Why Valve-type Lightning Arresters Exhibit High Residual Voltage？

Residual voltage represents the voltage drop across a lightning arrester during the discharge of a surge current. For valve-type arresters, maintaining this value within safe limits is vital to protect substation equipment. When residual voltage exceeds design specifications, the insulation of connected transformers faces significant risk of catastrophic failure.

Factors Contributing to High Residual Voltage

The performance of a lightning arrester depends heavily on the non-linear characteristics of its internal valve elements. In practical applications, a variety of factors can cause the residual voltage to be higher than expected.

1. Valve Element Resistance: Older valve-type designs use silicon carbide disks. Unlike modern metal-oxide varistors, these disks have a higher inherent resistance during high-current discharge, leading to elevated residual voltage.

2. Series Gap Response: Traditional arresters utilize spark gaps in series with the valve. The time delay in gap breakdown during fast-rising steep-front waves often results in a higher initial voltage peak.

3. Lead Inductance Effects: Long connecting leads increase the total inductive reactance. This added impedance contributes to the overall voltage seen by the protected equipment during a strike.

4. Aging and Contamination: Environmental moisture or internal degradation of the valve disks can shift the V-I characteristic curve, causing the device to maintain higher voltage levels than its original factory rating.

Comparison of Arrester Voltage Ratings

The following data illustrates the typical discharge voltage characteristics across different system categories.

Implementation in High Voltage Networks

Choosing the correct 33 kv lightning arrester requires a precise calculation of the protective margin. For instance, a 33 kv lighting arrester must ensure that its residual voltage stays at least 20% below the Basic Insulation Level (BIL) of the equipment it guards.

In transmission environments, the 220 kv lightning arrester is frequently deployed to handle massive energy dissipations. If the residual voltage is too high, the 220 kv lightning arrester fails to provide a low-impedance path, forcing the surge into the transformer windings instead. Proper grounding and short lead lengths are essential for these high-capacity units.

Recommendations for Reducing Residual Voltage Risks

To ensure optimal protection and minimize voltage stress on the power system, operators should follow these technical guidelines:

• Upgrade to Zinc Oxide Technology: Replace older silicon carbide valve arresters with gapless metal-oxide versions to achieve superior non-linear response and lower residual levels.

• Minimize Connection Length: Keep the top lead and the ground connection as short and straight as possible to reduce inductive voltage drops.

• Regular Diagnostic Testing: Conduct leakage current wattage tests and insulation resistance measurements annually to detect aging valve elements before they fail.

• Verify System Compatibility: Ensure the 33 kv lightning arrester or 33 kv lighting arrester matches the specific earthing conditions of the local grid to prevent over-voltage during temporary faults.