Switch Yard Erection(2)

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FOR INTERNAL CIRCULATION ONLY

user’s manual

of

Construction

(part two)

Sub-Stations

Volume-3

Switchyard Erection

Construction Management

Power Grid Corporation of India Limited

(A Government of India Enterprise)

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CHAPTER ONE

ELECTRICAL SUBSTATION

PAGE NO. 1.O INTRODUCTION 1 1.1 FUNCTIONS OF A SUB-STATION 2

1.2 VOLTAGE LEVELS IN AC SUBSTATIONS

AND HVDC SUBSTATIONS 3

1.3 FORMS OF SUBSTATIONS 4

1.4 TYPES OF SUBSTATIONS 6

1.5 ESSENTIAL FEATURES OF A SUBSTATION 7

1.5.1 SPECIAL FEATURES 12

1.6 SITE SELECTION 13

ANNEXURE - I

FORMAT FOR COMPARATIVE STATEMENT OF

SITES FOR SUBSTATION 14

1.6.1 LAND ACQUISITION 16

1.6.2 PROVISIONS UNDER THE LAND

ACQUISITION ACT, 1894 FOR SUB-STATIONS 16

1.6.3 LAND ACQUISITION ACT,1894 AS AMENDED

IN 1984 17

ANNEXURE - II

ACTIVITY CHART(TIME FRAME) 18

1.7 SUBSTATION PARTS AND EQUIPMENT

1.8 FUNCTIONS OF SUB-STATION EQUIPMENTS &

ASSOCIATED SYSTEMS

1.9 SUBSTATIN LAYOUTS, BUSBAR SCHEMES

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CHAPTER TWO

SWITCHYARD CIVIL WORKS

2.0 INTRODUCTION

2.1 SOIL INVESTIGATION

2.2 LEVELLING

2.3 FOUNDATIONS

2.4 FOUNDATIONS FOR TRANSFORMER & SHUNT

REACTORS

2.5 CABLE TRENCHES IN SWITCHYARD

2.6 CABLE TRENCH COVER SLABS

2.7 ANTI-WEED TREATMENT, MICRO LEVELLING’

GRAVEL FILLING & METAL SPREADING

2.7.1 ANTI-WEED TREATMENT

2.7.2 MICRO LEVELLING

2.7.3 METAL SPREADING IN SWITCHYARD

2.8 DO’S, DON’T’S & SPECIAL PRECAUTIONS

2.9 CHECK FORMAT

CHAPTER THREE

SWITCHYARD EARTHING

3.0 INTRODUCTION

3.1 FUNCTIONAL REQUIREMENTS OF EARTHING SYSTEM

3.2 EARTHNG SYSTEM IN SWITCHYARD

3.3 STEP AND TOUCH POTENTIAL

3.3.1 STEP POTENTIAL

3.3.2 TOUCH POTENTIAL

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3.5 EARTHING MATERIAL

3.6 EARTHING CONDUCTOR LAYOUT 45

3.7 EQUIPMENT AND STRUCTURE EARTHING

IN SUBSTATION 45

3.8 JOINTING 48

3.9 MEASUREMENT OF EARTH RESISTANCE 49

3.10 DO'S DON'TS AND SPECIAL PRECAUTIONS 50

3.11 CHECK FORMAT

CHAPTER FOUR

SWITCHYARD STRUCTURES

4.0 INTRODUCTION 54

4.1 STRUCTURE WORKS IN SUBSTATION

SWITCHYARD 54

4.2 RECEIPT OF MATERIAL & INSPECTION 54

4.3 STORAGE 55

4.4 ERECTION 55

4.4.1 ERECTION OF GANTRY & LATTICE STRUCTURES 55

4.4.2 ERECTION OF PIPE STRUCTURE 57

4.3 LIGHTNING MASTS 57

4.4 DO'S, DONT'S AND SPECIAL PRECAUTIONS 58

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CHAPTER FIVE

BUS POST INSULATORS & BUS BARS

5.0

INTRODUCTION 62

5.1 STEPS IN BUSBAR DESIGN 62

5.2 FORMS OF BUSBARS 63

5.2.1 ACSR 63

5.2.2 ALUMINIUM 63

5.3 CONFIGURATION OF BUSBARS IN

OUTDOOR SUBSTATION 64

5.4 RECEIPT AND INSPECTION OF MATERIAL

AT SITE 64

5.5 BUS POST INSULATORS 65

5.5.1 TECHNICAL PARAMETERS OF BUS POST

INSULATORS 66

5.6 ERECTION OF ALUMINIUM BUS BAR 67

5.6.1 BENDING PROCEDURE OF ALUMINIUM TUBE

DURING ERECTION 68

5.6.2 WELDING OF ALUMINIUM TUBE 68

5.7 WELDING PROCEDURE AND WELDER'S

QUALIFICATIONS 69

5.8 DO'S, DONT'S AND SPECIAL PRECAUTIONS 70

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CHAPTER SIX

STRINGING IN SWITCHYARD

6.0 INTRODUCTION 78 6.1 PRE-STRINGING CHECKS 78 6.2 STRINGING 79

6.3 T&P AND MATERIALS USED FOR STRINGING 79

6.4 DO’S DONT’S AND SPECIAL PRECAUTIONS 81

6.5 CHECK FORMAT 84

CHAPTER SEVEN

SURGE ARRESTER

7.0 INTRODUCTION 86

7.1 CONVENTIONAL GAPPED LIGHTNING ARRESTER

(VALVE TYPE ARRESTER) 86

7.2 METAL OXIDE LIGHTNING ARRESTERS 87

7.3 PACKING, TRANSPORT, HANDLING AND STORAGE 88

7.4 INSTALLATION 89

7.5 INSTALLATION OF SINGLE UNIT ARRESTER 89

7.6 INSTALLATION OF MULTI-STACK ARRESTER 89

7.7 DO'S, DONT'S & SPECIAL PRECAUTIONS 91

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CHAPTER EIGHT

ISOLATORS

8.0 INTRODUCTION 94 8.1 CONSTRUCTION FEATURES 94 8.1.1 SUPPORT STRUCTURE 95 8.1.2 BASE ASSEMBLY 95 8.1.3 INSULATOR ASSEMBLY 95

8.1.4 MALE AND FEMALE CONTACTS ASSEMBLY 96

8.2. OPERATING MECHANISM 96

8.2.1 GEARED OPERATING MECHANISM 96

8.2.2 MANUAL OPERATING MECHANISM 96

8.2.3 EARTH SWITCH ASSEMBLY 97

8.3 RECEIPT, HANDLING AND STORAGE 97

8.4 ERECTION/INSTALLATIONS 97

8.4.1 STRUCTURES 97

8.4.2 BASE ASSEMBLY 98

8.4.3 INSULATORS 98

8.4.4 CONTACTS ASSEMBLY (MALE AND FEMALE

ASSEMBLY) 99

8.4.5 CONNECTING DISCONNECTOR 100

8.4.6 CONTROLS FOR ELECTRICAL

OPERATING EQUIPMENT 101

8.5 CLOSING OPERATION OF ISOLATOR 101

8.6 TANDEM PIPE ASSEMBLY 102

8.7 EARTH SWITCH ASSEMBLY 102

8.8 DO'S, DONT'S AND SPECIAL PRECAUTIONS 104

8.8.1 ADJUSTMENT IN DRIVE/ASSEMBLY ERECTION 104

CHAPTER NINE

CURRENT TRANSFORMER

9.0 INTRODUCTION 109 9.1 CONSTRUCTION FEATURES 109 9.2 HERMETIC SEALING 111

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9.4 INSTALLATION/ERECTION 112

9.5 DO'S DONT'S & SPECIAL PRECAUTIONS 114

9.6 CHECK FORMAT 115

CHAPTER TEN

CAPACITIVE VOLTAGE TRANSFORMER

10.0 INTRODUCTION 117

10.1 DESCRIPTION & OPERATING PRINCIPLE 117

10.2 PACKING AND TRANSPORTATION 119

10.3 RECEIVING 120

10.4 UNLOADING 120

10.5 STORAGE 121

10.6 INSTALLATION 122

10.7 CONNECTION 122

10.8 DO'S, DONT'S AND SPECIAL PRECAUTIONS 125

10.8.1 INSPECTION BEFORE MOUNTING 125

10.8.2 DEFECT/DAMAGE 126

10.8.3 MINOR IRREGULARITIES 127

10.8.4 ERECTION 127

10.9 CHECK FORMAT 128

CHAPTER ELEVEN

POWER LINE CARRIER COMMUNICATION

11.1 PLC SYSTEM 129

11.2 COUPLING EQUIPMENT 129

11.3 COUPLING EQUIPMENT DESCRIPTION 130

11.4 CONSTRUCTION FEATURES 130

11.5 DATA TRANSMISSION 131

11.6 TELEPROTECTION 131

11.7 CARRIER PANEL 131

11.8 EARTHING 131

11.9 ERECTION OF PLCC AND ASSOCIATED

EQUIPMENT 132

11.9.1 OUTDOOR EQUIPMENTS 132

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11.10 CONNECTION OF HF CO-AXIAL CABLE 136

11.11 INSTALLATION OF EQUIPMENT AS PER

PLANNED SYSTEM 137

11.12 DEFECTIVE MODULES AND FAULT

RECTIFICATION AT SITE 137

11.13 DO'S, DON'TS AND SPECIAL PRECAUTIONS 139

CHAPTER TWELVE

CABLES

12.1 RECEIPT, INSPECTION AND STORAGE 144

12.2 CABLE LAYING IN SWITCHYARD 144

12.2.1 CABLE LAYING IN UNDERGROUND

(BURIE TRENCHES) 145

12.2.2 CABLE LAYING IN CABLE TRAYS 145

12.3 CABLE TERMINATION 146

12.4 DO'S DON'TS AND SPECIAL PRECAUTIONS 148

CHAPTER THIRTEEN

CONTROL AND RELAY PANELS

13.1 CONSTRUCTION FEATURES 155

13.2 SIMPLEX PANEL 156

13.3 DUPLEX PANEL 156

13.4 RECEIPT AND STORAGE AT SITE 156

13.5 ERECTION OF PANELS 157

13.6 MOUNTING ON PANELS 158

13.7 PANEL INTERNAL WIRING AND EQUIPMENTS

IN PANELS 158

13.8 PROVIDING TERMINAL BLOCKS 159

13.9 NAME PLATES AND MARKINGS 160

13.10 PANELS ACCESSORIES 160

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13.12 DO'S DON'TS AND SPECIAL PRECAUTIONS 162

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Chapter-1

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________________________________________________________________________________ _ CHAPTER ONE ________________________________________________________________________________ _ ELECTRICAL SUBSTATION

Back to contents page

1.0 Introduction

An electrical Network comprises of the following systems:  Generating Stations

 Transmission Systems  Receiving Stations  Distribution Systems  Load Points

In all these systems, the power flow of electrical energy takes place through Electrical Substations. An Electrical Substation is an assemblage of electrical components including busbars, switchgear, power transformers, auxiliaries, etc. Basically an electrical substation consists of a number of incoming circuits and outgoing circuits connected to common busbar system. Busbars are conducting bars to which a number of incoming or outgoing circuits are connected. Each circuit has certain electrical components such as circuit-breakers, isolators, earthing switches, current transformers, voltage transformers, etc. These components are connected in a definite sequence such that a circuit can be switched off/on during normal operation by manual/remote command and also automatically during abnormal conditions such as short-circuits.

A substation receives electrical power from generating station via incoming transmission lines and delivers electrical power via the outgoing transmission lines. Substations are integral parts of a power system and form important links between the generating stations, transmission and distribution systems and the load points.

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1.1 Functions of a sub-station:

An electricity supply undertaking generally aims at the following:

 Supply of required electrical power to all the consumers continuously at all times.

 Maximum possible coverage of the supply network over the given geographical area.

 Maximum security of supply.  Shortest possible fault duration.

 Optimum efficiency of plants and the network.

 Supply of electrical power within targeted frequency limits.  Supply of electrical power within specified voltage limits.

 Supply of electrical energy to the consumers at the lowest cost. As a result of these objectives, there are various tasks which are closely associated with the generation, transmission, distribution and utilisation of the electrical energy. These tasks are performed by various, manual, semi-automatic and fully automatic devices located in generating stations and substations.

The tasks associated with a major substation in the transmission system include the following:

 Controlling the exchange of energy  Protection of transmission system

 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.

 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.

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 Fault analysis and pin-pointing the cause and subsequent improvements.

 Securing supply by feeding the network at various points.

All these tasks are performed by the team work of load-control centre and control rooms of substations. The substations perform several important tasks and are integral part of the power system.

1.2 Voltage Levels in AC Substations and HVDC Substations

A substation receives power via the incoming transmission lines and delivers power via the outgoing lines. The substation may have step-up transformers or step-down transformers. Generally the switchyards at sending-end of lines have step-up transformers and switchyards at receiving-end have step-down transformers. The rated voltage level refers to nominal voltage of 3 phase AC system and is expressed as r.m.s. value between phases. An AC substation has generally 2 or 3 main voltage levels. The long distance transmission is generally at extra high voltages such as 132 kV, 220 kV, 400 kV AC The subtransmission is at medium high voltage such as 33 kV, 11 kV AC. In a generating station, the generator is directly connected to step-up transformer and secondary of the step-up transformer is connected to outdoor EHV switchyard. The switchyard in a generating station comprises generator transformer, unit auxiliary transformer and several out-going lines. In addition to the main EHV switchyard, a generating station has indoor auxiliary switchgear at two or three voltages such as 11 kV, 400 Volts.

The factory substations receive power at distribution voltage such as 11 kV and step it down to 440 volts AC. Larger factories receive power at 132 kV and have internal distribution at 440 volts AC.

The choice of incoming and outgoing voltages of substations is decided by the rated voltages and rated power of corresponding lines. Long distance and high power transmission lines are at higher voltages. The nominal voltages are selected from the standard values of rated voltages specified in Indian Standards or relevant national standard. The standards also specify the following reference values for each voltage level.

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 Nominal voltage e.g. 220 kV, 400 kV

 Highest system voltage, e.g. 245 kV, 420 kV  Lowest system voltage, e.g. 200 kV, 185 kV.

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Table 1: Reference Values of Nominal Voltages in AC and HVDC Substations AC Substation 765 kV, 400 kV, 220 kV, 132 kV, 66 kV, 33 kV, 11 kV HVDC Substation +400 Kv, +500 kV, +600 kV Station Auxiliaries Aux. AC Supply : 33 kV, 11 kV 400 V, 3 ph., phase to phase 230 V AC single phase Aux. LVDC : 220 V, 110 V, 48 V DC 1.3 Forms of Substations

For voltage upto 11 kV, the sub-stations are either in the form of indoor metal clad draw-out type Switchgear or Outdoor Kiosk. In indoor metal clad switchgear, the required number of factory assembled units are taken to site and placed in a row. SF6 Gas Insulated Switchgear has

been introduced for medium to high voltages such as 11 kV, 33 kV & upto 400 kV level.

For voltages of 33 kV and above, outdoor substations are generally preferred. In outdoor substations, the various equipments are installed in open.

The indoor and outdoor substations have similar components. However, configurations, assembly and dimensions of indoor sub-stations are quite different from those of outdoor subsub-stations.

SF6 Gas Insulated Substations (GIS) are preferred for the following

 EHV, HV Substations.

 Substations in urban areas, industrial areas, mountainous regions where land is costly and civil works are complex.

 Heavily polluted areas such as sea-shores, industrial areas, thermal power stations etc. Where open terminal substations experience frequent flashovers.

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Besides the main voltage levels, each substation has auxiliary AC and DC distribution systems for feeding the various auxiliary systems, protection systems and control systems. The reference values of auxiliary voltage are mentioned above in in Table -1.

High voltage DC Transmission systems (HVDC) have following parts at each end of the HVDC Transmission line.

 EHV AC yard which is at 400 kV AC or 220 kV AC

 HVDC yard which is at + 400 kV DC or + 500 kV DC etc.  Valve hall, Converter Transmission and AC Filters.  Electrode line, earth electrode.

Bipolar HVDC system has two poles, one of a positive and other

negative polarity with respect to earth. The nominal voltage + 500 kV refers to voltage of the two DC poles with respect to earth. The midpoint of converters is earthed through earth electrodes. One HVDC substation is required at each end of the long HVDC transmission line. In case of Back-to-Back HVDC substation, the long distance HVDC transmission line is eliminated and such substation has the following parts:

 AC Switchyard of one grid.  AC Switchyard of other grid.

 Back-to-back converter transformers and valves.

Such substations are used for asynchronous links between two AC systems for interconnection. The frequency fluctuations on one AC side are not reflected on the other AC side and the power can be transferred in either directions by adjusting the characteristics of the converter valves. Power can be exchanged rapidly and accurately in a controlled way.

1.4 Types of Substations

The substations can be classified in several ways including the following:

i) Classification based on voltage levels e.g.:

AC Substation: EHV, HV, MV, LV; HVDC substation ii) Classification-outdoor or indoor.

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Outdoor substation is under open sky. Indoor substation is inside a building.

iii) Classification based on configuration, e.g.: a) Conventional air insulated outdoor substation or

b) SF6 Gas Insulated Substation (GIS)

c) Composite substations having combination of the above two. iv) Classification based on application.

a) Distribution substation

b) Switchyard in Generating Station

c) Switching substation (without power transformers) d) Sending-end substation

e) Receiving substation f) Factory substation

g) Compensating substation e.g. having static var compensation etc. h) Load substation, e.g. arc-furnace substation.

Table-2 given below gives the Main Data about a typical 400/230 kV AC Substation.

Table 2: Main Data of a Typical 400/220 kV Outdoor AC Substation

Operating Voltage 400 kV 220 kV

Rated current 2000/3150 A 2000A

Maximum Short-circuit current in busbar 40 kA 40 kA

Minimum phase to phase clearance 5.75 m 2.5 m

Minimum phase to earth clearance 3.50 m 2.1 m

Number of horizontal levels of tubular busbars/flexible busbars

2 2

Height of tubular busbars of first level above ground

8 m 5.5 m

Height of tubular busbar of second level 13 m 4 m

Tubular Aluminium Busbar * 4” IPS 4” IPS

* It could be of suitable conductor also.

1.5 Essential Features of a Substation

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 AC Switchyard  Control Building

 DC Battery System and LT Distribution System  Mechanical, Electrical and other auxiliaries  Civil works.

An HVDC substation has following main parts:

 AC Switchyard

 Converter Transformers  AC Filter banks

 Valve Halls

 AC Switchyard, Smoothing Reactor, DC Filters  Mechanical, Electrical and other auxiliary systems

Each substation is designed separately on the basis of functional requirements, ratings, local conditions predominately based on load centres etc. For the same requirement, several alternative designs are possible. However, the principles and basic technical requirements of all the substations are similar and the substation is designed on the basis of these requirements and the earlier experience.

The Rihand-Delhi bipole project is the first commercial long distance transmission project in India employing High Voltage Direct Current (HVDC) Technology.

The main features of HVDC which distinguish it from high voltage AC transmission system are:

 It forms an asynchronous connection between two stations connected through HVDC link i.e. the transmission of power is independent of the sending and receiving end AC system frequency. Due to this, one of the major use of HVDC is to interconnect two regions which are usually operating at different frequencies.

 HVDC becomes economical for bulk power transfer beyond a certain transmission distance. This is due to the fact that the DC lines are much cheaper compared to the equivalent AC line(s) whereas the terminal equipment of DC are costlier compared to the AC terminal equipments.

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 Reduction in right of way. The DC line corridor being extremely compact, results in reduction of right of way requirement. The total requirement of the right-of-way reduces to about half, for the same quantum of power to be transmitted.

 The power flow through DC link can be precisely controlled under steady state as well as dynamic conditions. During steady state conditions, the power flow remain fixed at the ordered value and is independent of the conditions in the AC system.

 During dynamic conditions e.g. during power swings caused by faults, the power flow through DC link can be modulated in a way so as to assist the rest of the grid in damping the prevailing disturbance.

 Since a DC transmission line does not generate or absorb any reactive power, it helps to increase the capability of the link to transmit large quantities of power over long distances in an efficient and economical manner. Due to the absence of reactive power, the losses on a DC line are also low compared to an equivalent AC line. Due to absence of frequency factor on DC link, the skin effect does not play any part & complete cross section of the conductor can be effectively used and more power can be transmitted on the same size of the conductor. So HVDC transmission lines help in bulk power transmission in more efficient, economical way on long distances.

 The DC transmission linens do not contribute to short circuit levels at the terminals. This feature becomes important if two large networks are being connected where short circuit levels are in the vicinity of maximum values specified for the network.

In Rihand- Delhi HVDC link of Powergrid one of the converters of the project which operates as rectifier is located in the south eastern corner of UP near Rihand STPP. The other converter which operates as inverter is located in the western side of UP in the district Ghaziabad at Dadri which is about 50 km from Delhi. The project also includes two electrode stations one at Chapki, about 22 km from Rihand and the other at Dhankaur, about 25 km from Dadri. The PLCC communication system has two repeater stations along the route of the

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line: one at Katra, about 240 km from Rihand and the other at Jhinjhak, about 325 km from Dadri. The project transmits the power generated at the Rihand/Singrauli complex to Dadri from where it is further distributed to various beneficiaries states/union territories in the Northern Region. Typical Data of Rihand - Delhi HVDC link is given below in Table -3.

Table 3: Typical data of Bipolar HVDC Substation (Rihand - Delhi link)

1 Rated Capacity 1500 MW

2 Minimum power 40 MW/80 MW 3 Operating voltage-DC + 500 kV

4 AC side voltage range

For Performance 380-420 kV For Rating 360-440 kV 5 AC side frequency range

For Performance 48.5-50.5 Hz For Rating 47.5-51.5 Hz 6 Negative phase sequence unbalance

For Performance 1.0% For Rating 2.6%

7 Reduced Voltage Oprn. DC, 400 kV 8 Overload rating

(For 2 hrs, available after every 12 hrs if ambient temp of Delhi

or Rihand is more than 33o_{C 1650 MW}

9 Continuous over load 1650 MW

(If ambient temp at Delhi & Rihand is less than 33o_C)

10 Short time over load 1000 MW Per pole (For 5 Sec, available after every 5 min.)

11 Thyristor Valves

Thyristor type YST 45 Max. Voltage per thyristor 6.5 kV Current Rating

Continuous 1568 Amp. 2 Hr. Over Load 1725 Amp. 5 Sec. Over Load 2539 Amp. 12 Converter Type 12 Pulse

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13 Valve Type Quadruple Vertically

Suspended, 4 x 96 thyristors 14 Quadruple per Converter 3

15 Cooling Water 16 Converter Transformer

Type 10, 3 winding

Quantity 6 + 1 Spare per station Rating 315/305 MVA Tap Range + 14/-10 @ 1.25 % 17 Secondary Voltage For Delhi Delta 206 kV Star 119 kV For Rihand Delta 213 kV Star 123 kV 18 AC Filters

Numbers of Banks 3 per station Numbers of Sub-banks 3

Size of each Bank 230 MVAR

19 Oil Smoothing Reactor

Per pole per station 360 mH 20 Air Smoothing Reactor

Per pole per station 180 mH 21 DC Filters

Numbers per pole 2

Tuning Frequencies 12, 24 Hz 22 PLCC Frequencies

Data (pole & bipole) 2400 Bauds Per pole per station 180 mH

Repeater LAS to CU 600 Bauds Speech 100/50 Bauds

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23 Station Availability

Design target 99% Guaranteed 97% 24 HVDC LINE

DC voltage + 500 kV Configuration Horizontal bipole with a

pole spacing of 12750 mm 25 Name and type of conductor ACSR “BERSIMIS” / 35.1 mm 26 Number of conductors per pole 4

27 Insulators 160 kN HVDC disk insulator with zinc sleeve, 38 insulators used in each arm of ` V’ string. Porcelain & toughened glass insulators have been used

1.5.1 Special Features

In order to integrate the project with the AC system and to help the grid, a number of features have been incorporated into the project that take advantages of the HVDC transmission. Some of these features are

i) Power modulation

Under normal operating conditions a part of the Northern Region Ac system remains parallel to the Rihand-Delhi HVDC project. In case of any disturbance in the AC system e.g. caused by faults, switching actions, the power flow on the HVDC link is modulated to counteract the power swings. Depending upon the need, as determined through minimum power upto the five second overload rating of the HVDC link.

ii) Frequency control

At Rihand side, the rectifier is connected to the rest of the AC System through two 400 kV AC lines. In case of outages of these lines the power flow through the HVDC link is regulated to prevent the Rihand machines from putting out of the grid and

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maintain the frequency of the Rihand generators at a target value near 50 Hz.

iii) Reactive power control

This feature allows controlled switching of the available Ac harmonic filter (s) (i) to meet the target value of reactive power exchange with the Ac system at Rihand, and (ii) to meet the target value of AC system voltage or reactive power exchange at Dadri. While switching the Ac harmonic filter (s), proper care is taken of the harmonic performance criteria, operating mode, bipole power and the AC system conditions.

iv) Run back control

The flow through the HVDC link is also regulated following outages of AC lines at Dadri or generators at Rihand.

v) Control of sub-synchronous reasonance

Suitable subsynchronous resonance damping controllers have been incorporated to prevent any negative damping by the HVDC at the nearby generator’s natural resonating frequencies. This avoids any adverse interaction between HVDC and the generators at the natural resonating frequencies.

1.6 Site Selection

Before the actual switchyard erection works, the land selected for setting up the substation is acquired. A Proforma at Annexure- I gives the Format for selection of site for Sub-Station site

Annexure-1

Format for Comparative Statement of Sites For Sub-Stations

______________________________________________________________________________________________

Sl. No. Criteria Alternate-I Alternate-II Alternate-III

______________________________________________________________________________________________

1.0 Land

1.1 Size (Acre) (Mtr. x Mtr.)

1.2 Govt. Private/Forest land 1.3 Agriculture/Wasteland

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1.4 Development 1.5 Approximate cost 1.6 Type of soil 1.7 No. of owners

1.8 Environment/Pollution in the vicinity 1.9 Location with reference to nearest town 1.10 H.F.L. Data

1.11 Diversion of Nallah/Canal required 1.12 Slope

1.13 Extent of levelling required 1.14 Land acquisition feasibility 1.15 Rate of Govt. land

1.16 No. of owners 1.17 Exten. of approach

1.18 Planned/unplanned development 1.19 Size of sites

1.20 No. of families displaced 1.21 Required Government value 1.22 Level of site with ref. to road level 1.23 Distance from sea shore

2.0 Approach

2.1 What are the Obstacles in reaching site 2.2 Approach road

2.3 Length of approach road 2.4 Distance from main road

2.5 Unloading facility at Railway Station 2.6 No. of Culverts required

3.0 Community Facilities 3.1 Drinking Water 3.2 Drainage 3.3 a) Post Office b) Telephone c) Telex 3.4 Market

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3.5 Security 3.6 Amendability

3.7 Availability of construction water 3.8 Availability of water

3.9 Nearest EHV line 3.10 Length of line between

this site & nearest substation 3.11 Length of line estimate 3.12 Additional crossings 3.13 Frontage for line take off 3.14 Telephone/Telegraph line

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1.6.1 Land Acquisition

Land is a state subject. Land acquisition activity starts after the approval is obtained from the competent authority for the recommended site. Land is to be acquired for starting the construction activities. Typically for a 400 kV sub-station 50-80 Acre land is required. Land being the state subject, acquisition for the sub-station land is carried out through land acquisition deptt. of the concerned state govt.

Brief summary of Land Acquisition Process is given below

1.6.2 Provisions Under The Land Acquisition Act, 1894 For Sub-Stations

When land is acquired for sub-stations, POWERGRID will follow procedures laid down under the Land Acquisition Act (LA Act), 1894. POWERGRID sub-stations have never resulted in large scale displacement or loss of livelihoods. There have been only marginal impacts due to flexibility exercised by POWERGRID in selecting sites. The LA Act specifies that in all cases of land acquisition, no award of land can be made by the government authorities unless all compensation has been paid. POWERGRID has always followed a schedule for R&R (illustrated in Table below). These will be further reinforced taking into consideration POWERGRID’s entitlement framework and public consultation process.

Table 4: POWERGRID’s Activity Chart for Land Acquisition and R&R Activity

 Submission of cases for land acquisition  Section 4 draft notification

 Spot verifications

 Scope for objections from public  Publication of Section 6 draft declaration

 Marking of land, notice to persons and award by Collector  Finalisation of R&R package

 Payment of compensation and acquisition of land  Handing over land to POWERGRID

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1.6.3 Land Acquisition Act, 1894 as amended in 1984

This is the principal law dealing with acquisition of private land by the state for “a public purpose”. Progressive liberalisation and industrialisation have led to an increase in compulsory land acquisition. Land acquisition goes through a number of stages starting from notification to payment of compensation.

POWERGRID selects a suitable substation site only after the approval of the project by GOI. Attachment above shows the format for comparative statements of sites to be considered for construction of sub-stations. On the basis of data for the various parameters cited in the checklist a comprehensive analysis for each alternative site is carried out. Weightage given to the various parameters is often site specific. Due consideration is given to infrastructure facilities such as access roads, railheads etc.; type of land viz. Govt., revenue, private land, agricultural land; social impacts such as no. of families getting affected; and cost of compensation and rehabilitation.

The Activity Chart given in the Annexure-2 shows the time frame for the implementation of various sections of Land Acquisition Act (Section wise time schedule) as well as the time schedule for parallel R&R activities.

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Annexure-2

ACTIVITY CHART (TIME FRAME)

LAND ACQUISITION R&R ACTIVITY

(PARALLEL ACTIVITY)

SECTION 16- POSSESSION OF LAND ________ 1 MONTH

LINK

__________DISBURSEMENT OF COMPENSATION __________ FINALISATION OF RAP __________15 DAYS

SECTION 11- AWARD BY COLLECTOR

2 MONTHS __________1 MONTH PUBLIC CONSULTATION SECTION 9- NOTICE TO PERSONS

__________ 1 MONTH

COMPLETION OF S-E SURVEY SECTION 8- MEASUREMENT AND MARKING OF LAND

3 MONTHS ___________15 DAYS

SECTION 6-DECLARATION OF LAND FOR ACQUISITION

____________2 MONTHS SOCIO-ECONOMIC SURVEY LINK BY POWERGRID OR

OUT SIDE AGENCY

SECTION 4- PUBLIC NOTIFICATION ___________ 2 MONTHS

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1.7 Substation parts and equipment:

Outdoor Switchyard - Incoming & outgoing lines

- Busbars

- Transformers - Insulators

- Substation Equipment such as Circuit-breakers, Isolators, Earthing, Switches, Surge Arresters, CTs, VTs/CVTs

- Neutral Grounding Equipment

- Station Earthing system comprising ground mat, risers, earthing strips,

earthing spikes

- Overhead earthwire shielding against lightning strokes, or, lightning masts

- Galvanised steel structures for towers, gantries, equipment supports

- PLCC Equipment including line trap, tuning unit, coupling capacitor, etc.

- Power cables

- Control cables for protection and control - Roads, Railway track, cable trenches - Station lighting system

Main Office Building - Administrative building conference room etc.

11/ 33 kV Switchgear - 33 kV Outdoor Switchgear 11 kV Indoor Switchgear

LT Panels - Low voltage AC. Switchgear

- Control Panels, Protection Panels.

Battery room and - DC Battery system and charging

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Mechanical, Electrical - Fire fighting system Oil purification system and other auxiliaries Substation parts and equipment:

- Cooling water system - Telephone system - Workshop; stores etc.

Protection system - CTs, CVTs

- Protective Relays - Circuit breakers

SCADA(Supervisory - Computer/Microprocessors,

Data collection

Control and Data - system, Data processing system

Acquisition System) - Man-machine interface

- Expert system etc.

1.8 Functions of Sub-station Equipments & Associated Systems

i) Circuit Breakers

Circuit Breakers are the switching and current interrupting devices. Basically a circuit-breaker comprises a set of fixed and movable contacts. The contacts can be separated by means of an operating mechanism. The separation of current carrying contacts produces an arc. The arc is extinguished by a suitable medium such as dielectric oil, vacuum, SF6 gas. The circuit

breakers are necessary at every switching point in the substation.

ii) Isolators

Isolators are disconnecting switches which can be used for disconnecting a circuit under no current condition. They are generally installed along with the circuit breakers. An isolator can be opened after the circuit breaker. After opening the isolator, the earthing switch can be closed to discharge the trapped electrical charges to the ground.

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These transformers are used for transforming the current and voltage to a lower value for the purpose of measurement, protection and control.

iv) Surge Arresters

Surge Arresters divert the over voltages to earth and protect the substation equipment from over voltage surges.

v) Busbars

Busbars are either flexible or rigid. Flexible busbars are made of ACSR conductors and are supported on strain insulators. Rigid busbars are made up of aluminium tubes and are supported on post insulators.

vi) Galvanised Steel Structures

Galvanised Steel Structures are made of bolted/welded structures of angles/channels/pipes. These are used for towers, gantries, equipment, support structures etc. Galvanised structures provide rigid support to the various equipments and insulators. The design should be safe and economical.

vii) Power Line Carrier Current Equipment

PLCC is necessary for transmitting/receiving high frequency signals over the power line (transmission Line) for the following: a) Voice communication

b) Data transmission

c) Protection signalling d) Control signalling

A small power system is generally controlled by direct supervision of generating stations and substations through respective control rooms. A large network having several generating stations, substations and load centres is controlled from central load despatch centre. Digital or voice signals are transmitted over the transmission lines via the substations. The substations are linked with the load control centres via Power Line Carrier System (PLCC)/ microwave links and P&T phones. The data collected from major substations and generating stations is transmitted to the load control centre. The instructions from the load control centres are transmitted to the

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control rooms of generating stations and substations for executing appropriate action. Modern power system is controlled with the help of several automatic, semi-automatic equipments. Digital computers and microprocessors are installed in the control rooms of large substations, generating stations and load control centres for data collection, data monitoring, automatic protection and automatic control.

viii) Protective Systems in Substations

A fault in its electrical equipment is defined as a defect in its electrical circuit due to which the flow of current is diverted from the intended path. During the fault the impedance is low and fault current is high. Fault currents being high, can damage the equipments thro’ which it flows.

Fault in certain important equipment can affect the stability of the power system. For example, a fault in the bus zone of a substation can cause tripping of all the feeders and can affect the stability of the interconnected system.

The relays distinguish between normal and abnormal condition. Whenever an abnormal condition develops, the relay closes its contacts. Thereby the trip circuit of the circuit breaker is closed. Current from the battery supply flows in the trip coil of the circuit breaker and the circuit breaker opens and the faulty part is disconnected from the supply. The entire process, ‘occurrence of fault-operation of relay opening of circuit breaker to removal of faulty part from the system’ is automatic and fast. Besides relays and circuit breakers, there are several other important components in the protective relaying scheme, these include : protective current transformers and voltage transformers, protective relays, time delay relays, auxiliary relays, secondary circuits, trip circuits, auxiliaries and accessories, etc. Each component is important. Protective relaying is a team work of these components.

The function of different substation equipments and systems are tabulated below in Table -5.

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Table 5: Functions of different Substation Equipments & Systems Sl.

No.

Equipment Function

1. Bus-bar Incoming and outgoing circuits connected to bus-bar 2. Circuit-breakers Automatic switching during normal or abnormal

conditions. 3. Isolators

(Disconnectors)

Disconnection under no-load condition for safety, isolation and maintenance.

4. Earthing Switch To discharge the voltage on dead lines to earth. 5. Current

Transformer

To step-down currents for measurement, control, and protection.

6. Voltage Transformer

To step-down currents for measurement, control, and protection.

7. Lightning Arrester (Surge Arrester)

To discharge lightning over voltage and switching over voltage to earth.

8. Shunt reactor To provide reactive power compensation during low loads.

9. Series Reactors To reduce the short-circuit current or starting currents. 10. Neutral-Grounding

Reactors

To limit the earth fault current

11. Coupling capacitor To provide connection between high voltage line and power line carrier current equipment.

12. Line-trap To prevent high frequency signals from entering other zones.

13. Shunt capacitors To provide compensations to reactive loads of lagging power factors.

14. Power Transformer To step-up or step-down the voltage and transfer power from one AC voltage to another AC voltage at the same frequency.

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16. Substation Earthing (Grounding) System -Earth mat -Earthing spikes -Earthing risers

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.

17. Overhead earth wire shielding or lightning Masts.

To protect the outdoor substation equipment from lightning strokes. 18. Illumination system (lighting) -for switchyard -buildings -roads, etc.

To provide illumination for vigilance, operation and maintenance. 19. Protection System -protection relay panels -control cables -circuit-breakers -CTs, VTs, etc.

To provide alarm or automatic tripping of faulty part from healthy part and also to minimise damage to faulty equipment and associated system.

20. Control cabling For protective circuits, control circuits, metering, circuits, communication circuits.

21. Power cables To provide supply path to various auxiliary equipment and machines.

22. PLCC system power line carrier current system -line trap

-coupling capacitor -PLCC panels

For communication, telemetry, tele-control, power line carrier protection etc.

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23. Fire fighting system -sensors, detection system -water spray system -fire protection control 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 pin-point location of fire by indication in control room. 24. Cooling water system(HVDC) -coolers -water tank -piping -valves

This system is required for cooling the valves in HVDC substation. 25. Auxiliary stand by power system -diesel generator sets -switchgear -distribution system

For supplying starting power, stand by power for auxiliaries.

26. Telephone, Telex system, Microwave system

For internal and external communication.

1.9 Substation Layouts, Busbar Schemes

The term layout denotes the physical arrangement of various components in the substation relative to one another. Substation layout has significant influence on the operation, maintenance, cost

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and protection of the substation and these aspects are considered while designing the substation layout.

The reasoning behind the connections of components in each circuit and the busbars layout should be understood. Within the frame-work of the basic requirements, the substation layout can have several alternative arrangements. The substation layouts are selected on the basis of the size, the ratings, importance, local requirements and the prevailing practice of the supply authorities. The different bus-bar schemes in a substation with their relative advantages/disadvantages are described below:

The choice of busbar schemes for AC yards depend upon several factors mentioned above. The important busbar schemes include the following:

 Single busbar

 Double busbar with one breaker per circuit.  Double busbar with two breakers per circuit.  Main and transfer bus

 Ring bus

 Breaker and a half arrangement  Mesh arrangement etc.

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Table : 6 Various Bus-Bar Schemes Sl.

No.

Scheme Application Remarks

1. Single bus-bar Low voltage and medium voltage substations

Not preferred for important/ large substations

- Cheapest

- Total shutdown in case of a fault

- In case of maintenance of circuit breaker, associated feeder has also to be shut down

2. Duplicate Bus High voltage substations - Costlier than single bus - One bus can serve as a

reserve.

- During maintenance or fault, the reserve bus is used

- More flexibility of operation - Buses are sometime

sectionalised & the bus

coupler breaker is

connected in between two buses

3. Double Main and Transfer Bus

Important EHV substations - Additional flexibility for operation

- Fault on one bus will not cause a complete outage of the station.

4. Breaker & a half scheme

Important 400 kV

substations

- Uses three breakers for two circuits

- High flexibility operations - Higher costs

- Suitable for those substations which handle large amounts of power on each circuit

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5. Mesh System Used for large substations having many incoming and outgoing circuits.

- Costlier

- Gives good

operational flexibility

- Suitable where no. of circuits are comparatively few & chances of future expansion are less

1.10 Construction/Erection Drawings

Lists of construction/erection drawings used during Civil and other construction activities in a substation are enclosed at Annexure-3 and Annexure-4.

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Annexure-3

A. Control Room Building

1. Ground floor Plan & Elevators

2. Mezzanine Floor Plan & Elevations 3. Elevation, Section & Terrace Plan 4. Foundation Plan-Excavation drawing 5. Foundation & column up to first floor 6. Details of plinth beams

7. Mezzanine floor beams & reinforcement details 8. Mezzanine floor slab & reinforcement details 9. Mezzanine floor insert details

10. Lintel & Chhajja details

11. Roof slab reinforcemet details 12. Roof beam details

13. Roof slab insert details

14. Details of foundation for A/C plant room

15. GA & RCC details of foundation for cooling tower supporting structure 16. Internal cable trench details

17. Details of steel & window details 18. Aluminium glazing window details 19. Fire resistance door/siding door details 20. Details of toilet & pantry

21. Plumbing details 22. Details of septic tank 23. Finish schedule

24. Colour scheme

25. Electrical wiring drawings

B. DG Set Building

1. Plan elevations and sections

2. Foundation layout and RCC details of slab flooring, columns, beams. 3. Details of brick wall foundation, columns and intel.

4. Details of doors and windows.

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6. Colour scheme and misc. details, monorail fixing details. 7. Electrical wiring, insert fixing details.

C. F.F. Pump House

1. Plan, elevation and sections

2. Foundation layout, RCC details of slab, footing, column beam. 3. Terrace plan and Misc. Details.

4. Details of water tanks.

5. Details of doors, window, ventilators and rolling shutters.

6. Equipment foundation, cable trench layout and reinforcement details. 7. Electrical wiring drgs., insert details.

D. Internal Roads and Drains

1. Layouts of internal roads and drains.

2. Layouts and cross sectional details of roads and drains. 3. Layout of culverts and drains.

4. Details of culverts and drains.

E. Boundaries Wall and Fencing

1. Boundaries wall and fencing details 2. Fencing and gate details

F. Shunt Reactors

1. GA and foundation details. 2. Pylon support details

G. Auto Transformer

1. GA and RCC details of foundation, General arrangement 2. Pylon support details

3. Details of rail track

4. Fire protection wall between auto-transformer

H. Approach Roads and Drains

1. Layout of approach roads and drains. 2. Layout and C/S details of roads and drains. 3. Layout of drains and culverts

4. Details of culverts and drains.

I. Site Office and Store Complex

1. Material store plan, Elevation and sections 2. Crane store plan, Elevationa and Sections.

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3. Site office plan, Elevation and sections. 4. S/S store Plan, Elevation and sections. 5. Cement store Plan, Elevation and sections. 6. Details of raised platform.

7. Store complex layout plan. 8. Store complex TL material store. 9. Store complex TL material store.

10. Crane store foundation plan, roof plan and beam details. 11. S/S store foundation plan, roof plan and beam details. 12. Cement store foundation plan, roof plan and beam details 13. Details of entrance gate and fencing

14. Type section of tabular truss. 15. Details of doors and windows.

16. Finish schedule of site office and store complex. 17. Layout ext. drainage and sewerage system 18. Details of septic tank and soakpit.

19. Toilet and kitchen detail-site office 20. Toilet and kitchen details-S/S. store

J. Structural arrangement

1. Design of towers and beams

2. Fabrication drawings of tower & beams 3. Tower foundation and their designs 4. Design of equipment supporting structure

a) CT

b) CVT

c) LA

d) Bus Post Insulator e) Isolator

f) Wave Trap g) Circuit Breaker

5. Equipment supporting structure fabrication drawings

a) CT

b) CVT

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d) Bus Post Insulator e) Isolator

f) Wave Trap g) Circuit Breaker

6. Details of foundation bolts a) Equipment Structure b) Gantry Structure

7. Design of equipment foundations & foundation details 8. Cable trench layout

9. Cable trench section details 10. Cable trench road crossings 11. Marshalling box foundation 12. Sump pit

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List of construction Drawings for Township Work in a typical Sub-station A. Quarters for Type A,B, C and D

1. Architectural plan, Elevation 2. Architectural section, terrace plan 3. Foundation plan, Plinth beam layout 4. Details of foundation

5. Details of roof slab, first floor slab, lintel etc. 6. Electrical layout

7. Sanitary layout and plumbing details

A. Master Layout

1. Plan

2. Electrical layout 3. Sewerage layout 4. Plumbing layout

5. Layout of drains and road.

B. Overhead and underground Water-Tank

1. Architectural Drawings’ 2. Structural details 3. Foundation Details

C. Non Residential Buildings

(Nursery school, Dispensary and shopping centre) 4. Architectural plan and Elevation

5. Structural Details 6. Services

D. Administrative Building

7. Architectural plan and Elevation 8. Structural details

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Annexure-4

List of drawings for a typical Sub-station A. Sub-Station Drawings

1. Single line diagram

2. General arrangement of substation’ 3. Electrical layout (Plan and Section) 4. Electrical clearance diagram

5. Switchyard structural layout arrangement 6. Layout of equipment structures

7. Busbar support design and design calculations 8. Cable trench layout and foundation plan

9. Details of cable trench section 10. DSLP calculation

11. Drawing of DSLP scheme 12. Earthmat design calculation

13. Equipment/structure earthing details

(List all relevant drawings, under this heading) a) Earthmat layout

b) Erection key diagram (Plan and Section) c) Bill of Quantity

14. Short circuit force and critical span calculation(for spacers) 15. Design calculation for sag-tension and stringing chart 16. Power cable schedule

17. Inter pole cable schedule 18. Buried cable trench layout 19. OGA drg. for bus post insulator

20. Individual insulators detail drg. for bus post insulator 21. Detail drg. for bottom & inermediate flanges

22. Cap detail drg. for bus post insulator 23. Corona ring for bus post insulator 24. GA of bay marshalling kiosk

25. Schematic & wiring diagram of bay marshalling kiosk

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27. 120KN antifog disc insulator GA drg. 28. Clamps, connectors and spacers GA drg. 29. ACSR conductor, Al tube & shieldwire 30. GTP data sheets

31. Cable trays GA drawing

32. GA drg. for double compression type cable gland 33. Drum drg. for ACSR conductor and earthwire

B. 245KV SF6 Circuit Breaker

1. Outline general arrangement drawing of C.B. indicating major parameters. 2. Outline general arrangement drg. of control cabinets and their foundation plan

and separate drawing showing component layout. 3. Outline general arrangement drg. of support insulator.

4. Interrupter insulator, insulator & insulator for grading capacitor showing clearly the shed profile and parameters.

5. Support structure and foundation plan drawing with necessary support structure design calculations.

6. Electrical schematic diagram including brief write up on operation. 7. Rating and name plate drawing.

8. Air/SF6 gas connection diagram

9. Schematic diagram of electro hydraulic operated mechanism in case of hydraulic drive.

10. Wiring diagram

11. Terminal conenctor and corona ring drawings 12. Sectional view of SF6 gas couplings.

13. Sectional view of interruptor, voltage grading device identifying each part of the assembly.

14. Following additional drawings for Unit air compressor: a) Foundation plan and details for compressor and motor b) Unit of contact manometer assembly.

C. 245KV Isolator

1. Outline drawing of isolators with one E/S 2. Outline drawing of isolators with two E/S 3. Outline drawing of isoaltor without E/S 4. General arrangement of contact assembly.

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5. Terminal pad and hinge contract. 6. Loading data.

a) GA of motor operated mechanism b) GA of support insulator

7. Details of constructional interlock 8. Name Plate details

9. Drawings for terminal connector & corona rings. 10. Drawing for base frame.

11. Schematic drawings.

12. Wiring diagram & inerpole connection diagram.

13. Drawing for motor operated mechanism/manually operated mechanism, as applicable with door open and identifying all parts of the mechanism and the control panel.

14. Drawing for support structure.

D. 245KV Current Transformer

1. Outline drawing of C.T. indicating major parameters. 2. Sectional view of C.T.

3. OGA of marshalling box

4. OGA of secondary terminal box

5. Wiring diagram of marshalling box(including interpole wiring). 6. Magnetisation curve.

7. Name plate.

8. Drawing of terminal connectors. 9. Drawing of corona ring.

10. Drawing for stool/sub-structure, if applicable. 11. Drawing for support structure.

E. 245KV Capacitor Voltage Transformer

1. Outline drawing of CVT indicating major parameters. 2. Sectional view of CVT.

3. OGA of secondary terminal box. 4. OGA of marshalling box.

5. Wiring diagram of marshalling box (including interpole wiring) 6. Drawing for terminal connectors

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8. Drawing for stool/sub-structure, if applicable. 9. Drawing for support structure.

F. 245KV Class Surge Arrester

1. OGA of Surge Arrester indicating major parameters. 2. Foundation details.

3. Insulating base drawing.

4. Discharge counter/surge monitor drawing 5. Method of connecting surge monitor with SA 6. Electrial schematic diagram of surge monitor 7. Ground terminal bracket details

8. Name plate drawing

9. Line teminal bracket drawing along with corona rings 10. Residual voltage verses discharge current curves 11. Drawing for stool/sub-structure, if applicable 12. Drawing showing internal view of SA

13. Drawing of Insulator

14. Drawing showing pressure relief arrangement 15. Support structure drawing.

G. Power and Control Cables

1. Data sheet of all types of power cables 2. Data sheet of all types of control cables 3. Power cable schedule

4. Control cable sizing/section criteria

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List of Drawings for Erectin of C&R panels in a typical Sub-Station

1. Data requirement sheet with literature. 2. Type test report for all equipments.

3. Board formation redrawings. 4. Foundation details.

5. General arrangement of control panel/feeder. 6. General arrangement of relay panel/feeder. 7. Schematics of control panel/feeder.

8. Schematics of relay panel/feeder. 9. Cable schedule.

a) Inter panel schedule. b) Cable laying schedule. c) Cable terminating schedule. 10. Equipment layout drgs. 11. Relay settings.

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List of drawings for Erection of PLCC panels in a typical Sub-Station

1. Data requirement sheet with literature. 2. Type test report for all equipments. 3. General arrangement of PLCC system. 4. Equipment drgs.

a) PLCC panel for speech and data. b) PLCC panel for speech and protection. c) Protection couplet.

d) Wave Trap. e) Coupling Device. f) EPAX

g) 4 wire/2 wire Telephone 5. Frequency Plan

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Chapter-2

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CHAPTER TWO

SWITCHYARD CIVIL WORKS

2.0 Introduction

Civil works in a substation mainly comprise of :

 Construction of equipment foundations transformer/reactor plinth, structure foundations

 Cable trenches

 Fencing around switch yard

 Surface treatment, ground filling and sloping  Water supply system & Sewerage system  Construction of roads and drains

 Construction of control room building, compressor room, offices, repair / maintenance bay and other non-residential buildings

 Construction of railway, siding and railway track if required  Construction of residential colony

 Horticulture works

 Administrative Building, community centre, guest house/transit Camp, shopping complex & nursery school etc.

For carrying out the various civil works at site which is initially an open barren/cultivated land, initially survey of land is carried out alongwith the soil investigation. Survey is done to finalise the levels of switchyard, roads and design & layout of drainage system in the switchyard as well as in the township. Fix & permanent bench mark is provided for adopting it as a reference point for various works like laying out of control room, erection of gantries and various equipments, foundations and buildings in the switchyard that are done in reference to this permanent bench mark. Now grid lines are required to be marked in East-West and North-South direction by erecting the concrete grid

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pillars. Grid lines are marked on the land to fix the direction & orientation of various civil structures with reference to some fixed bench mark on the site. These gridlines help in implementing the erection, orientation and layout of foundations for various equipments & control room building which is later on helpful in laying out the other equipments and structures on the land.

2.1 Soil Investigation

 Soil investigation is carried out at site and result of soil investigation are forwarded to Corporate Centre for design of various foundations.

 Detailed soil investigation is carried out at site to arrive at sufficiently accurate, general as well as specific information about the soil profile and necessary soil parameters of the site in order that the foundations of various structures can be designed and constructed safely & rationally.

 The soil investigation tests should be conducted at all the critical locations i.e. control room building, auto transformer, shunt reactor, lightening masts, 400 KV tower locations etc.

 Engineering department at Corporate Centre prepares the foundation drawings and approved drawings are sent to site for casting.

 Engineering Department also releases various other erection drawings for different works like cable trench design drawings, cover slab design drawings, overall layout of equipments in switchyard, equipments erection key drawings etc. for erection works at site. During this period, the site levelling work is carried out at site in order to smoothen the undulations.

2.2 Levelling

The land acquired for substation may be barren/cultivated land. The soil may be rocky, black cotton, sandy or any other type. The acquired land may contain trees, bushes, crop, drains, etc. that require cleaning/ clearing before starting the levelling works in the yard.

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i) Switchyard area is important and preferably it should be brought to a single level. However, in only unavoidable circumstances or where it is uneconomical to go for levelling the soil than keeping a multi-layered/in steps levels, the different levels may be kept.

ii) Levelling may also be required in township area for bringing the land to a single level for designing the drainage system and residential quarters. In case of too much level difference the residences (categories) may be designed at different uniform levels but with good drainage system to avoid water logging.

iii) Before starting the levelling works the marked area of switchyard is cleaned. Any crop, bushes, trees, shrubs and structure that may cause hindrance or that are undesired are cleared from the yard area.

iv) Any drain, telephone line, building structure is also removed from the switchyard area, to a nearby suitable place.

v) Now spot levels will have to be taken in the yard area before making an assessment for the levelling i.e. for assessing the requirement of soil for low level areas and cutting of soil from high level area to bring the whole yard area to a normal formation level. vi) In the ideal case of levelling there is no requirement for borrowed

earth and quantity of earth excavated from the high level and fill it in the low lying areas is equal. This is the most economical method of levelling. Care is to be taken such that the earth is not excavated below the formation level.

vii) For compaction earth is filled in the low lying areas in layers of 20 cm thickness then watered and compacted by rollers/ dozers.

viii)The method and equipment used to compact the fill material to a density that will give the allowable soil bearing pressure required for the foundations, roads, etc. In each layer of fill material. Each layer of earth embankment when compacted should be as close to optimum moisture as practicable. Embankment material which does not contain sufficient moisture to obtain proper compaction should be wetted. If the material contains an excess of moisture, then it should be allowed to dry before rolling by hand rollers/dozers. No compaction is carried out in rainy weather.