PLANNING & DESIGN

OF SWITCHYARD

PLANNING STRATEGIES & CONSIDERATIONS

• PLANNING IS ESSENTIAL FOR SUCCESSFUL DESIGN, CONSTRUCTION AND OPERATION OF A SUBSTATION

• RELIABILITY

• FLEXIBILITY

• MAINTAINABILITY

• ECONOMICAL

BASIC DESIGN PARAMETERS• VOLTAGE• MVA• FAULT CURRENT• NUMBER OF BAYS• BUS CONFIGURATION• TYPE OF INSTALLATION – INDOOR /

OUTDOOR / UNDER-GROUND• STEP-UP / STEP-DOWN• AUTOMATION REQUIREMENTS

TYPE OF SWITCHYARDS

• AIR INSULATED (CONVENTIONAL)

• GAS INSULATED SWITCHGEAR (GIS)

• HIGH VOLTAGE POWER ELECTRONIC SUB-STATION (HVDC)

• FLEXIBLE AC TRANSMISSION SUB-STATION (FACT)

AIR INSULATED SWITCHYARD – BUS / SWITCHING CONF.

• There are 6 types of substation bus / switching arrangements commonly used in AIS

• Single Bus• Double bus single breaker• Double bus double breaker• Main and transfer bus• Ring bus• Breaker and a half

SINGLE BUS ARRANGEMENT

- This arrangement involves one main bus with all circuits directly connected to Bus

- Reliability Low, Entire substation is lost in case of a fault on the bus-bar or any bus-bar isolator and also in case of maintenance thereof

- One of the methods for reducing the number of circuits lost in case of a fault is to sectionalise the bus

- Additional by-pass isolators are provided to permit a circuit breaker to be taken out for maintenance without switching out the associated feeder.

MAIN BUS & TRANSFER• Essentially a single bus-bar arrangement with

the difference of by- passing a circuit breaker on-load.

• Each circuit is connected to the main bus-bar through a circuit breaker and through an isolator to the transfer bus-bar.

• As in the case of single bus arrangement, this scheme also suffers from the disadvantages that in the event of a fault on the main bus-bar or the associated isolator, there is a complete shutdown of the substation.

• Widely used in Step-down Sub-station

DOUBLE BUS-BAR SCHEME• Double bus-bar is provided and each

circuit can be connected to either one of these bus-bars through an isolator

• Bus coupler breaker is also provided so that the circuits can be switched on from one bus to the other on load.

• Double bus-bar system is very suitable for large generating stations as well as large grid substations

DOUBLE MAIN AND TRANSFER BUS-BAR

• In this arrangement, the circuit breaker which is to be maintained is transferred to the transfer bus without affecting the other circuits.

• This scheme has been widely used in 220 kV and 400 kV substations.

RING BUS ARRANGEMENT

• Each circuit is controlled by two circuit breakers, therefore, any one circuit breaker can be taken out for maintenance without affecting the security of supply.

• A circuit fault also is cleared by opening of two adjacent breakers.

BREAKER AND A HALF ARRANGEMENT

• In this arrangement three circuit breakers are used for controlling two circuits Normally, both the bus-bars are in service.

• A fault on any bus is cleared by the opening of the associated circuit breakers without affecting the continuity of supply.

• Similarly, any circuit breaker can be taken out for maintenance without causing any interruption.

• All load transfer is done by the breakers, therefore, the operation is simple.

Comparison of Configurations Configuration Reliability Cost Available Area

• Single bus Least reliable - single failure can cause complete outage Least cost (1.0) – fewer components Least area – fewer components

• Main bus and transfer Least reliable – same as single bus, but flexibility in operating and maintenance with transfer bus. Moderate cost (1.76) – fewer components Low area requirement - – fewer components

• Double bus, single breaker Moderately reliable – depends on arrangement of components and bus Moderate cost (1.78) – more components. Moderate area - more components

• Ring bus High reliability – single failure isolates single component Moderate cost (1.56) – more components. Moderate area – increase with number of circuits

• Breaker-and-a-half Highly reliable – single circuit failure isolates single circuit, bus failures do not affect circuits. Moderate cost (1.57) – breaker and a half for each circuit Greater area - more components per circuit

GAS INSULATED SWITCHGEAR

• GIS uses superior dielectric gas SF6 for phase - phase & phase - ground insulation

• SF6 has 2-3 times the insulating ability of air at same pressure

• SF6 is 100 times better than air for interrupting arcs

• HV conductors, devices are inside grounded metal enclosure filled with SF6

• GIS can be smaller to AIS by a factor of 10

• No deterioration of active parts from air, moisture, contamination, etc

• GIS is more reliable, less maintenance than AIS

• SF6 is used in GIS at 4 to 6 Atm.

CONSTRUCTION

• GIS is assembly of standard equipment modules to match SLD

• Modules are joined bolted flanges with “O” ring seals for enclosures and sliding plug -in contacts for conductor. Internal parts are supported by cast epoxy insulators.

• Up to 170kV, all 3 phases are often in one enclosure, above that 3-ph enclosure becomes very large, so 1-ph design is used

• Estimated Service life – 30 years

CONTROL & MONITORING• Local control cabinet (LCC) is provided for

each bay • Insulating & Interrupting capability of SF6

gas depends on minimum design density, so Gas Monitoring System provided.

• Gas compartments and zones• Most GIS designs have double bus, single

breaker arrangement giving good reliability , simple operation, easy protective relaying & excellent economy

INSTALLATION

• GIS is mostly installed on a monolithic concrete pad or floor of building

• Rigidly attached by bolting/welding GIS support frames to embedded steel plates

ENVIRONMENTAL FACTORS IN USE OF SF6

• SF6 is a strong greenhouse gas which could contribute to global warming

• Has long life in atmosphere (half life – 3200 yrs), so effect of SF6 is cumulative & permanent

• Standard requires GIS leakage less than 1% per year

HVDC Sub-stations

• HVDC converters convert AC power to DC power and vice versa.

• They terminate DC transmission lines or form back to back asynchronous AC system coupling

BASIC SWITCHYARD EQUIPMENT

• BAY COMPONENTS

• CONTROL ROOM EQUIPMENT

• STATION EQUIPMENT

• SUB-STATION STANDARD VOLTAGES

• 1.1kV, 3.3kV, 6.6kV, 11kV, 22kV, 33kV, 66kV, 132kV, 220kV, 400kV, 765Kv

BAY COMPONENTS

• TRANSFORMERS• CIRCUIT BREAKERS• ISOLATORS• INSTRUMENT TRANSFORMERS ( CT / PT )• LIGHTNING ARRESTORS• INSULATORS• CONDUCTORS• CARRIER COMPONENTS (WAVE TRAP, CVT)• STRUCTURES

CONTROL ROOM EQUIPMENT

• INDOOR HV SWITCHGEAR

• CONTROL & RELAY PANELS

• 110V / 220V DC SUPPLY SYSTEM (BATTERIES, CHARGERS & DCDB)

• RTCC PANELS

• ACDB

• PLCC EQUIPMENT

STATION EQUIPMENT

• STATION TRANSFORMERS

• REACTIVE COMPENSATION EQUIPMENT

• CONTROL PANELS

IMPORTANT FACILITIES / SYSTEMS

• OIL HANDLING EQUIPMENT: FOR TREATMENT OF INSULATING OIL IN TRANSFORMERS, PORTABLE OIL FILTERATION SET, DIELECTRIC STRENGTH

• COMPRESSED AIR SYSTEM: FOR OPERATION OF AIR BLAST CB, PNEUMATICALLY OPERATED CB’S AND ISOLATORS

FIRE FIGHTING SYSTEM

• EVERY HAZARD HAS FOLLOWING ATTRIBUTES

• Probability that a fire will occur during a specified time interval

• A magnitude of possible fire

• Consequences of the potential loss

FIRE PROTECTION MEASURES

• PASSIVE MEASURES

• Passive measures are measures that controls the spread of fire

• It confines fire to limited area

• Fire separators, Equipment spacing, use of non-combustible construction material, provision of gravels around oil filled equipment

• ACTIVE MEASURES• Automatic fire protection measures

designed to extinguish or control fire at early stage

• Automatic separation system consists of extinguishing agent supply, control valves, delivery system, fire detection and control equipment

• MANUAL MEASURES• Manual measures include manually

operated fire extinguisher, fire hydrant etc by staff

ILLUMINATION SYSTEM, Objective of Illumination System

Quality lighting is an important factor that ensures efficiency productivity and employees comfort at work place. All vision requires light and the quality, direction and diffusion of the light are all important in determining how well one sees.

Illumination design should be based on the achievement of desired illumination level concept with minimum glare. Also, the concept of aesthetics in lighting should also be taken into consideration. Illumination should be uniform and free from dark patches. Illumination design must be energy efficient and reasonably decorative.

SUBSTATION GROUNDING

• The Substation Grounding System is an Essential part of the overall Electrical System. Proper Grounding is Essential for following two reasons

• It provides a means for dissipating Electric Current into Earth without exceeding the operating limits of the Equipment.

• Provides a Safe Environment to protect personnel in the vicinity of grounded facilities from the danger Electric Shock under fault condition

• IMPEDENCE TO GROUND SHOULD BE AS LOW AS POSSIBLE

• WITHIN 1 OHM FOR LARGE SUBSTATION & 5 OHM FOR SMALL SUBSTATIONS

• CABLING : TRENCHES AND CABLE DUCTS – POWER CABLES IN FIRST RACK, LOWER RACK CONTAIN CONTROL CABLES, UN-ARMOURED CABLES IN BOTTOM MOST RACK

• CRANE FACILITY: LARGE S/S HAVE REPAIR BAY ALONGWITH CRANE

• PROVISION OF RAIL TRACK FOR MOVEMENT OF T/F TO REPAIR BAY

SAFETY CLEARANCES Highest System Voltage BIL Minimum Clearance Sectional

Clearance Ph – Earth Ph - Ph

• 36 170 32 40 300

• 72.5 325 63 75 350

SWITCHYARD AUTOMATION • Sub-station integration & automation can

be broken down into 3 levels or layers

• Level 1 – Field Devices –

• Level 2 – Substation Data Concentrator

• Level 3 – SCADA System

COMMUNITY CONCERNS

• NOISE: INDUSTRIAL ZONE <75dBA, Commercial Zone <65dBA, Residential Zone <55dBA

• ELECTRIC FIELDS: Dependent on Voltage, independent of Current, Magnitude varies is a function of operating voltage and decreases with square of distance from source. Could easily be Shielded

• MAGNETIC FIELDS: Dependent on Current, independent of voltage, decreases inversely with distance; Factors affecting – current magnitude, phase spacing, bus height, phase configuration, distance from source, phase unbalance; Difficult to Shield- special enclosures required

• AESTHATICS