Unformatted text preview: Substation Design Dr. Asanka Rodrigo Department of Electrical Engineering University of Moratuwa, Sri Lanka Introduction • Substation serve as sources of quality energy supply for the local area of distribution in which these are located. • Their main functions are to receive energy transmitted at high voltage from the generating station, reduce the voltage to a value appropriate for local distribution and provide facilities for switching • The assembly of apparatus used to change some characteristics (e.g. voltage, a.c. to d.c. ,freq, p.f. etc..)of electrical supply is called a substation. Outdoor Indoor Important Points • It should be located at a proper site(i.e. at the center of gravity of load). • It should provide safe and reliable arrangement. • It should be easily operated and maintained. • It should involve minimum capital costs. Classification of Substation
Substation According to service
requirement According to
constructional feature According to Service requirement According To Constructional Features • Transformer Substation: Transformer are installed to transform power from one level to another as per needs. • Switching Substations: This substation meants for switching operation of powerlines with out transforming the voltage. • Power factor correction Substation: This substation installed to increase the power factor to minimise losses. • Frequency Changer Substation: This substation installed where speed controlled of motor required. • Converting Substation: This substation convert a.c to d.c or vice versa. • Industrial Substation: This substation installed for supply power only to industry. • Indoor Substation: In this substation the apparatus are installed with in the substation building. This substation employed For voltage up to 11 kV. • Outdoor Substation: This subststion are installed in open land. This substation employed For voltage beyond 66 kV. • Underground Substation: This substation are installed under the ground in thicky populated city where cost of the land is more. • Pole‐Mounted Substation: This substation are erect for distribution of power in localities. This is employed for the transformer upto 250 kVA.). • Foundation Mounted Substation :This substation are installed for transformer which are too heavy.(rating beyond 250kVA). Substation equipments Bus bar:It is the conductor connecting power line to substation equipments. Insulators & fittings:Insulator fix and isolate the bus bar system. Isolating Switch:This is used for disconnecting equipment for maintance and repair. Relays & Circuit Breaker:CB open and close a circuit under normal and fault condition. Power Transformers:These are used in substation to step up or step down the voltage. Instrument Transformer:used for measuring . Metering & Indicating Instrument:used to watch over the circuit quantities. Power line carrier communication systems Coupling capacitors and wave traps Symbols Line Bay Transformer Bay Substation configuration • Single busbar configuration Substation configuration • Double busbars configuration with U‐from Substation configuration • Double busbar configuration Substation configuration • Triple busbars configuration Substation configuration • Double busbars configuration with bypass bus Substation configuration • 1 1/2 – breaker configuration Substation configuration • Double busbars configuration with bypass disconnector Substation configuration • Busbar coupling/sectionalizing Classical layout Classical layout – Centre‐break disconnector or vertical‐break disconnector are arranged side by side in line with the feeder below the busbars – Application up to 220 kV – Today, not so often used • Advantages – Narrow spacing between bays – Excellent ways for maintenance of busbars and busbar disconnectors • Disadvantages – Higher costs for portal structures and for means of tensioning the wires – At least one busbar are spanned by connecting wires In‐line layout In‐line layout • Poles of busbar Centre‐break disconnectors stand in line with the busbars • Application up to 132 kV • Advantages: – Lower costs for steel structures which are means of tensioning the wires (in case of tubular portals are needed only for the outgoing overhead lines) – Busbars not spanned by connecting wires • Disadvantages: – Wide spacing of bays – Maintenance at busbars more difficult – longer planned outage times Transverse layout Transverse layout • Busbar disconnectors are in a row at right angles to the busbar • Busbar can be of wire or tube (busbar can be directly installed on busbar disconnectors) • Application up to 245 kV • Advantages: – Narrow spacing between bays(width) – Excellent access to busbars • Disadvantages: – Wide spacing of substation (depth) – All busbars are spanned by connecting wires Diagonal layout Diagonal layout Minimum Clearances Diagonal layout • Busbar above: – Busbar portals with relatively big hight; dimensioned for high mechanical forces – More difficult access to busbar – Excellent maintenance access to busbar disconnectors • Busbar below: – Busbar mounted directly on disconnector→ reduced means for portals – Excellent access to busbars – Maintenance on disconnectors require de‐energzing of complete busbar Minimum Clearance Bay Width Clearance Diagram Bus and Bay Equipment Elivation Substation Components •
• Circuit Switches/Breakers Transformer Command and Control System Communication Network Circuit Breaker Interruption of fault current by a circuit breaker Beaker operation under typical fault conditions Types of CB The Stored‐Energy Spring Mechanism Air CB • • The contacts are opened in a flow of air‐blast established by the opening of blast valve. The air‐blast cools the arc and sweeps away the arcing products to the atomsphere. This rapidly increases the dielectric strength of the medium between contacts and prevents from re‐establishing the arc. – (i) Axial‐blast type ABCB • which the air‐blast is directed along the arc path – Cross‐blast type • which the air‐blast is directed at right angles to the arc path – (iii) Radial‐blast type • which the air‐blast is directed radially Oil Circuit Breakers • Bulk Oil • Minimum Oil • It consists of fixed and moving contacts enclosed in a strong weather‐tight earthed tank containing oil up to a certain level and an air cushion above the oil level. Sulphur Hexa flouride(SF6) Circuit Breakers • Sulphur hexa flouride(SF6) gas is used as the arc quenching medium. • TheSF6 is an electro‐negative gas and has a strong tendency to absorb free electrons. • The contacts of the breaker are opened in a high pressure flow of SF6 gas and an arc is struck between them. Advantages 1. Due to the superior arc quenching property of SF6, such circuit breakers have very short arcing time. 2. Since the dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers can interrupt much larger currents. 3. The SF6 circuit breaker gives noiseless operation due to its closed gas circuit and no exhaust to atmosphere unlike the air blast circuit breaker. 4. The closed gas enclosure keeps the interior dry so that there is no moisture problem. 5. There is no risk of fire in such breakers because SF6 gas is non‐inflammable. VACUUM CIRCUIT BREAKER • High values of dielectric strength of medium can be obtained at very low or very high pressure levels. CIRCUIT BREAKER RATINGS • The Rated Current – the rms value of current which the circuit breaker can carry continuously at rated voltage and frequency without exceeding the specified temperature rise. • Rated Symmetrical Breaking Capacity – the rms value of the a.c. component of fault current that can be interrupted. – Breaking capacity in MVA = 3 × rated symmetrical breaking current in kA × rated kV. • The Making Capacity – The breaker must be able to close onto a fault under the severest condition of maximum current asymmetry. • Rated Short‐time Current – The circuit breaker's ability to carry 'through ' short – circuits for a relatively long time is tested by the short‐time test. – The time interval is usually 3 seconds. • Rated Voltage – rms, line‐to‐line. Specifications Correction Factors • Calculation of Normal (Continuous) Current Ratings(Based on ambient temperature) Power Transformer Instrument Transformer Current Transformer (CT) Capacitive Voltage Transformer(CVT) Isolating Switch Pantograph Disconnector 1. Use three types of crystals Two locking One motive connected to stator 2. Locking mechanism Normally locked: Spindle will not move if no power
applied Normally free: Spindle moves under external force Lightning/Surge Arresters Protection Equipment ANSI/IEEE Standard Device Numbers (IEEE Standard C37.2‐2008) 1 ‐ Master Element 2 ‐ Time Delay Starting or Closing Relay 3 ‐ Checking or Interlocking Relay . . 21 ‐ Distance Relay 25 ‐ Synchronizing or Synchronism‐Check Device 27 ‐ Undervoltage Relay 32 ‐ Directional Power Relay 40 –Field (over/under excitation) Relay 50 ‐ Instantaneous Overcurrent B – Bus 51 ‐ AC Time Overcurrent Relay F ‐ Field 59 ‐ Overvoltage Relay G – Ground or generator 67 ‐ AC Directional Overcurrent Relay N – Neutral 87 ‐ Differential Protective Relay T – Transforme SCADA SCADA • Supervisory Control And Data Acquisition • Series of Inputs and Outputs Gas Insulated Substations – Digital – Analog • Master CPU or PLC • Communicates To/From Master Processor Gas Insulated Substations Gas Insulated Substations ...
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- Fall '06