GB2137284A

GB2137284A - Pumped hydro system with three reservoirs

Info

Publication number: GB2137284A
Application number: GB08308796A
Authority: GB
Inventors: Hitoshi Kinno
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-03-30
Filing date: 1983-03-30
Publication date: 1984-10-03
Also published as: GB8308796D0

Abstract

A pumped hydro system with three reservoirs has a upstream reservoir 4, an upper reservoir 5 and a downstream reservoir 6. Stored river water in the upstream reservoir 4 is pumped up to the upper reservoir 5 by pump 8 using surplus electric power and turbine 9 generates electric power at peak time using the level difference between upper reservoir 4 and downstream reservoir 6 at which mean pump head is about half of mean turbine head. Then turbine output power is larger than pump input power provided both operation times are the same. Low water level 16 of the upper reservoir 5 is higher than ground level 20 such that intake water can be taken out through gate 21. The turbine 9 may also drive pump 8 continuously in order to obtain continuous intake of water from upper reservoir 5. The latter in the arrangement shown is disposed between dams 2, 3 across the river, but in a modification may be disposed away from reservoirs 4, 6. <IMAGE>

Description

SPECIFICATION Pumped hydro system with three reservoirs The present invention relates in general to the pumped hydro system installed at river site, and it relates more particularly to a new and improved method and apparatus for the overall efficiency of the system.

It is well known in the conventional pumped hydro system with two reservoirs that it's overall efficiency equals to multiply of both efficiencies of pump and turbine that is about 70%. This is very bad efficiency.

Viewed from above aspect the present invention provides the three reservoirs by using an additional dam in order to increase the overall efficiency more than 100%. Where the three reservoirs are called, from upstream to downstream, the upstream reservoir, upper reservoir and downstream reservoir. The three reservoirs are arranged as in series on river or as the two reservoirs are in series and the other is off river, and as the all reservoirs are separated.

Their common conditions are as follows: The upstream reservoir is on the river that is made by a dam and water level of the upstream reservoir is between of both water levels of the upper reservoir and downstream reservoir. Water level of the upper reservoir is always higher than the neighbour ground level, then the upper reservoir is surrounded by dam and dyke. Where pump has a role to pumps up the water in the upstream reservoir to upper reservoir using surplus energy as midnight electric power or as excessive solar power, and the turbine generates electric power using the head between the upper reservoir level and the downstream reservoir level.

The remarkable difference of the present invention from the conventional pumped hydro is mean pump head is designed to about a one-half of the mean turbine head, on the contrary, in the conventional pumped hydro the both head of the pump and the turbine are same. As the result, the turbine output energy of the present invention becomes to twice of the conventional one despite of both pump input energy are same.

Fathermore, in the present invention, whole or a part of the water in the upper reservoir that was pumped up using cheap surplus energy can be used for sources of irrigation, drinking water, industry, cooling water, etc, by only opening the gate mounted on the upper reservoir, provided the ground level is situated between the low water level of the upper reservoir and the high water level of the upstream reservoir. The power generation and the intake water obtained from the water in the upper reservoir are convertible which is effective particularly in the agricultural region because water is not always need according to day or night and weather or seasons.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is the top view, partly sectioned, of the pumped hydro system according to the present invention; Figure 2 is the side view of Fig. 1, partly sectioned, that is a typical arrangement of the three reservoirs built in series on the river; Figure 3 is same with Fig. 2, but that is used for mathematical explaining of the system; Figure 4 is the top view of Fig. 5, partly sectioned that is the second case of the arrangement of the three reservoirs, where the upper reservoir is built at the river side, not on the river, but another two reservoirs are in series on the river; Figure 5 is the side view of Fig. 4, partly sectioned; Figure 6 ia a sectional diagram of Fig. 5;; Figure 7 is the top view of Fig. 8, partly sectioned, that is the third case where the upper reservoir is built at remote higher place than another two reservoirs and the pump and the turbine are set at the downstream reservoir site; Figure 8 is the side view of Fig. 7, partly sectioned; Figure 9 is a side view, partly sectioned, that is the fourth case where the three reservoirs are all separated and the pump is installed at the upstream site and the turbine is at the downstream site.

Referring paticularly to Fig. 2, there is shown a river 1 with a slope where two dams 2 and 3 are installed across the river 1. Then three reservoirs are made naturally that are called upstream reservoir 4, upper reservoir 5 and downstream reservoir 6, where the water level of the downstream reservoir 6 is kept in uniform level which is taken to the datum level 7. Pump 8 and gate 18 are installed in the dam 2 and the turbine 9 and the gate 1 9 are installed in the dam 3.

Initial condition of the pump hydro system of the invention can be made as follows: The pump 8 and the turbine 9 are rest and no discharge through them initially.

The gate 1 8 is opened but the gate 1 9 is closed. The river inflow 10 come into the upstream reservoir 4 and upper reservoir 5.

When water level of the upstream reservoir rose up above the low water level 1 3 the gate 18 is closed and the pump 8 pumps up the water in the upstream reservoir 4 to the upper reservoir 5. When water level of the upper reservoir 5 rose up to the low water level 1 6 the pump 8 is stopped and keeps the water level 1 6. Water level in the upstream reservoir 4 rises up to the high water level 11 which is the initial condition. If the water level in the upstream reservoir rises above the high water level 11 before the system starts, operate the pump 8 and open the gate 19 so as to keep the water level in the upper reservoir to the low water level 16.

Let assume, as an example, the pump 8 starts at 22.00 hrs at which pump 8 is driven by the surplus night-time electric power and the pump stops at 06.00 hrs in the next morning, and the turbine 9 starts at 1 0.00 hrs and stops at 18.00 hrs where both operating time are 8 hrs. While the pump is operating the water level 11 in the upstream reservoir 4 drops down to the low water level 13 and the water level 16 in the upper reservoir 5 rises up to the high water level 1 4. The turbine 9 generates electric power from 1 0.00 hrs to 18.00 hrs while the upper reservoir level 14 drops to the low water level 1 6. On the contrary, the upstream reservoir level 13 rises up to the high water level 11 while 06.00 hrs to 22.00 hrs.The upstream reservoir level 12 is mean water level and the water level 15 is mean water level of the upper reservoir 5.

The ground level 20 is used to be designed as come to between the water level 11 which is high water level of the upstream reservoir 4 and the water level 16 which is low water level of the upper reservoir 5. The upper reservoir 5 is surrounded by the dams 2, 3 and dyke 17 which are installed on both river banks. The water in the upper reservoir 5 can be taken out through the gate 21 which is mounted on the dyke 17 and channel 22.

Mathematical relations between input energy of the pump 8 and output energy of the turbine 9, and overall system's efficiency can be introduced as follows reffering Fig. 3: Symbols, Hp= mean pump head, m Ht = means turbine head, m Oo = inflow to the upstream reservoir, m3/s mean pump discharge, m3/s Qt = mean turbine discharge, m3/s Lp= pump input power, MW = 1 06Nms- Lt = turbine output power, MW Tp= pump operation time, s Tt = turbine operation time, s Ep = Lp X Tp = pump input energy, MJ Et = L,x Tt = turbine output energy, MJ Yw = specific weight of water, 9800 Nm-3 "p = mean pump efficiency 71t = mean turbine efficiency 1m = r1p X -71t= = mechanical efficiency 71all = Et/Ep = overall system efficiency The pump 8 and the turbine 9 can be operated under constant power and speed provided their blades have variable pitch one as Kaplan or Deriaz type.

The power of pump and the turbine can be obtained as, Lp = (Hp x Qp x Yw/71p)/ 106 (1) Lt =(H1xQ@xywx##)/106 (2) Discharge of pump and turbine become to Op = Q0(24 x 3600/Tp) (3) at = Qo(24 x 3600/Tt) (4) If Tp = Tt = 8 x 3600 s, Op =Ot=3Qo (5) Also Hp = Ht/2 (6) is specified.

Substitute equations (3), (4), (5) and (6) to equations (1) and (2), Ht Lp = (- x 30o x #w/##)/106 (7) 2 Lt = (H1 x 30 X y# x ##)/106 (8) From equations (7) and (8), Lt/ Lp = 2 x 71p x a7t = 277m (9) However, Tp = T@ = 8 x 3600 s, then 71all = Et/Ep = (Lt X Tt)/(Lp X Tp) = Lt/Lp = 271m can be obtained from equation (9).

The value of 7all is same for different value of Tpa and Tt, because L is inversely proportional to T. The value of #m is used to be taken to 0.7 in conventional pumped hydro system and it is approximately equals to the overall efficiency of the two reservoir system. Equation (10) means that the system efficiency of the present invention becomes to twice of the efficiency of conventional pumped hydro system.

Reffering to Fig. 4, Fig. 5 and Fig. 6 there is shown another alternetive embodiment of the invention which is supplied for the river having very large flow br having extreme large flood flow. Where an overflow dam 23 is installed across the main river 1. The upper reservoir 5 is installed St the river side as show in Fig. 4, that is surrounded by a dam 25 which is built along the river 1 and a dyke 24. The upstream reservoir 4 and the downstream reservoir 6 are situated on the river in series. The pump 8 is installed in the dam 25 at upstream side and the turbine 9 is in the dam 25 at downstream side.The pump delivery pipe 27 opens the mouth at the bottom of the upper reservoir 5 through the gate 29 and the turbine inlet pipe 28 opens the mouth at the bottom of the upper reservoir 5 through the gate 30. The pump 8 and the gate 29, and the turbine 9 and the gate 30 are set in the machine room 31 as show in Fig. 6.

The datum level 7 which is the water level of the downstream reservoir is kept in constant by using the auxiliary overflow dam 26 installed near the exit of the turbine 9. Let consider the inflow 10 is much larger than pump discharge and that makes overflow beyond the dam 23. The water level 1 2 is mean water level of the upstream reservoir 4. The pump 8 pumps up a part of the inflow 10 to the upper reservoir 5 using surplus electric power while the low water level 1 6 in the upper reservoir 5 rises up to the high water level 1 4. The water level 1 5 is mean water level of the upper reservoir that is two times higher than the mean water level 1 2 of the upstream reservoir. The turbine 9 generates electric power at peak time.

Mathematical treatment of this case is same to Fig. 3 because section a-a in Fig. 4 is same to Fig. 3, if it is assumed that Qo is the inflow assigned to the system. Merit of this case of the invention is no problem at flood condition occurs because the flood flow goes down through the overflow dam 23.

Fathermore this invention can be changed from pumped hydro operation which is alternate operation of pump and turbine to continuous operation where the turbine output power can be fed back to the pump input and drive the pump. The reason can be explained theoretically as follows: From equation (9) Lt=2nmXLp (11) If 71m = 0.75 is used because of the continuous operation can be done under maximum efficiencies of pump and turbine keeping the mean water levels 1 2 and 1 5 of the upstream reservoir 4 and the upper reservoir 5, respectively, Lt=1.5Lp (12) It is understood that the turbine output power is larger than the pump input power when Qp= = at. The excess power of the turbine that is coincides to 50% of pump power can be supplied to the grid as new energy.If 4 = Qp/1.5 = (2/3)Qp, 1= L, can beob- tained from equation (7) and (8). The excess pump discharge, (1 /3)Qp, can be used for the intake water from the upper reservoir continuously.

Referring to Fig. 7 and Fig. 8 there is shown another alternative embodiment of the invention which is applied for high head system where the three reservoirs are all separated. The pump is installed at beside of the downstream reservoir 6 which is remote and lower place from the upstream reservoir 4.

The suction pipe 32 of the pump 8 is connected to the upstream reservoir 4 through the valve 33 which is opened only at pump operation. The pump 8 is a reversible pumpturbine harnessed a motor-generator 39. The pump delivery pipe 38 is connected to the upper reservoir 5 which is remote and higher place than another reservoirs 4 and 6. The draft tube 36 is connected to the suction pipe through the T joint 34 and the valve 35 which is opened only at turbine operation.

The downstream reservoir level is kept in uniform level by using the overflow weir 37 installed at near the draft tube exit 36, that is used for the dtaum level 7 of the system. The mean water level 1 2 of the upstream reservoir is designed as to become one-half of the mean water level 1 5 of the upper reservoir 5 measured above the datum level. It means that the pump head is one-half of the turbine head where the water in the upstream reservoir 4 is pumped up to the upper reservoir 5 through the pipes 32, 38, the valve 33 and the pump 8. On the contrary, the turbine 9 generates electric power while the water in the upper reservoir 5 goes down to the downstream reservoir 6 through the pipe 38, 34, 36, the valve 35 and the turbine 9.

The merit in this type of the invention is able to be applied for wide range of head, for instance, from 5 m to 1 ,000 m for turbine head.

The intake water from the upper reservoir 5 can be taken out from everywhere along the pipe 38 through the valve 54 or from the upper reservoir 5 through the gate 40.

Reffering to Fig. 9 there is shown the other alternative embodiment of the invention which is applied for transport of water and electric energy from the upstream reservoir 4 to downstream reservoir site beyond a higher place or a mountain where the three reservoirs are all separated and the pump is installed at the upstream reservoir site 4 and the turbine is at the downstream reservoir site 6. Inlet of the pump suction pipe 41 opens in the upstream reservoir through the dam 2, and the pump delivery pipe 42 is connected to the upper reservoir 5 through the valve 46. The penstock 43 of the turbine 9 is conected to the upper reservoir 5 through the valve 47.

The turbine draft tube 48 enters to the downstream reservoir 6. The pump 8 is driven by the electric motor 44 and the turbine 9 drives a generator 45. The intake water pipe 49 can be situated everywhere along the penstock 43 through the valve 50. The datum level is taken to the water level 7 of the downstream reservoir 6. The mean water level 1 5 of the upper reservoir is higher two times than the mean water level 1 2 of the upstream reservoir 4 measured above the datum level 7. If the inflow 10 to the upstream reservoir 4 is same to Fig. 2, mathematical treatment to this case of the invention related input and output energy of the system becomes to same with equations (1) to (10).

Fathermore, this case of the invention can be changed from the pumped hydro operation to a continuous operation system where the turbine output power can be fed back to the pump input and drive the pump automatically using the electric cable 51 from the reason of equation (11) and (12). The merit in this operating method of the invention is the water discharged from the turbine 9 and the excess turbine energy which is about one-half of the pump power can be supplied to the region of the downstream reservoir beyond the higher place 52 or the mountain 53 which are lying between the upstream reservoir 4 and the downstream reservoir 6. The upper reservoir 5 can be used for a surge tank of the pipes 42 and 43, that can be made to very small size compared to the upper reservoir of the pumped hydro system.

Claims

1. A pumped hydro system with three reservoirs compring an upstream reservoir made by an upstream dam across a river in where the river water is stored, an upper reservoir of which water level is highest than another reservoirs, a downstream reservoir of which water level is lowest than another reservoirs, where mean water level difference between the upper reservoir and the upstream reservoir is less than mean water level difference between the upper reservoir and downstream reservoir, pump pumping up the upstream reservoir water into the upper reservoir using surplus electric power and turbine generating electric power at peak time using a head between the upper reservoir and the downstream reservoir.

2. A pumped hydro system with three reservoirs as claimed in Claim 1 wherein the upstream reservoir, the upper reservoir and the downstream reservoir are separated by an upstream dam including pump and a downstream dam including turbine in series along the river.

3. A pumped hydro system with three reservoirs as claimed in Claim 1 or Claim 2, wherein ground level is between low water level of the upper reservoir and high water level of the upstream reservoir in order to obtain intake water from the upper reservoir and to protect flood from the upstream reservoir.

4. A pumped hydro system with three reservoirs as claimed in Claim 2 or Claim 3, wherein water intake gate is installed at the dyke of the upper reservoir which is surrounde by the two dams and dykes at both riverbank.

5. A pumped hydro system with three reservoirs as claimed in Claim 1, wherein the upstream reservoir and the downstream reservoir are installed in series through an overflow dam across a river, and the upper reservoir is installed beside the river bank for protection of the river flood.

6. A pumped hydro system with three reservoirs as claimed in Claim 1, wherein the three reservoirs are all separated, and pump and turbine are set at downstream reservoir site from where pump suction pipe is connected to the upstream reservoir.

7. A pumped hydro system with three reservoirs as claimed in Claim 1, wherein the three reservoirs are all separated but pump is at upstream reservoir site and turbine is at downstream reservoir site for conveying water from the upstream reservoir to the downstream reservoir beyond the upper reservoir.

8. A pumped hydro system with three reservoirs substantially as described herein with reference to Figs. 1-9 of the accompanying drawing.

9. A method of operating a pumped hydro system with three reservoirs according to any of the preceding claims, wherein turbine output power, which is larger than input power of pump, drives pump continuously so as to be obtained water intake from the upper reservoir or from penstock of turbine continuously.

1 0. A method according to Claim 9, wherein excess output power of the turbine is supplied to grid.

11. A method according to Claim 9 or Claim 10, wherein excess output power of turbine and water intake are compatible according to demand of the excess electric power or the water intake.