Research on Measurement and Protection for SSO and Shaft Torsional Vibration
Sub-synchronous oscillation (SSO) can occur when a generator is connected to a series compensated network,or to a HVDC converter station.When disturbance occurs,it may induce SSO currents in the generator stator windings.And then,serious SSO currents are able to increase generator iron loss.Furthermore,if the frequencies of SSO currents are synchronous frequency complements of the torsional natural modes of the turbine-generator shaft,which is considered as a spring-mass system,it will lead to torsional interaction,which consists of mechanical SSO and electrical SSO.The sub-synchronous torsional vibration may cause fatigue life expenditure and possible damage of shaft system.Two protection schemes - torsional stress relay (TSR) and over-current relay are presented in this paper for SSO. TSR deals with mechanical SSO and calculates shaft fatigue based on the rain-flow algorithm by measuring SSO speeds of shaft. Two protection criteria are developed, namely SSO divergence protection, and shaft cross section fatigue protection. Speed signal is critical for this scheme. For the sake of redundancy, four speed sensors are installed, two at turbine end and two at exciter end. Signals from these sensors are compared with each other to find a credible value in the way of voting, and then the calculated average speed is compared with the electric frequency of generator when generator is energized. With redundant fault-tolerant measures of rotational speeds, the anti-disturbance performance of TSR is improved. Even if mechanical SSO does not happen, considering that SSO armature current increases eddy loss in rotor, a novel time-delay over-current protection method is proposed that SSO currents are converted to an equivalent negative sequence current to cover the effects of positive, negative sequence components and the slip frequencies. By using multi-order band-pass filter (BPF), all the modal SSO currents are separated. The center frequency and the bandwidth of every BPF must be carefully selected. Both definite-time and inverse-time schemes are used.
Sub-synchronous oscillation (SSO) Shaft Torsional Vibration Torsional Stress Relay (TSR) Time-delay Over-Current Protection Turbine Generator Negative Sequence Static Blocking Filter (SBF)
Zhang Qixue Wang Kai Niu Honghai Wang Guang Chen Jun Shen Quanrong Zhao Xicai
NR Electric Co., Ltd.China
国际会议
国际大电网会议组织保护与自动化专业委员会年度会议暨学术研讨会
南京
英文
1-7
2015-09-20（万方平台首次上网日期，不代表论文的发表时间）