No. 4 ESS: System Power

System Power By H. J. LUER and R. OSTAPIAK (Manuscript received July 26, 1976) The No. 4 ESS system is powered from a 140-volt battery plant. Modular dc-to-dc converters located in system frames are used to change the 140 volts to the many well regulated voltages needed by the ESS circuitry. The 24- and 48-volt power required by the system is provided by bulk dc-to-dc converters with 140 volts as an input. The modular converters require no field adjustments, are pluggable, and contain many alarm and shutdown features, some of which are routinely tested by the system. The 24- and 48-volt bulk converters are available in 2.5- and 5-kilowatt sizes and, similar to the modular converters, contain many alarm and shutdown features for the protection of their 24- and 48-volt buses. All converters are designed for low EMI (electromagnetic interference) emission and to operate in a room ambient of 0 to 50°C with inframe ambients as high as 75°C. As a function of the output voltage, efficiencies range from 65 to 85 percent. Most converters regulate remotely with typical end-of-life regulation performance of better than ±2.5 percent. I. INTRODUCTION 1.1 Basic powering arrangement Although No. 4 ESS requires less power per trunk than its predecessor No. 4A crossbar, because of its larger trunk capacity, total power required for a typical No. 4 ESS office (over 500 kW) is larger than that for a typical 4A office. The most significant difference in the power required by the two systems is that most of the power used in the 4A equipment is taken directly from a 48-volt battery plant, whereas most of the power for No.