COMPRESSER

The types of compressor are used in railway coaches- shielded and unshielded type. Shielded type is used in rmpu and unshielded in under slung coaches.

This compressor is of single action reciprocation type and has four cylinders. The cylinder block arrangements of SMC-4-65 are of ‘V’ design and have following details-

               Compressor type                  : 4-65

               Arrangements of cylinders   : V

               No. of cylinders                   : 65

               Cylinders diameter (mm)     : 50

All the compressors are fitted with an automatic capacity control device, which varies the capacity of the compressor according to the variation of refrigeration load requirements, and also allows the compressor to start partially unloaded.

The compressor has following technical constructional data:

Compressor Frame- Cast in one piece of the height quality alloy cast iron fitted with large inspection covers on both sides.

Cylinder Liners- Cast from highly wear resistant alloy provisionally bored.

Pistons- Cast in Al alloy of high wear and corrosion resistance. Pistons are oval ground with two compression rings and one scraper ring.

Suction and discharge value- Ring plate type with valve plate made from finest quality strip steel.

Crankshaft- Of graphite cast iron of high tensile strength, exceptionally wear resistant, dynamically balanced to ensure vibration free operation.

Main Bearing- Precision made, steel backed white metal bushes.

Connecting rods- Die forged with white metal, steel backed big end bearings.

Lubrication System- Crankshaft drive, gear type pump draws oil from the sump via large fine mesh strainer, this being easily removable for cleaning. The pump delivers oil the main, and big end bearings, the crankshaft seal and also to the unloading and capacity control system. Correct pressure can be maintained by adjustable spring loaded valve.

Shaft Seal- Sliding ring type.

Unloading Mechanism- While the compressor is at standstill, the suction valve plates are lifted free from their seats (in case of 3 of the 4 cylinders) by springs in the unloading mechanism and the cylinder thus unloaded. When the compressor is started the action of the spring is counteracted by oil pressure. When the compressor is started the action of the spring is counteracted by oil pressure after which the suction values can operate.

Capacity Regulator- The unloaded mechanism is used as capacity regulator by which two of the cylinders can be rendered inoperative by means of solenoid valve. The standard compressor has manual capacity control, but automatic control is supplied for railway application.

Suction Strainers- Large, fine meshes and can easily remove for cleaning.

Safety devices- Compressor is protected by a discharge high pressure switch & suction low pressure switch.

The compressor is equipped with a crankcase oil pump for maintaining force feed lubrication to all bearing surface. The compressor crankshaft seal is of the metallic rotary type, the stationary and rotating scaling surface continuously immersed in oil.

CONVERTOR-:

          

It consists of following parts:

M.C.C.B:-It is the main circuit breaker which trips when the current increases beyond 130Amp due to overloading.

Earth leakage detector (E.L.D.):- It checks the earth leakage current in the output circuit and after a specified leakage current it trip the M.C.C.B.

DC-DC converter:- It gets 100-140 volt dc supply MCCB. The function of this converter is to convert this supply to 24volt dc and this 24 volt is send to booster and inverter.

DC choke:- It is at positive input supply in the circuit after MCCB and fuse. This device is used in the process of boosting of 650 volt DC.

Booster unit:- It gets 100-140 volt dc supply through MCCB and main fuses (F₁₁, F₁₂). After passing through F₁₁ this goes to dc choke and booster, where the combine effect of choke and booster unit change this supply to 650 volt DC.

Inverter unit:- This gets input supply of 650 volt dc, which is the output supply of booster. It converts this supply into 3-phase, 415 volt 50Hz ac volt.

Cubical fan:- It work on 415 volt, 50Hz ac supply. The main function of this fan is to exits the heat produce in the converter.

Operation of converter:-

             When we switch on MCCB, input supply of 100-140 volt dc reaches to DC-DC converter and after passing through main fuses (F₁₁, F₁₂) and choke it reaches to booster unit. 24 volt dc output obtained from DC-DC converter goes to fan through contacts (13, 14) of MCCB to the switch (S-1). When we switch on the S-1 booster unit begins to work. At inverter 24 volt dc is reaches directly and when booster unit begins to work, inverter unit also begun to work.

In this way dc supply obtained from booster is changed to 3-phase, 415volt, 50Hz ac supply.