IEC 62271-200 Clause 8.104 states that if the switchgear is installed, operated and maintained according to the instructions of the manufacturer, there should be less probability that internal arc occurs. Failure within the switchgear due to a defect or an exceptional service condition or maloperation may cause an internal arc, which is a hazard if persons are present.
Faults are more likely to occur inside a switchgear enclosure than in other locations. IEC 62271-200 Table 102 provides a list of locations where faults are most likely to occur, the causes of failure and possible measures to decrease the possibility of internal arc faults, most of which are applicable to installation, commissioning, operation and maintenance.
| Locations where internal arc faults are most likely to occur (1) |
Possible causes of internal arc faults (2) |
Examples of possible preventive measures (3) |
|---|---|---|
| Connection compartments | Inadequate design | Selection of adequate dimensions Use of appropriate materials |
| Faulty installation | Avoidance of crossed cables connections. Checking of workmanship on site. Correct torque | |
| Failure of solid or liquid insulation (defective or missing) |
Checking of workmanship and/or dielectric test on site. | |
| Disconnectors Switches Earthing switches |
Maloperation | Interlocks. Delayed reopening. Independent manual operation. Making capacity for switches and earthing switches. Instructions to personnel |
| Bolted connections and contacts | Corrosion | Use of corrosion inhibiting coating and/or greases. Use of plating. Encapsulation, where possible Supplemental heating to prevent condensation. |
| Faulty assembly | Checking of workmanship by suitable means. Correct torque. Adequate locking means | |
| During racking-in or rackingout of withdrawable parts. E.g. due to dielectric change of state in combination with damage or distortion of the plugging contacts and/or shutters |
Checking of workmanship at site. | |
| Instrument transformers | Ferro-resonance | Avoidance of these electrical influences by suitable design of the circuit |
| Short circuit on low-voltage side for VTs | Avoid short circuit by proper means for example, protection cover, low-voltage fuses | |
| Circuit-breakers | Insufficient maintenance | Regular programmed maintenance Instructions to personnel |
| All locations | Error by personnel | Limitation of access by compartmentalisation. Insulation embedded live parts. Instructions to personnel |
| Ageing under electric stresses | Partial discharge routine tests | |
| Pollution, moisture ingress of dust, vermin, etc. | Measures to ensure that the specified service conditions are achieved (refer to clause 2). Use of gas-filled compartments |
|
| Overvoltages | Surge protection. Adequate insulation co-ordination. Dielectric tests on site |
Reference: IEC 62271-200 (2011)