needed. If VAR information is available from SCADA to a local control center, it may prove more economical to employ a more widespread approach of switching feeder capacitors remotely based on feeder VAR data. A limited number of software and hardware companies (such as Cannon Technologies and RCCS) offer systems that initiate capacitor switching commands based on feeder SCADA.
For simplicity, signals can be sent one-way via utility radio, local paging, and cellular control channel (such as Telemetric). Software monitors feeder VAR response after a switching command is sent to confirm capacitor operation and logs suspected switching failures. Capacitor control receivers may be equipped with voltage override. Software allows adjustments in feeder VAR requirements and also permits capacitor banks to be manually switched to respond to abnormal feeder voltage or transmission system needs. Operating one distribution capacitor may be imperceptible on the transmission system, but a global command to switch all distribution capacitors on or off should be evident. For wide-scale implementation, SCADA VAR control capacitor switching is recommended due to its response to reactive power compensation needs with the flexibility of global or individual capacitor manual override. Using such a system, one utility reports replacing all fixed capacitors with switched ones to automatically flag cases of blown fuses as the software systematically cycles capacitors during early morning hours to test them.
Typically, distribution transformers use copper conductor windings to induce a magnetic field into a grain-oriented silicon steel core to step feeder voltage down for customer use. Therefore, transformers have both load loss and no-load core loss. As in other conductors, transformer copper losses vary with load based on the resistive power loss equa-
tion (Ploss = I2R). For some utilities, economic transformer loading means loading distribution transformers to capacity—or slightly above capacity for a short time—in an effort to minimize capital costs and still maintain long transformer life. However, since peak generation is
usually the most expensive, total cost of ownership (TCO) studies should take into account the cost of peak transformer losses. Increasing distribution transformer capacity during peak by one size will often result in lower total peak power dissipation—more so if it is over-loaded.
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