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Xie X.,Tsinghua University | Guo X.,Northern United Power Corporation | Han Y.,Tsinghua University
IEEE Transactions on Power Systems | Year: 2011

The Shangdu power plant has four 600-MW turbine-generators connected to the North-China Grid through two 500-kV transmissions, which are compensated with 45% fixed series capacitors. Extensive studies conducted on the system model indicate that the system suffers from multimodal subsynchronous resonance (SSR). To solve the problem, a countermeasure is developed by combining the supplementary excitation damping control (SEDC) and the torsional stress relay (TSR). In this paper, the characteristics of the SSR problem are investigated. Then the developed SEDC is presented. To validate the effectiveness of the proposed SEDC as well as the results of model studies, field tests were conducted under various operating conditions. The tests fully exposed the realistic threat of SSR in the system. Meanwhile, it is demonstrated that the developed SEDC can improve torsional damping significantly, and thus solve the multimodal SSR problem effectively. This is the first time in China that practical SEDCs have been developed and their ability to mitigate multimodal SSR has been verified in a real series-compensated system. © 2010 IEEE.

Xie X.,Tsinghua University | Wang L.,Tsinghua University | Guo X.,Northern United Power Corporation | Jiang Q.,Tsinghua University | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2014

This paper presents a novel controlling device, named generator terminal subsynchronous damper (GTSSD), to mitigate subsynchronous resonance (SSR) in the power system. The proposed GTSSD consists of a multimodal complementary current calculator (MCCC) and a complementary current generator (CCG). The CCG is composed of a current tracking controller and a power-electronic converter. The rotor speed deviation of the generator is fed back to the MCCC to calculate the current references of the CCG. The outputs of CCG consist of both sub-and supersynchronous complementary current, part of which flows into the generator and creates damping torque on the rotor. The relationship between the control parameters of the GTSSD and the resultant damping improvement is derived. A 10-MVA GTSSD prototype has been developed and tested in an actual series-compensated power system. The experimental results fully demonstrate its ability to enhance torsional damping and to depress subsynchronous oscillation, proving that the GTSSD provides a new and effective approach to solve SSR problems. © 2013 IEEE.

Xie X.,Tsinghua University | Dong Y.,Tsinghua University | Liu H.,China Electric Power Research Institute | Kang J.,Northern United Power Corporation
International Journal of Electrical Power and Energy Systems | Year: 2014

Torsional parameters, especially modal frequencies and mechanical damping, of large turbine generators play critical roles in evaluating and solving the subsynchronous resonance or oscillation (SSR/SSO) problem. To accurately identify these torsional parameters, this paper proposes a systematic approach based on the supplementary-excitation-signal-injection test. The identification process is fulfilled via three steps, i.e., (i) accurate detection of modal frequencies by stimulating controllable torsional vibration with the injection of supplementary modal signals into the excitation system; (ii) online identification of total modal damping using modal filtration, improved discrete Fourier transform (DFT) and least-square fitting technique; (iii) separating electrical damping from the identified modal damping to get the pure mechanical modal damping. The proposed approach was verified through digital simulation and then was applied to the torsional-parameter identification of four practical turbine-generators in Shangdu Power Plant. The results demonstrated that, with the proposed approach, the modal frequencies and mechanical damping can be obtained accurately, intactly and without interfering with the normal operation of on-grid generators. © 2013 Elsevier Ltd. All rights reserved.

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