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Central Electricity Authority Regulation 2023
Based on the Central Electricity Authority (Measures relating to Safety and Electric Supply) Regulations, 2023, the guidelines for products and installations are generally categorised by voltage levels.
In the context of Indian regulations, "Medium Voltage" in modern industrial terms, products often fall into the 11 kV to 33 kV range.
1. General Safety Requirements (All Voltages)
Suitability : All electrical apparatus must be of sufficient rating for power, insulation, and estimated fault current. They must be mechanically strong enough for the duty cycle and environmental conditions.
Standards : All material and apparatus used must conform to the relevant Indian Standards (BIS) or International Standards (IEC/IEEE).
Location : Electrical equipment must be installed above the Highest Flood Level. If not possible, it must be as per IP protection.
2. Products Operating at Voltage like 11kV to 33kV
A.) Protection and Control
Circuit Breakers : For supplies at 11 kV and above, a circuit breaker is mandatory.
Fault Protection : Systems must have protection to automatically disconnect supply in case of over-current or earth faults.
Interlocks : Isolators and controlling switches must be interlocked with the circuit breaker to prevent opening or closing under load.
B.) Transformer Guidelines
Protection Relays : Transformers of 1000 kVA and above must have Buchholz relays, pressure relief devices, and winding/oil temperature protection.
Differential Protection : Transformers of 10 MVA and above require differential protection.
Fire Safety :
◦ Installations with more than 2000 liters of oil require proper oil draining arrangements.
◦ Transformers of 10 MVA or reactors of 10 MVAR and above must have an automatic fire fighting system.
◦ Cables connected to the transformer must be Fire Retardant Low Smoke Low Halogen (FRLSH).
C.) Capacitors
Discharge : Static condensers (capacitors) must be provided with automatic or manual discharging devices to discharge stored energy when the supply is cut off.
3. Cabling and Earthing
Cable Sheathing : Cables for voltage exceeding 650 V (unless they are thermoplastic/XLPE insulated without screens) must have metal sheathing that is electrically continuous and earthed.
Earthing Mat : Substations and switchyards must utilise an earthing mat that limits touch and step potential to tolerable values.
Lightning Protection : Lightning arresters must be provided for protection against lightning for installations exceeding 650V.
4. Inspection and Self-Certification
Self-Certification : The owner or supplier must inspect, test, and self-certify electrical installations of notified voltages before the commencement of supply. This implies that manufacturers and installers must ensure products are ready for this certification process.
Testing : No new apparatus or cable exceeding 650 V can be commissioned unless subjected to site tests as per relevant standards.
5. Summary of Safe Clearances (Working Distances)
For maintenance and safety, specific clearances must be maintained based on voltage levels:
• 11 kV : 0.61 Meters (610 mm)
• 33 kV : 0.71 Meters (710 mm)
• 66 kV : 0.91 Meters (910 mm)