Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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66 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 MATERIALS SELECTION & DESIGN Current Creep in Insulator Polluted air forms a deposit on the sur- face of insulators. With increasing humidity, rain, or snow, the resistance of the deposit greatly decreases and high voltage current can creep onto the surface of the insulator and form a spark. Electrical heat from creep current exchanges among power lines, the grounding system, and power pole is high enough to melt the surface of insulators. When this occurs, a portion of the air pollu- tion deposits diffuses into insulators and decreases their resis- tance. The surface of the insulator becomes rough and can attract a d d i t i o n a l d e p o s i t s from polluted air. The next creep current may affect the surface of the i n s u l a t o r. T h i s c a n punch holes in the insu- lator (Figure 5). In this condition, power lines may be released from th eir clamps w h en a fault current o ccurs, cutting of power. The following solu- tions for creep current have been proposed: References 1 A . A g h aja ni , M . A . G o l oz a r, A . S a at chi , K. Raeissi, M. Urgen, S. Shabani, "Stray Alter- nating Current and Environmental Effects on Concrete Power Poles," MP 52, 8 (2013): pp. 30-34. 2 A . A g h aja ni , M . A . G o l oz a r, A . S a at chi , K. Raeissi, S. Shabani, M. Urgen, "Stray Alter- nating Current Problems in Concrete Power Poles," MP 52, 5 (2013): pp. 36-39. 3 A . A g h aja ni , M . A . G o l oz a r, A . S a at chi , K. Raeissi, M. Urgen, S. Shabani, "Protecting Concrete Power Poles from Stray Alternating Current," MP 52, 10 (2013): pp. 30-33. 4 J.F. Malone, "Painting Hot Galvanized Steel," MP 31, 5 (1992): pp. 39-42. 5 P. Maass, P. Pei ssker, ed s., Handbook of Hot-dip Galvanization (Weinheim, Germany : Wiley-VCH Verlag, 2011). ABBAS AGHAJANI is a Ph.D. student of the Dept. of Materials Engineering, Isfahan University of Technology (IUT), Isfahan 84154, Iran. He is also on the faculty of the Subsea R&D Center of IUT, e-mail: aghajani@cc.iut.ac.ir. He has conducted research at the university for 19 years and has published more than 25 project reports in the fields of stray alternating current and direct current in concrete, cathodic protection, and coatings. He has also published more than 30 papers, 10 journal articles, and one book. MUSTAFA URGEN is a professor at ITU, Dept. of Metallurgical and Materials Engineering, Maslak Campus 34469, Istanbul, Turkey, e-mail: urgen@itu.edu.tr. He teaches and conducts research and development in the area of surface treat- ments. He has published more than 70 papers. He is an active member of the Turkish Corrosion Association at the national and international levels. FIGURE 4 A typical polymer cross arm for use on concrete power poles. FIGURE 5 Typical punching of the surface of an insulator after experiencing creep current. • Increasing creep distance of insula- tors by replacing them with insula- tors that maximize the length of the leakage path. • Pe r i o d i c w a s h i n g o f i n s u l a t o r s (weekly or monthly), especially dur- ing the winter season. • Replacing m etal cross arms with polymer composite cross arms. • Increasing the quality of concrete power poles to increase their resis- tance against fault current. • Modification of the grounding system. Conclusions Controlling the effects of air pollution is the best method to mitigate the corrosion problems of electrical fittings. In polluted areas, replacing galvanized cross arms on concrete power poles with glass-reinforced polymer composite material is desirable. Doing so also reduces current creep across insulators in wet polluted air. Sealing the surface of cable clamps reduces damage to the clamps and the possibility of releasing a cable. Acknowledgment The assistance of the head of the Mate- rial and Structure Group at the Subsea R&D Center at Isfahan University of Technology, and scientific staff member F. Samiei, is greatly acknowledged. The 2015 MP Media Kit is Now Available Plan your 2015 advertising schedule by visiting the Publications area of the NACE Web site: nace.org, or request a hardcopy of the kit from Brenda Nitz at +1 281-228-6219 or brenda.nitz@nace.org.

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