IEC 60034-29 pdf download – Rotating electrical machines – Part 29: Equivalent loading and superposition techniques – Indirect testing to determine temperature rise

IEC 60034-29 pdf download – Rotating electrical machines – Part 29: Equivalent loading and superposition techniques – Indirect testing to determine temperature rise
5 superposition method
5.1Basic principles
5.1.1General
Superposition tests may be applied to any d.c. or a.c. machine.The method comprises a
series of tests at operating conditions other than rated load, for example: reduced load, no load.short circuit, reduced voltage, positive (inductive) or negative (capacitive) reactive load.
The method allows the full-load temperature rise of various component parts of the machineto be deduced.For each component, the loss shall be known at each particular test conditionand at full load.The machine should be tested with the same cooling conditions as whenoperating at rated load. Hence, a locked-rotor test will not be suitable as the air-flowdistribution and magnitudes will be incorrect.
On completion of the individual tests, a series of equations based on equivalent thermalcircuit theory is constructed, each equation being of the form:
l 1m =K11P1m +K12 P2m + K13 P3m
where
l 1mis the measured temperature rise of component 1 for test condition m;Pim，P2metc. is the loss in component 1, 2,etc. for test condition m;
K11，K12,
etc. are the slope factors of temperature rise determining the temperature riseof component 1 due to losses in component 1, and the temperature rise of
component 1 due to losses in component 2, etc.
Components 1, 2, and 3 may be, for example, the stator winding, the rotor winding, and thestator liron.
ln some test conditions, certain losses may be equal to zero,and hence the related term inthe equation disappears.For example,using the above assligned subscripts, a synchronousmachine has K11P1= 0 a no load and K13 P3 = 0 a short circuit.
The method is based on the principle that the coefficients K do not change from test to test,i.e. that the cooling conditions are invariable between tests , which requires the speed to bethe same in each test The method is also based on the principle of linear thermal conditionsso that temperature rises in one case can be added to those for another case. lt requires thellosses in the relevant component parts to be known with sufficient accuracy for each case,either by calkculation or measurement.
When the tests have been completed and the equations compiled, the coefficients K can bederived by simple arithmetic.These are then used in a final equation with the losses for therated load condition to cakculate the temperature rise of component 1.By slmilar means, thetemperature rises at rated load of components 2, 3，etc. can be derived.
lf any component loss is temperature dependent （for example, stator copper loss), then thecalculation procedure has to be repeated using values for the loss corrected for the estimatedtemperature rise. lt is normally necessary to do this iteration once only.For the calculation ofwinding temperature rises corrected to a reference ambient temperature equations in closedform are also provided.
The method may be used to determine the temperature rise of any component at any load ifthe losses at that load are known.The slope factors of temperature rise (K12, etc.) may beuseful in other thermal modelling studies, for example, in analysing the response to supplyunbalance , voltage reduction, etc.
In all superposition tests, correction is necessary for variation in heat exchanger performance (if one is fitted to the machine), as the thermal performance of the heat exchanger will partly depend on the total loss in each test. 5.1.2 Temperature rise When determining the temperature rise values of machine parts by superposition tests, the variations from the results that should be obtained at rated-load test are always to be considered. The uncertainty value   (%) for rated load is defined:
NOTE 1 The uncertainty values obtained by superposition tests may be negative (test temperature rise is lower than under normal operation) or positive (test temperature rise is larger than under normal operation). Consequently, for comparing with the temperature rise values given in IEC 60034-1 , test results have to be multiplied with a correction factor σ: