is described. Themodel is mathematically proved together with the block diagram of the measurement elements.KEY WORDS: compressor, induction motor, mathematical model, diagnosticsIntroductionThe obtaining of high pressures in single-stage compressors causes difficulties due to severalreasons:1. gas in a compressor is compressed according to polytrope law with the index of polytropen>1. The temperature of the compressed gas significantly exceeds the initial. Under this condition itcan achieve the temperature of cylinder oil flash, i.e. resulting in "diesel" effect;2. at high temperatures the process of cylinder oil oxidation is significantly accelerated;3. increasing of the ratio of initial pressure to its final value P 0 /P 2 results in decreasing of thecompressor effectiveness factor. For improvement of the effectiveness it is necessary to enlarge thesizes of the stage. This will result in the increasing of the mechanical and dynamic loads as well ascompressor sizes and weight;4. with the increasing of the ratio P 0 /P 2 the value of volume factor of the compressor stage isdecreasing. Thus all the compressed gas can be located in the volume of the died space and theexhaust valve will not open.1. Differential double-stage compressorFig. 1 demonstrates a differential double-stage compressor. Pistons of the first stage (lowpressure) 11 and high pressure 12 are one whole element. Air with its initial pressure Р 0 is inhaustedthrough filter 1 and through inhaust valve 2 of the first stage is proceeding to the cylinder space of thelow pressure. While piston 11 goes up the compressed air is extruded through the exhaust valve 3 tothe pathway of the average pressure Р 1 . This pathway is equipped with protective valve 5, sensor ofinstant pressure 6, refrigerator 7, moisture oil separator 8. Cooled and cleaned air of average pressureР 1 goes to the high pressure cylinder through exhaust valve 9. The compression of gas in the highpressure cylinder takes place due to the down movement of valve 11, 12. Relatively to thecompressing period in the cylinder of low pressure the compressing period in the second stage isshifted for 180 0 rotation angle of the crankshaft. It allows aligning of the torques on the shaft of thecompressor. The compressed gas of high pressure through the exhaust valve of the second stage 10and refrigerator 13 goes to moisture oil separator 16 and further to receiver 17 and then to consumers.The pathway of the high pressure has protective valve 14 and sensor of instant pressure 15. Theflywheel of the compressor has sign of top dead centre (TDC) with sensor of TDC 18. For defining theangular velocity and angular acceleration of the crankshaft the uniformly placed magnetic signs 20 andsensor of angular velocity 19 are used. The compressor is driven by means of three-phase inductionmotor 21.25