Insulation levels

The insulation of a substation's equipment is rated per voltage level. The design takes these ratings per level from its level table: the highest system voltage $U_m$, the lightning impulse withstand voltage, the switching impulse withstand voltage where the level has one, and the rated voltage of the surge arresters.

1The ratings of a levelCopy link to The ratings of a level

The highest system voltage $U_m$ is the first rating of a level, and the design names the level's equipment by it. The lightning impulse withstand voltage is a peak value. The design prints it as the basic lightning impulse insulation level (BIL), in kVp. The switching impulse withstand voltage (SIWL), also in kVp, is carried at the highest levels only.

IEC 60071-1:2019 divides the levels by $U_m$. A level with $U_m$ up to 245 kV is in range I, and Table 2 lists its standard insulation levels. A level above it is in range II, Table 3, and the design carries a switching impulse withstand for it. The compliance checklist cites the table of the high-voltage (HV) level's range.

The design takes one rated voltage per level for the surge arresters at the line entries and at the transformers. That rating is a value of the level table, not the result of a study (The surge arrester rating).

2The IEC + CEA / CBIP setCopy link to The IEC + CEA / CBIP set

The CEA Construction Regulations 2022 set the highest system voltage and the lightning impulse withstand per level (Reg. 45(1), Table 9), and those of 33 kV in Reg. 50(1), Table 14. The checklist states the HV level's $U_m$ and BIL against them. The design's values per level are in the table.

The levels of 400 kV and 765 kV are in range II. The design takes their switching impulse withstand as 1050 kVp and 1550 kVp.

The checklist item for the collector bus checks that its BIL is a standard value of IEC 60071-1:2019 Table 2 for its $U_m$. Those values are 60 kVp, 75 kVp or 95 kVp at 12 kV, and 145 kVp or 170 kVp at 36 kV.

3The ANSI / IEEE setCopy link to The ANSI / IEEE set

The ANSI / IEEE set takes the rated maximum voltage and the BIL of its levels from IEEE C37.04-2018 Table 6. At 345 kV it also takes the basic switching impulse insulation level (BSL) of that table, 825 kVp. The station arresters have a duty-cycle rating per level, the design's value (the table).

4AltitudeCopy link to Altitude

The design does not correct the insulation levels for altitude. Above 1000 m, the Altitude input gives a warning that the insulation levels are not corrected and are to be confirmed at detail design.

The clearances are corrected above 1000 m. The IEC + CEA / CBIP set multiplies them by the altitude factor of IEC 60071-2 (Electrical clearances, Correction for altitude). The ANSI / IEEE set takes the clearances of a higher BIL, while the level's own BIL stays as the table lists it (Clearances of the ANSI / IEEE set, Altitude).

5The surge arrester ratingCopy link to The surge arrester rating

The rating of an arrester depends on the temporary overvoltage (TOV) at its location, which the neutral earthing study gives. IEC 60099-4:2014 lists the standard rated voltages (§5.1, Table 2) and the arrester's power-frequency voltage versus time characteristic (§6.12).

The design takes the rated voltage of its level table and does not calculate the temporary overvoltage. The checklist item "Arrester rated voltage against temporary overvoltage" is therefore Needs your review. Answer it from the neutral earthing study. In the ANSI / IEEE set, the checklist has an item for the arresters' ratings and their application, answered in the same way.