EQUATION1456 V1 EN (Equation 358)
Where:
L represents the length of the arc (in meters). This equation applies for the distance protection zone
1. Consider approximately three times arc foot spacing for zone 2 to get a reasonable margin against
the influence of wind.
I
is the actual fault current in A.
In practice, the setting of fault resistance for both phase-to-ground RFPE and phase-to-
phase RFPP should be as high as possible without interfering with the load impedance in
order to obtain reliable fault detection.
8.13.3 Series compensation in power systems
The main purpose of series compensation in power systems is virtual reduction of line
reactance in order to enhance the power system stability and increase loadability of
transmission corridors. The principle is based on compensation of distributed line
reactance by insertion of series capacitor (SC). The generated reactive power provided by
the capacitor is continuously proportional to the square of the current flowing at the same
time through the compensated line and series capacitor. This means that the series
capacitor has a self-regulating effect. When the system loading increases, the reactive
power generated by series capacitors increases as well. The response of SCs is automatic,
instantaneous and continuous.
The main benefits of incorporating series capacitors in transmission lines are:
• Steady state voltage regulation and raise of voltage collapse limit
• Increase power transfer capability by raising the dynamic stability limit
• Improved reactive power balance
• Increase in power transfer capacity
• Reduced costs of power transmission due to decreased investment costs for new
power lines
8.13.3.1 Steady state voltage regulation and increase of voltage collapse limit
A series capacitor is capable of compensating the voltage drop of the series inductance in
a transmission line, as shown in figure
68. During low loading, the system voltage drop is
lower and at the same time, the voltage drop on the series capacitor is lower. When the
loading increases and the voltage drop become larger, the contribution of the series
Section 8 1MRK 506 369-UUS -
Impedance protection
400 Line distance protection REL670 2.2 ANSI
Application manual
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