Pumped-storage system operation computer modelling.

Grigoriu, Mircea ; Gheorghiu, Liviu ; Hadar, Anton 等

1. INTRODUCTION

The operation of a hydraulic pumping system may be described in stationary regimes based on plotting of head--capacity curves. The rated head and rate of flow is obtained by the intersection of the pump curve by the maximum efficiency with those from the hydraulic network. This optimal designed situation reflects the best mass and energetic equilibrium.

Knowing the rated regime's parameters in the hydraulic network namely the head [H.sub.0] = 247 m and the discharge in the pipes 2[Q.sub.0] = 6 [m.sup.3]/s, it will be calculated the constant C of the network with the formula:

[H.sub.r] = [h.sub.0] + C[(2[Q.sub.0]).sup.2] = [H.sub.0] (1)

It results: C = 1/6 [s.sup.2]/[m.sup.5].

Taking into account the turbo-machinery similitude formulas:

Q = [k.sub.Q]n (2)

H = [k.sub.H] [n.sup.2] (3)

the calculus of the parameters of the extreme regimes means solving the systems of equations (4) (5) and (6), respectively (7) (8) and (9):

[H.sub.m] = ([H.sub.0] / [(2[Q.sub.0]).sup.2]) [Q.sub.m.sup.2] (4)

[H.sub.m] = [h.sub.m] + C [Q.sub.m.sup.2] (5)

[n.sub.m] = ([n.sub.0] / [Q.sub.0]) [Q.sub.m] (6)

The results are: discharge [Q.sub.m] = 5.438 [m.sup.3]/s, head [H.sub.m] = 202.929 m and speed [n.sub.m] = 906.4 rot / min.

[H.sub.M] = ([H.sub.0] / [(2[Q.sub.0]).sup.2]) [Q.sub.M.sup.2] (7)

[H.sub.M] = [h.sub.M] + C [Q.sub.M.sup.2] (8)

[n.sub.M] = ([n.sub.0] / [Q.sub.0]) [Q.sub.M] (9)

The results are: discharge [Q.sub.M] = 6.148 [m.sup.3]/s, head [H.sub.M] = 259.299 m and speed [n.sub.M] = 1024.6 rot/min.

Analyzing the universal characteristics of the pumps, figure 1, it may be interpolated and estimated the corresponding efficiencies and powers. (Grigoriu, 2006).

The maximum efficiency gains are about [DELTA][[eta].sub.AC] = 1.63% and [DELTA][[eta].sub.BD] = 7.23%. These values give a measure of the effectiveness of the speed control in comparison with the operation at constant speed or the throttling control of the pumps.(Hadar et al., 2007)

[FIGURE 1 OMITTED]

2. THE POWER ELECTRIC DRIVING SYSTEM

The power electric driving system, shown in the Figure 5, is at variable controlled speed for pumps, operates at specific hydro-constraints, and offers some remarkable advantages. However, the most important among these advantages, remains the higher efficiencies over constant speed or throttling; also we have to add the more reliable working with lower speeds, plus better computer controlled speed changes for preset operating conditions (head, discharge flow) (Grigoriu, 2005).

The method of speed control over the hydraulic turbo-machinery may be used in any hydraulic system, especially for higher power ratings of MW, as it could be seen in this herewith focused practical example (Grigoriu, et al., 2005).

The power electric energy--at variable frequency is to be power plant HPP, working in this particular case with one single generator rated--24 MVA, 10/110 kV; it is injecting its MVA in islanding conditions of operation, through its second separate power electric overhead line, LEA 110 kV.

[FIGURE 2 OMITTED]

The other one hydro generator HG from the HPP could remain connected to the system at fixed frequency; the two units are to be separated by one coupling cell deliberately newly-introduced in this scheme, in order to gain elasticity for the new operational regimes. The powerful pumping station PPS--rated 2 [right arrow] 10 MW, 110/6 kV, 2 [right arrow] 3[m.sup.3]/s, 1000 rot/min is located at 30 km distance approximately, up in the mountains; it is loaded by the specific hydraulic conditions given by the two lakes' levels, of small and bulky capacity 1, L.

[FIGURE 3 OMITTED]

The two levels are to be communicated via GPS to the basic generating HPP, and the whole driving system power electric energy--is working at the requested variable frequency, in order to gain the overall maximum efficiency for the PPS in question (Lupea, Cormier, 2007).

As far as the local conditions for this--quite unique application, we can suggest how favourable these are, represented by the existing infrastructure, so: the neighbouring generating HPP where only one single unit is able to perfect match the requested power for both motor units at the PPS.

3. CONCLUSIONS

The results (fig. 2) released from the simulations are based on the standard synchronous machine's equations. So, one small step-up, average 10 rev x min-1 or equivalent 3% increased during seconds the hydro generator's HG speed, by opening its turbine's gate: the remote motor slower responds by reaching its upper speed limit of 1025 rot/min over some delay, but no more than 10-15 s.

On the HG side (fig. 2), as a result of increased active torque, promptly increases the stator current and the active power injected at the terminals (small reverse swings probably mark the AVR's small delayed intervention).

On the motor's side at the PPS (fig. 3), as a result in promptly command of increased frequency coming from HG via 110 kV line, clearly we can see the same prompt responses with increased stator current, absorbed active power and dropping in stator voltage (small reverse oscillations probably mark also here the AVR's small delayed intervention).

[FIGURE 4 OMITTED]

However, as stated above the motor's response in speed-up is much slower--as a mechanical parameter, while the internal load angle displacement marks one intermediate time evolution.

In conclusion, the discussion over the simulated behaviour for the first time in this particular back-to-back powerful scheme running at variable speed and exploiting the local favourable conditions, as we can hope--this exercise proves to be a successful one.

4. REFERENCES

Grigoriu, M. (2006), Pumps and Pumping Systems. Ed. Printech, Bucharest, Romania.

Grigoriu, M. (2005), Pumps, Fans, Compressors. Ed. Printech, Bucharest, Romania

Grigoriu, M.; Guzun, B.; Barglazan, M. (2005), Optimal High Powerful Pumped Storage System, Rev. Energetica, 487491 pg., No. 11.

Hadar, A., Constantinescu, I.N., Jiga, G., Ionescu, D.S. (2007), Some Local Problems in Laminated Composite Structures, Mat. Plast., Vol. 44, No. 1, p.354-360

Lupea, I., Cormier, J., (2007), Size and Shape Optimization of a Polymeric Impact Energy Absorber by Simulation, Mat. Plast., Vol. 44, No. 4, p.339-344