High voltage power point presentation and title

high voltage

1. HIGH VOLTAGE TESTING & INSULATION COORDINATION High voltage testing of electrical power apparatus as per International and Indian standards – Power frequency, impulse voltage and DC testing of Insulators, circuit breakers, bushing, isolators and transformers- Insulation Coordination

2. INSULATION COORDINATION Insulation coordination Insulation coordination is the process of determining the proper insulation levels of various components in a power system as well as their arrangements

3. Electric systems insulation Choose insulation levels for components that would withstand all kinds of over voltages. Consider protective devices that could be installed at the sensitive points to limit over voltages .

4. Insulation level of an Apparatus Insulation level’ is defined by the values of test voltages which the insulation of equipment under test must be able to withstand

5. Insulation level of an Apparatus Insulation level’ is defined by the values of test voltages which the insulation of equipment under test must be able to withstand

6. Basic impulse level (BIL) The basic impulse level (BIL) is the maximum impulse voltage that electrical equipment can withstand without damage. The BIL of a power system is usually chosen as 25% to 30% more than the protective level offered by the protective devices .

7. Necessity of insulation coordination To ensure reliability and continuity to the utility concerns. To minimize the number of failures of lines and substations due to over voltages. To minimize the cost involved in the design, installation and operation of protective devices. To maintain the flash over should be minimum for insulators .

8. The insulation problems in a power system It occurs due to the following Determination of line insulation. Selection of Basic Impulse insulation level and insulation levels of other equipment. Selection of Lightning Arresters

9. The ideal requirements of a protective device connected in parallel It should not usually flashover for power frequency over voltages . The volt-time characteristics of the device must lie below the withstand voltage of the protected apparatus or insulation. It should be capable of discharging high energies contained in surges and recover insulation strength quickly.

10. Volt-time characteristics of transformer rod gaps and surge diverters

11. Proper insulation coordination would be ensure that the volt-time characteristics of the equipment will be lie above the volt-time characteristics of the protective devices. It gives the relative insulation strengths of the transformer (curve A), rod gaps (curves B and C), and that of a lightning arrester (curve D). A lightning arrester (D) protects the transformer insulation (A) during the entire time region.

12. Case ( i ): Assuming the surge voltage rise is as shown by curve 1, The rate of rise of surge is less than the critical slope (curve X). The rod gap flashes and protects the transformer insulation. Case (ii): Assuming the surge voltage rise is as shown by curve 2, The rate of rise of surge is greater than the critical slope (curve X). The rod gap cannot protect the transformer insulation. Only the surge diverter can protect the transformer insulation

13. Insulation Co-ordination in EHV and UHV Systems Stations have transformers and other valuable equipment that have non-self-restoring insulation, and The protective levels for lightning surges and switching surges are almost equal and even overlap. ◦ If the basic impulse level for the equipment or the system is chosen, then this level cannot give protection against the switching impulses. ◦ Hence, a separate switching impulse level (SIL) has to be chosen. ◦ It is desirable to use protective devices for limiting both lightning and switching over voltages . ◦ As such, the SIL above the controlled switching surge level has to be adopted. ◦ So that the surge diverters operate only rarely on switching over voltages when the controls of the control devices for switching voltages fail