Технические науки/5. Энергетика

Candidate of Science N.L. Batseva, student Yu.P. Zagainova

Tomsk Polytechnic University, Russia

The analysis of the generators dropping effectiveness as the control action for Sayano–Shushenskaya hydro power plant transient stability improvement

Nowadays the capacity of Sayano–Shushenskaya hydro power plant (HPP) is 6400 MW, but the power output is limited because of transfer capability deficit of the transmission lines 500 kV Sayano–Shushenskaya HPP – Novokuznetskaya and Sayano–Shushenskaya HPP – Oznachennoye. Restrictions are imposed according to the transient stability retention of Sayano–Shushenskaya HPP generators. Therefore the analysis of Sayano–Shushenskaya HPP generator transient stability and the control action effectiveness under reference incident showed in [1] is outstanding.

The main task of the transient control in any power system (PS) is change-over PS to stable post emergency conditions by means of the control action.

The information parameters for the control action choice are determined in each case by particular conditions and tasks, among them it is possible to single out the typical kinds of the information used in the most cases [2, 3]:

1. Information about the PS scheme and the regime under before emergency conditions: calculation correctness depends on the accuracy which the basic elements of PS are described with – primarily generators with regulation systems and loads.

2. Information about disturbances: for the organization of sustainable control providing PS stability it is necessary to know the destabilization reasons and the most typical kinds of disturbances which cause problems. The typical disturbances disrupting PS transient stability are short circuits.

3. Information about emergency power imbalance: power imbalance must be such as power flows in any other cross-sections do not exceed emergency permissible values during the control action.

The most widely spread control action applied in HPP is the generators dropping by means of high maneuverability of hydroelectric units which is determined by the wide range of power changing and short start time. The generators dropping provides the rise of the steady-state stability level under post emergency conditions, influences the control action conditions and it is realized by disconnection of a generator or block circuit-breakers with a minimal delay with reference to the moment when emergency disturbance is appeared [2]. The appearance of increased load upon a foot bearing and a generator field winding should be referred to the generators dropping negative effects. Therefore the cycle life (frequency of the dropping and switching on) of generators is limited.

Figure 1 shows the position of generator and turbine power-angle curves under normal, emergency and post emergency conditions when generators are dropped.

Figure 1 – Generator and turbine power-angle curves

After short circuits the power imbalance appears between turbine mechanical power and generator electric power in consequence generator rotor speeds up. The generators dropping reduces turbine power thereby the available power imbalance is diminished. Due to this diminishing the break function area increases and in case of fast generators dropping speed-up area reduces. This fact allows keeping synchronism of remaining generator parallel work with PS.

At the first stage it is necessary to avert a destabilization: in other words to quantify dropped generators on the basis of the most credible development of the accident scenario.

At the second stage (after removal of a disturbance) to identify the post emergency situation and if it is required to produce the additional generators dropping for averting of a destabilization.

For the analysis of the generators dropping effectiveness the scheme of Khakasskaya PS has been simulated in RUStab software and the most serious normative disturbance (group III) – transmission line 500 kV Sayano–Shushenskaya HPP - Novokuznetskaya tripping with the help of stuck breaker protection during the one-phase short circuit close to 500 kV Sayano–Shushenskaya HPP busbar with the stuck breaker phase fault in 500 kV Sayano–Shushenskaya HPP switchgear has been distinguished.

Figure 2 demonstrates the result dependences.

Figure 2 – The regime of transmission line Sayano–Shushenskaya HPP – Novokuznetskaya one-phase short circuit, clearing of transmission line with the help of stuck breaker protection with a phase fault of stuck breaker, unsuccessful one-phase automatic reclosing, generator capability – 5100 MW

At the moment of the short circuit the generator active power reduces to 480 MW, then power fluctuations are happened in wide range; the generator rotor angle rises and at 3.12 seconds from the beginning of the process the first generator crank is happened, then the growing excess torque which is caused the difference between turbine and generator power begins to influence the rotor. This process leads to the further angle rising. When the rotor speed is higher than the synchronous one the slip s is appeared. The slip rises with the increasing of the diversity between the rotor angle speed and the stator magnetic field.

For the generator pulling into the synchronism after the first crank Sayano–Shushenskaya HPP generator load shedding is necessary. It is provided by the generators dropping (Figure 3).

Figure 3 – The regime of transmission line Sayano–Shushenskaya HPP – Novokuznetskaya one-phase short circuit, clearing of transmission line with the help of stuck breaker protection with a phase fault of stuck breaker, successful one-phase automatic reclosing, dropping of 2 generators, generator capability – 5100 MW

According to Figure 3 at the moment of time equals to 4.5 seconds Sayano–Shushenskaya HPP generators dropping №3 and №4 is appeared, the power imbalance is reduced, the amplitude of the power oscillations is decreased, but the steady regime is not achieved. This process shows that the control action is not enough, therefore the additional generators dropping is needed (Figure 4).

Figure 4 – The regime of transmission line Sayano–Shushenskaya HPP – Novokuznetskaya one-phase short circuit, clearing of transmission line with the help of stuck breaker protection with a phase fault of stuck breaker, successful one-phase automatic reclosing, dropping of 4 generators, generator capability – 5100 MW

Figure 4 shows that at the 9^th second from the beginning of the process the transient is accomplished, the slip transition above zero is showed that the transient stability is achieved, in other words 4 generators dropping provides the transient stability during the parallel operating between Sayano–Shushenskaya HPP and Khakasskaya PS.

References

1. Methodical Guidelines for Power System Stability: approved by the order of Ministry of Energy 30.06.2003 № 277. – Moscow: Publishing House “ENAS”, 2004. – 21 p.
2. Y.E. Gurevich, L.E. Libova, A.A. Okin. Calculations of stability and emergency control system in power systems. – Moscow: Energoatomizdat, 1990. – 390 p.
3. M.G. Portnoy, R.S. Rabinovich. Power system management for the stability providing. – Moscow: Energiya, 1978. – 352 p.
4. E.V. Kalentionok. Stability of energy systems. – Minsk: Technoperspectiva, 2008. – 375 p.