Rotary kinetic fluid motors or pumps – Method of operation
Patent
1979-12-04
1982-10-19
Casaregola, Louis J.
Rotary kinetic fluid motors or pumps
Method of operation
415 36, F03B 1508
Patent
active
043548008
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a pump turbine and, more particularly, to a method of controlling a high head pump turbine which inevitably exhibits S-characteristic in the turbine operation area.
List of Prior Art References
The following references are cited to show the state of the art: Sept. 8, 1976
List of Prior Application References
The following reference is cited to show the prior application which has been already filled by the present applicant: Okumura, filed May 22, 1978
Description of the Prior Art
Generally, components of a pump turbine such as a runner, particularly of a high head type, are designed to achieve sufficient centrifugal pump action so as to provide a high discharge head during its pumping operation. This design, however, adversely affects the turbine operation of the pump turbine. The performance of the pump turbine designed in this manner can be shown by a performance curve representing the relationship between speed per unit head (N.sub.1) and discharge per unit head (Q.sub.1) under a predetermined opening of wicket gates. This curve envolves, in the turbine operation area, a first section where the value of Q.sub.1 reduces with the increase of the value of N.sub.1 and a second section where the value of Q.sub.1 reduces with the decrease of the value of N.sub.1. For convenience of explanation, the second section will be referred in this specification to as "S-section". Further, the pump-turbine performance in the S-section will be hereinafter referred to as "S-characteristic". During the turbine operation in the S-section, the value of torque per unit head (T.sub.1) also is reduced as the value of speed per unit head (N.sub.1) decreases.
Ordinarily, the turbine operation of the pump-turbine is effected in the abovementioned first section. However, in the case where the speed per unit head (N.sub.1) is suddenly increased because of, for example, a removal or loss of load carried on the pump-turbine, the pump-turbine operation is shifted to the S-section. As the pump-turbine starts to operate in the S-section, the discharge per unit head (Q.sub.1) and speed per unit head (N.sub.1) are first reduced tracing the characteristic curve of the S-section from one end to the other, and thereafter Q.sub.1 and N.sub.1 are increased tracing the same curve in the opposite direction in the same manner as the swing back of a pendulum. This reciprocal tracing on the S-region is repeated almost endlessly, as long as the wicket gates are kept opened beyond the predetermined opening and would never be terminated unless a suitable measure is taken. Also the torque per unit head (T.sub.1) is repeatedly reduced and increased during this pump-turbine operation. The pump-turbine operation in the S-section is preferably avoided or minimized, since this operation causes in the upstream penstock and the downstream draft tube, as well as in the pump-turbine, an abnormal hydraulic pressure variation incurring a large pressure rise and drop with the resultant severe water hammer and, in some cases, water column separation.
The abovementioned removal of load takes place, when, for example, a generator which is being driven by the pump-turbine loses its load due to an opening of the circuit breaker or failure or burn-out of the transformer. The water hammer is heavy particularly when the either one or both of the penstock and the draft tube are long.
The characteristic of a pump-turbine exhibiting S-characteristic in the turbine operation area is illustrated in FIGS. 1A and 1B. More specifically, FIG. 1A illustrates the pump-turbine performance as the relationship between speed per unit head (N.sub.1) and discharge per unit head (Q.sub.1) with a parameter of wicket gate opening, while FIG. 1B illustrates the performance as the relationship between the speed per unit head (N.sub.1) and torque per unit head (T.sub.1) making use of the same parameter, N.sub.1, Q.sub.1 and T.sub.1 are given by the following equations: ##EQU1##
In these equations, c
REFERENCES:
patent: 3403888 (1968-10-01), Hartland
patent: 4201925 (1980-05-01), Kuwahara et al.
Casaregola Louis J.
Hitachi , Ltd.
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