Rotary kinetic fluid motors or pumps – Method of operation
Reexamination Certificate
2000-10-27
2003-08-05
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Method of operation
C415S030000, C415S036000
Reexamination Certificate
active
06602044
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a pump turbine using a runner to work as a pump and a turbine by changing the rotational direction of the runner, a method of controlling said pump turbine, and a method of stopping said pump turbine.
BACKGROUND OF THE INVENTION
Generally, the runner of a pump turbine, especially a high head pump turbine, is designed so as to realize a sufficient centrifugal pump action to obtain a high head during pump running.
However, this design adversely affects the turbine operation of the pump turbine. Especially when so-called S-characteristics appear as an example, it is considered to be difficult to avoid them perfectly.
It has been recognized that the S-characteristics are a bottleneck especially for high-head pump turbines in civil designing of upstream and downstream waterways, heights of installation elevation of pump turbines, and so on. Therefore, there have been various proposals to control such S-characteristics. For example, Japanese Non-examined Patent Publication S53-143842 (1988) proposes a method of temporarily opening guide vanes of a pump turbine while the running point of the pump turbine is moving along a flowrate decreasing direction on the S characteristics after a load rejection and quickly closing the guide vanes when the running point of the pump turbine starts to move along a flowrate increasing direction on the S characteristics or when the flowrate becomes almost zero, as shown in the accompanying FIG.
1
.
However, this proposal is designed to reduce the rotational speed (which temporarily increased after a load rejection) straight down to a predetermined rotational speed or its vicinity which is determined by a governor setting. For this purpose, the temporarily-opened guide vanes are closed as quickly as the sudden closing after a load rejection instead of using the so-called buckling manner which changes limitation of the closing speed of the guide vanes from the “fastest” rate to a “slow” rate when the opening of the guide vanes Y is smaller than Ya. This is very dangerous in case the S-characteristics controller is disabled. Further this proposal assumes that the temporarily-opened guide vanes start to close when the flowrate starts to increase (from the end of decreasing) or when the flowrate becomes almost zero. However, it is very difficult to detect a flow rate finely (at high resolution) and timely in the transient status of the pump turbine. Even if a high-resolution flowrate is detected, it is very difficult to suddenly reverse the operation of the guide vanes and it can be easily inferred that the guide vanes are opened too much. Particularly, when you keep on operating the guide vanes even after the running point on the S characteristics ends moving along the flowrate decreasing direction and starts to move along the flowrate increasing direction, the influence by the S characteristics may be greater.
Judging from the above, it can be inferred that the method in accordance with Japanese Non-examined Patent Publication S53-143842 (1988) cannot assure the steady performance in case a plurality of pump turbines share an identical penstock or particularly when the flowrate of a pump turbine changes variously not only by its own running status but also by mutual hammering by other pump turbines.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a stable pump turbine capable of suppressing water hammer phenomena and other transient influences from the S-characteristics at a load rejection which the conventional pump turbines cannot solve.
The present invention is characterized by a pump turbine which solves the above problem. The present invention is also characterized by controlling a governor to increase a target rotational speed of the runner after a load rejection which shuts off power generated by its generator, generator motor.
The present invention is also characterized by providing a governor designed to detect the rotational speed of the runner and control a discharge regulator such as guide vanes to get a predetermined rotational speed of the runner constantly and controlling the governor to make the target rotational speed only at the transient status immediately after a load rejection substantially higher than the target rotational speed at the steady status in case of the occurrence of a load rejection which shuts off power generated by a generator motor.
The present invention is also characterized by building up a system to increase and correct the preset rotational speed of the governor in the transient status immediately after a load rejection.
Further, the present invention is characterized by building up a system to increase and correct the preset rotational speed of the governor as the rotational speed increases immediately after a load rejection.
Further, the present invention is characterized by building up a system to increase and correct the target rotational speed as the rotational speed increases immediately after a load rejection, to gradually release (or decrease) the correction control after the rotational speed starts to go down, and to release the correction control substantially completely in the steady status.
Further, the present invention is characterized by building up a system to increase the preset rotational speed a little below and along the increasing speed curve while the rotational speed is increasing immediately after a load rejection.
The governor of the pump turbine in accordance with the present invention comprises a closing speed limiter which limits the closing speed of the discharge regulator according to the opening of the discharge regulator. If the closing speed limiter is designed to limit the closing speed of the discharge regulator to a second predetermined value or less which is comparatively higher while the opening of the discharge regulator is larger than a first predetermined value and to a third predetermined value or less which is comparatively lower after the opening of the discharge regulator is smaller than the first predetermined value, the correction control must not block the natural closing action of the discharge regulator by the governor until the opening of the discharge regulator is larger than the first predetermined value at least immediately after a load rejection.
After a load rejection, the present invention closes the discharge regulator when the opening of the discharge regulator is higher than the first predetermined value and temporarily opens the discharge regulator after the closing speed of the discharge regulator is once transferred below the third predetermined value in spite of a Closing command being given from the governor.
The present invention is also characterized by temporarily opening the discharge regulator by correction-control when the rotational speed stops increasing and starts decreasing after a load rejection. (The rotational speed value at this point is called a first peak value.)
In the present invention, the opening of the discharge regulator is made greater temporarily by the correction-control when the rotational speed starts to go down over this peak after a load rejection and consequently, the rotational speed stops decreasing and starts increasing at a much higher value than a natural target value in the steady status given by the governor. (The rotational speed value at this point is called a first bottom value.)
In other words, in the present invention, the opening of the discharge regulator is made greater temporarily by the correction-control when the rotational speed starts to go down over the first peak after a load rejection. This temporary opening operation continues to an inflection point at which the rotational speed curve turns from a convex curve to a concave curve. As the result, the rotational speed stops going down and starts going up at this much higher value than a natural target value in the steady status given by the governor. (The rotational speed value at this point is called a first bottom value.)
The present invention is characterized by st
Hagiwara Haruki
Katayama Kei
Kuwabara Takao
Nakagawa Hiroto
Edgar Richard A.
Look Edward K.
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