GUIDELINES FOR SUBSTATION AND POWER DISTRIBUTION SYSTEM OF BUILDINGS
Introduction:
1.1 In India commercial use of electricity started in 1891 though it picked up after independence due to large number of thermal and hydro power stations set up in the public sector. The power generation capacity in India has increased from 1362 MW in 1947 to more than 4, 00,000 MW in 2018.
1.2 Electricity has become essential for modern life. Practically, like air and water, electricity has become a basic requirement. We require it to run our houses, water supply, lights, fans, domestic appliances, lifts, TV, internet, communication, transportation, hospitals, offices, schools, colleges, industries, infact everything connected with day to day life.
1.3 While, in advanced countries availability of quality and uninterrupted power supply is taken for granted, in our country, this is subject to frequent interruptions due to various factors i.e. inadequate supply, inefficient/overloaded power distribution, over loading, use of obsolete technology, inefficient maintenance etc. Often our offices are subject to power interruptions on account of inadequate planning and design and overlooking modern technology including inadequate attention to proper routine and preventive maintenance.
1.4 The parameters for quality electric supply are:
• Voltage: steady voltage, variation within permitted limits.
• Frequency
• Absence of harmful harmonics
• Protection against surge/lightning
1.5 CPWD for last several decades have been following modern practice for
substation and power distribution. While the whole nation has been following pole mounted transformers and overhead distribution, CPWD for last 50 years has been distributing power through indoor substations and underground cabling system. Now the central government wants to change the overhead system into underground system all over the country, responsible for power breakdowns and theft
1.6 Also, on account of digital and computerised working of our offices and institutions, it has become necessary to provide uninterrupted and quality electric supply.
2. Objective of modern power distribution system:
2.1 To provide quality and uninterrupted power supply to the building so that there is no disruption to the productive operation of various services operating in the building to ensure human comfort.
3. Design considerations.
3.1 Indoor Substations and Underground Cable power distribution:
3.1.1 CPWD substation specifications are based on Indoor substations with standby equipments and UG cabling for ensuring service with minimum breakdowns to overcome the disadvantages of outdoor substations as:
i) Outdoor substations are subject to dust, rain, storm, extreme heat and theft leading to breakdowns and higher maintenance. During winds, cyclones and storms, the entire distribution system including poles, and conductors collapse taking long time to restore the power supply.
ii) The indoor substations work at much lower ambient, say at 28 Degree C, when the outside temperature may be above 40 degree C. Similarly the UG cable of power distribution is far superior to overhead system.
3.1.2 Substation with DG Backup: Uninterrupted power supply is supplied by the substation to cater to various loads based on DG Backup and UPS backup. The decision on central vs. building wise UPS provisions are tobe taken after careful technical and economical consideration and user requirements. For meeting critical UPS loads which require high quality power input without harmonics/surges etc., suitable Isolating transformer needs to be provided after the UPS.
Design Notes: Substation and Power Distribution Systems for Buildings
The design of substations and power distribution systems for buildings is a critical process in ensuring the reliable and efficient supply of electricity. This involves integrating key components and adhering to safety standards to meet the building's power demands while accommodating future growth and energy efficiency goals. Whether for residential, commercial, or industrial applications, proper design ensures uninterrupted power supply, operational safety, and cost-effectiveness.
Key Considerations in Substation and Power Distribution Design
1. Power Demand Estimation
Load Calculation:
- Assess the building's total electrical load, including lighting, HVAC systems, elevators, appliances, and industrial equipment (if applicable).
- Use demand factors and diversity factors to determine the maximum expected load.
Future Expansion:
- Design with scalability to accommodate future increases in load demand.
2. Selection of Voltage Levels
High Voltage (HV) Supply:
- For large buildings or industrial complexes, HV supply (e.g., 11 kV or 33 kV) may be required, necessitating an on-site substation.
Low Voltage (LV) Distribution:
- For smaller buildings, direct LV supply (e.g., 415V/230V) may suffice.
3. Substation Design
Location:
- Position substations near the building's load center to minimize power losses.
- Ensure compliance with zoning laws and safety regulations.
Components:
- Transformers: Step down high voltage to usable levels. Choose between oil-filled or dry-type transformers based on space, environment, and safety considerations.
- Switchgear: Includes circuit breakers, isolators, and relays for switching and protection.
- Busbars: Conductors that distribute power to different feeders.
- Earthing System: Ensures safety by grounding fault currents.
- Backup Systems: Include generators or battery storage for power continuity during outages.
Safety Features:
- Provide proper ventilation, fire protection systems, and physical barriers to ensure the safety of personnel and equipment.
4. Power Distribution System Design
Main Distribution Board (MDB):
- Acts as the central point for distributing power from the transformer to various loads.
Sub-Distribution Boards (SDBs):
- Divide power into smaller, manageable circuits for specific zones or functions within the building.
Cabling and Wiring:
- Select appropriate cable sizes to handle current without excessive voltage drops.
- Use conduit or trunking systems for protection and aesthetic integration.
Power Factor Correction (PFC):
- Install capacitor banks to improve power factor and reduce reactive power charges.
5. Energy Efficiency Measures
- Incorporate energy-efficient transformers and low-loss cables.
- Utilize energy management systems (EMS) to monitor and optimize power usage.
- Design lighting and HVAC systems with energy-saving technologies.
Design Process
Requirement Analysis:
- Understand the building's functional needs, power consumption patterns, and operational requirements.
System Design:
- Develop single-line diagrams (SLDs) to illustrate the electrical network.
- Select equipment based on load requirements, efficiency, and reliability.
Regulatory Compliance:
- Ensure adherence to national and international electrical standards (e.g., IEC, IEEE, or BIS standards).
Safety Planning:
- Incorporate earthing, surge protection, and fire safety systems.
- Plan for safe maintenance access and operational procedures.
Installation and Testing:
- Oversee the installation of equipment and conduct commissioning tests to ensure proper operation.
Key Components in Substation and Power Distribution
1. Transformers
- Step down utility supply voltage to levels suitable for building use.
- Types:
- Oil-Filled: High capacity, suitable for outdoor use.
- Dry-Type: Compact, safer for indoor installations.
2. Switchgear
- Protects against overcurrent, short circuits, and other faults.
- Includes breakers, fuses, and isolators.
3. Distribution Boards
- Main and sub-distribution boards to divide power across circuits.
- Equipped with protective devices like MCCBs, MCBs, and RCDs.
4. Cables and Busbars
- Cables: Carry power with minimal losses. Insulated for safety.
- Busbars: Facilitate high-current connections within switchgear.
5. Earthing Systems
- Essential for safety, ensuring fault currents are safely dissipated into the ground.
6. Backup Systems
- Generators, UPS systems, or battery storage for uninterrupted power supply.
7. Monitoring Systems
- Energy meters, power quality analyzers, and SCADA systems for operational efficiency and diagnostics.
Challenges in Design
Space Constraints:
- Substations and equipment rooms often compete with usable space in buildings.
Environmental Factors:
- Addressing heat dissipation, noise, and ventilation in indoor substations.
Load Fluctuations:
- Designing for diverse loads such as high-rise HVAC systems, elevators, or industrial machinery.
Regulatory Compliance:
- Adapting designs to meet local codes and standards.
Cost Management:
- Balancing initial investment with long-term operational costs.
Future Trends in Substation and Power Distribution Design
Smart Distribution Systems:
- Integration of IoT and AI for real-time monitoring and predictive maintenance.
Renewable Energy Integration:
- Designing systems to accommodate solar panels, wind turbines, and energy storage solutions.
Microgrids:
- Decentralized energy systems for greater reliability and energy independence.
Sustainability Goals:
- Emphasis on green buildings with energy-efficient designs.
Conclusion
The design of substations and power distribution systems for buildings is a meticulous process that requires balancing technical, safety, and economic factors. By following well-documented design notes, engineers can ensure that electrical systems are reliable, efficient, and future-ready. Proper planning and execution not only enhance the building's operational performance but also contribute to energy conservation and safety compliance.
