ABSTRACT
As power systems grew, bulk power needed to be transferred over long distances without great losses. The answer was to increase transmission voltage, thereby decreasing the current and consequently the losses. The power transmission capability is, approximately given by the equation: Active power in megawatts = E 2 Z 0 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203735176/b4f0dfd7-dea4-4b91-a159-8f99f4b34e98/content/eq48.tif"/>
where E = line to line voltage kV, RMS
Z 0 = surge impedance of line = 300–400 ohms
For such high-voltage lines, the overcurrent relays were found to be inadequate. This led to development of distance relays.
