EMCO URGES QESCO, MEPCO to review policy on foreign polymer insulators

ISLAMABAD: M/s EMCO Industries has suggested QESCO and MEPCO to review procurement policy for foreign goods (Polymer Insulators) due to forex constraints and give preference to local procurement.
The firm has submitted its proposals with reference to tenders’ advertisement published in which QESCO and MEPCO have required Non-Ceramic insulators for its 132kV Transmission line (Qty 2500) due to open on September 30, 2025.
The firm which has conveyed serious reservations on mass scale use of the composite insulators in the country on the basis of the international experience gained so far.
The firm has submitted following for consideration of both the DISCOs before taking any policy decision in this regard ;(i) the life expectancy is lower and unpredictable ;(ii) they require very careful handling during transport, storage and installation. They can easily get bent, resulting in development of cracks that lead to moisture ingress to core and ultimate failure ;(iii) highly susceptible to scratches and any scratch on rubber will kill its dielectric feature ;(iv) in storage it is prone to attack by rodents and in the field, it is prone to bird pecking ;(v) any problem, anywhere in the insulator (rod, sleeve or sheds), needs replacement of full insulator string, whereas in a string of disc insulators, only the defective disc has to be replaced ;(vi) besides bird pecking, the silicone rubber is also sensitive to fungus and other inferior plants (such as moss or lichen). Their deposition on the surface of the insulator will lead to water retention and thus deterioration of dielectric strength and the hydrophobic properties ;(vii) as the shed diameter is much greater as compared to ceramic insulators, so the sheds are more prone to shearing due to sustained strong winds and birds pecking ;(viii) the top large shed provides a good landing/ resting place to birds. As a result, the bird’s excrement deposits on the top shed, which badly distorts the electric field distribution, so after some time, the composite insulators are more prone to flash overs as compared to ceramic insulators ;(ix) the hydrophobicity of composite insulators reduces with ageing. Resultantly, the pollution flash over withstand capability also reduces, which cannot be restored by washing/ cleaning ;(x) the formation of nitric acid as a result of corona discharge in presence of water causes erosion of metal end fittings and deterioration of the core. These defects which can cause breakage of the string and conductor fall down are difficult to be detected by distant visual inspection ;(xi) the monitory inspection is costly. A variety of in-service monitory methods are available but most do not meet the criteria of being simple, effective and convenient ;(xii) a report from China shows that the composite insulators need to be very promptly monitored for a lightning flashover. In such cases the composite insulator is immediately replaced to avoid subsequent core failure and conductor droppage. Contrarily, ceramic insulators may withstand 3 or even more flash-overs before failure ;(xiii) even in higher polluted areas the polymer insulator will require washing especially in areas which have low rainfall. However high-pressure washing cannot be done owing to fragility of the sheds; and (xiv) generally, for an equivalent length of string, a good quality of polymeric insulator will be more expensive.
According to M/s EMCO Industries, although the composite insulators (Non-ceramic) have shown higher growth rates in recent past, their long-term reliability is not yet established so their future is not clear. However, porcelain insulators still have the major share in the overall market. There are quite a few positive indications that in future RTV-coated ceramic insulators will dominate the market as they combine the advantages of the reliability of ceramics and better pollution performance of silicone rubbers.
In view of world-wide experience and trends, the mass scale use of the composite insulators in Pakistan does not appear to be advisable.
The major problems for transmission in Pakistan occur in areas south of Hyderabad, where the presence of sand storms, deposition of fine dust, marsh land together with industrial deposits and no rainfall will need continuous monitoring. However, to gain experience with this type of insulators, some short 132kV lines may be built with composite insulators and any major decision in this regard could be made after watching the performance of these experimental lines for a reasonable time period. It is also suggested to install a test rack in the field energized at 132 kV, with appropriate instruments to record weather conditions, leakage current etc. The test rack should use various types of shapes and materials to compare and determine the longer-term performance of various shapes and materials.
In addition, the conditions of the country in respect of foreign exchange has deteriorated as compared to the previous year and the GoP is striving hard to save each penny of the foreign exchange. The DISCOs’ policy to procure foreign made Polymer insulators for their 132kV system, when most of 132kV and 220 kV transmission lines throughout the country are running satisfactorily with locally made porcelain insulators, is absolutely not understandable.
In view of submissions, the firm has anticipated and expects that both DICOs’ to review current policy to procure foreign goods (Polymer Insulators) in the broader interest of the country and all stakeholders and should follow standard bidding procedure. The firm has also requested that tenders for Polymer insulators be cancelled and add following quantity in porcelain disc as an equally acceptable option. Ends