BS 5860:1980

National foreword
Cooperating organizations
1 Object and scope
1.1 Purpose of this standard
1.2 Excluded topics and limitations
1.3 Principle
2 Terms, definitions, symbols, units
3 Procedure for measurement of mechanical energy per
     unit mass
3.1 General
3.2 "Direct" operating procedure
3.3 "Partial expansion" operating procedure
3.4 Expansion procedure for thermometer calibration
4 Determination of hydraulic energy per unit mass
5 Apparatus
5.1 Main measurements
5.2 Auxiliary measurements
6 Conditions for taking measurements - Corrective
     terms
6.1 Measuring section and "sampling" conditions
6.2 Particular flow arrangements
6.3 Instability of total energy at inlet
6.4 Extraneous exchanges
6.5 Limitation of corrections
6.6 Unfavourable conditions for some systems
7 Precision of measurements
7.1 Estimation of error due to determination of the
     main terms (fem)1
7.2 Estimation of error in corrections due to
     secondary phenomena (fem)2
7.3 Errors due to faulty exploration of flow
     distribution (fem)3
Comments on the origin of the values for the
thermodynamic properties of water
Tables
I Values of the volume of water per unit mass v
II Values of the isothermal factor a
III Values for heat per unit mass cp

Serves as a basis for the measurement to be made on hydraulic turbines, storage pumps and pump-turbines for the computation of their efficiency applying the thermodynamic method.

1.1 Purpose of the standard

This standard serves as a basis for the measurements to be made on hydraulic turbines, storage pumps and pump-turbines and for the computation of their efficiency applying the thermodynamic method. This method is based on the evaluation of the energy per unit mass of water delivered to a turbine shaft or received by water from a pump shaft. It may be determined by measurements of the performance variables (pressure, temperature, velocity and level) and from the thermodynamic properties of water.

This standard may be used for acceptance tests or for any other efficiency test.

1.2 Excluded topics and limitations

Technological aspects of instrumentation have been dealt with in a general way taking into account the fact that the apparatus presently available varies widely and may possibly become obsolete in the future. The only requirements of instruments are to satisfy conditions stipulated in this standard (accuracy, heat exchange, etc.).

Due to the lack of uniformity in values measured at the inlet and outlet sections of the machines, the limitations of measuring equipment and the relatively high magnitude of the corrective terms originating from the imperfect measuring conditions, the scope of this method is limited and it can only be used for heads in excess of 100 m. However, under highly favourable conditions, the range could be extended to cover lower heads subject to an analysis of the accuracy of the measurements.

1.3 Principle

The thermodynamic method results from the application of the principle of conservation of energy (first law of thermodynamics) to a transfer of energy between water and the machine through which it is flowing.

In the case of actual machine operation, the energy per unit mass delivered to a turbine shaft or received by water from a pump shaft may be determined by measurement of the performance variables (pressure, temperature, velocity and level) and from the thermodynamic properties of water. This exchange of energy will be referred to as “mechanical energy per unit mass?? (see Sub-clause 2.2 and Clause 3).

In the case of ideal operation, i.e. frictionless flow (assuming identical pressures at the inlet and at the outlet and an identical temperature at the inlet as in actual operation), the same application can be used for calculating the ideal energy per unit mass delivered to a turbine shaft or received from a pump shaft. Such energy is dependent solely upon the properties of the water and the characteristics of the hydroelectric plant. It is referred to as “hydraulic energy per unit mass?? (see Sub-Clause 2.1 and Clause 4).

The need to measure mass rate of flow is eliminated by using the two values of energy per unit mass calculated as above.

The above principle presupposes that all losses in hydraulic machines are dissipated in the flow. In actual operation, friction losses in the bearings may be dissipated differently. In this case, a corresponding correction is made to mechanical energy per unit mass (see Sub-Clause 2.4).