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Presentation by ABS Ennin, George Coleman, David Dadson & Anthony Ansah

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Introduction Modern day users of electricity demand a constant and unvarying voltage and frequency to operate new sophisticated equipment. Customers also expect electric power 24 hours a day, seven days a week. Many unpredictable incidents can interrupt the continuous operation of a power system. Overhead lines may be struck by lightning; untrimmed trees can fall or blow into a line; strong winds can cause lines to fall or make contact with each other; ice can accumulate resulting in overstressed conductors; cars can hit utility poles during an accident; electrical equipment can fail due to poor maintenance; contractors can dig into an underground cable; operating personnel can make switching errors. Yet, customers still expect electric power, on demand. Substations play a significant role in meeting these requirements. 2

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OBJECTIVES Upon completion of this module the participant should be able to: Describe the purpose of a substation. List the types of substations. State the advantages of various switching configurations. List the basic components of a substation. List methods of voltage control in a substation. Describe the function of metering in a substation. Describe the function of relaying in a substation Describe the function of equipment in the control room. List and describe the function of equipment at the switchyard. 3

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Purpose of a Substation Substations play an important role in a power system. Basically, a substation has three main functions; switching, transform the voltage, and control the voltage. An electrical power system is designed so that service will continue despite any damage or impairment to other components of the system by natural disaster or other phenomena. When a single element of the system is out of operation for a period of time, be it a few seconds or several days, the power system shall be capable of meeting the usual needs of the customer. Substations represent an important role in providing this reliability. 4

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Purpose of a Substation One important function of substations is switching. Whether it is switching normal load currents or fault currents, switching protects the power system and equipment in the event of trouble. Normally, the switching is done automatically with relaying and circuit breakers or switches. However, non-automatic switching of circuits can be done if it becomes necessary to improve reliability or security of the system. 5

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Purpose of a Substation Secondly, substations function to transform the voltage. For economic reasons, different voltages are used in various parts of the system, ranging from 11.5kV or lower in distribution systems, up to 330kV in bulk transmission systems. High voltages are desirable when the amount of power is great or the distance of transmission is very long. Lower voltages are advantageous where the amount of power is small or transmission distances are short. When a substation uses transformers, it represents a division between sections of the power system with different voltages. 6

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Purpose of a Substation Substations also function to control the system voltage. Various types of equipment are used to accomplish this. Voltage regulators and load-tap changers (LTCs) modify the voltage directly; whereas synchronous condensers, capacitor banks, static voltage compensator (svc) and shunt reactors control system voltage by modifying the reactive power flow. 7

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Substation Design Stage Construction Stage A substation can be describe into two areas as: Switchyard Controlroom 8

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Switchyard A Switchyard comprises of: A Line Gantry Incoming Line Outgoing Line Bus Configuration Transformer Bank Feeder Structure Earthing Voltage Control 9

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Switchyard Equipment Lines Incoming Line Gantry Outgoing Line Gantry Shield Wire Network Line Insulators/Arcing Horns Wave Traps Line CVTs Line Lightning Arrestors/Shaded Rings Skywire or Shieldwire Line Disconnecting Switches By-pass Switches Line Breakers Dead and Live Tanks Line Ground Switch 10

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Switchyard Equipment - Line Gantry 11

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Switchyard Equipment - Line Gantry 12

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Switchyard Equipment - Line Insulator/Wave Trap/Arcing Horns 13

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Switchyard Equipment Arcing Horns 14

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Switchyard Equipment Free Standing CTs for SF6 Breaker Live Tank 15

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Switchyard Equipment 16 Lightning Arrestor with Shaded Ring

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Switchyard Equipment - Surge arresters act to discharge any power surge (transient currents) high enough to cause serious damage. During normal operating conditions, surge arresters appear in the system as open circuits. When a disturbance occurs, such as from a lightning strike or switching surge, surge arresters discharge transient voltages that can cause serious equipment damage to ground. 17 Lightning Arrestor with Shaded Ring

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Switchyard Equipment Free Standing CTs for SF6 Breaker Live Tank 18

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Switchyard Equipment 19 Live Tank SF6 Circuit Breaker

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Switchyard Equipment Live Tank SF6 Breaker 20

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Switchyard Equipment Dead Tank SF6 Breaker 21

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Switchyard Equipment 22 Dead Tank

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Switchyard Equipment 23 SF6 Circuit Breaker

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Switchyard Equipment 24 SF6 Circuit Breaker

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Switchyard Equipment 25 Disconnect Switch

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Switchyard Equipment 26 Lightning Arrestor with Shaded Ring

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Switchyard Equipment 27 CVT with WAVETRAP

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Switchyard Equipment 28 CVT with Carrier Mounting Device

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Switchyard Equipment Busbar Conductors Hollow Bus Busbar Insulator Support Bus PTs Bus CVT/CTs Bus Ground Switch 29

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Substation Bus Configuration Single Bus 30

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Substation Bus Configuration Transfer Bus 31

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Substation Bus Configuration Double Bus 32

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Substation Bus Configuration Reserve Bus 33

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Substation Bus Configuration Ring Bus 34

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Substation Bus Configuration Breaker and Halve (Mesh) Bus 35

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Switchyard Equipment BUS PT 36

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Switchyard Equipment Transformer Bank Transformer Breakers Breaker CTs Isolating Switches Motorized Disconnect Switch (MOD) Transformers Free Standing CTs Lightning Arrestors /Shaded Rings CVTs Reactors 37

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Switchyard Equipment Feeder Structure Feeder Breakers Feeder CTs Feeder PTs Station Service Transformer Fused Switches Grounding Transformer Customer Connections Capacitor Banks Capacitor Bank Breaker Capacitor Bank Ground Switches Capacitor Bank Disconnect Switches 38

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Switchyard Equipment 39 Current Transformer

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Switchyard Equipment 40 Voltage Transformer

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Switchyard Substation Earthing System Earthing Alternatives There are three basic alternatives, isolated systems with no intentional connection to earth, impedance earthed systems with connection through a reactor or resistor and directly earthed systems where transformer neutrals are connected directly to earth. 41

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Substation Earthing Earthing of fences Fences around the substation are might be energised through induced currents from overhead lines passing above. They should always be connected to encircling earth wires. The best is to put the earth wires outside the fence, but risks for theft often makes more practical to put them inside the fence. The most common practice is to connect the fence at corners and every 50m along straight stretches. Gateposts shall always be connected. Fences inside the substation area must also be connected to the earth grid in the same way. However, for straight stretches, connect at every 10m. NOTE: if the fence surrounds an air-core reactor group, the fence must be connected to earth at one place only, and that should be by one gatepost (if there is a gate). If the fence is connected at more than one place, the magnetic field surrounding the reactors will drive very 42

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Switchyard Voltage Control Capacitor Banks Transformers SVC Static Voltage Compensators Reactors Synchronous Condenser 44

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45 Controlroom Equipment Annunciator Panel Relay Panel Protective Relays Control Panel Indicating Lamps AC 400v Station Service Panel DC 125V Rectifier DC 48V Rectifier 125v Battery Banks 48v Battery Bank DC/DC Converters

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Controlroom Equipment Annunciator Panel 46

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Controlroom Equipment Annunciator Panel 47

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Controlroom Equipment Relay Panels 48

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Controlroom Equipment Relay Panel 49

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AC Station Service Panel 50

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Controlroom Equipment 51 DC 125V Rectifier

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Controlroom Equipment 52 DC 125V Panel

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Controlroom Equipment 53 DC 125V Rectifier

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Controlroom Equipment 54 DC 48V Rectifier

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Controlroom Equipment 55 125v DC battery Bank 48v DC battery Bank