INTRODUCTION
General Guidelines for
765/400/220/132kV substations and
switchyard of Thermal/ Hydro Power Projects
i) This document is an effort to consolidate maximum possible technical information/ data pertaining to switchyard for thermal/ hydro power projects and also sub-stations as per general prevailing practices for the use/ guidance. However, the site specific requirements need to be looked into by the owner/ developer of the systems.
ii) The sub~stations/ switchyards constitute of transmissiOn system, which interconnects power transmission · circuits and transformation between networks of different voltages. It is required to pay careful attention in planning, designing and constructing the sub-stations/ switchyards, since its reliability directly affects the power supply availability. Sub-stations generally comprise of switchgear, power transformer, control, protection, monitoring and· automation equipment. The highest transmission system voltage in operation in the country is 800kV. Further, 1200kV level is also under consideration in near future.
iii) The sub-stations are of three types based on its use, viz Substations attached to
thermal/ hydro power stations (which is generally called as Switchyard), interconnecting sub-stations, step-down (EHVIHV, EHVIMV, HVIMV) substation. However, the sub-stations shall be of Air insulated sub-station (AIS), Gas insulated sub-stations (GIS) or Hybrid sub-stations.
AIS is most commonly used so far; however, GIS/ hybrid substation may be
adopted considering techno-economic viability. GIS is generally preferred, where availability of space and safety are major constraints, seismic prone areas, coastal areas and very heavily polluted areas etc.
Hybrid sub-station (combination of AIS and GIS) are available upto 220kV
level which requires comparatively less space than AIS. For renovation/
augmentation of existing AIS, hybrid option may be adopted considering
space constraints and techno-economic viability.
iv) This document describes salient parameters and technical features of
equipment required for sub-stations and switchyard associated with thermal/
hydro generating stations. Specific details in respect of GIS and hybrid sub-
station have been covered in Annexure-A and B.
SYSTEMPARAMETERS
The system parameters for 765kV, 400kV, 220kV, 132kV and 33kV are given
in Schedule - 1
3.0 SWITCHING SCHEMES
The selection of switching schemes depends on operational flexibility, system
safety, reliability & availability, ability to facilitate the system control and cost.
However, other types of switching schemes can be considered, if system
demands.
Following switching schemes shall generally be adopted at various voltage levels
of switchyards/ sub-stations. The various types of switching schemes are shown
in the Annexure -C."
General Guidelines for
765/400/220/132kV substations and
switchyard of Thermal/ Hydro Power Projects
The actual layout shall depend upon the type of sub-station! switchyard (viz Air
insulated sub-station (AIS), Gas insulated sub-station (GIS) or Hybrid sub-station). The area required would depend on voltage level, switching schemes,number of feeders of different voltage levels, no. of transformers, compensating equipments and possibility of future expansion.
In case of thermal power stations, the location of the switchyard shall be decided
depending upon the wind profile to avoid additional pollution on account of
water droplets from cooling towers.
Designing, constructing, and operating high-voltage substations and switchyards (765/400/220/132 kV) for thermal and hydroelectric power projects require adherence to a set of guidelines to ensure safety, reliability, and efficiency. These substations form critical nodes in the power transmission system, serving as points for voltage transformation, power control, and distribution. The following are general guidelines for such high-voltage substations and switchyards:
1. Site Selection and Layout
- Location: The substation should be located close to power generation plants (thermal or hydro) to minimize transmission losses. Considerations include accessibility, proximity to load centers, environmental impact, and ease of integration with the transmission network.
- Land Area: The area should be sufficient to accommodate all substation components, including transformers, switchgear, control rooms, and future expansion possibilities. The layout should ensure safe separation distances between equipment.
- Geotechnical Investigation: Conduct soil testing to determine load-bearing capacity, soil resistivity for earthing systems, and seismic suitability, especially for hydro projects in mountainous regions.
2. Design and Equipment Standards
- Voltage Levels: Follow standardized voltage levels (765 kV, 400 kV, 220 kV, 132 kV) as per regional grid requirements and international standards (like IEEE, IEC). These standards help ensure interoperability and compatibility with existing power systems.
- Insulation Coordination: Design for proper insulation levels based on system voltage and anticipated overvoltage conditions like lightning strikes and switching surges. Use surge arresters and properly rated insulators to ensure safety and reliability.
- Substation Configuration: Common configurations include:
- Double Bus Single Breaker: For increased flexibility and reliability.
- One and a Half Breaker Scheme: Provides higher reliability but requires more equipment.
- Double Bus Double Breaker: Offers greater operational flexibility but is more expensive.
- GIS (Gas Insulated Switchgear): Recommended for space-constrained areas, especially in hydro power projects where space may be limited.
3. Protection and Control Systems
- Relay Protection: Use advanced protective relays for equipment protection (transformers, transmission lines, busbars). Relays should detect faults like short circuits, overvoltage, and overcurrent to ensure quick isolation of faulty components.
- SCADA and Automation: Implement Supervisory Control and Data Acquisition (SCADA) systems for real-time monitoring, control, and automation. SCADA enables remote control of breakers, isolators, and tap changers.
- Backup Protection: Design for redundancy in protection systems to ensure that a backup protection scheme is available in case the primary fails, enhancing overall system reliability.
- Fire Protection: Implement fire detection and suppression systems for critical equipment like transformers, control rooms, and battery rooms.
4. Earthing (Grounding) System
- Grounding Design: Design a robust grounding system to safely dissipate fault currents into the ground, protecting equipment and personnel. A low-resistance earthing system is essential for high-voltage substations.
- Mesh Grounding: Use a grid or mesh grounding system beneath the substation yard to provide uniform potential and prevent dangerous step and touch voltages.
- Grounding of Neutral Points: Properly ground the neutral points of transformers and generators to maintain system stability during fault conditions.
- Lightning Protection: Install lightning arresters and shield wires to protect equipment from lightning-induced overvoltages, especially in areas prone to lightning strikes.
5. Substation Equipment and Layout Design
- Power Transformers: Select transformers with ratings appropriate for the load and voltage level of the substation. The design should include provisions for oil containment pits and firewalls to prevent oil spillage in case of leakage.
- Switchgear: Use circuit breakers (SF6 or vacuum breakers) suitable for high voltage levels to manage the interruption of fault currents. Isolators, current transformers (CTs), and potential transformers (PTs) are also integral components.
- Busbar Design: Design busbars to handle the maximum load current with adequate margins. Use tubular or ACSR (Aluminum Conductor Steel Reinforced) conductors for higher current-carrying capacity. Ensure proper spacing to avoid electrical flashover.
- Control and Relay Panels: Install control and relay panels in a protected control room environment with easy access for operations and maintenance personnel.
6. Thermal and Hydro-Specific Considerations
- Thermal Power Plants: For substations connected to thermal plants:
- Ensure proper cooling mechanisms for transformers due to the heat generated by thermal plants.
- The design should include auxiliary power supply arrangements for station service loads.
- Hydro Power Plants: For substations linked to hydro power:
- Consider the impact of fluctuating water levels and seasonal variations on generation capacity.
- The substation should be located at a safe elevation to avoid flooding risks.
- Address potential issues with remote location access, especially in mountainous areas.
7. Safety, Health, and Environment (SHE) Requirements
- Safety Protocols: Establish strict safety protocols for construction, operation, and maintenance. Personnel should be trained in working around high-voltage equipment and emergency response procedures.
- Clearances: Maintain safe clearances between live parts and grounded structures as per standards to avoid accidental contact and ensure safe working conditions.
- Noise Control: Install noise-dampening barriers or equipment to reduce noise levels from transformers and switchgear, especially in residential or environmentally sensitive areas.
- Environmental Compliance: Follow regulations regarding emissions, waste disposal, and protection of local ecosystems. This is especially critical for hydro power projects where ecological impacts on water bodies must be minimized.
8. Testing, Commissioning, and Maintenance
- Testing and Commissioning: Perform testing of all substation components before commissioning, including insulation testing, relay calibration, and system integration checks.
- Routine Maintenance: Develop a maintenance schedule for transformers, breakers, and other critical equipment to ensure long-term reliability and prevent unexpected outages.
- Condition Monitoring: Implement condition monitoring systems like dissolved gas analysis (DGA) for transformers, partial discharge monitoring, and infrared thermography for detecting hot spots.
9. Operational Flexibility and Expansion Planning
- Future Expansion: Design the substation with provisions for future expansion. This could include space for additional bays or transformers, ensuring that the substation can handle increased load demands.
- Operational Flexibility: Ensure that the layout allows for maintenance activities without causing major disruptions to the power flow, such as by incorporating bypass arrangements or ring bus configurations.
Conclusion
The development and operation of 765/400/220/132 kV substations and switchyards for thermal and hydro power projects require adherence to well-established guidelines and standards. These guidelines ensure that the infrastructure is safe, reliable, and capable of handling the dynamic nature of power generation and distribution. By addressing aspects like site selection, equipment design, protection systems, and environmental considerations, operators can achieve efficient power system performance while maintaining safety and operational excellence.
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