ELECTRIC POWER SUBSTATIONS, COMPONENTS AND FUNCTIONS BY ENGR. ISIBOR SIMEON, MNSE, MNIEEE, MAIP MD/CEO SIB ENGINEERING LTD CIVIL SERVICE CLUB, MABUSHI-ABUJA PRESENTED AT THE INTERNATIONAL CONFERENCE AND EXHIBITION ON POWER AND TELECOMMUNICATIONS (ICEPT 2015), OSHOGBO.
OUTLINE Introduction Basic Power System Substations Classifications of Substatations Components of Substations Conclusion
ABSTRACT This paper is an overview of major components used in power system. All components of power system are virtually seen in substations. This discussion focuses on substation, classifications and on some major components that can be found and are in regular use in substations. 1
INTRODUCTION Electric power is produced at the power generating stations, which are generally located far away from the load centers. High voltage transmission lines are used to transmit the electric power from the generating stations to the load centers. Substations are basically transformation or switching stations. They receive power transmitted at high voltage from the generating stations and reduce the voltage to a value suitable for distribution.. 2
BASIC POWERR SYSTEM Electric Power Systems are comprised of components that transform other forms of energy into electrical energy and transmit this energy to a consumer. Electric power system equipment are electrical components used in the generation, transmission, protection, distribution, control and utilization of electric power in the industries, factories, offices and homes. [1, 2] 3
Single line schematic arrangement of power substation SUBSTATIONS Substations are assembly of electrical components to form a link between generating stations, transmission systems and distribution systems.[3] 4
CLASSIFFICATION OF SUBSTATION Substations may be classified in according to service requirements and constructional features. According to service requirements it is classified into: Transformer Substations: They are used to transform power from one voltage level to another voltage level. They are further classified into Step-up substations, Primary grid substations, Secondary substations and Distribution substations. Switching substations: These substations are meant for switching operations of power lines without transforming the voltage. Converting substation: are meant for either converting AC to DC or vice versa. Some are used to change the frequency from higher to lower or vice versa for industry utilizations. 5
CLASSIFFICATION OF SUBSTATION According to constructional features, substations are classified into: Indoor substations: All equipment of the substation are installed within the station buildings. Outdoor substations: All equipment such as transformers, circuit breakers, isolators, etc., are installed outdoors. Underground substations: In thickly populated areas where the space is the major constraint, and cost of land is higher, under such situation the substations are laid underground Pole mounted substations: This is an outdoor substation with equipment installed overhead on a H pole or 4 pole structure. 6
COMPONENTS OF SUBSTATION Power Transformers: Power transformers are used in generation and transmission network for stepping-up the voltage at generating station and stepping-down the voltage for distribution. Figure 3.Power Transformer [5] 7
Instrument Transformer a. Current transformer Instrument transformers are used to stepdown the current or voltage to measurable values. They provide standardized, useable levels of current or voltage in a variety of power monitoring and measurement applications. These are further classified into two types. a. Current Transformers b. Voltage Transformers Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. [3] b. Potential Transformer 8
Circuit breakers Circuit breakers are used for opening or closing a circuit under normal as well as abnormal (faulty) conditions. The circuit breakers are used to break the circuit if any fault occurs in any of the instrument. Different types of CBs which are generally used are oil circuit breaker, air-blast circuit breaker, vacuum circuit breaker and SF6 circuit breaker. 9
Isolators or Isolating switches: Isolators are employed in substations to isolate a part of the system for general maintenance. Isolator switches are operated only under no load condition. They are provided on each side of every circuit breaker. Lightning arresters (LA): Lightning arresters are the protective devices used for protection of equipment from lightning strokes. They are located at the starting of the substation and also provided near the transformer terminals. Earth switch: It is a switch normally kept open and connected between earth and conductor for the purpose of safely discharging the residual charges on the conductor or circuit to earth. They are provided for the safety of personnel carrying out work on a piece of equipment. Wave trap: This equipment is installed in the substation for trapping the high frequency communication signals sent on the line from remote substation and diverting them to the telecom panel in the substation control room. [3]. 10
Coupling capacitor: A coupling capacitor is used in substations where communication is done by AC power line. It offers very low impedance to high frequency carrier signal and allows them to enter the line matching unit and blocks the low frequency signal. Auto-Reclosure Facility This facility is normally incorporated into High Voltage circuit breakers that are used for controlling the operation of overhead transmission lines and distance protection scheme. This type of circuit breaker restores continuity of supply after a transient fault interruption. Otherwise, it will open permanently if the fault persists. [2] Insulator The purpose of the insulator is to insulate the electrically charged part of any equipment from another charged part or uncharged metal part. In case of the high voltage overhead transmission and distribution insulators are used to insulate the live conductor from the transmission towers. The insulators used in transmission and distribution system are also required to carry large tensional or compressive load. 11
Capacitor Voltage Transformer (CVT): A capacitor voltage transformer (CVT) is a transformer used in power systems to step-down extra high voltage signals and provide low voltage signals either for measurement or to operate a protective relay. DC Power Supply DC power is used to feed essential services such as circuit breaker trip coils and associated relays, supervisory control and data acquisition (SCADA) and communications equipment. Bus bar: This is a very low impedance and high current carrying capacity conductor having multiple numbers of incoming and outgoing lines electrically connected and operating at the same voltage. Bus scheme: The Bus scheme is the arrangement of overhead bus bar and associated switching equipment in a substation. The operational flexibility and reliability of the substation greatly depends upon the bus scheme. 12
Criteria for Selection of Bus Bar Scheme The Main Criteria to be considered during Selection of one Particular Bus Bar Arrangement among Others are (i) Simplicity of system. (ii) Easy maintenance of different equipment. (iii) Minimizing the outage during maintenance. (iv) Future provision of extension with growth of demand. Bus Bar Arrangements Some very commonly used bus bar arrangements are: Single Bus System Single Section Bus System Double Bus System Double Breaker System One and Half Breaker Bus System Transfer Bus System Double Bus System with Bypass Isolator Ring Bus System Their single line representation are as shown in the next slide. 13
Fig 6.1 Single Bus System Fig 6.2 Single Section Bus System Fig 6.3 Double Bus System Fig 6.4 Double Breaker System Fig 6-56 One and Half Breaker Bus System Fig 6.6 Transfer Bus System 6.7 Double Bus System with Bypass Isolator Fig 6.8 Ring Bus System 14
S/N System Function 1. Substation Earthing system - Earth mat - Earthing spikes - Earthing risers 2. Overhead earth wire shielding or Lightning masts. 3. Illumination system (lighting) - for switchyard - buildings - roads etc. 4. Protection system - protection relay panels - control cables - circuit breakers - CTs, VTs etc. To provide an earth mat for connecting neutral points, equipment body, support structures to earth. For safety of personnel and for enabling earth fault protection. To provide the path for discharging the earth currents from neutrals, faults, Surge Arresters, overheads shielding wires etc. with safe step-potential and touch potential. To protect the outdoor substation equipment from lightning strokes. To provide proper illumination to substation yard. To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to faulty equipment and associated system. 5. Control cable For Protective circuits, control circuits, metering circuits, communication circuits 6. Power cable To provide supply path to various auxiliary equipment and machines. 7. PLCC system power line carrier communication system For communication, telemetry, tele-control, power line carrier protection etc. 8. Telephone, telex, microwave, OPF For internal and external communication 9. Auxiliary standby power system For supplying starting power, standby power for auxiliaries. 10. Fire Fighting system ASSOCIATED SYSTEM IN SUBSTATION Functions of Associated System in Substation is as shown in table below Table: Functions of Associated System in Substation [3] - Sensors, detection system - water spray system - fire port, panels, alarm System. - water tank and spray system To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to affected region to pinpoint location of fire by indication in control room. 15
CONCLUSION This paper provided an insight into the basics of substations and major components of power systems. The functions of some components and different type of substations were discussed. It is not exhaustive. The associative systems in a substation were highlighted in the table. Discussions on them may be subsequent or at other fora. However, these basics are enough as guide to an interested investor and for engineering personnel in the sector. 16
THANK YOU 17
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