FAILURE ANALYSIS OF A 360 MW POWER UNIT GENERATOR

摘要

Agios Demetrios is one of the largest lignite power stations of the Public Power Corporation of Greece-PPC, situated in the North-West area of Greece. It consists of four Units of 360 MW nominal capacity (No 1 to 4) and a step-up to 400 kV substation. Late in the evening of 25-12-2001 (exactly at 21:11) explosion of the 400 kV voltage transformer occurred (in phase A of the Unit No 4) that resulted in the destruction of the generator of Unit No 2 and in extensive consumers interruption. This happened due to the fact that catapulted fragments of the exploded voltage transformer, provoked serious damage of one of the 400 kV isolators of the Unit No 2, so that the phase B of the Unit remained connected to the power system, although the main circuit breaker was opened by the operation of the protective relays. As a result, the generator of the Unit was destroyed by overheating. In this paper, first, a short presentation of the power station and a description of the events and damages are given. Next, the detailed analysis of the failure is effectuated by simulation, using the equivalent circuits of the main components of the system. Based on this analysis the behavior of the damaged generator during the fault is assessed. The results are compared to the registration of the instruments of the power station and the distance relays of the nearby substations. The expected overheating of the rotor is also assessed. The correctness of the simulation of the failure was verified by the comparison of recorded real values to the corresponding calculated ones. The results are presented and discussed in detail.