Substations are the key assets in any power system and serve as important nodes in a transmission and distribution network. Substations thus handle multiple voltages in a given location and link two or more systems of different voltages. In the first part of this two part certificate series, the participants were given a thorough understanding of the basic principles of substation design, configuration of a substation, the specification/selection of equipment based on a selected configuration, conducting system studies to verify/correct the initial assumptions and to plan the layout of the substation.

In this part, the focus will be on the other subsystems that perform essential functions in substations. These include earthing, lightning protection of outdoor equipment and substation buildings, power system protection, control and interlocking equipment including the auxiliary power sources and various switchyard facilities such as foundation, structures, cable routing, lighting, fire protection and surveillance equipment.

Earthing of a HV switchyard requires careful design as it has a direct bearing on safety. The design approach to switchyards will be discussed and the basic methods of calculation will be outlined. Lightning is a common occurrence which poses a threat to substation equipment and supply reliability by causing overvoltage surges resulting in insulation failure or spark over. While lightning cannot be prevented, its effects can be minimised by proper lightning and surge protection measures.

Any electrical equipment is susceptible to insulation failures. Protection against such failures and the resulting short circuits is a vital need in power systems. The various protection options available to the designer and the protection of busbars, transformers and substation feeders will be discussed in two parts. Another essential system is the control of switchyard equipment and the auxiliary power supply required for control. Ac auxiliary power is generally used for operation of isolators/disconnectors, the operating mechanism of circuit breakers and for substation lighting. Essential functions are powered through dc supply backed with batteries for reliability. This includes control, annunciation and protection functions, breaker close and trip commands and in some cases emergency lightning.

A switchyard has to be properly planned by preparing the site, measuring earth resistivity required for earthing design/optimisation, earth work, foundations, cable trenches inside the switchyard, draining arrangements etc. These aspects will be covered in detail in a separate module. The last module will discuss about gas insulated switchgear as an alternative to outdoor open type switchyards.

All the above topics will be dealt in this course using a simple step-by-step approach through real life examples. At each step, the basic design approach and calculations will be performed by the students to clearly understand the concepts that are being taught.

There will be 12 modules covered in over 3 months to give the students adequate time to try and apply the concepts learnt in the modules in the context of their workplace and discuss them with the course facilitator. The contents and sequence of the modules can be seen in the course outline.

YOU WILL LEARN HOW TO:

  • Perform the design of substation earthing so as to ensure safety of personnel and equipment under all conditions
  • Design appropriate protection against the direct and indirect effects of lightning strikes on substations and the incoming/outgoing overhead lines
  • Select and apply appropriate power system protection to protect equipment and personnel from abnormal system conditions including short circuits and earth faults
  • Determine the auxiliary power requirements and perform sizing calculations for the battery backup of essential dc power supply
  • Understand the requirements for site preparation, foundations, structures, cable trenches and draining arrangements to effectively coordinate with design teams of related disciplines
  • Select and apply gas insulated switchgear if outdoor type HV substations cannot be used due to any site-related constraints and adjust the other design elements to suit this option

Course Outline

MODULE 1: EARTHING SYSTEM OF SWITCHYARDS

  • Basics of functional and protective earthing
  • Touch and step voltages in substations
  • Design of earth grid-basic considerations in conductor sizing and mesh spacing
  • Safety mesh at operating points
  • Role of gravel layer in safety
  • Transferred voltage hazards and planning isolation of outgoing services to avoid transfer voltage

MODULE 2: EXAMPLE OF SWITCHYARD EARTHING SYSTEM DESIGN

  • Based on the layout and data of a given HV switchyard:
  • Perform earthing calculations including sizing of earthing conductors
  • Calculate the earth mesh size for the switchyard
  • Develop a layout for the mesh and show the other connections required to avoid transferred voltages
  • Show the size of safety mesh to be provided and the operating points on the layout
  • Draw up the installation specification for the earthing system

MODULE 3: LIGHTNING PROTECTION OF SWITCHYARDS

  • Basics of lightning and hazards
  • Role of shield wire and lightning masts
  • Typical configurations of lightning protection of switchyards
  • Analysis of hazard using cone of protection and rolling sphere methods
  • Selection of lightning arrestors-Types, class and ratings

MODULE 4: EXAMPLE OF SWITCHYARD LIGHTNING AND SURGE PROTECTION DESIGN

  • Design the lightning protection of a typical HV switchyard based on a given layout and analyse the adequacy of protection
  • Locate and select surge protection (lightning arrestors) of the above HV switchyard

MODULE 5: PROTECTION DESIGN FOR SUBSTATION-1

  • Brief overview of protection
  • Over current protection
  • Current transformers requirements for protection
  • Protection relays
  • IEDs and communication options
  • Protection coordination

MODULE 6: EXAMPLES/CASE STUDIES OF MV SUBSTATION PROTECTION

  • Based on the data/SLD for a typical MV substation work out:
  • Suggested protective devices for over current and earth fault
  • Suggested settings
  • Select the specifications of CT and VT
  • Checking of CT burden
  • Protection coordination checking
  • Explore substation automation system using IEDs provided for protection
  • Prepare an ordering specification

MODULE 7: PROTECTION DESIGN FOR SUBSTATION-2

Protection of transformers
Busbar protection
Feeder protection
Equipment requirements for substation automation
PLCC applications in protection and communication
PLCC hardware and integrating them with the switchyard equipment

MODULE 8: EXAMPLES/CASE STUDIES OF HV SUBSTATION PROTECTION

  • Using the data/SLD of a typical HV outdoor switchyard, work out the following:
  • Suggested protection schemes for all the feeders of the switchyard, its busbars and transformers
  • Explore use of PLCC for line protection and communication
  • Prepare an ordering specification for protection equipment

MODULE 9: SWITCHYARD CONTROL AND INTERLOCKING

  • DC power requirements for switchyard equipment
  • DC equipment configuration and specifications
  • DC distribution for switchyard equipment
  • Battery calculations basis
  • Space planning and related facilities for a battery installation
  • AC auxiliary power for switchyard systems-loads which require AC power
  • Possible source options
  • AC auxiliary distribution for switchyard equipment and support systems
  • Control scheme of disconnectors and circuit breakers
  • Control interconnection approach
  • Use of optical fibre-based control scheme
  • Role and location of marshalling kiosks in different bays

MODULE 10: EXAMPLE CASE  STUDY OF DESIGN OF HV SUBSTATION CONTROL AND AUXILIARY SYSTEMS

  • Based on the data of typical substation with both HV and MV switchgear, work out the following:
  • DC auxiliary requirements
  • Battery sizing calculation
  • DC auxiliary equipment and their ratings
  • DC distribution SLD
  • Layout of dc equipment
  • AC auxiliary power requirement
  • Sources and rating
  • AC auxiliary system SLD
  • Layout of auxiliary switchgear
  • Interconnections of AC and DC auxiliary power and switchyard controls

MODULE 11: SWITCHYARD-FACILITY PLANNING

  • Site preparation, levelling
  • Earth resistivity measurement and its role in design verification
  • Civil works such as equipment foundations, cable trenches, control building, storm drains, transformer oil collection pit
  • Structures and their design requirements
  • Substation fence and physical security
  • Surveillance
  • Planning water requirements and supply arrangement
  • Fire protection, lighting and ventilation of control room and other equipment

MODULE 12: GAS INSULATED SWITCHGEAR (GIS) AS AN ALTERNATIVE TO OUTDOOR SWITCHYARD

  • HV gas insulated substation-an alternative to outdoor HV switchyards
  • SF6 properties, advantages and environmental impact
  • Typical substation configurations in SF6
  • Indoor/outdoor options
  • Gas safety considerations
  • Equipment for handling SF6
  • SF6 substation layout planning and earthing considerations
  • Cable terminations to SF6 equipment

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