# Electrophysical Method for Identifying the Causes of Excessive Hydro Generator Vibration
## 3 External Power Supply Diagram  
The hydropower plant cascade under study operates mainly for the aluminum smelter (AS) needs. City networks are also among the consumers of the cascade. A simplified diagram of the AS external power supply is shown in Figure 1. The power source of the enterprise is its 10 kV switchgear (SWG). Electrical energy is supplied to the busbars of the 10 kV SWG by the busbars of the 10 kV generator switchgear (GSWG) of the HPP-I of the cascade and by the 110/10 kV substation (SS-I) of the power system.  
The smelter is connected to the 10 kV GSWG of the HPP-I by two busbars with the exact length of 1.44 and 1.36 km (feeder 3 and feeder 6, respectively). About 42 MW is transmitted through busbar 6 and 44 MW is transmitted through busbar 3. The maximum throughput of the busbars is designed for a current load of about 3000 A.  
The energy-intensive equipment of the AS (conversion units of electrolysis row consisting of three-winding transformers, bridge rectifier units and saturable reactors) is powered by the 10 kV busbars of the SS-I substation. In this scheme, the 10 kV SWGR is the auxiliary switchgear of the hydropower plant.  
The HPP-I has its own 110 kV outdoor switchgear (OSWG) to transmit power to the power grid. The 110 kV OSWG of the HPP-I is connected to the busbars of the 110 kV OSWG of the HPP-II of the cascade by 110 kV transmission lines (L-7 and L-8). The SS-I transformers (the smelter) are connected to the 110 kV network by two sub-branches, BL-7 and BL-8, of transmission lines L-7 and L-8, respectively. The HPP-I is the main power supply of the smelter. It has three 38.5 MW hydro generators and one 40 MW generator of the SV-655/110-32 type. According to the HPP-I operation service, at least three generators are constantly in operation.  
Thus, the power supply system of the smelter has distinctive construction features compared to other similar enterprises. The main loads are the conversion units fed by various power supplies (the 10 kV busbars of the HPP-I and the 10 kV busbars of the 110/10 kV SS-I substation). This load affects all consumers of this network section, which is proven by recordings performed.  
The recording of parameters of electrical energy flows and power quality indices was carried out on the busbars of the 10 kV GSWG of the HPP-I using certified recorders. During recording of steady-state mode parameters of electrical energy transmitted through busbars (electric power characteristic, dynamics of load variation recorded at time intervals of 1 min, limit values, etc.), voltage imbalance, current imbalance and harmonic content of voltage were obtained.  
Figure 1: Simplified diagram of the smelter external power supply.  
In addition, a specially designed metering complex was used. It allowed a long-term detailed recording of current impacts to be performed on hydro generators of the HPP-I, which allowed us to identify subharmonic and ultralow-frequency (UFL) components of current unrecorded before and transients with superposition of aperiodic component and pulses of current.  
The description of the recording method is given in Appendix A. The experimental results obtained are given in Appendix B.