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Basic Structure and Working Characteristics of Diesel Generator Set

Basic Structure and Working Characteristics of Diesel Generator Set

Diesel generator is a mechanical device that converts the chemical energy of diesel into mechanical energy, and then from mechanical energy into electrical energy. Its power generation principle is to drive the crankshaft of the diesel generator through other auxiliary power to make the piston move up and down on the top of the closed cylinder. When the piston moves from top to bottom, the cylinder intake valve opens, and the outdoor air enters the cylinder after being filtered by the air filter device to complete the intake stroke. When the piston moves from bottom to top, the intake and exhaust valves of the cylinder are closed. Under the upward squeeze of the piston, the gas volume is rapidly compressed, causing the temperature in the cylinder to rise rapidly, completing the compression stroke. When the piston reaches the top end, the fuel filtered by the oil filter device is atomized and sprayed by a high-pressure fuel injector, and mixed with high-temperature and high-pressure air to burn vigorously. At this time, the gas volume expands rapidly, pushing the piston downward to do work. Each cylinder performs work sequentially in a certain order, and the thrust acting on the piston becomes the force that pushes the crankshaft to rotate through the connecting rod, thereby driving the crankshaft to rotate and complete the work stroke. After the work stroke is completed, the piston moves from bottom to top, the exhaust valve of the cylinder opens to exhaust, and the exhaust stroke is completed. The crankshaft rotates half a circle for each stroke. After several working cycles, the diesel engine set gradually accelerates the rotation work under the inertia of the flywheel.

What is going on in the above process is the conversion of chemical energy and mechanical energy, so how is mechanical energy converted into electrical energy? Structurally, the synchronous alternator is coaxially installed with the crankshaft of the diesel generator, and the rotation of the diesel generator is used to drive the rotor of the generator to rotate. Due to the remanence of the pole core of the generator, the armature coil cuts the lines of magnetic force in the magnetic field. According to the principle of electromagnetic induction, the generator will output the induced electromotive force, and the current can be generated through the closed load circuit.

As we all know, synchronous generators require DC current excitation. The power supply and its auxiliary equipment that supply the excitation current of the synchronous generator are collectively called the excitation system, which is generally composed of an excitation power unit and an excitation regulator. The excitation power unit provides excitation current to the rotor of the synchronous generator, and the excitation regulator controls the output of the excitation power unit according to the input signal and a given regulation criterion.

Among them, the excitation system provides an important role for the safe and stable operation of the generator itself: 1) Adjust the excitation current according to the change of the downstream load of the generator system to maintain the output voltage of the generator; 2) Control the generators in the parallel system Reactive power output; 3) Improve the static stability and transient stability of the parallel operation of generators; 4) Realize the maximum and minimum excitation limits according to the generator operating conditions; 5) When a fault occurs in the generator system, Autonomous de-excitation operation to reduce the degree of failure loss.