Reciprocating engines

Aircraft engines, marine engines, automotive engines and stationary engines are examples of reciprocating engines. Engine can be designed on the basis of the otto cycle where fuel is mixed with air before compression. In otto engine, combustion takes place with no excess air. In diesel engines, fuel is injected near the end of the compression and combustion takes place with much excess air. Spark ignition is employed in otto engines where volatile fuels are used. Low volatile fuels are used for its operation in diesel engines where ignition is by compression. Depending upon the number of piston strokes required for the complete combustion cycle, there exist two varieties in the engine- two stroke and four stroke. In two stroke engines, piston uncovers exhaust ports in the cylinder wall near the end of the expansion stoke and permits the exhaust gases to flow out. The various events that occur in four stroke engine are stroke, exhaust, suction and compression. According to the arrangement of cylinders with each other and the crankshaft, there exist three types of engines. They are three-cylinder in-line engine, five-cylinder in-line engine and V-type engines. V-type engine has two banks of in-line cylinders connected to a single crankshaft.

Protecting a transformer

Mainly there are two faults that can occur in transformers. They are internal faults and external faults. Internal faults are of three types. They are incipient faults, winding faults and terminal faults. The main incipient faults are fault due to the breakdown of core lamination, breakdown of bolts and clamps, earthing fault, coolant failure, oil flow fault etc. Terminal faults are associated with high voltage or low voltage terminals and winding faults are associated with windings. External faults include the appearance of overcurrent for short duration, short circuit outside the transformer and overloading. Different methods employed for the protection of transformers are electromagnetic protection, differential protection, percentage biased differential protection, tank leakage protection, restricted earth fault protection and digital protection.