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Rural electrification systems tend to use higher distribution voltages because of the longer distances covered by distribution lines (see Rural Electrification Administration). 7.2, 12.47, 25, and 34.5 kV distribution is common in the United States; 11 kV and 33 kV are common in the UK, Australia and New Zealand; 11 kV and 22 kV are common in ...
For example, a 100 miles (160 km) span at 765 kV carrying 1000 MW of power can have losses of 0.5% to 1.1%. A 345 kV line carrying the same load across the same distance has losses of 4.2%. [25] For a given amount of power, a higher voltage reduces the current and thus the resistive losses.
For example, an electrical network may have a transmission network of 110 kV/33 kV star/star transformers, with 33 kV/11 kV delta/star for the high voltage distribution network. If a transformation is required directly between the 110 kV/11 kV network an option is to use a 110 kV/11 kV star/delta transformer.
For example, in the United States, the most common voltage is 12.47 kV, with a line-to-ground voltage of 7.2 kV. [7] It has a 7.2 kV phase-to-neutral voltage, exactly 30 times the 240 V on the split-phase secondary side.
They were developed by Oliver Heaviside who created the transmission line model, and are based on Maxwell's equations. Schematic representation of the elementary component of a transmission line. The transmission line model is an example of the distributed-element model. It represents the transmission line as an infinite series of two-port ...
Applying the transmission line model based on the telegrapher's equations as derived below, [1] [2] the general expression for the characteristic impedance of a transmission line is: = + + where R {\displaystyle R} is the resistance per unit length, considering the two conductors to be in series ,
Illustration of the "reference directions" of the current (), voltage (), and power () variables used in the passive sign convention.If positive current is defined as flowing into the device terminal which is defined to be positive voltage, then positive power (big arrow) given by the equation = represents electric power flowing into the device, and negative power represents power flowing out.
The telegrapher's equations then describe the relationship between the voltage V and the current I along the transmission line, each of which is a function of position x and time t: = (,) = (,) The equations themselves consist of a pair of coupled, first-order, partial differential equations. The first equation shows that the induced voltage is ...