Surge arresters

Protection from such surges is tichieved by using a distribution class surge arrester at the receiving end of the supply. Generally no protection is therefore necessary for the semiconductor devices. For more details see Chapter 18. 

With the use of surge arresters and surge capacitors (Section 17.10)... 

In HT switchgear assemblies provide a surge arrester or a lightning arrester, wherever necessary. Also refer to Section 17.11. 

L/R - local/remote. A/M- auto/ manual) Surge arrester... 

All electrical equipment are designed for a specific BIL, as indicated in Tables 11.6, 13.2, 14.1, and 32.1(A) for motors, switchgears and bus systems respectively, and Tables 13.2 and 13.3 for the main power system (line clearances and insulators). If the actual severity of a prospective surge, i.e. its amplitude and/or rise time or both, is expected to be higher than these levels (higher amplitude and lower rise time) the same must be damped to a safe level, with the use of surge arresters, surge capacitors or both as discussed later. 

Figure 17.5 Oscillograms showing the effectiveness of a surge arrester on a 6.6 kV motor...

This is the winding insulation to the body, whicli is more vulnerable to prospective voltage peaks. V,. as a result of TRVs. When the TRV exceeds the BIL of the machine, it can be dampened to a safe limit with the use of a surge arrester, say, from peak to ih, as illustrated in Figure 17.21. Details of a surge arrester and the procedure for its selection are discussed below. See also Example 17.6. The selection of the arrester w ill also depend upon the method of star (neutral) formation of the stator s... 

Curve-Oa, - Original steep fronted TRV, r.r.rv. = — Curve-0a2 - Damped TRV2 with the use of a surge arrester alone, r.r.r.v. may still be higher than recommended tor Va... 

Curve-0b2 - Tamed and damped TRV with the use of a surge capacitor and a surge arrester... 

A surge arrester is not able to reduce the steepness (r.r.r.v) of a surge. While motors with single-turn coifs may be safe as turn to turn insulation becomes the same as the major insulation with respect to the body, motors... 

Since the amplitude of the FOW is more than permissible (16.2 kV for a normal design and 26.9 kV for a special design motor Table 11,6) it is advisable to dampen the amplitude with the help of a surge arrester. Using a 6 kV station class surge arrester of Example 17,6,... 

Figure 17.23 Use of a surge capacitor in association with a surge arrester to provide taming as well as dampening effects to a steep fronted TRV...

Select the nearest voltage rating of a station class surge arrester (see also Section 18.8) from the manufacturer s catalogue, (Table 18.8) as 6 kV which has the following protective levels ... 

The current limiting gaps, as noted above, in series with the non-linear resi.stors make it possible to adjust the protection level of the surge arrester for different values of discharge currents. They also help to maintain... 

Figure 18.1(a) A typical power circuit of a non-linear resistor-type surge arrester... 

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