For selecting switchgears, in addition to normal factors current, voltage and frequency, the fault withstanding capacity is of prime importance. The allowable fault current depends on the capacity of supply company as well as the load and nature of fault. The fault level withstand capacity is known as rupturing capacity (Typical values of rupturing capacity are 250 MVA at 11 kV and 350 MVA at 22 kV).
The rupturing capacity of HV switchgear is taken to be equal to the rupturing capacity of supplier's HV switchgears, if the interconnecting cable between these two points is not large.
The withstand capacity of MV switchgear is calculated as follows:
Short circuit MVA = (transformer capacity in kVA × 100) / (1000 × % impedance of transformer).
Typical MV switchgear withstand capacities are 25 - 35 MVA at 415 V.
| Lower rated voltage(KV) | Upper rated voltage (kV) | Current Rating (A) | Rated breaking capacity (MVA) | Rated making current (peak) (kA) | Rated impulse current (peak) (kA) | Rated short time current (1 s) (kA) |
|---|---|---|---|---|---|---|
| 10 | 12 | 400 | 150 | 25 | 30 | 20 |
| 630 | 250 | 40 | 50 | 25 | ||
| 350 | 55 | 60 | 40 | |||
| 500 | 80 | 100 | 60 | |||
| 1250 | 350 | 55 | 60 | 40 | ||
| 500 | 80 | 100 | 60 | |||
| 30 | 36 | 1250 | 750 | 35 | 60 | 30 |
| 1500 | 65 | 75 | 50 |
| Width | 610 mm |
| Height | 2565 mm (Including relay panel) |
| Depth | 1625 mm (In closed position) |
| Depth | 1625 + 711 mm (In service draw out position) |
| Rear access required | 610 mm (min.) |
| Rated Voltage | 11 kV | 22 kV | 33 kV |
|---|---|---|---|
| Insulation level | 27 kV | 50 kV | 70 kV |
| Rated current | 1600 A | 1600 A | 1600 A |
| Short time withstand current (3 s) | 28 kA | 20 kA | 16 kA |
| Symmetrical breaking capacity | 40 kA | 25 kA | 16 kA |
| Making capacity (Peak) | 100 kA | 63 kA | 40 kA |
| Oil content per breaker in litres | 10 | 10 | 18 |
| Closing mechanism | ---------------- | Manual/Motor driven | ---------------- |
| Opening time | ---------------- | Less than 3 cycles | ---------------- |
| Closing time | ---------------- | Less than 5 cycles | ---------------- |
Courtesy: M/s. Eswaran and Sons Engineers Ltd.
| Lower rated voltage (kV) | Upper rated voltage (kV) | Current Rating (A) | Rated breaking capacity (MVA) | Rated making current (peak) (kA) | Rated impulse current (peak) (kA) | Rated short time current (1 s) (kA) |
|---|---|---|---|---|---|---|
| 10 | 12 | 400 | 150 | 25 | 30 | 20 |
| 630 | 250 | 40 | 50 | 25 | ||
| 350 | 55 | 60 | 40 | |||
| 500 | 80 | 100 | 60 | |||
| 1250 | 350 | 55 | 60 | 40 | ||
| 500 | 80 | 100 | 60 | |||
| 30 | 36 | 1250 | 750 | 35 | 60 | 30 |
| 1500 | 65 | 75 | 50 |
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