Unlike in certain industries where rapid technological change is the norm, the key goal for an electric power system is reliability. Since much of Korea’s transmission system operates at 345 kV, any system failure can have a ripple effect and become a great concern given that important local industries such as semiconductors, steel and chemicals all require a high quality, stable power supply.
Based on experience, some 80% of transmission system failures in Korea are caused by natural events such as lightning strikes. Ageing and failure of insulators is another key factor that can impact power supply. Therefore, proper scrutiny management of the insulator population is critical to prevent line failures. The Korea Electric Power Corp (KEPCO) conducts several monitoring programs to avoid problems with insulators – the leading cause of transmission line failures.
This edited article, contributed by Hyunmin Park, Bong Gyu Park and Chang Bae Moon of KEPCO’s Transmission Operation Department, discusses recent programs to verify the integrity of the insulator population through analysis and testing.
Porcelain accounts for about 99% of all insulators used by KEPCO. In the past, these were imported but domestic producers have been supplying 154 kV lines since the mid-1980s and have grown to more recently also supply 345 kV class 210 kN and 300 kN insulators and even 400 kN insulators for 765 kV lines. Since domestically produced insulators have had quality issues in the past, KEPCO introduced the power arc test (before it was internationally standardized) and also raised quality control test requirements by combining mechanical and electrical strength testing. As a result, there have been no reports of failures of domestically produced insulators since 1998 and this confirms that quality level has stabilized. In addition, local steep front of wave flashover test requirements have been revised in Dec. 2007 to reflect international standards and since Sept. 2011 have also been applied to HV suspension insulators. This is expected to further increase reliability of suspension insulators in service on Korea’s transmission system.
Table 1: Insulator Failures in Korea Due to Separation
|Number of Failures||5||4||3||4||2|
General Performance Diagnostics
To verify the condition of porcelain insulators, KEPCO diagnoses their integrity every 5 years using an electromagnetic faulty insulator detector. A detector, developed by KEPCO, is used to diagnose insulation resistance as well as electric field on 154 kV lines.
Table 2: Defective Insulators Detected/Year
|Number of Faulty Insulators||427||280||702||365||205||395.8|
Since South Korea has the sea on three sides, insulators must also be washed regularly.
Table 3: Cleaning Cycle in Contaminated Areas
|Clean Area||Grade A||Grade B||Grade C||Grade D|
|Industrial Area||–||–||Light industry/metal
industry, dusty areas
Evaluating Insulator Performance in Heavily Contaminated Areas