System grounding insulation

The fully ionic solids (region I) afforded band insulators, 1 1 Mott insulators with ground states of antiferromagnets (E b(21) and F b(22) in Fig. 1) or spin-Peierls systems, ferroelectrics, ferromagnets, spin-ladders, and nonlinear transport materials (switching and memory). 

Our experimental setup is illustrated in Fig. 2. The electrowetting system comprised a photolithographically patterned control electrode array (made from chromium or indium tin oxide, ITO) on a glass substrate and a continuous ground plane (ITO on glass) parallel to it. Both electrode surfaces were covered by a film of hydrophobic insulation (e.g. a Teflon AF 1,600 film, with a contact angle of 104° with water) that was insufficient to electrically insulate the ground... 

The leakage current is measured as in lEC 60298. This method is generally applicable to an HT system by applying the full rated voltage between the insulating surface, say, between a phase and the ground. The leakage current thus measured should not exceed 0.5 mA. 

Table A16.8 6.35/11 kV (Grounded system) paper insulated belted cables (IS 692)...

For instance, when lightning of, say, a nominal discharge current of 10 kA strikes a 400 kV (r.m.s.) overhead line, having a surge impedance of 350 Q, then two parallel waves will be produced each of amplitude 10 x 350/2 or 1750 kV which may be more than the impulse withstand level of the system and cause a flashover between the conductors and the ground, besides damaging the line insulators and the terminal equipment (Table 13.2). It is therefore imperative that the system is protected against such eventualities. 

For non-effectively grounded systems, having a GFF of more than 1.4, a higher level of insulation (BIL) will be essential for all equipment being used on the system to withstand a higher level of a one-minute power frequency voltage test as well as an impulse voltage withstand test if such levels (Lists I, II and III) are prescribed in the relevant standards. If not, then it may be assumed, that the prescribed test values take account of such an... 

In the preceding paragraphs we have analysed the behaviour and characteristics of a system when grounded or left isolated. The ground fault factor (GFF) plays a very significant role in the selection of insulation level (BIL) and its coordination with the different equipment connected on the system. The application of a particular method of grounding would thus depend upon... 

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