Distributed Renewable Energy Operating Impacts and Valuation Study

Modeling Assumptions
• Distribution Transformers
– 50% of distribution transformers did not have kVA size designation
– Estimated size based on number of customers connected and 10 kVA/customer
– Standard transformer sizes used
• Distribution Transformer Loss Data
– No test data available for transformers in circuit
– used typical loss data provided by APS for xfmrs they had purchased within the past 8 years
to assign load and no-load losses per transformer
– Loss data based on kVA size of transformer (~ 1% for load losses, ~0.22% for no-load
losses)
• Feeder capacitor control
– No formal control algorithm provided
– Assumed capacitor bank switched on during peak period (June – September)
• Load Data
– Size of individual loads were unknown
– Maximum feeder loading per-phase was used to allocate load levels throughout the feeder
– Power factor: Residential – 0.9, Commercial – 0.87
• Annual load shapes
– Historical 8760 currents per phase for feeder at substation utilized as load shape applied to
loads on each phase
© 2008 Electric Power Research Institute, Inc. All rights reserved.
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