Turbomachine

A method for obtaining an estimate for a process quantity related to a turbomachine that comprises a chamber having an inlet and an outlet for fluid to be moved and an impeller placed in the chamber for moving the fluid, the method comprising:

• measuring (301) first process quantities related to the turbomachine, and
• calculating (302) an estimate for a second process quantity related to the turbomachine on the basis of measured values of the first process quantities and a reference table of interrelations between process quantities prevailing in reference inlet conditions which correspond to a pre-defined inlet fluid temperature, a pre-defined inlet fluid pressure, and pre-defined fluid properties at the inlet,
• characterized in that the reference table and the measured values of the first process quantities represent such a set of data values that the estimate is obtainable on the basis of different sub-sets of the set of data values, and, in the calculation of the estimate, more weight is given to a first sub-set of the set of data values which has a smaller error estimate than to a second sub-set of the set of data values which has a greater error estimate in order to increase the accuracy of the estimate, the error estimate related to each sub-set being proportional to a scalar product of a vector of squares of sensitivities of the estimate with respect to the data values of that sub-set and a vector of variances of the data values of that sub-set.

A turbomachine system comprising an inlet (202) and an outlet (203) for fluid to be moved and at least two turbomachines (200, 220, 230) each of which comprises:

• a chamber connected between the inlet and the outlet,
• an impeller placed in the chamber for moving the fluid, and
• equipments for measuring first process quantities related to that turbomachine,
• the turbomachine system further comprising a processor (208) arranged to calculate for each of the turbomachines an estimate for a second process quantity related to that turbomachine on the basis of measured values of the first process quantities and a reference table of interrelations between process quantities prevailing in reference inlet conditions which correspond to a pre-defined inlet fluid temperature, a pre-defined inlet fluid pressure, and pre-defined fluid properties at the inlet, characterized in that the reference table and the measured values of the first process quantities represent such a set of data values that the estimate is obtainable on the basis of different sub-sets of the set of data values, and the processor is arranged to give, in the calculation of the estimate, more weight to a first sub-set of the set of data values which has a smaller error estimate than to a second sub-set of the set of data values which has a bigger error estimate in order to increase the accuracy of the estimate, the error estimate related to each sub-set being proportional to a scalar product of a vector of squares of sensitivities of the estimate with respect to the data values of that sub-set and a vector of variances of the data values of that sub-set, and the processor is arranged to start and stop one or more of the turbomachines so as to keep the estimates related to running turbomachines on a desired range.

A computer program for obtaining an estimate for a process quantity related to a turbomachine that comprises a chamber having an inlet and an outlet for fluid to be moved, an impeller placed in the chamber for moving the fluid, and equipment for measuring first process quantities related to the turbomachine, the computer program comprising computer executable instructions for controlling a programmable processor to calculate an estimate for a second process quantity related to the turbomachine on the basis of measured values of the first process quantities and a reference table of interrelations between process quantities prevailing in reference inlet conditions which correspond to a pre-defined inlet fluid temperature, a pre-defined inlet fluid pressure, and pre-defined fluid properties at the inlet, characterized in that the reference table and the measured values of the first process quantities represent such a set of data values that the estimate is obtainable on the basis of different sub-sets of the set of data values, and the computer program comprises computer executable instructions for controlling the programmable processor to give, in the calculation of the estimate, more weight to a first subset of the set of data values which has a smaller error estimate than to a second sub-set of the set of data values which has a greater error estimate in order to increase the accuracy of the estimate, the error estimate related to each sub-set being proportional to a scalar product of a vector of squares of sensitivities of the estimate with respect to the data values of that sub-set and a vector of variances of the data values of that sub-set.