SUBSTATION DESIGN Ir SURYA HARDI 1 CHAPTER I

SUBSTATION DESIGN Ir. SURYA HARDI 1

CHAPTER I INTRODUCTION What is a Substation? 1. S/S are integral parts of a power system and form important link between the generating stations, transmission syst. , distribution syst. and the load. [James R. Lusby] 2. S/S is an installation that interconnects elements of an electric utility’s system. (include generator, transmission line, distribution lines and even neighboring utility syst. [ Jhon D. Mc. Donald] 3. An electrical S/S is an assemblage of electrical components including busbars, switchgear, power transformer, auxiliaries, etc [S. Rao] 2

Figure 1. 3

THE FUNCTION of A SUBSTATION 1. To isolate a faulted element from the rest of the utility system. 2. To allow an element to be disconnected from the rest of the utility syst. for maintenance or repair. 3. To change or transform voltage levels from one part of the utility system to another. 4. To control power flow in the utility system by switching elements into or out of the utility system. 5. To provide sources of reactive power for power factor correction or voltage control. 6. To provide data concerning system parameters (voltage, current and power flow) for use in operating 4 the utility system).

KIND OF AC SUBSTATIONS 1. Generating station S/S, transform generation voltage (15 - 23 k. V) up to Trans. Network (69 -500 k. V). 2. Transmission Switching S/S, interconnect portions of the utility syst. Transmission network. 3. Transmission step down (or step up, depending on your point of view) S/S, interconnect portion of the utility syst. Transmission network, and include transformation between trans. Network voltage levels. 4. Distribution step-down S/S, include transformation between Trans. Network and Dist. Network voltage levels, and interconnect portions of the utility syst. Dist. Nework. 5. Distribution S/S, interconnect portions of the utility Sys. Dist. network (transformation between Dist. Voltage Level 5

Chapter 1. INTRODUCTION 6

PARTS OF SUBSTATION 1. Site related system 2. Switchyard system 3. Control Building Syst. 4. Protection, control, and metering system 5. Auxiliary system 7

PARTS OF SUBSTATION A). Site Related Systems (security, site access, Site grading, Drainage, and Surfacing syst. ). B). Switchyard Systems (Switching equipment systems, Power transformation eq. , Bus, Measuring and Relaying Commu. Eq. , Direct stroke and Surge protection, Grounding, Switchyard support structure, Race way ). Control Building System (Building: Architectural, Structural, Grounding, Raceway, lighting and comunication) D). Protection, Control, and Metering Systems (Protective Relay, control, metering, Indication and Annunciation syst. E). Auxiliary Systems (AC station service, Fire Protection. 8

Site Related system • Security fence/Wall system, to prevent entry of unauthorized person to substation, provides adequate electrical clearance from energized buses and equipment to areas accessible to the public, and provide entry to the substation for equipment delivery, removal and maintenance. • Site access system, This system allow access to the substation from public roads, and access inside the substation fence/wall for the installation, removal, and maintenance of the substation equipment, bus-work, and structure. 9

• Site grading, drainage, and surfacing system. To provides a reasonably level switchyard for access to equipment, a drivable surface within switchyard, and a layer of constant resistivity crushed rock above grid for personal safety. • Site Landscaping system, The site landscaping system beautifies the site and complements the substation fence/wall to screen the substation from public view. 10

SWITCHYARD SYSTEM • Switching equipment system, This equipment to connects and disconnects elements of the substation or utility system from the rest of the s/s or utility system. (Eq. CB, DS, Circuit Reclocer). • Power Transformation Eq. System, To Transfers power between voltage levels in the utility system. • Bus system, to interconnects the high voltage portions of the various components of the switchyard to form the required bus configuration for the substation. 11

• Measuring and relaying communications eq. system, to provides low voltage or low current inputs to the protective relaying and metering eq. (Eq. PT’s, CCVT’s, CT’s, BCTs, Line trap, etc). • Reactive power compensation Eq. , this equipment supplies large quantities of capacitive or reactive power for power factor improvement or voltage control, limit fault current (reactor) • Direct stroke and surge Protection system, to protect the switchyard and control building from being struck by ligthning, and protect the insulation system of the switchyard equ. From transient, traveling wave. (Eq. Shielding mast, wire and surge arrester. 12

• Switchyard support structure system, to provides support for the switchyard eq. and bus at the elevations needed for adequate electrical clearance from grade to the bus or eq. live parts. • Grounding system, to protects personnel within s/s from encountering large potential difference during voltage, provides a low impedance path to true earth for proper protective relaying operation and dissipates into the earth large current flows from lightning strikes or faults. • Raceway system, contain supports, and protects from physical damage control and power cables within switch yard. • Control Building systems will be explained next time. 13

Protection, control, and Metering Systems. • Protective relaying system, to protects s/s eq. or the utility system from damage and limits the damage of faulted eq. by monitoring the operation of the utility system. The parameters being monitored can be voltage, current, or frequency, or some combination of the three. • Control system, To provides a means of manually operating electrically operated device, either from a remote operating facility. Device that are manually operated by this system can iclude CB, Circuit switchers, power trans. Load tap changers, and motors operated DS. • Metering system, provides a quantitative measurement of system parameters and displays those measurements for operator information or for record. The metering system can also input to the SCADA eq. , displaying readings of system parameters at the remote dispatch center. 14

Auxiliary system. • AC station service system, to supplies electric power for normal operation of eq. auxiliaries, space conditioning, and ligthning within the s/s. (Eq. Power trans. Cooling pumps and fans, power transf. load tap, CB operating mechanism compresor motor, etc) • DC Station service system, supplies reliable electric power for operation of the protection and control system for emergency. • Fire Protection system, to detect and alarms fires within the control building or in the area of major switchyard eq. or provides a means of extinguishing fires. 15

The task associated with major substations • Protection of transmission system • Controlling the exchange of energy • Ensuring steady state and transient stability. • Load shedding and prevention of loss of synchronism. • Maintaining the system frequency within targeted limits. • Voltage control; reducing the reactive power flow by compensation of reactive power, tap changing. 16

Cont…. • Securing the supply by providing adequate line capacity and facility for changing the transmission paths. • Data transmission via power line carrier for the purpose of network monitoring; control and protection. • Determining the energy transfer through transmission lines and tie lines. • Securing supply by feeding the network at various points. • Establishing economic load distribution 17

Types of substations a)Classification based on voltage levels: AC substation: EHV, MV, LV; HVDC substation Table 1. Classfication based on voltage Designation Descriptions Range LV or LT Low voltage or low Below 1000 V AC tension HV or HT High voltage or high All AC voltages above tension 1 k. V MHV HV Medium voltage high Between 1 k. V and 33 k. V High voltage Between 110 k. V EHV Extra high voltage 220 k. V, 400 k. V UHV Ultra high voltage 760 k. V, 1100 k. V HVDC 33 k. V and HHigh voltage ± 100 k. V; ± 200 k. V; ± direct current 400 k. V ; ± 500 k. V 18

Classification based on installation • Outdoor Substation (Switchyard) under open air ( 33 k. V and above is preferred) • Indoor substation in side building for example; (distribution substation) Gis (Gas Insulating S/s) 19

Classification based on configuration: Conventional air insulated substation (AIS): SF 6 Gas insulated substation (GIS): There are compact and require modest maintenance. In GIS the various substation equipment like CTs, VTs, busbar, circuit breakers, surge arresters, isolators, earthing switches, etc are in the form of metal enclosed SF 6 gas filled modules. Composite substations having combination of the above two (Hybrid substations), It is a combination of the conventional air insulated substation and GIS. 20

Conventional air insulated substation (AIS): In such substations busbar and connectors can be seen by naked eye. In such a substation, circuit breakers, isolators, transformers, CTs, VTs, etc are installed outdoor. SF 6 Gas insulated substation (GIS): There are compact and require modest maintenance. In GIS the various substation equipment like CTs, VTs, busbar, circuit breakers, surge arresters, isolators, earthing switches, etc are in the form of metal enclosed SF 6 gas filled modules. Composite substations having combination of the two above 21

Classification based on application • Switchyard in the generation station • Switching substation • Sending end substation • Receiving substation • Factory substation • Compensating substation • Load substation 22

Substation Categories, Type and Design (According to TNB standards) • Transmission Main Intakes (Pencawang Masuk Utama – PMU) Transmission Main Intake is the interconnection point of 132 k. V or 275 k. V to the distribution network. The standard transmission capacity and voltage Transformation provided at PPU are as follows: 132/33 k. V, 2 x 90 MVA 132/22 k. V, 2 x 90 MVA 132/11 k. V, 2 x 30 MVA 23

• Main Distribution Substation (Pencawang Pembahagian Utama – PPU) • Main Distribution Substation is normally applicable to 33 k. V for interconnecting 33 k. V with 11 k. V network through a standardized transformation of 33/11 k. V, 2 x 30 MVA. • Main Switching Station (Stesyen Suis Utama – SSU) • Main Switching Substation at 33 k. V, 22 k. V and 11 k. V are established to serve the following function: 1. To supply a dedicated bulk customer (33, 22, 1 k. V) 2. To provide bulk capacity injection or transfer from a PMU/PP to a load center for further localized distribution. 24

Distribution Substation (Pencawang Elektrik) Distribution substations have voltages are points from 11 k. V, 22 k. V and sometimes 33 k. V systems to the low voltage network (415 V, 240 V). Typical capacity ratings are 1000 k. VA, 750 k. VA, 500 k. VA, 300 k. VA and 100 k. VA. Conventional substation designs are indoor type (equipment housed in a permanent building) and outdoor type (ground mounted or pole mounted) 25

Design, Construction, and Commissioning Process Figure 1: Flow chart illustrated steps involved in establishing a new substation 26

PROJECT PLANNING The major steps in executing project include the following • Award of contract • Preparation of quality of plan • Design of civil work, layout and Design of equipment • Opening of site office and preparation of site • Civil works: excavation, foundation, support structures, finishing • Receipt of equipment, structure at site, storing • Laying control cable and power cables • Laying of ground grid, ground spikes and ground riser • Installation of overhead shielding wire, steel structures, equipment • Transportation of power transformers • Installation on plinth, drying out and pre-commisisoning • Quality check of equipment, connection of control cables • Final commisionning and observation • Handing over to the customers operating staff 27

Substation design considerations • Security of supply • Extendibility • Maintainability • Operational flexibility • Protection arrangements • Short circuits limitation • Land area • Cost 28

Security of supply Loss of plant arising from a fault conditions or outages due to the maintenance. Extendibility The design should allow for future extendibility. Adding Bays of switchgear to a substation is normally possible and care Must be taken to minimize the outages and outage durations for construction and commissioning. Maintainability The design must take into account the electricity supply company system planning and operations procedures together with the knowledge of reliability and maintenance requirements for the proposed substation equipment. 29

Operational flexibility The physical layout of individual circuits and groups of circuits must permit the required power flow control. In a two transformer substation operation of either or both transformers on one in-feed together with the facility to take out of service and restore to service either transformer without loss of supply would be a normal design consideration. Protection arrangements The design must allow for the protection of each system element by provision of suitable CT locations to ensure overlapping of protection zones. The number of circuit breakers that require to be tripped following the fault 30

Short circuits limitation In order to keep fault levels down parallel connections (transformers or power sources feeding the substation) should be avoided. Multi bus-bar arrangements with sectioning facilities allow the system to be split or connected through a fault limiting reactor. Land area The cost of purchasing a plot of land in a densely populated area in considerable. Therefore there is a trend towards compact substation design. Cost A satisfactory cost comparison between different Substation layout designs is extremely difficult because of the differences in performance and maintainability 31