employed to balance the transformer loads and also to provide reactance sufficient for multiple source supply when that might become available. The network capacity was sufficient to carry the rated load with the failure of a transformer. The primary feeders were controlled from the transformer substation, which gave operators the ability to reduce transformer reactive power loss during times of minimal load by disconnecting some transformers. The savings over a 24-h period was said to equal the cost of the protective relays. The transformer reactance was approximately 300% of normal to ensure an equal division of loads. The transformer substation operators regulated feeder voltage and monitored overcurrent protection to isolate defective transformers or feeder faults. The Palmer network switch proved highly successful as detailed event records of the first year of network operation showed it to be nearly trouble free (see Figure 4). The stated goal of the engineers was to develop units with a reliability equal to that of railroad signal relays, which had undergone three decades of development. The fuses between the relay and the network provided protection to the network should a fault not burn clear. The cables had to have a total capacity of 25 kVA to provide a voltage gradient of 6 V per 100 ft to ensure that faults would burn clear. The faults burned clear as long as transformer capacity provided adequate burning current. United carried out extensive research on the issue of fault currents and the current needed to ensure that they would burn clear. Experience with dc had shown that larger cables tended to sustain faults as the greater surface area spread the arc, and the more molten the material, the stronger the arc. It was also determined that the impedance of the larger cable impacted the striking and sustaining of the arc. The cables of 250 mcm or less would burn clear satisfactorily. A fault on the secondary side would burn clear at lower voltages, thus no protection was needed as long as the cable size was limited. An extensive review of these tests was included in " Underground Alternating Current Network Distribution for Central Station Systems " and " Low Voltage A-C Networks Part I Application " (see the " For Further Reading " section). The network did not combine both power and lighting loads but was superior to radial distribution and produced innovation. Over the next three years, a rapid increase in load required the use of separate (apparently meaning multiple) single-phase networks to permit rapid change of distribution from radial to network. Each network tied into one phase of a three-phase feeder to allow the best overall distribution of load across the feeders. Thus, lighting load was quickly networked while power load remained on radial distribution. It was engineered to make use of radial system transformers and primary feeders while the network was substituted. figure 2. The Network Street vault relays and switches. (Courtesy of AIEE Transactions.) 68 ieee power & energy magazine The Combined Network The combination of light and power load on a single automatic network was march/april 2022