Fault resistance
The performance of distance protection for single phase-to-ground faults is very
important, because normally more than 70% of the faults on transmission lines are
single phase-to-ground faults. At these faults, the fault resistance is composed of three
parts: arc resistance, resistance of a tower construction, and tower-footing resistance.
The arc resistance can be calculated according to Warrington's formula:
EQUATION1456 V1 EN (Equation 121)
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 the zone 2 and wind speed of
approximately 30 m/h
I is the actual fault current in A.
In practice, the setting of fault resistance for both phase-to-ground (RFPG) and phase-
to-phase (RFPP) must be as high as possible without interfering with the load
impedance to obtain reliable fault detection.
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 transient stability limit
• Improved reactive power balance
• Increase in power transfer capacity
• Active load sharing between parallel circuits and loss reduction
• Reduced costs of power transmission due to decreased investment costs for new
power lines
Section 3 1MRK504116-UUS C
IED application
204
Application manual
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