“Alfa-Energo” has recently launched production of 220 kV voltage class IPRP insulators based on the glass-fiber pipe impregnated with silicon foam.

The coupling flange is a key component of the structure. For the sake of fault-free operation of the insulator the design of a coupling flange shall provide maximum decrease of electrostatic field strength in the area of its coupling with the insulating unit. Fault-free and reliable operation of IPRP insulators under high voltage is achieved by means of a thorough analysis of electric field and due to measures targeted at decrease of its strength to the permissible level.

Fig. 1 shows the segment of a design model of the 220 kV class post insulator in the section of high-voltage flange. The high-voltage flange potential is considered equal to highest y-voltage (146 kV for 220 kV voltage class). The specific inductive capacity of the silicon-organic coating is considered to be equal to 4.0, while for the glass-fiber material this indicator equals 5.0.

The main peculiarities of the chosen form of high-voltage flanges are:
a)  Flattened curves of the surface of lower face of a flange
b) Usage of dielectric gap with a length of 3-5 mm between metallic section of the lower part of flange and the surface of the glass-fiber

The results of calculations are depicted on fig. 2 as diagrams of tension distribution and in TABLE 1.

The chosen form of the high-voltage flange provides absence of internal discharges both in the solid dielectric and in the open air at the surface of the metallic welding rod. This is confirmed by the high-voltage testing results, which showed that really achievable level of internal discharges does not exceed 2 pC.

The post insulator of 220 kV voltage class designed and developed by “Alfa-Energo” has the following technical specifications:

• Overall mounting height – 2100/2200/2300 mm;
• Glass-fiber pipe outer diameter – 140 mm;
• Maximum deflection under flexure stress of kN does not exceed 25 mm

The insulator is more preferable than its porcelain counterparts because of its lightweight and safety of operation. Flanges made of aluminum alloy are corrosion-free. At the moment more than 200 IPRP-8-220 type insulators were manufactured and various electricity supply grids in Russia successfully use majority of them. For instance, the fig. 2 demonstrates polymer insulators of 220 kV voltage class mounted at Ochakovo substation of OJSC “Mosenergo” as components of disconnectors.

TABLE 1

Electric field strength (kV/mm of actual current) at the design model components (fig. 1) for the 220 kV voltage class post insulator

Number	Position	E, kV / mm
1	Upper flange of upper insulator (high potential) R 15/ R 10 mm in the open air	1.99
2	Separation border between the glass-fiber pipe and coating in the vicinity of the upper flange of the upper insulator (in the coating substance) R 60	0.58
3	Outer surface of coating in the vicinity of upper flange of upper insulator in the open air in the vicinity of flange at the brim of the knuckle	1.20 0.98

Fig. 1 220 kV voltage class design model of the post insulator of (segment)

Fig. 2 220 kV voltage class polymer post insulators of as a component of an out-door type disconnector at the Ochakovo substation