Auxiliary System in an AC Sub-station PDF

Auxiliary System in an AC Sub-station Module for Certified “Transmission Asset Operator” Training Program Module: Auxiliary System in an AC Sub-station Index S. No Description Page No. 1.0 Substation...

Auxiliary System in an AC Sub-station Module for Certified “Transmission Asset Operator” Training Program Module: Auxiliary System in an AC Sub-station Index S. No Description Page No. 1.0 Substation 02 2.0 Auxiliary System 03 2.1 AC LT System 03 2.2 Battery System 07 2.2.1 Battery Features 08 2.2.2 Battery Capacity Requirements 09 2.2.3 Battery Charger 10 2.2.4 DC Distribution System 12 2.3 Fire Fighting System 13 2.3.1 Hydrant System 14 2.3.2 High Velocity Water Spray system 15 2.3.3 Fire Detection & Alarm system 18 2.3.4 Portable Fire Extinguisher 19 2.3.5 Wheel/Trolley Mounted Fire Extinguisher 19 2.3.6 Water Supply and Pumping System 19 3.0 Nitrogen Injection & Fire Protection System 23 4.0 Alarms of Auxiliary System 26 Page 1 of 29 Module: Auxiliary System in an AC Sub-station 1. Sub-Station Substation is the part of a power system, concentrated in a given place, including mainly the terminations of transmission or distribution lines switchgear and housing and which may also include transformers. It generally includes facilities necessary for system security and control (e.g. the protective devices). Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. Types of Sub-station based on insulating medium: a) Air Insulated Sub-station (AIS) An air-insulated substation is one where the main circuit potential is insulated from the ground by air using porcelain or composite insulators and/or bushings. AIS is fully composed from air-insulated technology components such as circuit breakers, disconnecting switches (disconnectors), surge arrestors, instrument transformers, power transformers, capacitors, bus bars, and so on, and the components are connected to each other by stranded flexible conductors, tubes, or buried power cables. AIS is the most common type of substation, accounting for more than 70% of substations all over the world. b) Gas Insulated Sub-station (GIS) A Gas-insulated substation is a station with compact multifunction assembly, enclosed in a grounded metallic housing in which the primary insulating medium is SF6 and normally includes buses, switches, circuit breakers, and other associated equipment. In GIS, no live part is exposed to human touch or environmental atmosphere, except from point of interfacing with overhead transmission lines. The atmospheric air insulation used in a conventional (AIS) requires meters of air insulation to do what SF6 can do in centimeters. GIS is used where space is limited, for example, extensions, in city buildings, on roofs, on offshore platforms, industrial plants and hydropower plants. This type of switchgear is available from 12 KV systems to 800 KV system. c) Hybrid Insulated Sub-station (HIS) Switchgear assemblies which incorporate a mixture of the insulating characteristics of both AIS and GIS and/or which implements traditionally discrete functions (devices) in a compact and/or combined design in such a way that they can no longer be considered for the purposes of design and testing, in isolation. Page 2 of 29 Module: Auxiliary System in an AC Sub-station 2. Auxiliary System Substation secondary equipment provides the interface to facilitate functional control, protection, and supervision of the primary plant and indeed the overall power system network. The purpose of auxiliary power supply systems is to cater for the necessary energy for the operation of primary and secondary devices at the substation. The auxiliary power supplies are sourced from the AC network and distributed as required: 1. To AC loads over the substation low-voltage AC network These include supply loads such as transformer cooling, oil pumps, and load tap changers, circuit breaker air compressors and charging motors, DS/ES motor supply, outdoor device heaters, switchyard lighting and receptacles, equipment JBs supply, CRP panels, AC cooling system, AHU system, office supply load, Fire Fighting system motor/panel supply etc. 2. Following rectification, to DC loads over the DC network These include station battery banks, protection and PLCC panels, inverter supply for IT network, equipment interlocking and control circuit, CB/DS/ES motor supply, equipment status indication circuit, DC emergency lighting system etc. 2.1 AC LT System To achieve desired availability, AC system is to be duplicated. HT connections from two independent sources are obtained, one from respective SEB that is stepped down by LT Transformer and other from auxiliary power transformer, which is connected to the tertiary of the ICT. In case ICT is not available the second connection can be obtained from SEB from another source. In addition to above one DG set of suitable rating is also to be provided at each substation. Generic SLD for an AC LT Distribution system is attached as Annexure-A. The AC LT system comprises of following distribution panels: a) MSB: Main Switch Board. b) ACDB: AC Distribution Board. c) MLDB: Main Lighting Distribution Board. d) ELDB: Emergency Lighting Distribution Board. Figure-I diagram depicts a simplified ACDB system along with details of transformer, breaker and busbar. In general, three sources are available at substation i.e., SEB Feeder, Tertiary and DG Set. The HVW Motor in Fire Fighting system is connected to the MSB Section and DG set is connected to ACDB section. Main Incomers (SEB/ICT) are available in MSB section. In the LT system, MSB /ACDB consists of Air Circuit Breakers and MCCBs capable of breaking Fault Currents. The MSB section feeds loads such as colony, Transformer Filtration supply JB etc. MSB supply is then extended to ACDB section through a MCCB of suitable rating. Critical station loads such as Battery charger supply, CRP panels, Equipment JBs, outdoor supply Page 3 of 29 Module: Auxiliary System in an AC Sub-station receptacles, EOT Crane (in case of GIS), AC and Ventilation system, Transformer CMB supply etc. are extended through multiple MCCBs in ACDB panel. MSB supply is also extended to a MLDB Panel through a suitable rated MCCB via LT transformer (1:1 ratio) which caters the needs for station lighting system such as switchyard and office. LT Transformers are installed mainly to reduce the fault level at main-bus of MLDB & ELDB and for electrical isolation of lighting distribution circuit. In addition to above, supply from ACDB panel is also extended to an ELDB panel via LT transformer (1:1 ratio) which takes care of certain identified strategic lighting locations in case of failure of both supplies. Under normal circumstances, this distribution board is fed from main supply through auxiliary transformers, however in case of emergency, the board is fed by DG set of substation. 25% of Lighting fixtures shall be connected on AC emergency lighting panel. DG is intended to supply power only during an emergency for essential services and may be idle for long periods. When there is a total failure of main power supply, DG set must operate continuously at full load for a period of time which may exceed even 24 hours. DG Set Specification/Rating: ◆ 765/400 kV-500 kVA ◆ 400/220 kV- 250 KVA ◆ 132/33 kV-100 kVA Automatic supply changeover is implemented among these three sources. Automatic changeover takes place between Incomer I, Incomer II and DG set automatically comes into service whenever both sources fail. After the restoration of the supply, system shall be restored to normal condition automatically. Timers are provided in the control system for each incomer to regulate the closing on failure on supply. Scheme Operation: Under normal conditions i.e., when supply is available in both the incomers, incomers I&II of 415V Main switchboard, ACDB shall be in closed condition and Bus couplers and DG set breakers shall be in open condition. In case of failure of either of the sources in MSB, the incomer of that source shall trip through its UV relay. VMR (Voltage Monitoring Relay) for this incomer then shall drop and status of VMR along with open status of failed incomer CB (through NO/NC contacts), will allow for closing of Bus-coupler CB in MSB section. In ACDB section, VMR relay for associated incomer to failed source in MSB shall drop on loss of supply voltage and extend trip command to its CB. This VMR status along with ACDB incomer open status will allow Bus-coupler CB in ACDB to close. On restoration of supply, normal conditions described above are to be established automatically. Page 4 of 29 Module: Auxiliary System in an AC Sub-station Example: Incomer-I Source in MSB Fails- Incomer-I Source in MSB Restores- 1. Incomer-I in MSB shall Trip. 1. Bus-coupler Trip in MSB. 2. Bus-coupler close in MSB. 2. Incomer-I in MSB shall close. 3. Incomer-I in ACDB shall Trip. 3. Bus-coupler Trip in ACDB. 4. Bus-Coupler close in ACDB. 4. Incomer-I in ACDB shall close. In case of failure of supply in both the sources, both incomers of MSB and associated incomers of ACDBs shall trip and both source VMRs will drop in MSB as well ACDB. DG Set shall then start automatically as command is extended to DG on dropping of both VMRs in MSB section. The VMR drop status along with open status of ACDB incomer CBs will allow for closing of DG set breaker in ACDB Panel. On restoration of one or both sources, DG set breaker shall trip, DG set will stop and normal conditions described above shall be restored. Incomer-I Source in MSB Fails- 1. Incomer-I in MSB shall Trip. 2. Bus-coupler close in MSB. 3. Incomer-I in ACDB shall Trip. 4. Bus-Coupler close in ACDB. Incomer-II Source in MSB Fails- 1. Incomer-II in MSB shall Trip. 2. DG set start command extended. 3. Incomer-II in ACDB shall Trip. 4. DG Set Breaker close in ACDB. 5. Bus-Coupler remains closed in MSB/ACDB. Incomer-I Source in MSB Restores- 1. Incomer-I in MSB shall close. 2. DG set stop command extended. 3. DG Set CB Trip in ACDB. 4. Incomer-I in ACDB shall close. Incomer-II Source in MSB Restores- 1. Bus-Coupler Trip in MSB. 2. Incomer-II in MSB shall close. 3. Bus Coupler Trip in ACDB. 4. Incomer-II in ACDB shall close. Page 5 of 29 Module: Auxiliary System in an AC Sub-station Figure-1: Simplified AC Distribution System Page 6 of 29 Module: Auxiliary System in an AC Sub-station Protection relays for over current, under voltage and ground fault protection are also available in the LT system. A master trip relay is proved for tripping the MSB CBs whenever these protection relays or any external equipment protection (e.g.: OTI/WTI) detect any faults/over current in the distribution system. Yearly Maintenance of LT switchgear is recommended in Control document for Preventive Maintenance which include activities such as Cleaning of Panels, Bus Bars Insulators etc. in LT panels, checking of indicating meters, checking of auto change over facility (MSB,LT,DG) CBs, Maintenance of CB/CT/PT and LT Transformer in switchyard, Checking for Cleaning, Tightness, Healthiness of Panel Meters, Indicating Lamps for all Distribution boards for LT system, Relay (UV/OC/EF) checking and trip test etc. 2.2 Battery System A substation battery system ensures that all the essential electrical systems in a substation continue to operate in the event of a power outage. The DC system is the most important component of a high voltage industrial/utility substation. Since the DC system supplying specially relay protection, control, and interlocking circuits is of paramount importance, the energy supply has to be always available. The need for this reliable supply becomes even more important in the high- or medium-voltage primary circuits. The battery system supplies the energy needed to manage the protective devices and high voltage components and allows electrical faults to be safely isolated. Most high voltage substations house either a sealed or flooded cell battery bank. In a normal functioning system, the batteries provide very little current. A continuous load current maintains a constant charge on the battery. The battery charger provides a current if the charge exceeds the output capability An average battery load profile can last for up to 8 hours with the options to adjust the duration to suit the requirements of the installation or application. Installing the correct charging system is vital as it increases the service and the longevity of the battery system. Selecting the correct substation battery charger system requires consideration of key factors, such as environment, duty cycle and battery type. For 765, 400 & 220 kV sub-stations, DC System shall consist of two (02) float-cum-boost chargers and two (02) battery sets for each of 220V and 48 V systems respectively. For 132 kV sub-stations, DC System shall consist of two (02) float-cum-boost chargers and two (02) battery sets for 220V/110V system. For 48 V system, DC scheme shall consist of one (01) battery and two (02) float-cum-boost chargers. The number of cells, float and Boost voltage are selected to achieve following system requirement: Page 7 of 29 Module: Auxiliary System in an AC Sub-station Maximum Voltage Minimum voltage available when no System Minimum Nos of during Float charger working and battery fully Voltage Cells operation discharged up to 1.85V per cell 220 Volt 242 Volt 198 Volt 107 110 Volt 121 Volt 99 Volt 54 48 Volt 52.8 Volt 43.2 Volt 23 Battery sizing calculations is done as per IEEE- 485 on the basis of following duty cycle: Voltage level Load Duration Type of Load Relays, IEDs, Station HMIs, spring charging, Continuous load 03 hours Isolator interlocking load, Miscellaneous permanently connected loads etc. 220V DC System Emergency load 01 hour Substation emergency lighting loads. Breaker closing, Tripping loads (taking Momentary load 1 minute simultaneous occurrence as per system) Continuous load associated with PLCs, Continuous load 03 hours 48V DC when speech is not working system Loads associated with PLCs when speech is Momentary load 15 minutes working 2.2.1 Battery Features The DC Batteries are VRLA (Valve Regulated Lead-Acid) type with Normal Discharge. In VRLA battery (Type: AGM (absorbed glass mat) battery), the acid is completely absorbed into glass mat separators which are sandwiched between the lead plates. It's a totally sealed and maintenance free design. There are no discharge tubes or fillers caps, which eliminates the need to maintain water levels. These are suitable for a long life under continuous float operations and occasional discharges. The 220 V DC system is un-earthed and 48 V DC system is + ve earthed system. Protective transparent front covers with each module are provided to prevent accidental contact with live module/electrical connections. The container material used for battery has chemical and electro- chemical compatibility and is acid resistant. The porosity of the container is such as not to allow any gases to escape except from the regulation valve. The tensile strength of the material of the container should handle the internal cell pressure of the cells in the worst working condition. Cell shall not show any deformity or bulge on the sides under all working conditions. The containers are enclosed in a steel tray. Page 8 of 29 Module: Auxiliary System in an AC Sub-station The cell covers are made of suitable material compatible with the container material and permanently fixed with the container. It shall also be capable of withstanding internal pressure without bulging or cracking. It shall also be fire retardant. Fixing of Pressure Regulation Valve & terminal posts in the cover is done in such a way that the seepage of electrolyte, gas escapes and entry of electro-static spark are prevented. The separators used in manufacturing of battery cells, are generally of glass mat or synthetic material having high acid absorption capability, resistant to sulphuric acid and good insulating properties. Each cell is provided with a pressure regulation valve. The valve is self-re-sealable and flame retardant and it cannot be opened without a proper tool. The valve shall be capable to withstand the internal cell pressure specified by the manufacturer. Both +ve and –ve posts are marked clearly and unambiguously identifiable. Where it is not possible to bolt the cell terminals directly to assemble a battery, separate non-corroding lead or copper connectors of suitable size are provided to enable connection of the cells. Copper connections are suitably lead coated to withstand corrosion due to sulphuric acid at a very high rate of charge or discharge. Nuts and bolts for connecting the cells are made of copper, brass or stainless steel and are lead coated to prevent corrosion. Stainless steel bolts and nuts can be used without lead coating. All inter cell connectors are protected with heat shrinkable silicon sleeves for reducing the environmental impact including a corrosive environment. All batteries are mounted in a suitable metallic stand/frame. The frame is painted with the acid resistant paint. The suitable insulation shall be provided between stand/frame and floor to avoid the grounding of the frame/stand. Normally the battery is designed to give a certain performance at a particular temperature 27°C. So, the battery gives its optimum life when operated at that temperature. But when the battery operated at elevated temperatures, like any other lead acid battery, the life will get adversely effected while the discharge performance improves, and vice versa. As a rule of thumb for every 10°C raise in average ambient temperature from the designed temperature the life of the battery gets reduced by half. Healthiness and working of AC system installed in Battery room is therefore essential in enhancing battery life. 2.2.2 Battery Capacity Requirements When the battery is discharged at a 10-hour rate, it shall deliver 80% of C (rated capacity, corrected at 27º Celsius) before any of the cells in the battery bank reaches 1.85V/cell. The battery shall be capable of being recharged from the fully exhausted condition (1.75V/cell) within 10 hrs up to 90% state of charge. All the cells in a battery shall be designed for continuous float operation at the specified float voltage throughout the life. The capacity (corrected at 27ºCelcius) shall also not be less than C and not more than 120% of C before any cell in the battery bank reaches 1.75V/cell. The battery voltage shall not be less than the following values, when a fully charged, battery is put to discharge at C/10 rate: Page 9 of 29 Module: Auxiliary System in an AC Sub-station (a) After Six minutes of discharge : 1.98V/cell (b) After Six hours of discharge : 1.92V/cell (c) After 8 hours of discharge : 1.85V/cell (d) After 10 hours of discharge : 1.75V/cell Loss in capacity during storage at an average ambient temperature of 35º Celsius for a period of 6 months shall not be more than 60% and the cell/battery shall achieve 85% of its rated capacity within 3 charge/discharge cycles and full rated capacity within 5 cycles, after the storage period of 6 months. Voltage of each cell in the battery set shall be within 0.05V of the average voltage throughout the storage period. The battery shall be capable of giving 1200 or more charge/discharge cycles at 80% Depth of discharge (DOD) at an average temperature of 27º Celsius. DOD (Depth of Discharge) is defined as the ratio of the quantity of electricity (in Ampere-hour) removed from a cell or battery on discharge to its rated capacity. Depending on the DOD, the required quantity of active material only takes part in the chemical reaction and the remaining material will not participate in the chemical reaction. Hence, lower the DOD, higher the life in cycles, and higher DOD lowers the life in cycles. The battery sets shall have a minimum expected life of 20 years at float operation. 2.2.3 Battery Charger The DC system for 220 V DC is unearthed and for 48 V DC is +ve earthed. The Battery Chargers as well as their automatic regulators are of static type compatible with offered VRLA batteries. Battery chargers are capable of continuous operation at the respective rated load in float charging mode, i.e. Float charging the associated Lead-Acid Batteries at 2.13 to 2.27 Volts per cell while supplying the DC load. The chargers are also capable of Boost charging the associated DC Battery at 2.28 to 2.32 volts per cell at the desired rate. Battery Chargers are provided with facility for both automatic and manual control of output voltage and current. A selector switch is provided for selecting the mode of output voltage/current control, whether automatic or manual. When on automatic control mode during Float charging, the Charger output voltage shall remain within +1% of the set value, for AC input voltage variation of +10%, frequency variation of +5%, a combined voltage and frequency variation of +10%, and a DC load variation from zero to full load. Battery chargers have a constant voltage characteristic throughout the range (from zero to full load) at the floating value of the voltage so as to keep the battery fully charged but without harmful overcharge. Battery chargers have load limiters having drooping characteristic, which shall cause, when the voltage control is in automatic mode, a gradual lowering of the output voltage when the DC load current exceeds the Load limiter setting of the Charger. The Load-limiter characteristics Page 10 of 29 Module: Auxiliary System in an AC Sub-station shall be such that any sustained overload or short circuit in DC System shall not damage the Charger, nor shall it cause blowing of any of the Charger fuses. The Charger shall not trip on overload or external short circuit. Uniform and step less adjustments of voltage setting (in both manual and automatic modes) is provided on the front of the Charger panel covering the entire float charging output range specified. Step less adjustments of the Load limiter setting is also possible from 80% to 100% of the rated output current for Charging mode. During Boost Charging, the Battery Charger operates on constant current mode (when automatic regulator is in service). It is possible to adjust the Boost charging current continuously over a range of 50 to 100% of the rated output current for Boost charging mode. The Charger output voltage automatically goes on rising, when it is operating on Boost mode, as the Battery charges up. For limiting the output voltage of the Charger, a potentiometer is provided on the front of the panel, whereby it is possible to set the upper limit of this voltage anywhere in the output range specified for Boost Charging mode. Suitable Filter circuits are be provided in all the chargers to limit the ripple content (Peak to Peak) in the output voltage to 1%, irrespective of the DC load level, when they are not connected to a Battery. Battery Chargers have 02 Nos. MCCBs on the input side to receive cables from two AC sources. The rectifier assembly is fully/half-controlled bridge type and is designed to meet the duty as required by the respective Charger. The rectifier is provided with heat sink having their own heat dissipation arrangements with natural air cooling. Necessary surge protection devices and rectifier type fast acting HRC fuses are provided in each arm of the rectifier connections. A Blocking diode is provided in the positive pole of the output circuit of each charger to prevent current flow from the DC Battery into the Charger. Audio-visual indications through bright LEDs are provided in all Chargers for the following abnormalities: a) AC power failure b) Rectifier/chargers fuse blown. c) Over-voltage across the battery when boost charging. d) Abnormal voltage (High/Low) e) Any other annunciation if required. Potential free NO Contacts of above abnormal conditions are provided for common remote indication “CHARGER TROUBLE” in Control Room/SCADA. Indication for charger in float mode and boost mode through indication lamps is also provided for chargers. Page 11 of 29 Module: Auxiliary System in an AC Sub-station 2.2.4 DC Distribution System DC in a substation is distributed through what is known as DCDB (DC Distribution Board). For 02 Battery Banks, 02 (two) individual distribution boards are provided for each voltage level. DCDBs have separate MCCBs for Battery charger and Battery bank which are coupled inside DCDB. Further, a battery curative discharge feeder is also provided through MCCBs to facilitate for C10 discharge test. The DC is then distributed though individual MCBs to CRP panels, Control room inverter for IT network, Emergency DC Lighting panel, auxiliary supply for ACDB/ELDB/MSB/MLDB, Firefighting system, PLCC Panels etc. It is also possible to couple both battery banks to one charger which is required generally during Battery discharge test. MCCBs/Air break switch of suitable rating are provided in each DCDB panel which couple the Busbar of individual DCDB panels. After shutting down the battery charger for the battery bank under test, charger is to be disconnected from DCDB. This is done by tripping the MCCB for Battery charger in DCDB. The MCCBs/Air break switches are then closed in both DCDB panels thereby coupling their busbar and allowing for one charger to feed both battery banks. A simplified distribution scheme for understanding is as below: Figure-2: Simplified 220V DC Distribution System Page 12 of 29 Module: Auxiliary System in an AC Sub-station Example: For C10 Test of Battery Set-I 1. Shutdown the Battery Charger-I Input and Output supply. 2. Trip MCCB of Battery Charger-I in DCDB-I. 3. Close DP switches (circled) to couple both battery sets and DCDBs on Battery Charger-II. 4. Open Bus-Coupler switch in DCDB-I. Battery system-I is now isolated. 5. Close Curative discharge feeder MCCB and proceed with discharge test. 6. After completion of discharge test, open curative discharge feed MCCB. 7. Close MCCB for charger in DCDB-I and switch on Battery charger-I thereby connecting battery set with the charger. Charge the Battery bank as per procedure. 8. After completion of charging, open MCCB for Battery charger-I. 9. Close Bus-coupler switch in DCDB-I. 10. Open DP switches (circled) to disconnect Battery charger-II from DCDB-I. 11. Close MCCB for Battery charger-I in DCDB-I. Relays such as under-voltage, Over-voltage and Earth fault are provided in DCDB panels for monitoring of DC system. Batteries are subjected to monthly as well as yearly testing as per present control document. Monthly activities include Checking of electrolyte level and topping up with DM water (as applicable), checking of emergency DC lighting to Control Room, Noting of Voltage of each for VRLA Batteries by dis-connecting the battery bank from charger & connecting the battery to station load for 4 hours, Measurement of Specific gravity and *voltage of cell with Charger OFF, in case of flooded cells. C10 discharge test is done as a yearly activity. Yearly Maintenance is carried out for Battery charger which include checking of Charger Panel for Electrical connection tightness and cleanliness, Healthiness of Indicating meters like Voltmeter, Ammeter & Indicating Lamps and relay checking. Besides, this monthly measurement of ripple content is also recommended. 2.3 Fire-Fighting System In the present power distribution scenario, the availability of equipment is one of the major objectives. Once the equipment is ready to be energised, then before commissioning of this equipment for the required commercial operation, one has to take care the protection and safety required for this equipment. EHV Sub stations consists of transformers/reactors, which contains large volume of oil. There is always chance of fire hazard occurring in this type of equipment, to protect this equipment and prevent maximum damage against fire hazards, fire protection system is implemented in a substation. The fire protection system is generally comprised of following sub-systems: Page 13 of 29 Module: Auxiliary System in an AC Sub-station a. Hydrant System b. High Velocity Water (H.V.W) Spray System c. Fire Detection and alarm System d. Portable Fire Extinguishers e. Wheel/ Trolley mounted Fire Extinguishers 2.3.1 Hydrant System A well designed and well laid hydrant system is the backbone of the entire firefighting operations and fights fire in all cases of risk and continuous to be in full operation even if part of effected building / equipment has collapsed / damaged and also keeps cool all the adjoining areas thereby minimizing the exposure hazards. Hydrant system of fire protection essentially consists of a large network of pipe, both underground and over ground which feeds pressurised water to a number of hydrant valves, indoor (if applicable) as well as outdoor. These hydrant valves are located at strategic locations near buildings, Transformers and Reactors. Hose pipes of suitable length and fitted with standard accessories like branch pipes, nozzles etc., are kept in Hose boxes. In case of emergency, these hoses are coupled to the respective hydrant valves through instantaneous couplings and jet of water is directed on the equipment on fire. At least one hydrant post is provided for every 60m of external wall measurement of buildings. a) Control room building b) L.T. Transformer area. c) Fire Fighting pump House. d) Stores e) Transformers f) Shunt Reactors/ Bus Reactors. Figure-3: Hydrant System Page 14 of 29 Module: Auxiliary System in an AC Sub-station A warning plate shall be placed near the hydrant points for the transformers and reactors substations to clearly indicate that water shall be sprayed only after ensuring that the power to the transformer/ reactor which is on fire is switched off and there are no live parts within 20 metres of distance from the personnel using the hydrant. 2.3.2 HIGH VELOCITY WATER (H.V.W) Spray System Automatic high velocity water spray system refers to the use of water in a form of conical spray consisting of droplets of water traveling at high velocity. The HVW spray system extinguishes the fire rapidly by removing two basic factors of fire, namely heat by cooling and cut off oxygen making water curtain around the protected equipment. H.V.W. spray type fire protection essentially consists of a network of projectors and an array of heat detectors around the Transformer/Reactor to be protected. Each transformer/reactor/ equipment protected by HVW spray system is provided with spray piping rings/network with spray nozzles strategically located to cover the complete surface of transformer/reactor by uniform spray. This piping is normally dry and connected to the deluge valve downstream side. On operation of one or more of heat detectors (QB detectors), Water under pressure is directed to the projector network through a Deluge valve from the pipe network laid for this system. The system is designed in such a way that the same can be extended to protect additional Transformer/ Reactor to be installed in future. The main header pipe size in the yard is generally 250mmNB (for 400kV and above level substations) and 200mmNB (for 220kV & 132kV substations). Branch to the equipment (not be more than 20 metres length) is of the same size as of the deluge valve. The Electrical clearance between the Emulsifier system pipe work and live parts of the protected equipment shall not be less than the values given below: 1. 765 kV bushing: 4900 mm 2. 420 kV bushing: 3500 mm 3. 245 kV bushing: 2150 mm 4. 145 kV bushing: 1300 mm 5. 52 kV bushing: 630 mm 6. 36 kV bushing: 320 mm System is designed in such a way that the Water pressure available at any spray nozzle is between 3.5bar and 5.0bar. Water is applied at a minimum rate of 10.2 LPM/M2 of the surface area of the transformer / Reactor including radiator, conservator, oil pipes, bushing turrets, etc. (including bottom surface for transformer). The nozzle arrangement is done in such a way that it ensures direct impingement of water on all exterior surfaces of transformer tank, bushing turrets, conservator and oil pipes except underneath the transformer, where horizontal spray may be provided. Page 15 of 29 Module: Auxiliary System in an AC Sub-station Deluge Valve Deluge Valve is water pressure operated manual reset type. The Deluge valve is closed water tight when water pressure in the heat detector pipe work is healthy and the entire pipe work is charged with water under pressure up to the inlet of the Deluge valve. On fall of water pressure due to opening of one or more heat detectors, the valves open and water rushes to the spray water network through the open Deluge valve. The valves manually reset to initial position after completion of operation. Each Deluge Valve is provided with a water motor gong which sounds an alarm when water after passing through the Deluge valve, is tapped through the water motor. Each Deluge valve is also provided with a local panel with provision of opening of Deluge valve from local and remote from control room/ remote centre. In addition to this, each valve is provided with local operation latch. Deluge valves of 100mmNB size is used if the flow requirement is ≤ 200m3/hr and 150mmNB size is used for flow requirement >200m3 /hr. Figure-4: Deluge Valve High Velocity Spray Nozzles (Projectors) and Heat Detectors High velocity spray system is designed and installed to discharge water in the form of a conical spray consisting of droplets of water travelling at high velocity, which shall strike the burning surface with sufficient impact to ensure the formation of an emulsion. At the same time the spray shall efficiently cut off oxygen supply and provide sufficient cooling. The heat detectors, Quartzoid bulb type, are mounted on a pipe network charged with water at suitable pressure. On receipt of heat from fire, the heat detector releases the water pressure from the network. This drop in water pressure actuates the Deluge valve and water is let out through projectors. Minimum set point of the heat detectors used in the HVW spray system is around 79oC. Page 16 of 29 Module: Auxiliary System in an AC Sub-station Operating concept: When heat is sensed by any of heat detector (QB type) surroundings the transformer/reactor, the quartzoid bulb will burst at 79º C temperature. This will create a pressure drop in the detection line due to release of pressurized water. The water supply forces the deluge valve to open automatically, permitting flow of water to the system piping. Water flowing through alarm connection of the valves actuates the water motor gong. Water is discharged through the nozzles in the form of conical spray. When heat is sensed by any of Q.B. detector surrounding the transformer/reactor/equipment, water will be released through it and pressure switch mounted on detection line generates the “FIRE” annunciation in the both annunciation panel located in Fire Water Pump House and Control Room and second pressure switch mounted on spray line generates the “SPRAY ON” annunciation in the annunciation panel located in the Fire Water Pump House. Local testing can be done by test drain connection provided on deluge valve trims Figure-5: Heat detector, nozzle and Spray System Page 17 of 29 Module: Auxiliary System in an AC Sub-station 2.3.3 Fire Detection and Alarm System This system is provided for control room building and Switchyard panel rooms of substations. Fire detection and alarm system generates audio – visual alarm at the incipient stages of fire by sensing heat and smoke detectors. Fire alarm system consists of ionization type smoke detectors, photoelectric type smoke detectors, and heat detectors, manual call points (Break Glass Type), hooters and response indicators located at strategic points, and one No. fire alarm panel located in control room. Fire detectors are equipped with an integral L.E.D. so that it’s possible to know which of the detectors has been operated. Fire detectors are located at strategic locations in various rooms of the building. Each Switchyard panel room is considered a separate zone. Adequate number of extra zones are often provided for Switchyard panel rooms for future bays identified in Single line diagram of the substation. The fire alarm system is capable of identifying the fire at the incipient stages so that firefighting personnel are informed about the fire status handling them to take prompt action to extinguish the fire and restrict the spreading of fire. The operation of any of the fire detectors/ manual call point should result in the following: a) A visual signal exhibited in the annunciation panels indicating the area where the fire is detected. b) An audible alarm sounded in the panel, and c) An external audible alarm sounded in the building, location of which is decided during detailed engineering. d) If the zone comprises of more than one room, a visual signal is exhibited on the outer wall of each room. Each zone is provided with two zone cards in the Fire Protection panel located in control room so that system will remain healthy even if one of the cards becomes defective. Coverage area of each smoke detector is not more than 80sqm and that of heat detectors of 40sqm. Ionisation type smoke detectors are in all areas except pantry room where heat detectors shall be provided. If a detector is concealed like above false ceiling and normally closed rooms etc, a remote visual indication of its operation. Manual call points (Break glass Alarm Stations) are also provided at strategic locations in the building for manual alarm. Figure-6: Fire detection and alarm system Page 18 of 29 Module: Auxiliary System in an AC Sub-station 2.3.4 Portable Fire Extinguishers Adequate number of portable fire extinguishers of pressurised water, dry chemical powder, and Carbon dioxide type are provided in suitable locations in control room building and FFPH building as indicated in the drawing. In addition to this one (1) CO2 type fire extinguisher of 4.5kg capacity is provided for each Switchyard panel room. These extinguishers will be used during the early phases of fire to prevent its spread and costly damage. 2.3.5 Wheel/ Trolley mounted Fire Extinguishers Wheel/Trolley mounted Mechanical foam type fire extinguishers of 50litre capacity, conforming to IS:13386, are provided for the protection of the following: 1. Transformers and reactors in 220kV and 132 kV substations where Hydrant/HVWS system is not available. Two (2) nos. for each 220kV or 132kV transformer and reactor. 2. LT transformers in all substations. One (1) no. for each LT transformer. 2.3.6 Water Supply and Pumping System Water storage tank with two compartments of adequate capacity is provided for water supply. For 400kV and above level substations, water for hydrant & HVW system is supplied by one electrical motor driven pump of rated capacity 410m 3/h, at 70MWC head & for 220kV and 132kV substations water for hydrant & HVWS system shall be supplied by one electrical motor driven pump of rated capacity 273m3/hr, at 70MWC head, with another pump of same capacity, driven by diesel engine, provided as standby. The whole system is kept pressurised by providing combination of air vessel and jockey pump of 10.8M3/hr. capacity at 80MWC. The capacity of air vessel shall not be less than 3m 3. Minor leakages are taken care of by Jockey pump. One additional jockey pump is provided as standby. All pumps are of horizontal centrifugal type. Pumps and air vessel with all auxiliary equipment are located in firewater pump house. A pressure relief valve of suitable rating is provided in water header to release excess pressure due to atmospheric temperature variations. The complete piping network is normally kept pressurized at 8.0 kg / cm² pressure. If the pressurization system is unable to cover the system leakages or if the hydrants are opened, the fire water pump shall come into operation automatically, sequentially. This is achieved by various pressure switches (continuous 'C' bourdon type) provided with different pressure settings in the Main Header pipe (settings may vary from station to station) as follows: 1. Jockey pump–1 will start automatically at a pressure of 6.5 kg / cm² through its Pressure switch. 2. Jockey pump–2 will start automatically at a pressure of 6.0 kg / cm² through its Pressure switch. 3. Electric Motor Driven main pump will start at 4.0 kg / cm² through its Pressure switch. 4. Diesel Engine Driven stand by pump will start at 3.0 kg / cm² through its Pressure switch. Page 19 of 29 Module: Auxiliary System in an AC Sub-station The control and interlock system for the fire protection system shall meet the following requirements: 1. Electric Motor Driven Fire Water Pump Pump should start automatically when the System header pressure is low. Pump should be stopped manually only. Pump should also be started manually if required from local control panel. 2. Diesel Engine Driven Standby Pump The pump should automatically start under any of the following conditions: System Header pressure low. Electric motor operated fire water pump fails to start. Pump should be stopped manually only. Pump should also be started manually if required from the local control panel. 3. Jockey Pump It shall be possible to select any one of the Jockey pumps as main and the other as standby. Main Jockey pump shall start automatically when water pressure in header falls below the set value. If the main jockey pump fails to start then the standby should start. Jockey pump shall stop automatically when the pressure is restored to its normal value. Manual starting/stopping is also possible from the local control panel. Figure-7: Fire Fighting Pumps Page 20 of 29 Module: Auxiliary System in an AC Sub-station The induction motors used for Jockey Pump and Motor Fire Pump are of squirrel cage type unless specified otherwise. The motors are suitable for continuous duty in the specified ambient temperature. These Motors shall be capable of giving rated output without reduction in the expected life span when operated continuously in the system. The induction motors used are suitable for full voltage direct on-line starting. These are capable of starting and accelerating to the rated speed along with the driven equipment without exceeding the acceptable winding temperature even when the supply voltage drops down to 80% of the rated voltage. The starting current of the motor at rated voltage should not exceed six (6) times the rated full load current. The Diesel Engine used is a multicylinder type four-stroke cycle with mechanical (airless) injection, cold starting type. The continuous engine brake horse power rating (after accounting for all auxiliary power consumption) of the engine at the site conditions is at least 20% greater than the requirement at the duty point of pump at rated RPM and in no case, less than the maximum power requirement at any condition of operation of pump. For Diesel Engine, automatic cranking is affected by a D.C. motor having high starting torque to overcome full engine compression. Starting power is supplied from either of the two (2) sets of storage batteries. The automatic starting arrangement includes a 'Repeat Start' feature for 3 attempts. The battery capacity is adequate for 03 (three) consecutive starts without recharging with a cold engine under full compression. The battery cells are of lead-acid type and the battery used is of automotive type. These batteries are used exclusively for starting the diesel engine and be kept fully charged all the time in position. The batteries are charged through 02 nos of battery chargers having sufficient capacity to restore a fully discharged Battery to a state of full charge in eight (08) hours with some spare margin over maximum charging rate. Arrangement for both trickle and booster charge is provided in the battery charger. The charger unit is capable of charging one (01) set of battery at a time. Provision shall, however, can be made so that any one of the charger units can be utilised for charging either of the two (2) batteries. Under normal operation, all the pumps are kept in automatic and pumps are brought into operation at pre-set pressure. Fire pumps are allowed to be stopped only manually. Manual start/stop provision is provided in local control panel for all pumps. Annunciations of the hydrant & HVW spray systems are available in fire water pump house and repeated in the control room. The layout of Fire Fighting system described above is depicted in the figure below for reference: Page 21 of 29 Module: Auxiliary System in an AC Sub-station Figure-8: Piping and Distribution layout of FF System Page 22 of 29 Module: Auxiliary System in an AC Sub-station 3. Nitrogen Injection Type Fire Prevention & Extinguishing System Nitrogen Injection Type Fire Protection System (NIFPS) is designed to prevent explosion of transformer tank and the fire during internal faults/arc. The system works on the principle of drain & stir. On activation, it drains a predetermined quantity of oil from the tank top through drain valve to reduce the tank pressure, isolates conservator tank oil and injects nitrogen gas at high pressure from the bottom side of the tank through inlet valves to create stirring action and reduce the temperature of oil below flash point to extinguish the fire. On operation, the quantity of oil removed from the tank shall be such that adequate amount of oil shall remain to cover active part (i.e. core coil assembly). Electrical isolation of transformer shall be an essential pre-condition for activating the system. Operational Controls The system operates automatically and activates from the required fire and other trip signals. In addition to automatic operation, remote operation from control room/ remote centre and local manual control in the fire extinguishing cubicle is also be provided. System shall operate on following situations: 1.0 Prevention of transformer from explosion and fire: To prevent transformer from explosion and fire in case of an internal fault, signals given by operation of Electrical protection relays (Differential / Restricted earth fault) and tripping of circuit breaker of transformer and operation of either Buchholz relay or pressure relief valve (PRV) shall be used to activate the system. The exact logic for system activation is finalized during detailed engineering. 2.0 Prevention of transformer from fire In case of fire, sensed by fire detectors, the system is activated only after electrical isolation (generally through PRV/Buchholz relay) of the transformer, confirmed by breaker trip. If the fire detection is not associated with any other fault, the system activation is to be done manually. Manual operation switch is provided in the control room with a cover to avoid accidental operation of it. Operation of System On receiving activation signal, the following takes place: i) Opening of drain valve to drain the top layer oil. ii) Shutting off the conservator isolation valve to prevent flow of oil from the Conservator tank to the main tank. iii) Opening of N2 injection valve to inject Nitrogen into the transformer tank to create stirring of oil. Interlock is provided to prevent activation of the system, if the transformer is not electrically isolated. Provision is also provided for isolating the system during maintenance and/or testing of the transformer. Page 23 of 29 Module: Auxiliary System in an AC Sub-station The Nitrogen regulator valve is designed in such a way that the Nitrogen shall not enter the transformer tank even in case of passing/ leakage of. Two distinct station auxiliary DC feeders are provided for NIFPS for control purposes. The system generally works on station DC supply with voltage variation defined in the GTR. The control box of fire protection system receives these feeders for auto changeover of supply. Following components primarily comprise the NIFPS: 1. Fire extinguishing cubicle mounted 5-7 m from transformer with base frame and containing at least the following: a) Nitrogen gas cylinder of sufficient capacity with pressure regulator and manometer with sufficient number of adjustable NO contacts. b) Oil Drain Assembly including oil drainpipe extension of suitable size for connecting pipes to oil pit. c) Mechanical release device for oil drain and nitrogen release. d) Limit switches for monitoring of the systems. e) Flanges on top of the panel for connecting oil drain and nitrogen injection pipes for transformer. f) Back up pressure switch to operate nitrogen gas valve. g) Pressure indicators for Nitrogen pressure of the cylinder and actual injection through Nitrogen regulator. h) Oil leakage detection arrangement for detecting oil leakage from drain valve and alarm for the same. 2. Control box in the control room of the station for monitoring system operation, automatic control and remote operation, with alarms, indications, switches, push buttons, audio signal, suitable for tripping and signalling. 3. Fire detectors located in strategic locations 4. Flow sensitive conservator Isolation valve to isolate the conservator oil from the main tank is being provided by the transformer supplier. This valve is located in the piping between the conservator and the Buchholz relay. 5. Under Ground Oil Storage Tank having non-Corrosive, waterproof, epoxy coated (from Inside) mild steel (minimum thickness 5 mm) to store drained out oil on operation of NIFPS. The total capacity of storage tank is at least 10% of transformer tank oil to avoid overflowing of oil considering that drained oil volume shall be around 10% of transformer tank oil. Necessary arrangement is made on underground storage tank so as to take out the drained oil from the tank for further processing and use. The storage tank is placed in the pit made of brick walls with PCC (1:2:4) flooring with suitable cover plates to avoid ingress of rainwater. Page 24 of 29 Module: Auxiliary System in an AC Sub-station Figure-3: Typical Arrangement of NIFPS System Page 25 of 29 Module: Auxiliary System in an AC Sub-station 4. Alarms of Auxiliary System For monitoring of Auxiliary system, various alarms are integrated to local SAS/RTAMC/NTAMC. These alarms alert the system operator about certain discrepancy or activation of a sub-system of Auxiliary system. Timely intervention after receipt of alarm can prevent failure of the system and ensure its availability during an emergency. The critical alarms for an Auxiliary system which are required to be reported are as below: S.No Alarm Description Section/Source A ACLT System 1 ACDB Incomer-x UV protection operated ACDB Incomer-1/2 Undervoltage Relay 2 ACDB Incomer-x OC protection operated ACDB Incomer-1/2 Overcurrent Relay 3 ACDB Incomer-x EF protection operated ACDB Incomer-1/2 Earth Fault Relay 4 ACDB BC CB Spring charged ACDB Bus-Coupler Circuit Breaker 5 ACDB Incomer-x CB Spring charged ACDB Incomer-1/2 Circuit Breaker 6 ACDB Local Switch Auto Mode ACDB A/M switch 7 ACDB Local Switch Manual Mode ACDB A/M switch 8 LT Trafo-x Buchholz Alarm LT Transformer-1/2 Buchholz Relay 9 LT Trafo-x OTI Alarm LT Transformer-1/2 Oil Temp. Indicator 10 LT Trafo-x WTI Alarm LT Transformer-1/2 Winding Temp. Indicator 11 LT Trafo-x Buchholz Trip LT Transformer-1/2 Buchholz Relay 12 LT Trafo-x OTI Trip LT Transformer-1/2 Oil Temp. Indicator 13 LT Trafo-x WTI Trip LT Transformer-1/2 Winding Temp. Indicator 14 MSB Incomer-x UV protection operated MSB Incomer-1/2 Undervoltage Relay 15 MSB Incomer-x OC protection operated MSB Incomer-1/2 Overcurrent Relay 16 MSB Incomer-x EF protection operated MSB Incomer-1/2 Earth Fault Relay 17 MSB BC CB Spring charged MSB Bus-Coupler Circuit Breaker 18 MSB Incomer-x CB Spring charged MSB Incomer-1/2 Circuit Breaker 19 MSB Local Switch Auto Mode MSB A/M switch 20 MSB Local Switch Manual Mode MSB A/M switch 21 MSB Incomer-x Phase Sequence negative MSB Incomer-1/2 Phase Sequence Relay 22 HVW Electric Pump ACB ON HVW Incomer CB in MSB 23 MSB Control Supply Supervision MSB DC supervision relay 24 ACDB Control Supply Supervision ACDB DC supervision relay/contactor 25 CB Trip Tertiary Supply Control Panel 26 CB Interlock enabled Tertiary Supply Control Panel 27 Isolator Interlock enabled Tertiary Supply Control Panel Page 26 of 29 Module: Auxiliary System in an AC Sub-station 28 DG Set on Battery Set-x DG Set AMF Panel 29 DG Battery Charger-x ON DG Set AMF Panel DG Set Protection Optd. (Alternator fault, 30 DG Set PCC (Power Command Control) Panel Fail to start etc.) 31 DG Engine Overheat Alarm DG Set PCC Panel 32 DG High cooling water temperature Alarm DG Set PCC Panel 33 DG Low oil pressure trip DG Set PCC Panel 34 DG Set Tank low oil level Alarm DG Set PCC Panel 35 DG Set Overspeed Trip DG Set PCC Panel 36 DG Set I/C in Auto/Manual ACDB Panel A/M Switch 37 DG Set I/C Protection Optd. (EF/OC/UV) ACDB Panel Relays for DG 38 DG I/C CB Spring Charged ACDB Panel DG CB B Fire Protection System 1 Electric Motor Driven Fire Water Pump Start Pressure switch for Electric Motor Electric Motor Driven Fire Water Pump Fail 2 Pressure switch for Electric Motor to Start 3 Electric Motor Pump in Auto A/M Switch for Electric Motor 4 Motor Panel Supply Fail AC Contactor in LCP for electric motor 5 Diesel Engine Driven Fire Water Pump Start Pressure switch for Diesel Engine Diesel Engine Driven Fire Water Pump Fail 6 Pressure switch for Diesel Engine to Start 7 Diesel Engine Pump in Auto A/M Switch in Engine LCP 8 Diesel Engine on Battery-x Battery Panel for Diesel Engine 9 Diesel Engine Battery Charger-x ON Battery Panel for Diesel Engine 10 Diesel Engine Fuel Level Low DG Protection System 11 Diesel Engine Panel Supply Fail AC contactor in Diesel Engine LC Panel 12 Diesel Engine Control Supply Fail DC contactor in Diesel Engine LC Panel 13 Diesel Engine Over Speed Trip DG Protection System 14 Diesel Engine Low Oil Level Trip DG Protection System 15 Diesel Engine High Temp. Alarm DG Protection System 16 Jockey Pump-x Main/Standby Status LCP Panel M/S Switch for Jockey Pump-1/2 17 Jockey Pump-x Running Pressure Switch for Jockey Pump-1/2 18 Jockey Pump-x Fail to Start Pressure Switch for Jockey Pump-1/2 19 Jockey Pump-x Trip Jockey Pump LCP Panel 20 Panel Control Supply Fail AC contactor in Jockey Pump LCP Panel Page 27 of 29 Module: Auxiliary System in an AC Sub-station 21 Jockey Pump-x in Auto Mode Jockey Pump-1/2 LC Panel A/M Switch 22 Water Storage Tank-x Water Level Low Float Switch for Water Tank 23 FF Main Header Pressure Low Pressure Switch in Main Header Fire Annunciation Panel-Through Smoke/Heat 24 Fire Detected in Zone-x Detectors Fire Annunciation Panel-Through Smoke/Heat 25 Common Fire Alarm Detectors 26 Fire Annunciation Panel Faulty Internal signal in FAP 27 Fire Annunciation Panel Control Supply Fail AC contactor in FAP 28 Fire in Transformer-x Pressure switch in Deluge Valve System 29 Deluge Valve Operated for Transformer-x Pressure switch in Deluge Valve System 30 Fire in Bus/Line Reactor-x Pressure switch in Deluge Valve System Deluge Valve Operated for Bus/Line 31 Pressure switch in Deluge Valve System Reactor-x C DC Distribution 1 220V DC Source-x Earth Fault 220V DCDB-1/2 Earth Fault Relay 2 220V DC Source-x UV Alarm 200V DCDB-1/2 Under Voltage Relay 3 48V DC Source-x Earth Fault 48V DCDB-1/2 Earth Fault Relay 4 48V DC Source-x UV Alarm 48V DCDB-1/2 Under Voltage Relay 5 220V Battery Charger-x on Float Mode 220V Battery Charger-1/2 Panel 6 220V Battery Charger-x on Boost Mode 220V Battery Charger-1/2 Panel 7 48V Battery Charger-x on Float Mode 48V Battery Charger-1/2 Panel 8 48V Battery Charger-x on Boost Mode 48V Battery Charger-1/2 Panel 9 220V Battery Charger-x Trouble 220V Battery Charger-1/2 Panel 10 48V Battery Charger-x Trouble 48V Battery Charger-1/2 Panel D NIFPS Pressure regulator for N2 cylinders in NIFPS 1 Nitrogen cylinder pressure low Control Panel 2 Fire in Transformer Fire detectors 3 Oil drain started/Valve open NIFPS Control Panel 4 Conservator oil isolation valve closed NIFPS Control Panel through TCIV 5 Nitrogen injection started NIFPS Control Panel 6 Gas inlet valve closed NIFPS Control Panel 7 Oil drain valve closed NIFPS Control Panel 8 Control Supply Fail NIFPS Control Panel Page 28 of 29 Module: Auxiliary System in an AC Sub-station 9 PRV Trip NIFPS Control Panel from Transformer CRP 10 Buchholz Trip NIFPS Control Panel from Transformer CRP 11 Differential Trip NIFPS Control Panel from Transformer CRP In addition to above, status of circuit breakers as well as voltage, current, frequency analog values are also reported to SAS for various sections. Commands for CB operation, DG Set start, Motor start, Deluge valve operation, NIFPS operation etc. are also possible in SCADA system for control and feedback. The alarms tabulated above are common and critical alarms available for Auxiliary system in a Substation. The alarm list above is not exclusive for the Auxiliary system and additional alarms for AC/DC/FF sections may also be available as per scheme. ************************************************************* Page 29 of 29