Wikimiras

The voltage of large generators usually is in the range of 13.8 kV to 24 kV. Large modern generators, however, are built for voltages ranging from 18 kV to 24 kV. No standard for generator voltages has been adopted.Generator voltage is stepped up to transmission levels in the range of 115 to 765 kV. The standard high voltages (HV) are 115, 138, and 230 kV. Extra-high voltages (EHV) are 345, 500, and 765 kV. Research is being conducted on lines in the ultra high voltage (UHV) levels of 1000 to 1500 KV.

The first step-down of the voltage from transmission levels is at bulk power substation, where the reduction is to a range of 34.5 to 138 kV sub-transmission voltage. Some industrial customers may be supplied at these voltage levels.

The next step down in voltage is at the distribution substation, where the voltage on lines leaving the substation ranges from 4 to 34.5 KV and is commonly between 11 and 15 kV. This is the primary distribution system. A very popular voltage at this level is 12.47 KV line to line, which is equivalent to 7.2 KV line to ground, or neutral. This voltage is usually described as 12,470Y/7200 V. A lower primary-system voltage which is less widely used is 4160Y/2499 V.

The lowest voltage which is also the utilization voltage for commercial and residential costumers is at the secondary distribution lines. Here, the voltage is 240 V or sometimes 120 V. Other secondary circuits are three-phase four wire systems rates 208Y/120 V or 480Y/277 V.