Medium Voltage Application Guide
Medium Voltage Application Guide
Medium Voltage Application Guide
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13754.A<br />
SWITCHGEAR<br />
Distance<br />
This protection is predominantly used on long transmission lines running between primary substations, with radial<br />
feeders along the length of the transmission line. The distance to a fault is determined by calculating the line fault<br />
impedance with a healthy line impedance. Both line voltages and currents are measured to calculate the fault<br />
impedance.<br />
Selective line isolation is achieved by setting a trip zone within the protection device. This trip zone covers a specific<br />
distance along the length of the transmission line from where the protection device is installed. Protection devices<br />
are used in pairs installed at each end of a transmission line, and a fast speed, real-time communication link is required<br />
between devices.<br />
Distance protection system<br />
2<br />
CT<br />
Za<br />
Zb<br />
CT<br />
1<br />
VT<br />
VT<br />
5<br />
4<br />
4<br />
3<br />
Substation A<br />
Radial feeders<br />
Communication link<br />
Distance protection device<br />
Substation B<br />
<strong>Voltage</strong><br />
<strong>Voltage</strong> protection is often used on transformers, motor, generators and power factor banks which can be damaged<br />
due to long term undervoltage or overvoltage conditions.<br />
If the average 3-phase or any individual line voltage falls outside a specific range for a specific period, a trip will occur.<br />
A time delay is used to override temporary surges and dips in the mains voltage.<br />
Page 124 <strong>Medium</strong> <strong>Voltage</strong> <strong>Application</strong> <strong>Guide</strong> 710-12280-00A
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