Causes of Faults at Transmission Line

Transmission line faults can arise due to various reasons, and they can be categorized into several causes:

1. Weather Conditions - Adverse weather conditions like lightning, heavy storms, strong winds, ice, or snow can cause faults by physically damaging the transmission lines or creating conditions conducive to electrical faults.

2. Equipment Failure - Malfunction or failure of components such as insulators, conductors, transformers, switches, etc can lead to faults along the transmission line.

Transformer insulation breakdown

3. Human Error - Mistakes made during maintenance, repair, or operational procedures can result in faults. Accidental contact with equipment or improper handling of the infrastructure can cause disruptions.

Crane encroachment [1]

The Difference between Transient & Permanent Faults

Transient Fault

• Transient faults are those that disappear when power is interrupted and then restored.
• Often caused by occurrences like lightning, momentary tree contact, or contact with animals.
• In such cases, the line can be successfully re-closed after it's been tripped.

Source: A.A.Z. Zin, S.P.A. Karim, The application of fault signature analysis in Tenaga Nasional Berhad Malaysia

Permanent Fault

• Permanent faults persist even when power is restored.
• These faults stem from prolonged issues such as tree or crane encroachment, insulation breakdown, tower collapse, or cable damage.
• Reclosing the line fails because the fault persists during the attempt to restore it.

Source: A.A.Z. Zin, S.P.A. Karim, The application of fault signature analysis in Tenaga Nasional Berhad Malaysia

Industrial Visit to HVDC Converter Station, Gurun, Kedah

HVDC Converter Station, Gurun, Kedah is a high-voltage direct current (HVDC) electrical power conversion station located in the Malaysian state of Kedah. It converts alternating current (AC) electricity generated by power plants into direct current (DC) electricity for long-distance transmission, and vice versa. HVDC technology is used to transmit large amounts of electrical power over long distances with minimal power loss.

This converter station is located in Gurun, Kedah and is connected to converter station at Khlong Ngae, Thailand through 300 kV DC transmission line. This HVDC grid connection increase the power system stability and security for the grid at North region of Peninsular Malaysia by connecting the grid of both countries. 

Fault Resistance of the Fault Arc

Source: Jianping Wang, ABB, 2013-06-14 KTH

Arc which developed at the transmission line during fault occurrence can be due to an object very near to the line or due to lightning which make the fault current to jump to the transmission tower (earth). This arc representing an equivalent value of fault resistance, Rf. This Rf value is depends on the arc length and fault current. The longer the arc length, the higher the Rf while the higher the fault current the lower the fault resistance as shown by the equation in the figure above. 

The value of Rf can affects the accuracy of fault locating device and also the protection relay which uses the impedance based method (such as distance relay). For impedance based method relay, Rf can affects the accuracy of the relay in determining the tripping signal decision especially for fault near to the setting of zone reach. 

Charging Current Compensation of Differential Relay

For underground cables and long transmission lines, there will be significant effects of charging current on the accuracy of the protection relay. This charging current is the result of the distributed capacitance along the transmission line or underground cables as shown by figure below. The effects of the charging current for short transmission line is insignificant and can be neglected.

This charging current can introduces error in fault detection by installed protection relays. Some protection relays adapted with charging current compensation to eliminate the error in their algorithms.

One of the relay is line differential relay GRL100 by Toshiba. The charging current is also depending on value of the line voltage. So, the charging current is continuously calculated by the relay depending on the value of current line voltage and compensates it in the differential current calculation.

The procedure is the capacitance of the line be divided into two. Then, each terminal of the relay calculates the value of charging current at each terminal using the equation below.