Determination of inertia by load rejection
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This document provides procedures for determining the moment of inertia, stored energy constant, and acceleration time of a machine set by conducting a load rejection test on site. The test involves operating the generator at 10-20% load, disconnecting it from the network, and recording the change in speed over time. The moment of inertia and other quantities are then calculated using fundamental equations, based on the tangent or differential quotient of the speed-time curve at nominal speed. Any deviations from nominal values require a nonconformity report.
Determination of inertia by load rejection
- 1. English translation: Table of Content: 1 Objective.......................................................................................................... 2 Scopes................................................................................................................... 3 Referenced Documents....................................................................................... 4 Definitions and Abbreviations.............................................................................. 5 Determination of inertia by load rejection............................................................ 5.1 Conduction of test............................................................................................. 5.2 Evaluation of test............................................................................................... 6 Proceeding in case of deviations ......................................................................... 1 Objective Determination of moment of inertia J, stored energy constant H and acceleration time τJ of the rotating parts of a machine set by the load drop test. 2 Scope This procedure for the determination of inertia quantities is valid in the cross function GP for all types of synchronous machines on site. For determination of inertia the load drop test is preferred when separate losses for efficiency are not determined by the retardation method. Also, in any case load rejection tests are performed by "Protection and Excitation" during putting into service of the generator. 3 Referenced Documents IEC 34-4 (EN 60034-4), 70, 71 4 Definitions and Abbreviations None 5 Determination of inertia by load rejection 5.1 Conduction of test - The machine operates as a generator on the network. - The turbine speed regulator is taken out of service - The generator is regulated to supply active power P1 of 10 to 20 % of the rated load (i.e. power factor close to cosϕ = 1,0). - During the test the excitation of the generator remains unchanged - The generator is suddenly disconnected from the network and the change of speed with time (curve n = f (t) and/or dn/dt = f´(t)) is recorded with appropriate instruments (e.g. by means of the ELIN Digital Speed Analyzer DAS). - At about 10 % overspeed the turbine speed regulator is put back in service 5.2 Evaluation of test - In the point of nominal speed of the measured speed-time curve n = f (t) the tangent ∆n/∆t resp. the differential quotient dn/dt is determined (Note: The measured curve normally starts smoothly. dn/dt will be found by extrapolation from the point of inflection 8/25/2005 0:23 a8/p8 © Page 1 of 3
- 2. down to nN ). speed and/or its derivation starts smoothly it must be extrapolated down to rated speed). For determination of the inertia quantities the following fundamental equations are used (all quantities are here indicated in coherent international SI-units): 8/25/2005 0:23 a8/p8 © Page 2 of 3
- 3. 6 Proceeding in case of deviations Any nominal value, minimum value, maximum value, tolerance etc given in an instruction is intended to serve for quality control purposes only. In the case of deviations, a nonconformity report has to be written according to PNG Power Standard 8/25/2005 0:23 a8/p8 © Page 3 of 3