INDUSTRIAL TRAINING OVERVIEW OF G I S SUBSTATION

INDUSTRIAL TRAINING OVERVIEW OF G. I. S SUBSTATION UNDERTAKEN AT POWERGRID CORPORATION OF INDIA LIMITED (PGCIL), MAHARANIBAGH, NEW DELHI BY: DEBASHREE GANTAYAT 8 EL-015 4 TH YEAR BRANCH: ELECTRICAL ENGG.

POWERGRID CORPORATION OF INDIA LTD. Incorporated on 23 rd October, 1989 for the Establishment and Operation of Regional and National Power Grids to facilitate transfer of electric power within and across the regions with reliability, security and economy, on sound commercial principles. Started commercial operation from 1992 -93 with amalgamation of assets and manpower from power utilities with diverse culture. Power Grid wheels about 51% of the total power generated in India on its transmission network. Power Grid has a pan India presence with around 82, 045 Circuit-km of Transmission network and 135 nos. of EHVAC & HVDC substations with a total transformation capacity of 91, 945 MVA. Govt. of India has conferred NAVRATNA status to POWERGRID in May` 08, the highest honour for a Public Sector Enterprise.

PGCIL - AREAS OF OPERATION 1. Development of Central Sector Transmission System 3. Telecom (handled by POWERTEL) 2. Grid Management 4. Consultancy National & International • POWERGRID is also carrying out projects related to distribution, sub-transmission and rural electrification works in some states.

SUBSTATION- INTRODUCTION • SUBSTATION: The assembly of apparatus which can be used to change the characteristics of electrical supply is called a substation. • FUNCTIONS OF SUBSTATION: 1. It reduces voltage to a low level. 2. Can be used as switching stations. 3. Can be used as converting stations. • TYPES: 1. AIR INSULATED SUBSTATION (AIS): An electric power substation that has the bus bars and equipment terminations generally open to air and utilizes I insulation properties of ambient air for insulation to ground is known as air insulated substation. 2. GAS INSULATED SUBSTATION (GIS): A gas insulated substation is an electrical substation in which the major structures are contained in a sealed environment with sulphur hexafluoride gas as the insulating medium.

POWERGRID – G. I. S SUBSTATION

ADVANTAGES OF GAS INSULATED SWITCHGEAR (GIS) SUBSTATION • • • Less space requirement and flexible design. Reduced maintenance. High Reliability and safety. Less Manpower requirement. Less time for Erection as compared to AIS substation. SF 6 Gas is used as insulating medium : good Dielectric strength. • GIS can even be installed in a building & in hilly regions (uneven surface). • No noise & Radio interference.

SWITCHYARD EQUIPMENTS LIGHTNING ARRESTER • • POSITION IN SWITCHYARD: positioned always at the entry of any incoming or outgoing transmission lines. They are connected very first to the HV lines; secondly it is also connected at the terminals of costly equipments (like Transformers and shunt reactors) in parallel. • USE: Lightning Arrester protects the transmission line and Power equipments from switching surges and lightning surges. • TYPES: - Basically there are two types of lightning arresters. i. Gapped lightning Arresters. ii. Gapless lightning Arresters.

LIGHTNING ARRESTER. . . CONNECTION: - Normally LA is connected across the conducting terminal (of transmission line & power equipments) and earth via surge counter. WORKING: • It basically consists of a stack of Zn. O discs mounted in sealed porcelain housing. • Acts as non-linear resistor: it provides high resistance to power frequency voltages and low resistance to switching and lightning over voltages. During high switching surges or during heavy lightning over voltages LA divert the surge through it to protect power equipments. Zn. O Grain Resistance Barrier Capacitance Fig: - Equivalent Circuit of LA

CAPACITIVE VOLTAGE TRANSFORMER (CVT) (PARALLEL CONNECTION WITH GROUND) • CVT is the equipment immediate next to the lightning arrester at terminal end of power transmission line. • CVT has following main three functions- 1. Reduce. S the high voltage at measurable level. 2. 3. 4. Metering. Protection. PLCC (Power Line Carrier Communication) A B HF POINT CORE-1 – CVT has 3 cores. Its output voltage is 110 V. CORE-2 EMU CORE-3 NEUTRAL POINT

WAVE TRAP (IN SERIES WITH GROUND) POSITION IN SWITCHYARD: The Wave trap is inserted between the carrier coupling point of CVT and the station equipments. PURPOSE: - FROM BUS SIDE WT FROM LINE SIDE A • To provide high impedance to carrier frequencies while maintaining negligible impedance to power frequency current. • Line traps have to carry the power line current continuously and under system fault condition heavy short circuit current flow through them momentarily. CVT B HF POIN CORE T-1 CORE -2 CORE -3 NEUTRAL POINT EMU

FIGURE SHOWING L. A, WAVE TRAP AND C. V. T

INTER-CONNECTING TRANSFORMER (ICT) • The primary and secondary windings are connected to the respective voltage level bus via Circuit breaker, Current transformer and Isolators. • The main purpose of ICT: 1. transform the power from higher voltage level to low voltage level (i. e. from 400 k. V to 220 k. V). 2. It also provides power to the substation using the tertiary windings (33 k. V). IV coil Taps LV coil HV coil Fig: -Equivalent Circuit of ICT

INTER-CONNECTING TRANSFORMER (ICT) CONSTRUCTION- 1. 2. TRANSFORMER CORE TRANSFORMER WINDINGS FITTINGS & ACCESSORIES • • • MAIN TANK CONSERVATOR RADIATORS TRANSFORMER OIL OLTC (On-Load Tap Changer) BUSHINGS BUCHHOLZ RELAY PRV (Pressure Relief Valve) COOLING PUMPS SILICA GEL BREATHERS MARSHALLING BOX TURRET CT’s & NEUTRAL CT’S TERMINAL WINDING CORE Fig: - Internal Structure of Transformer tank

BUS ISOLATOR • • Bus Isolator is placed after the Circuit breaker (CB) seeing from line incoming end. Earth switch is also coupled there with the isolator at line side. CORONA SHIELD MALE CONTACT FEMALE CONTACT SUPPORT INSULATOR • Bus Isolator has following main functions: 1. To isolate the bus during shutdowns after opening of CB. 2. To provide earthing by associated earth switch to bus. STRUCTUR E • It basically consist of two contacts namely male contact and female contact. ISOLATOR MB E/S MB

BUS BARS: • Bus Bar is spread through out the sub station area for connecting various lines and ICT’S on it. • Purpose of Bus bar is to provide connectivity between input and outgoing circuits. DOUBLE BUS SINGLE BREAKER SCHEME 220 KV BUS-1 220 KV BUS-2 TRANSFER BUS

CIRCUIT BREAKER • Circuit breaker is connected after the line isolator if we watch from line side (between line isolator & bus isolator) Pre-Insertion Resistance • The main function of Circuit Breaker (CB) is to make and break the circuit online i. e. on-load condition • The pole of Circuit breaker is made up with three main components: 1. The interrupter chambers 2. The support column 3. The housing of the mechanism Grading Capacitance Fig: - Equivalent Circuit of CB Main Interrupter

CURRENT TRANSFORMER (CT) • • • Current transformer is placed just after the circuit breaker towards line side. CT consists of 5 cores. Current transformer is used for following two purposes: 1. Protection of Line or Equipments. 2. Monitoring of primary currents. Current transformers step down the current from high value to a low value. Their current ratio is substantially constant for given range of primary current and phase angle error is within specified limits. Primary winding Secondary winding Fig: - Equivalent circuit of Current Transformer

PROTECTION SYSTEM • Relays are replaced over the years, thereby helps in reduction in size and improvement in function. • Various relays used are : 1. ELECTROMECHANICAL RELAYS - They work on the principle of a mechanical force. 2. STATIC RELAYS - Their design is based on the use of analog electronic devices. 3. DIGITAL RELAYS – They use a microprocessor to implement the protection algorithm 4. NUMERICAL RELAYS – They are viewed as natural developments of digital relays.

FIRE FIGHTING SYSTEM – Fire fighting system consists of: 1. Smoke detectors. 2. Fire extinguishers. 3. Hydrant system. 4. Emulsifier system. • It is placed in control room premise in separate room where HVW motor, Jockey pump and Diesel pump all things are kept. • It is used in substation for extinguishing fire of any nature on ICT’s, Reactors and other Control room equipments. • It consists of HVW motor, Diesel Engine, Jockey pumps.

POWER LINE CARRIER COMMUNICATION (PLCC) • High Voltage (HV) and Extra High Voltage (EHV) Transmission lines themselves act as a medium for sending communication signals apart from electric power. • 1. 2. 3. 4. 5. Various equipments used are. Wave trap Capacitor voltage transformer Line Monitoring Unit Balancing of transformer Lightning arrester, earth switch, ADVANTAGES OF PLCC: • Transmission reliability is high. • Transmission is not subjected to any variation from atmospheric or ionosphere conditions. DISADVANTAGES OF PLCC: • Cost of insulation of communication equipment and transmission lines is very high. • Noise level will be high because of interference of corona. • High speed data transfer is not possible because of band width limitations.

SCADA • SCADA (supervisory control and data acquisition) generally refers to industrial control systems: computer systems that monitor and control industrial, infrastructure, or facility-based processes. • 1. 2. 3. 4. Basically consist of following components – Human - machine Interface (HMI) Supervisory system Remote terminal Units (RTU) Programmable Logic Devices (PLC)