Synchronous generator Loss of Excitation (LOE) if dose not detected rapidly; not only has a harmful affect on the generator, but also has a devastating impact on power system stability. This paper presents a novel method for detecting Loss of Excitation in synchronous generator based on change in the magnetic flux linkage. Generator air gap flux linkage is measured via search coils sensor installed under the stator wedges. The searchcoil sensor is widely used in electrical machine monitoring in recent years. Theoretical approach based on Finite Element Method (FEM) together with experimental results derived from a 4-pole, 380V, 1500 rpm, 50 Hz, 50 KVA, 3-phase salient-pole synchronous generator confirm the validity of the proposed method. Extensive simulations show that the proposed method has various distinct features that are advantageous over existing schemes. Speed and sensitivity are the main points featured in the proposed method. The effectiveness of the proposed protection is demonstrated by comparing with conventional LOE protection. INTRODUCTION The generators are the main and significant parts of power system and their failure can cause severe damage on the machine, interruption of electrical supply, and consequently economic loss. A synchronous generator requires sufficient DC voltage and current to its field winding to retain synchronism with a power system. As a rule, the generator field is adjusted so that reactive power as well as real power is delivered to power system. The excitation may be completely or partially lost due to accidental tripping the field breaker, field open circuit, flashover of the slip rings, regulator failure or loss of supply to the excitation system. The behavior of a generator in any case of field loss will depend on its initial loading, machine and system characteristics and the governor. If the field loss occurs at full load the stator currents may be as high as twice the full load current and high currents may be induced in the rotor. An overheating of the generator may occur quickly under these circumstances. The condition must be rapidly distinguished and to 10-E-CAP-1278

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