TAVRIDA ELECTRIC VCB Series, User Manual

Page: 43 / 142

43
Electromagnetic clearances
Short-circuit current magnetic field influences the ISM magnetic actuator.
To avoid unwanted tripping, the minimum clearances between busbars and
the ISM frame should be not less than 120 mm (Figure 69).
Figure 69
Electromagnetic clearances
Insulation clearances
The recommended minimum phase-to-phase and phase-to-ground air
clearances are stated in Table 3. Shorter clearances shall be verified by a
voltage test.
Table 3 - Minimum clearances due to rated insulation voltage
Power frequency rated voltage
Impulse test voltage
(BIL)
Minimum clearance
(b)
for LD series ISM
12 kV 75 kV 120 mm
17.5 kV 95 kV
140 mm
(160mm for ISM15_LD_8)
24 kV 125 kV 220 mm
Figure 70
LD ISM dielectric clearances
Coordination of minimum clearances
Based on electromagnetic influence and rated insulation voltage, the
greater clearance should be selected.
Measures for complying with the rated insulation
level
Insulation cap set CBkit_Ins_3 for ISM25_LD
To comply with the rated impulse withstand voltage of 125 kV according to
IEC 62271-1 it is recommended to cover the top terminals of the
ISM25_LD_1 and ISM25_LD_3 with insulation cap set CBkit_Ins_3. The
arrangement is shown in Figure 72.
Figure 71
Clearance coordination