This kind of transmission line uprating can result in a much higher rating increase than thermal uprating. Besides that, transferring the same amount of power in a higher voltage level reduces the line current, and consequently, line losses and voltage drops.

However, voltage uprating is typically more expensive than thermal uprating due to the need of also uprating the voltage class of the terminal substations equipment.

Effectiveness. This kind of uprating can be a good option when: the line loading is limited by voltage drop or stability considerations; the line has margins in terms of electrical clearances; the uprating can be done with minimal line modifications or it will be applied to several circuits simultaneously, or the line design criteria can be relaxed.

Previous Analysis to Perform. Before proceeding with a transmission line voltage uprating it is necessary to analyze tower clearances, conductor-to-ground clearance, corona performance, electric fields, ROW issues, and sometimes structural strengths.

Some Usual Voltage Uprating Techniques. Some of the techniques used to perform transmission line voltage uprating are described as follows:

• Addition of insulator units to the transmission line insulator strings
• Replacement of standard insulator units by polymeric or antifog units
• Application of strut insulators (or V strings) to prevent swinging of suspension strings
• Keeping appropriate conductor-to-ground clearances while increasing the transmission line operating voltage
• Retensioning the existing conductors
•  Performing sag adjustments (cutting out conductor lengths, sliding conductor clamps)
• Increasing the conductor height at the attachment support (converting suspension strings to pseudo dead-end strings)
•  Increasing the attachment support height
•  Raising towers
• Moving towers
• Inserting additional towers
• Performing terrain contouring (rural areas)
• Bundling the original line conductor with another one, or replacing the line conductor by a bigger one, to assure a good corona performance
• Performing Line Compaction
• Converting a 3-phase double-circuit line to a 6-phase single-circuit line
• Converting a low voltage double-circuit line to a high-voltage single-circuit line
• Converting HVAC lines to HVDC lines

Some of these techniques have large structural impacts.

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