132kv file.pptx learning more about it btech

132/33kb file

1. PREFACE I have ex perienc e d vo c a tio n a l tr a in in g in 13 2 K V s u b s ta tio n B a r e illy to w n fo r th a t I am ve r y th an k fu l to a ll o ffic e r s w h o ga ve m e va lu ab le re c e p tio n an d th e ir p r e c io u s tim e fo r m e .W e have an an e le c tr ic la b in o u r co lle g e w h e r e I ha ve b e e n tr a in e d in in d u s tr ia l e n v ir o n m e n t w h ic h w ill be he lp fu l fo r m e in fu tu re . B y th a t p r a c tic a l kn o w le d g e th e ir ap p lic a tio n I am ge ttin g he lp fu l to re a liz e th e th e o r e tic a l kn o w le d g e th e re fo r I am ve r y th an k fu l to U .P .P .T .C .L 13 2 K V s u b s ta tio n fo r a llo w in g m e to p e r fo rm th is s o r t o f p e r fo rm th is b y vo ca tio n tr a in in g in th e ir s u b s ta tio n . i 1

2. Acknowledgement I am ve r y th an k fu l to th e tr an s m is s io n de p a r tm e n t o f U .P .P .C .L au th o r ity fo r p r o v id in g m e th e o p p o r tu n ity o f vo c a tio n a l tr a in in g a t th e ir s u b s ta tio n . I am s p e c ia lly th an k fu l to M r .D e e p ak K au s h a l 13 2 k v s u b s ta tio n to B a r e illy to w n fo r h is k in d a tte n tio n . I am a ls o th an k fu l to th e o th e r o ffic e r s fo r s h a r in g th e ir va lu ab le e x p e r ie n c e s a t th e yard b y m ak in g m e aq u in te d w ith p r a c tic a l p h e n o m e n o n th e o ve ra ll v ie w o f g r id s y s te m ap a r t fr o m th e s tr u c tu r e o f s u b s ta tio n an d th e de ta ile d o f its va r io u s s u b s ta tio n s . S o I fe e l th an k fu l to a ll o f th e m to w h o m ad e th is p o s s ib le . i 2

3. 1 INTRODUCTION TO 132/33KV SUBSTATION BAREILLY 132/33 KV substation TOWN DIVISION BAREILLY UTTAR PRADESH. It is situated near beside Gandhi Udhyan. It was opened and started in 1989. It is a grid power substation i.e. from here supply can also taken or given. At this substation voltage is stepped down 132/33 KV for distribution to other substation known as Secondary distribution respectively. From here 2 lines of 132 KV and 9 lines of 33 KV are connected. At this substation there is a big switch yard which is divided into 3 sections namely: 132 KV Yard. 33 KV Yard. Capacitor Bank Section.

4. SUBSTATION A substation is a crucial component in the electrical power system used for transforming voltage levels , monitoring load flow , and ensuring system reliability . It acts as an interface between generation , transmission , and distribution networks. Purpose & Function Converts high-voltage electricity from transmission lines to lower voltage for distribution. Facilitates switching, protection, and control of power flow. Enhances grid reliability and load balancing across networks. 2 Major Components Transformers : Change voltage levels to suit transmission or distribution. Circuit Breakers & Isolators : Control and isolate electrical circuits for maintenance and fault protection. Busbars : Conduct electricity within the substation. Current & Potential Transformers (CT & PT) : Measure electrical parameters for monitoring and protection. Lightning Arrestors & Surge Protectors : Shield equipment from overvoltages caused by lightning or switching surges.

5. 3 Types of Substations Type Transmission Substation Distribution Substation Switching Substation Description Links generating stations with high-voltage lines. Steps down voltage for end-user consumption. Facilitates circuit connections without transforming voltage. Converts AC to DC or vice versa for specific applications. Converter Substation Layout Considerations Safety clearance and zoning. Efficient grounding and earthing. Accessibility for maintenance and operation. Provisions for future expansion. Safety & Maintenance Regular inspections of insulation and connections Thermographic surveys to detect overheating Protective relaying systems to handle faults quickly.

6. TRANSFORMERS A transformer is an essential electrical device that operates on the principle of electromagnetic induction to transfer energy between two or more circuits. Its primary function is to modify voltage levels, making it possible to transmit high-voltage power over long distances with minimal losses and then reduce it for safe use in homes, industries, and commercial establishments. The core of a transformer is composed of iron laminations around which insulated copper windings are wrapped—called the primary and secondary windings. Depending on whether the voltage needs to be increased or decreased, transformers either “step up” or “step down” the voltage. This ability to manage voltage effectively helps maintain grid stability, minimize energy wastage, and protect electrical equipment from damage. Transformers are found throughout the power system—from generating stations to distribution networks—and are engineered to handle different loads and environmental conditions. Their design includes cooling systems, insulation materials, and safety protections that make them reliable and durable in industrial applications. Regular maintenance like oil testing, insulation checks, and thermal imaging ensures efficient performance and extends service life. Types of Transformers  Power Transformer – Used in transmission networks for high-voltage applications; efficient during heavy load conditions. Distribution Transformer – Operates at lower voltages to supply electricity directly to consumers. Auto Transformer – Has a single winding and is compact; suitable for voltage adjustments within close ranges. Instrument Transformer – Includes current and potential transformers for accurate measurement and protection. Isolation Transformer – Provides electrical separation between circuits for safety purposes. Three-phase Transformer – Preferred in industrial settings for handling large power loads efficiently. 4

7. 5 40 MVA Transformer Rating – Enhanced Specification Table Parameter Rated Capacity Voltage Class Frequency Cooling Method Details 40 MVA (Mega Volt-Amperes) Remarks/Notes Represents apparent power; includes both real and reactive components Depends on system design and grid configuration As per IS & IEC standards Oil Natural Air Natural / Oil Natural Air Forced—affects load handling capacity Operates without forced cooling—base load rating Allows short-duration overload with forced air cooling Common for industrial and grid-scale applications Limits fault current; varies based on design High efficiency reduces energy losses Defines winding configuration and phase shift Allows voltage adjustment as per load conditions Determines thermal withstand capacity Should follow thermal limit guidelines per standards Rating assumes standard weather conditions Covers design, testing, insulation, temperature rise, and short-circuit requirements Common: 132/33 kV, 66/11 kV 50 Hz (standard in India) ONAN / ONAF ONAN Rating 40 MVA continuous ONAF Rating Up to 50 MVA Phase Type Impedance (Typical) Efficiency Three-phase 10–12% 98–99% Vector Group Dyn11 (typical) Tap Changer Insulation Class Overload Capacity Ambient Conditions Reference Standards On- load or Off- load (±10% range) Oil-filled, Class A or Class B Permitted under controlled conditions 30–40°C nominal temperature IS 2026 Parts 1–5, 7, 8<br>IEC 60076 Series<br>CEA Manual 2021

8. 6 63 MVA Transformer Rating – Enhanced Specification Table Parameter Rated Capacity Voltage Class Frequency Cooling Method Details 63 MVA (Mega Volt-Amperes) Common: 220/33 kV, 132/33 kV, 110/20 kV 50 Hz (standard in India) ONAN / ONAF Remarks/Notes Apparent power rating; includes both active and reactive components Depends on grid configuration and application As per IS & IEC standards Oil Natural Air Natural / Oil Natural Air Forced—affects overload capability Base rating without forced cooling Enhanced capacity with forced air cooling Standard for industrial and utility-scale systems Helps limit fault current; varies by design High efficiency reduces operational losses Defines winding configuration and phase displacement Allows voltage regulation under load conditions Determines thermal endurance and safety margins Ensures safe operation under fault or abnormal conditions Rating assumes standard environmental conditions Covers design, testing, insulation, temperature rise, and short-circuit withstand ONAN Rating 63 MVA continuous ONAF Rating Up to 80 MVA Phase Type Impedance (Typical) Efficiency Three- phase ~10–12% ~98–99% Vector Group Dyn11 (typical) Tap Changer Insulation Class Protection Devices Ambient Conditions Reference Standards On-load Tap Changer (OLTC), ±10% range Oil-filled, Class A or B Buchholz relay, temperature indicators, pressure relief device 30–45°C nominal temperature IS 2026 Parts 1–5, 7, 8<br>IEC 60076 Series<br>CEA Manual (2021)

9. 7 TRANSFORMERS IN 132 KV YARD Transformers in a 132 kV yard are critical for stepping down high-voltage electricity to lower levels suitable for distribution. Typically oil-immersed and three-phase, these units operate with ONAN/ONAF cooling and are rated between 40 to 100 MVA. They feature OLTC for on-load voltage regulation and protective devices like Buchholz relays and pressure relief valves to ensure safe operation. The yard facilitates grid stability, minimizes transmission loss, and complies with standards such as IS 2026 and IEC 60076. Routine testing and maintenance enhance reliability, making these transformers essential for efficient and secure power transfer across industrial and utility networks. INSTRUMENT TRANSFORMERS Instrument transformers are precision devices used to measure high voltages and currents in power systems safely and accurately. They act as intermediaries between high-voltage circuits and monitoring or protective equipment, ensuring electrical isolation while scaling down values to manageable levels. By replicating voltage or current in proportionally reduced values, they allow meters, relays, and control systems to function without being directly exposed to dangerous electrical levels. These transformers are especially critical in substations and switchyards where reliable protection and real-time system data are essential for grid health. There are two primary types of instrument transformers, each tailored for specific functions: Current Transformer (CT) – Measures large currents by producing a smaller, proportional current in its secondary winding. Potential or Voltage Transformer (PT/VT) – Steps down high system voltage to safe, measurable levels for meters and protection devices. Combined CT/PT Units – Integrate both current and voltage measurement in compact form, ideal for space-constrained switchgear. Optical Instrument Transformers – Use light-based technology for non-intrusive and ultra-accurate readings in advanced systems. Instrument transformers enhance safety and improve the efficiency of protection schemes. Their accuracy ensures precise operation of relays during fault conditions, and they support energy auditing, load analysis, and tariff calculations. Factors like system voltage, burden rating, insulation type, and accuracy class affect their selection. Proper installation and periodic testing—such as ratio checks and insulation resistance—maintain long-term performance. These transformers are indispensable for modern power management, offering both safety and insight in high-voltage environments. CURRENT TRANSFORMERS A Current Transformer (CT) is an instrument transformer designed to scale down high current levels from power circuits to lower, measurable values suitable for metering and protection. It ensures electrical isolation between the primary circuit and the secondary monitoring devices, allowing safe operation of ammeters, energy meters, and protective

10. relays without exposure to full system current. CTs are indispensable in high-voltage environments like substations and switchyards, where accurate current measurement is essential for load monitoring, system control, and fault detection. The CT operates using electromagnetic induction: a conductor carrying load current acts as the primary winding, and a wound coil forms the secondary. Standard secondary current ratings are typically 5 A or 1 A , and the transformation ratio determines the scaled output. CTs must be selected based on system current, burden rating, and required accuracy class to ensure reliable performance across various operating conditions. Types of Current Transformers: Wound Type CT – Dedicated primary and secondary windings for precision applications. Bar Type CT – Uses busbar as primary; common in substations. Window or Ring Type CT – Load conductor passes through a toroidal core; economical and compact. Split-Core CT – Opens for retrofit installation without disconnecting the circuit. Summation CT – Combines current from multiple circuits into a single output. 8

11. POTENTIAL TRANSFORMERS A Potential Transformer (PT) , also known as a Voltage Transformer (VT) , is a precision instrument transformer used to measure high voltage levels by stepping them down to standardized, lower voltages suitable for meters and protective devices. PTs are essential in substations and switchyards, where system voltages—such as 132 kV or above—must be monitored safely and accurately. By isolating measurement equipment from dangerous voltage levels, PTs ensure operational safety and protect devices from electrical stress. PTs operate on the principle of electromagnetic induction, much like power transformers, but with emphasis on accurate voltage reproduction and insulation. The primary winding is connected directly to the high-voltage circuit, and the secondary winding provides a proportionally reduced voltage—often standardized at 110 V —used by voltmeters, relays, and energy meters. A key feature of PTs is their ability to maintain high accuracy across a range of operating conditions, making them vital for fault detection, system control, and tariff metering. Types of Potential Transformers : Electromagnetic PT – Conventional type using laminated core and windings; common in grid applications. Capacitor Voltage Transformer (CVT) – Used in extra-high voltage systems; incorporates capacitive voltage divider. Optical Voltage Transformer – Employs fiber-optic sensors and digital processing for advanced monitoring. Indoor vs. Outdoor PT – Chosen based on installation environment and insulation medium. 9

12. CAPACITIVE VOLTAGE TRANSFORMERS These are the transformers which performs the two works, for potential transformers and second is of the communication. It filters the frequency for data communication . Capacitive Voltage Transformer (CVT) is a specialized instrument transformer used in extra-high voltage (EHV) systems—typically above 100 kV—to step down voltage for metering, protection, and communication purposes. Unlike conventional electromagnetic PTs, CVTs use a capacitive voltage divider combined with an auxiliary transformer and a compensating reactor to deliver accurate low-voltage signals. 10

13. SWITCH GEAR Switchgear refers to a collection of electrical devices used to control, protect, and isolate electrical equipment within power systems. It plays a vital role in ensuring safety, reliability, and efficient operation across generation, transmission, and distribution networks. Switchgear includes components such as circuit breakers, isolators, relays, fuses, and control panels that work together to interrupt power flow during faults and allow maintenance without risking personnel or system integrity. High-voltage switchgear is commonly installed in substations like 132 kV yards, where it safely manages large amounts of electrical energy and coordinates with protection systems. Depending on voltage level and application, switchgear is classified into low-voltage , medium-voltage , and high-voltage categories. Metal-clad and gas-insulated switchgear designs offer compactness and improved safety in modern substations. Features such as automatic tripping, remote control, and fault diagnosis enhance performance and minimize downtime. Overall, switchgear ensures stable power distribution and protects expensive equipment from damage during overloads, short circuits, or system faults. 11

14. BUS BARS Bus Bars are metallic strips or bars that conduct electricity within a substation or switchgear system. They serve as common connection points for multiple incoming and outgoing circuits, enabling efficient distribution of electrical power. Bus bars are typically made of copper or aluminum , chosen for their excellent conductivity and mechanical strength. In high-voltage systems like a 132 kV yard, they handle large amounts of current safely and reliably. Bus bars are crucial for system flexibility, allowing easy connection or isolation of feeders and transformers. Depending on the layout and operational requirement, bus bar arrangements vary and include single bus , double bus , main and transfer bus , ring bus , and breaker-and-a-half schemes . These configurations affect maintenance flexibility, fault tolerance, and switching operations. Their construction ensures minimal voltage drop and heat generation, and they are mounted using insulators to maintain safe clearance and prevent flashovers. To enhance safety and reliability, bus bars are enclosed in metal-clad switchgear or supported on gantries with proper spacing. Regular inspection for signs of corrosion, joint looseness, and thermal stress is necessary to maintain performance. Overall, bus bars are fundamental to substation design, enabling secure, stable, and scalable power flow within electrical networks. Bus bars not only serve as vital junction points in electrical systems but also contribute significantly to the flexibility, reliability, and maintainability of power flow within a substation. Their design is governed by factors such as current rating, fault withstand capacity, temperature rise limits, and material selection. Copper is often favored for its superior conductivity, while aluminum offers lightweight cost-effective alternatives in certain 12

15. 13 applications. Bus bar sizing depends on the maximum current load, short-circuit ratings, and permissible voltage drop, ensuring safe and efficient operation. Several standard bus bar arrangements are used depending on substation complexity and required redundancy: Single Bus System – Simple and cost-effective; used in low-demand setups, but lacks flexibility. Double Bus System – Offers redundancy; one bus can be maintained while the other carries load. Main and Transfer Bus – A hybrid system providing maintenance support with bypass capabilities. Ring Bus – Each feeder connects in a loop; improves reliability and fault isolation. Breaker-and-a-Half Scheme – Each circuit is protected by 1.5 breakers, balancing cost and flexibility; used in high-voltage substations. Bus bars must be properly supported using insulators, spacers, and clamps to avoid mechanical stress or flashover risks. Temperature monitoring, joint integrity checks, and corrosion prevention are part of routine maintenance protocols. In GIS (Gas-Insulated Substations), bus bars are enclosed in pressurized SF₆ compartments for compact design and enhanced insulation. Overall, bus bars form the backbone of power routing and management inside substations, delivering performance that underpins grid reliability.

16. Circuit Breaker A circuit breaker is an automatic switching device designed to protect electrical systems from damage caused by overloads, short circuits, or other fault conditions. It interrupts the flow of current when a fault is detected and can be reset manually or automatically once the fault is cleared. Unlike fuses, circuit breakers are reusable and offer selective isolation, making them essential in substations, switchyards, and industrial power systems. They consist of fixed and moving contacts, and when these contacts separate during a fault, an arc forms which must be extinguished quickly to prevent equipment damage. Various arc- quenching mediums are used depending on the voltage level and application, including oil, air, SF₆ gas, and vacuum. Sulphur Hexafluoride (SF₆) An SF₆ circuit breaker uses sulphur hexafluoride gas as the arc-quenching and insulating medium. SF₆ is a colorless, odorless, non-toxic, and highly electronegative gas with excellent dielectric properties. When the contacts open, an arc forms, and SF₆ gas absorbs free electrons, forming heavy negative ions that suppress the arc rapidly. These breakers are widely used in high-voltage applications (up to 800 kV) due to their compact design, low noise, and high reliability. Key Features: 14

17. 15 High dielectric strength and arc-quenching capability. Suitable for harsh environments and outdoor installations. Minimal maintenance and long service life. Often used in gas-insulated switchgear (GIS) Note: SF₆ is a potent greenhouse gas, so modern systems include gas monitoring and recycling mechanisms to minimize environmental impact. Vacuum Circuit Breaker (VCB) A vacuum circuit breaker uses a sealed vacuum interrupter to extinguish the arc. When the contacts separate, the arc is formed by metal vapor from the contact surface. Due to the high dielectric strength of vacuum and rapid deionization, the arc is extinguished almost instantly at current zero. VCBs are ideal for medium-voltage applications (typically 11 kV to 33 kV) and are known for their fast operation and minimal maintenance. Key Features: Compact and robust design No risk of fire or gas leakage Excellent arc interruption with minimal contact erosion Long mechanical and electrical life VCBs are commonly used in indoor switchgear, industrial plants, and distribution substations where reliability and safety are critical. INSULATORS Electrical insulators are materials or devices that prevent the unwanted flow of electric current by offering high resistance. In power systems, they are used to support and separate conductors, ensuring that electricity flows only through intended paths. Insulators are essential in overhead transmission lines, substations, and switchgear to maintain system safety and reliability. Common materials include porcelain, glass, polymer composites, and ceramics—chosen for their dielectric strength, mechanical durability, and resistance to environmental stress. Suspension Type Insulator Suspension insulators are widely used in high-voltage transmission lines (typically above 33 kV). They consist of a series of disc-shaped porcelain or glass units connected by metal links to form a flexible string. The conductor is suspended from the bottom of the string, while the top is anchored to the tower cross-arm. Key Features:

18. 16 Each disc is rated for ~11 kV; multiple discs are strung together for higher voltages. Flexible design allows the string to swing, reducing mechanical stress. If one disc fails, it can be replaced without disturbing the rest of the string. Offers partial protection against lightning due to conductor placement below the insulator. Types: Cap-and-Pin Type – Uses ball-and-socket joints for flexibility. Interlink (Hewlett) Type – Uses steel links through porcelain channels; mechanically stronger. Strain Type Insulator Strain insulators are designed to withstand high mechanical tension, especially at dead ends , sharp bends , or long spans in transmission lines. They prevent electrical leakage while bearing the pull of conductors. Key Features: Typically arranged horizontally to counteract tensile forces. For high voltages, multiple suspension discs are connected in series. For low voltages (up to 11 kV), shackle insulators may serve as strain insulators. Used in river crossings, terminal poles, and corner towers. Advantages: High mechanical strength and electrical insulation. Modular design allows scalability for different voltage levels. Durable under environmental stress like wind, rain, and pollution. ISOLATORS An electrical isolator is a mechanical switching device used to disconnect a part of the circuit from the power system for safe maintenance and inspection. Unlike circuit breakers, isolators are operated only under no-load conditions and do not have arc-quenching capabilities. Their primary function is to ensure that a section of the system is completely de- energized before any work is carried out, thereby protecting personnel and equipment. Isolators are typically installed on both sides of circuit breakers in substations, allowing safe disconnection of breakers and associated equipment. They are manually or motor- operated depending on voltage level—manual for up to 145 kV and motorized for higher voltages like 245 kV or 420 kV. Isolators are visible-break devices, meaning their open or closed status can be visually confirmed, which adds an extra layer of safety.

19. Types of Isolators Single Break Isolator – One contact breaks the circuit; simple and compact. Double Break Isolator – Two contacts break simultaneously; offers better isolation. Pantograph Isolator – Vertical movement; used in space-constrained substations. Bus Side / Line Side / Transfer Bus Isolators – Classified based on installation location in the substation. 17

20. LIGHTNING ARRESTORS A lightning arrestor is a protective device used in electrical power systems to safeguard equipment from high-voltage surges caused by lightning strikes or switching operations. It provides a low-impedance path to ground, allowing excess energy to bypass sensitive components and discharge safely. Installed near transformers, circuit breakers, and bus bars—especially in substations like 132 kV yards—lightning arrestors are essential for maintaining system stability and preventing insulation breakdown. Under normal conditions, the arrestor remains non-conductive. When a surge occurs, the voltage across its terminals exceeds a threshold, causing the device to conduct and divert the surge to earth. Once the surge subsides, the arrestor returns to its insulating state. This rapid response protects equipment from flashovers, insulation damage, and service interruptions. Types of Lightning Arrestors Rod Gap Arrestor – Simple air gap between two rods; used in low-voltage systems. Horn Gap Arrestor – V-shaped electrodes with air gap; arc rises and extinguishes naturally. Expulsion Type Arrestor – Uses a vented chamber to expel ionized gases during surge. Valve Type Arrestor – Combines spark gaps with non-linear resistors for high-voltage protection. Metal Oxide Varistor (MOV) Arrestor – Most common type; uses zinc oxide discs for precise surge suppression. Station Class Arrestor – Designed for substations; handles large surge currents. Distribution Class Arrestor – Used in distribution networks for transformer. 18

21. METERING AND INDICATION EQUIPMENT PANELS An electrical panel is the central hub for power distribution in any electrical system. It receives electricity from the utility supply or transformer and channels it to various circuits through protective devices like circuit breakers or fuses. Panels ensure safe, organized, and efficient control of electrical power across residential, commercial, and industrial setups. They also serve as a point of isolation during maintenance or fault conditions. 19

22. RELAYS A relay is an electromechanical or solid-state switching device used to control the flow of electricity in a circuit. It allows a low-power signal to operate a high-power circuit, providing electrical isolation between control and load sides. Relays are widely used in protection, automation, and control systems across substations, switchgear, and industrial panels. When energized, the relay coil generates a magnetic field that moves an armature, opening or closing contacts to switch the circuit. Relays are essential in fault detection, load control, and system automation. They can be configured to respond to overcurrent, undervoltage, reverse power, frequency deviation, and other abnormal conditions. Protective relays are often paired with circuit breakers to isolate faulty sections of the network, minimizing damage and improving system reliability. 20

23. Types of Relays (Based on Function and Construction) Electromechanical Relay (EMR) – Uses a coil and moving contacts; common in traditional control systems. Solid-State Relay (SSR) – Uses semiconductor switching; faster and more durable with no moving parts. Thermal Relay – Operates based on temperature rise; used for motor protection. Time Delay Relay – Introduces intentional delay in switching; used in sequencing operations. Differential Relay – Compares current between two points; used in transformer and generator protection. Distance Relay – Measures impedance to detect faults along transmission lines. Reverse Power Relay – Prevents power flow from load to source; used in generator protection. Frequency Relay – Monitors system frequency; trips during abnormal frequency conditions. 21

24. CAPACITOR BANK A capacitor bank is a group of capacitors connected in series or parallel to provide reactive power compensation in electrical systems. It improves power factor , reduces line losses , and stabilizes voltage levels —especially in substations and industrial networks. Capacitor banks are typically installed in shunt configuration (parallel to the load) and are rated in kVAR (kilovolt-ampere reactive). They help offset the inductive effects of motors, transformers, and long transmission lines. Capacitor Bank Section 22

25. 23 A capacitor bank section refers to a modular unit or subdivision within the overall capacitor bank. Each section is designed to handle a specific portion of the total reactive power requirement and may consist of: Capacitor units (e.g., 3-phase or single-phase) Fuses (internal or external) Switching devices (contactors or breakers) Protection relays (for unbalance, overcurrent, or harmonics) Sections are often arranged in steps to allow automatic regulation based on load variation. For example, a 600 kVAR bank may be split into 3 sections of 200 kVAR each, switched in or out as needed. Battery Bank Section A battery bank section is a part of a larger DC power backup system , typically used in substations, control rooms, and telecom setups. It consists of multiple batteries connected in series (to achieve desired voltage, e.g., 48V or 220V) and parallel (to increase ampere-hour capacity). Each section may include: Battery cells or blocks (e.g., 2V, 12V units) Battery racks or enclosures Monitoring systems (voltage, temperature, charge status) DC distribution panels and fuses Battery bank sections ensure uninterrupted power for control circuits, protection relays, and emergency lighting during outages. They are critical for DC supply reliability in substations. PROTECTION OF SUBSTATION Transformer protection ensures safe operation and prevents damage due to faults, overloads, or abnormal conditions. Key protection schemes include: Differential Protection – Compares current entering and leaving the transformer; trips during internal faults. Buchholz Relay – Detects gas accumulation from internal faults in oil-filled transformers. Overcurrent Protection – Uses IDMT relays to trip during excessive load or short circuits. Restricted Earth Fault (REF) – Provides sensitive protection for winding-to-earth faults near the neutral. Over-temperature Protection – Monitors oil and winding temperatures using sensors and triggers alarms or trips. Over-fluxing Protection – Prevents core saturation due to high voltage or low frequency. Pressure Relief Device – Releases excess pressure to avoid tank rupture.

26. 24 Conservator and Breather These accessories manage transformer oil volume and protect against moisture ingress: Conservator Tank – A cylindrical reservoir mounted above the main tank. It accommodates oil expansion and contraction due to temperature changes. Breather – Contains silica gel that absorbs moisture from air entering the conservator during breathing cycles. Moisture-free air prevents oil degradation. Breather Color Indicator – Silica gel turns from blue to pink when saturated, indicating replacement is needed. Together, they maintain oil quality and extend insulation life. Marshalling Box The marshalling box is a control and monitoring hub mounted near the transformer. It houses: OTI (Oil Temperature Indicator) and WTI (Winding Temperature Indicator) Terminal blocks for connecting protection relays, sensors, and alarms Auxiliary relays , fuses, and contactors Heater and CFL lamp for moisture control and visibility Transparent window for easy inspection It simplifies wiring, enables remote monitoring, and ensures organized interfacing between field devices and control panels. Transformer Cooling Cooling systems dissipate heat generated by core and winding losses. Common methods include: ONAN (Oil Natural Air Natural) – Natural convection of oil and air; used in small transformers. ONAF (Oil Natural Air Forced) – Fans force air over radiators; used in medium transformers. OFAF (Oil Forced Air Forced) – Oil pumps and fans circulate oil and air; used in large transformers. OFWF (Oil Forced Water Forced) – Oil cooled via water-cooled heat exchangers; used in high-capacity units. ODAF (Oil Directed Air Forced) – Oil directed through winding paths for efficient heat removal. Proper cooling ensures thermal stability, insulation longevity, and uninterrupted performance.