Technical aspects of the failure of the second generating set at the Sayano-Shushenskaya HPP

Abstract

Conditions under which hydromechanical processes proceeded immediately prior to the start of and during the failure of the second generating set at the Sayano-Shushenskaya HPP are examined.Since 2002, the Sayano-Shushenskaya HPP has been drawn into secondary frequency regulation within the power system, and capacity transfers. A signal for a change in the output of the HPP is delivered from the Centralized Dispatching Regulator "Sibir'" to the Group Active-Power Regulator (GAPR) of the hydroelectric plant, and from there to individual turbine-speed regulators controlling the variation in active power through variation in flow rate.The algorithm used for operation of the system for active-power regulation was developed in conformity with characteristics of the turbines at the Sayano-Shushenskaya HPP. It considers that within the range of average capacities, any Francis turbine exhibits increased pressure pulsations in the setting, which may be accompanied by vibration of subassemblies in the generating set (Zone II in Fig. 1). This is dictated by increased flow circulation at the discharge from the impeller, the existence of a low-frequency vortex core in the draft tube, and other transient effects owing to the low efficiency of the turbine at rather high flow rates.The region with increased pressure pulsations is bounded on the left by the basic adjusted range of the turbine (Zone III in Fig. 1), which falls within the limits from 490 to 640 MW with the turbine under the design head of 194 m, and decreases with increasing head. (Prior to the failure of 17 August 2009, the range was all of 70 MW under a head of 212 m -from 570 to 640 MW).Zone I with capacities ranging from 0 to 265 MW acted as the operating zone to broaden the plant's maneuvering potential. Transfer of the sets from operating Zone III to Zone I was carried out alternately in conformity with the priority system adopted. A certain priority ranging from 1 to 10 had been assigned to each set. When the regulated range for unloading into Zone I had been exhausted by the plant, the set with the highest priority was transferred from the operating range into Zone III. Accordingly, when the regulated range for loading had been exhausted, the set with the lowest priority was transferred from operating in Zone I to Zone III.Thus, the switching of Zone I into the operating regimes controlled by the GAPR increased the number of transfers of sets through Zone II during load adjustment. Previous transfers had occurred only during startups and shutdowns. The operation of some sets under individual regulation had also contributed to the increase in the number of the transfers through Zone II, reducing the regulated range of the HPP.In the period preceding the failure, nine generating sets (with the exception of GS6, which was being overhauled) were operating at the Sayano-Shushenskaya HPP. The following control scheme was in effect in conformity with the assignment made by the on-duty shift supervisor: sets GS1,

The Impact of Water Hammer on Hydraulic Power Units

“…The failure at Sayano-Shushenskaya HPP revealed a whole series of problems. The technical problems include: significant wear of basic hydropower equipment, lack of comprehensive monitor-ing of the technical condition, lack of automated systems and production safeguards for hydropower unit with respect to a number of important critical factors and vibrations that exceed an established threshold [100,101]. Another accident happened at the Lapino hydropower plant in 1997 after 70 years in service.…”

Possible Probabilistic Safety and Longevity Evaluations of the Metal in the Studs of the No. 2 Generating Set at the Sayano-Shushenskaya HPP

“…2 generating set found so heavily damaged by fatigue, and why had they failed simultaneously, while on other generating sets the studs were found to be in satisfactory condition when subjected to special examination after the failure [1]; and, -could these situations be predicted for other HPP. Before answering these questions, it is necessary, firstly, to focus attention on certain principal positions of the active procedures employed to evaluate static and cyclical strength and longevity.…”

“…2 generating set [1]. This is most likely associated with vagueness as to what processes, effects, or forces that normally act on a stud during start-up, in the operating regime, or during closure of the vane guide (VG) of the turbine led to the failure [2].…”

Resonance phenomena in pressure conduits and draft tubes at HPP

“…Experience with analysis of the failure at the Sayano-Shushenskaya HPP has indicated the utility of a mathematical model of the HPP, which has made it possible to reestablish the complete picture of development of the failure [1]. This failure has again raised questions concerning evaluation of the pulsation status of the turbine system -the flowthrough run under steady-state conditions and during transitional processes, the stability of the conditions at the HPP during forced fluctuations in carrying capacity and pressure.…”