Power plants – Pressure fluid source and motor
Reexamination Certificate
2000-11-08
2002-01-08
Nguyen, Hoang (Department: 3748)
Power plants
Pressure fluid source and motor
C415S017000, C415S038000
Reexamination Certificate
active
06336322
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of controlling a pump turbine which switches a runner to work as a pump and as a turbine (by changing the rotational direction of the runner).
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, 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 immediately after a load rejection instead of using the so-called buckling manner which changes the speed of closing the guide vanes from “limit” to “slow” 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) 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
In a normal loaded operation, the pump turbine unit is linked to a huge electric power system and stability of speed control is no longer the subject to be concerned. Therefore, the governor is set in favor of response speed rather than stability. After a load rejection, however, the pump turbine must continue a no-load operation singly. Therefore, the governor is required to be set so as to assure sufficient stability in speed control.
The S-characteristics region through which the running point of the pump turbine transitionally passes has not been considered to be a condition for setting the governor gains for a no-load operation. The governor gains have been enough to assure the stability only in the first region outside the S-characteristics region in which the Q
1
value decreases as the N
1
value increases, but have not been sufficient to assure the stability of operation in the S-characteristics region in which a positive feedback operation works.
Switching from a setting for a loaded operation (which is in favor of higher response of the arithmetic means in the governor) to a setting for a no-load operation (which is in favor of stability) is automatically made when the actual speed is well higher than a preset speed, when a circuit breaker opens, or such conditions of load rejection occurs.
An object of the present invention is, therefore, to provide a method of controlling a pump turbine to suppress influences by water hammering due to the S-characteristics or the like and other transient phenomena and to stabilize the operations of the pump turbine.
The present invention provides a method of controlling a pump turbine to solve the above problems.
In other words, the present invention obtains the expected result by designing and/or setting the arithmetic means of a governor so that a discharge controller being closed opens temporarily at least in the leading half of the first speed decrease curve after the speed increasing upon a full load rejection (which suddenly shuts off power generated by a generator motor) turns to decrease over a first peak while the pump turbine is running in the power generation mode, to stop the first speed decrease at a point which is higher than a rated rotational speed by one third of the difference between the first speed peak and the rated speed or more, and to turn the speed to increase from the point.
In this case, the present invention controls settings of the arithmetic means of the governor to be automatically switched in order to increase the response speed before the pump turbine after a load rejection is finally settled in a no-load operation. Further the present invention automatically switches the settings of the arithmetic means of the governor when the discharge controller closes to a predetermined opening value or below after a load rejection. Furthermore the present invention automatically switches the settings of the arithmetic means of the governor when the rotational speed decreases to a predetermined value or below after a load rejection. Additionally, the present invention automatically switches the settings of the governor so that the response speed of the governor may be in the order of normal loaded operation (fastest), no-load steady state operation, and earlier stage of the first speed decrease just after a load rejection (slowest).
This switching of the settings of the governor is made without a bump. The governor is a PID governor equipped with proportion, integration, and differentiation elements and only its integral gain is switched. 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 controller according to the opening of the discharge controller. The closing speed limiter limits the closing rate of the discharge controller to a second predetermined value or less which is comparatively higher while the opening of the discharge controller is larger than a first predetermined value and to a third predetermined value or below which is comparatively lower after the opening of the discharge controller goes below the first predetermined value. The arithmetic means of the governor is controlled or adjusted so as not to start the temporary opening of the closing discharge controller until the opening of the discharge controller goes below the first predetermined value after a load rejection.
The arithmetic means of the governor is also controlled or adjusted to start the temporary opening of the discharge controller after the rotational speed increasing to the first peak upon a load rejection turns to decrease over the peak and to continue the temporary opening until the speed reaches an inflection point at which the rotational speed curve turns from a convex curve to a concave curve. The arithmetic means of the gov
Hagiwara Haruki
Katayama Kei
Kuwabara Takao
Nakagawa Hiroto
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Nguyen Hoang
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