WECC Air Conditioner Motor Model Test Report

Many utilities continue to experience slow voltage recoveries after system faults; these slow voltage recoveries have been attributed to stalling air conditioners (A/C). In 2006 and 2007 Bonneville Power Administration (BPA), Electric Power Research Institute (EPRI), and Southern California Edison (SCE) tested more than 25 residential air conditioners (RAC) to assess their response during under-voltage transients and sags. EPRI conducted the testing for Arizona Power Services (APS). Every RAC tested stalled and a majority remained stalled until their internal overload protection tripped them off from the system. These RAC tests validate the hypothesis that stalling air conditioners result in slow voltage recoveries after system faults. After analysis of the RAC tests, the WECC developed an air conditioner motor model in EPCL language. General Electric incorporated its performance features into its new PSLF A/C motor model (ldlpac).

The WECC tested the ld1pac to assess its response during under-voltage transients, voltage oscillations, and frequency oscillations. This report contains a detailed account of these tests, which determined that the ld1pac model has the capacity to:

A) Stall the A/C load within 1 cycle of a predetermined under-voltage transient – its stall time can be adjusted
B) Model the A/C’s I, P, and Q stall and non-stall parameters
C) Operate power contactor model within 2 cycles of certain under-voltage transients
D) Model the restart of A/C load – load restarting time can be adjusted
E) Model the aggregated behavior of the A/C thermal protection switch
F) Model under-voltage protection relay with a response time of 2 cycles

The ld1pac model test results indicate that this model’s performance is very close to the actual A/C test data and the aggregated A/C behavior under-voltage transients, voltage oscillations, and frequency oscillations. Various extreme tests including prolonged faults and high concentration of A/C load do not show numerical instability. This model is currently being incorporated in the new GE composite load model (cmpld) and will be tested in the near future.