We are rather unique among electric utilities in that we have a relatively compact system. This allows us to operate with relatively short distribution circuits and relatively flat voltage profiles on our circuits. We often talk about the voltage levels on our circuits on a 120 volt base. A voltage of 120 volts indicates we are running our primary at our nominal voltage. Utilities with long circuits may want to operate at 126 volts at the substation to allow for voltage drop on the system. Our management has observed that keeping the primary voltage at the nominal level reduces losses on our system from what they would be for higher distribution voltages. This will also be true for the losses on the customer’s system. Our management has also chosen to utilize 636 Kcm all aluminum conductor. This is relatively large compared to many utilities. This results in lower line losses and a flatter voltage profile.
Our distribution voltage is 7,620 grounded wye / 13,200 volts. Depending on where it is in our system, we can feed a load of up to 5,000 KVA with one of these lines. If the customer wants service at 277 grounded wye / 480 volts, we try to limit our pad mounted transformers to 1,500 KVA. If one of these becomes overloaded, we can replace it with a 2,500 KVA pad mounted transformer. If a customer wants to own their own transformers, our rate LP rate gives them a credit of $0.29 per KVA of billing maximum load each month.
Our sub-transmission distribution voltage is 34.5 KV. This supplies the energy to our 13.2 KV substation sources. If a customer wanted service at 34.5 KV, we would ask that they plan ahead to the time when our sub-transmission voltage will go to 69 KV. This may happen in the 2016 to 2020 time period. We currently build our sub-transmission at 69 KV and buy dual voltage supply transformers to accommodate a future conversion.
In the material previously mentioned, you see that the Indiana Municipal Power Agency (IMPA) is our only energy supplier. If a customer has a need for more energy than we have discussed so far, we would go to IMPA and ask them to discuss other connections with other utility high voltage lines in the area. Our 34.5 KV system is supplied from 138 KV lines in the area and the IMPA peaking plant on the southwest side of our system. IMPA has one 80 megawatt (MW) unit and two 45 MW units. American Electric Power (AEP) has 138 KV supply at 3 substations in Anderson and several 138 KV lines coming into Anderson. If the demand is larger, IPALCo (AES Energy) has a 345 KV line passing the IMPA peaking plant. It goes to the AEP 345 to 138 KV substation 17 miles south and to the PSI (Duke Energy) substation north of Noblesville.
The IMPA peaking plant units can run on either diesel oil or natural gas. The cost of these fuels limits the hours for which these units are economical. They do supply a source to Anderson for islanding us if our external sources of supply are compromised. The peakers will be utilized at times of system peaks when the load exceeds the capacity of lower cost sources.