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Modernization and Digitization in Power Grid Sub-Stations– The Prime tool for Multi Objective Optimization Methods.

Prashanta Kumar Pattanaik

Abstract


All Grid Sub-stations has four sections to control, operate and protect the large gamut electrical Power for its smooth flow till to the end customer.

1.      Generation, Loading, Conversion and Carrier Devices: We have generators as generation device, Motors and other electrical equipment as Loading device, Transformers as conversion device and Electrical Conductors as Carrier device. On technology front in this section, we have not experienced much technological changes. Only the economical size as per the situational requirement has been changed on its design.  

2.      Primarily Devices: Circuit Breakers and Isolators are grouped under this section, focused for the operation and control on situational practices. The best and suitable technology on its design has been focused on its compact size, keeping these devices in side insulated gas, we call it as GIS (Gas Insulated Sub-Station).

3.      Sensors: Current and Voltage transformers (CT & VT) are grouped under this section that monitor and protect electrical current and voltage during normal and abnormal conditions. We have experienced remarkable change on this technology starting from Copper to Fiber concept. The conventional principle is of electromagnetic Induction, involved with heating due to iron loss, copper loss and quick deterioration and severe damage consequences. The recent technology is focused with fiber optic transformers that work on the principle of total polarization of light with easier connectivity to advance digital systems.

4.      The Processing Devices: This is the integration platform, where all the Sub-station devices get connected to the operators’ desk/panel to attend the functions like Monitoring, Supervision, Control, Operation and also protection in easier possible way.

We have emerging technologies that grouped under modernization and data management that grouped under digitization. Both these modernization and digitization can attain our prime focus in electrical system to achieve the Power with Quality, Reliability, Safety and Security (PQRS).

OPTCL (Odisha Power Transmission Corporation Limited), the backbone of Odisha Power System, the strategic link between Power Generation and Distribution. We have already complied our vision document in five-year business plan, emphasizing quick adoption of modernisation and digitisation in our system. Many of the initiatives enlisted in the vision document have already hit the road of success. Still to come with a long way in improving the standards of performance of OPTCL and to enhance its brand image.


Keywords


Modernization, Digitization, PQRS, Sub-Station Automation, Grid sub station

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References


Abstract:

All Grid Sub-stations has four sections to control, operate and protect the large gamut electrical Power for its smooth flow till to the end customer.

Generation, Loading, Conversion and Carrier Devices: We have generators as generation device, Motors and other electrical equipment as Loading device, Transformers as conversion device and Electrical Conductors as Carrier device. On technology front in this section, we have not experienced much technological changes. Only the economical size as per the situational requirement has been changed on its design.

Primarily Devices: Circuit Breakers and Isolators are grouped under this section, focused for the operation and control on situational practices. The best and suitable technology on its design has been focused on its compact size, keeping these devices in side insulated gas, we call it as GIS (Gas Insulated Sub-Station).

Sensors: Current and Voltage transformers (CT & VT) are grouped under this section that monitor and protect electrical current and voltage during normal and abnormal conditions. We have experienced remarkable change on this technology starting from Copper to Fiber concept. The conventional principle is of electromagnetic Induction, involved with heating due to iron loss, copper loss and quick deterioration and severe damage consequences. The recent technology is focused with fiber optic transformers that work on the principle of total polarization of light with easier connectivity to advance digital systems.

The Processing Devices: This is the integration platform, where all the Sub-station devices get connected to the operators’ desk/panel to attend the functions like Monitoring, Supervision, Control, Operation and also protection in easier possible way.

We have emerging technologies that grouped under modernization and data management that grouped under digitization. Both these modernization and digitization can attain our prime focus in electrical system to achieve the Power with Quality, Reliability, Safety and Security (PQRS).

OPTCL (Odisha Power Transmission Corporation Limited), the backbone of Odisha Power System, the strategic link between Power Generation and Distribution. We have already complied our vision document in five-year business plan, emphasizing quick adoption of modernisation and digitisation in our system. Many of the initiatives enlisted in the vision document have already hit the road of success. Still to come with a long way in improving the standards of performance of OPTCL and to enhance its brand image.

Keywords: Modernization, Digitization, PQRS, Sub-Station Automation, Grid sub station

Introduction:

Electrical Network is embracing the major disruptive changes. The substantial growth in all categories is making the situation bit complex due to huge approach of RE (Renewable Energy) and its integration with the ever-increasing load demands. Moreover, the inter-connected GSS (Grid Sub-Station) suffers the challenge of handling this complex power that flows in different directions aiming towards the system availability for 24×7 with multiple and multi-pattern generators, modern concept of prosumers with DER (Distributed Energy Resources) [1]. The other multi-bound practical issues make the situation still critical, like running the system with existing old-ageing infrastructures, reluctant approach of end users on the acceptance to the advanced technologies, their over-conscious approach to the techno-economical aspects etc… Energy utilities being the actual end users face the real junk of these challenges during the initial take off and acceptance of the innovative technologies.

Digital systems are becoming an integral part of the new electricity grid, which provides all the control parameters at the HMI (Human Machine Interface) screen for pro-active action towards proper regulation of voltage and other important parameters. The use of these digital system is gaining popularity both in transmission and distribution level. These systems are equipped with intelligent electronic devices, and smart monitoring and automated diagnostics features.

The EHV equipment condition is monitored continuously and evaluated for appropriate asset management decisions. Asset management needs to be both cost-effective and reliable, sensing solutions that provide asset managers with actionable intelligent data.

We have now some emerging Technologies for the focus towards Quality Power.

a. Internet of Things (IoT): Inter-connection of each device by digital code.

b. 4G & 5G Networks: High speed Data/ signal transfer capability

c. Big Data Technology: Data management on real time base and necessary control

a. Nanotechnology Sensors: Smallest detection link with transfer capability

b. Advanced Energy Storage: Devices for Energy storage for future use

c. Superconducting Technology: Efficient Electrical Energy Transfer

d. Solid State Transformers: Special technology for RE integration.

e. Smart Metering: AMI, AMR for Two-way metering scheme as energy index

f. WAM with PMU: Wide Area Monitoring with Phasor Monitoring System.[2-3]

g. Cyber Security Zone: Technology with code for safety security

h. Smart Equipment: Smart Equipment like CT/PT, Transformers, Breakers etc.

i. Smart Networks: FACTs, HVDC, SVC, EHVAC, HTLS system

(Power with Quality, Reliability, Safety and Security) should be considered as the prime thought for the engineers, technocrats, Product developers to enhance its application capability and capacity in real field use purpose.

Why Modernisation:

Initial days during 1950’s, the system was called Local network, restricted with the confined area vicinity to the generation being connected with small transmission line. Then development enters to the concept of State Grid i.e the networks got connected to the restricted state transmission with State generators during the 1960’s. The concepts of Regional Grid enter to the power sector system for the development of better stability during 1970’s and these concepts continues for a period of pretty long time from 1970’s to 2000. During the year 2000, the concept of National Grid [4-7]. originates and brings the revolution in the power sector regarding the stability and reliability. This concept also helps the right consumers to get right quality power of required quantity due to the origin of different power system models like OPEN ACCESS, ABT, UI mechanism etc.. So to maintain the qualitative and quantitative power to the consumers, new technologies have crawled to the power system and occupied the position of its application.

All electrical equipment’s have certain limit to work with the electrical parameters like Voltage and Current during normal working condition. These equipment’s are also designed with the capability to withstand for the abnormal parameters during the fault condition. In earlier days’ designers were not serious about the break-even point of the equipment among the cost, size and longevity of the product. The complexity of the electrical network was not there due to the local transmission of the circuit with limited consumers. But now the complexity has been developed, network has been extended to the national level being involved with large quantity of power transactions. So the quality, standard, and technology for the development the equipment has become the prime factors for the factors like cost, size and longevity. It is felt very important to use quality and upgraded electrical equipment’s in the system. So modernization finds its way to get involved in the system for the ease of the operation and control.

MODERN SUB-STATION EQUIPMENTS

In the following table we will learning more about Equipment’s and their developments. (Table 1)

Table 1: Different types of equipment’s.

Sl. Equipment/Items Developments

Surge Arrestor MOV Zinc Oxide Arrestor with Multi-stack type

Isolator Breaking at center point with electrical Interlock

Insulator Stack Composite Material Insulator

Wave Trap Inductive Reactance Trap with Anti-corrosion material

CVT Instrument with facility of both Potential Divider and coupling Capacitor

CT Top Tank Primary winding type CT, Combined CT& PT unit and Polycrete wound CT are the latest development

Switchgear Up to 36 KV VCB type with spring mechanism

Switch gear above 72 KV SF6 medium with spring spring mechanism

Transformer Maximum care on core , winding and insulation with protection control by TRANSFORMER MANAGEMENT RELAY

GIS (Gas Insulated System) Compact Grids,[8-12] equipped with EHV items in side Gas chamber

OTHER ADVANCE TECHNOLOGIES FOR SUB-STATION

• Enhancing the capacity of existing system

– Tr. asset management

– Enhancement of Thermal capacity

– Up gradation to higher voltage line

– Series Compensation (Fixed as well as TCSC)

– Static Var Compensator(SVC)

• State-of-the-Art maintenance techniques being practiced

– Hot Line Helicopter supervision

– Thermo-Vision Camera

– High Temp endurance conductor for increased Loading

– Multi-conductor Bundle line

– Satellite imagery for Transmission Line Survey (Survey through GIS/Digital Terrain Model/Airborne Laser Terrain Mapping (ALTM))

– Tall & Multi ckt Towers to avoid deforestation and protection of wild life

– Compact Tower / Pole Tower to reduce Right Of Way

– Substation Compaction to reduce land requirement

– Automation of Sub-stations

– Unified Load Dispatch & Communication centers at all region integrated with State-of-the-Art SCADA/EMS

Why Digital System

In practice, the better system operation always demands, the quick availability of signals at the interface point for detail processing and subsequent real time action execution. The quick availability of signals depends upon the medium/communication channel through which it is transmitted. Moreover, the risk of the signal loss or breakage is also another important reason of delay or failure of the work execution. In broad sense, this medium is considered as hardware type or software type. Say an example, transfer of signal in the form of energy pocket by the use copper wire is termed as the hardware signal. Transfer of signal by the wireless form or by use of fibre optics is termed as software type. The faster availability can be attained by software form and the possibility of loss or breakage of the signal is also less in this form. So continuation of the signal availability can help us for perfect actuation of the work management. We have the following advantages for digitisation of the process.

• Extensive self-diagnosis through sensors used in the system ensures the maximum up-time.

• Sequential seamless control and operation with interlocks for safety of equipment and working personnel.

• Increased system Reliability, Safety Security, and Efficiency.

• Optimisation of Transformer operation that reduces the operational and maintenance cost.

• Easy Data recording helps for improved measurement accuracy and subsequent Analysis for corrective action towards repair and maintenance.

• Reduction of Copper wire and possibility of signal loss due to looseness, breakage or short-circuit.

• Improved Communication capabilities like data exchange between intelligent devices intra and inter-substation.

• Better EMC performance and quick isolation of circuits as per requirement.

• Less or nil dependence on human beings

Basic Working Action:

Digital transformer system network largely contains three important areas (Hardware, Software and Process Application).

a. Hardware part is the primary device that used in the transformer to collect the system parameters for the application process at the CCS (Central Control Station). This basically are called sensors, transducers, converters, instruments etc fitted inside or outside of the transformer at the suitable region. In digital system we call it as AI (Analog Input).

b. Software part is the intermittent device that manages to convert the hardware signal to the scalable digital signal for readiness to the application purposes at the CCS. These include the device called A to D converter (Analog to Digital), Opto-couplers etc... The output of this software part reports directly to the process bus for the integration to the automation network. Now for perfect system operability a common communication is chosen and presently IEC 61850 is the protocol that interconnects all soft logics for seamless deliver towards reliability and efficiency of the device. In this digital system we call as BI or DI (Binary or Digital Input).

c. Application Process is the final process bus part of the system for real time action towards supervision, control and monitoring of the system. Built-in components like digital sensors, dissolved gas analysers and digital safety devices collect data for monitoring, diagnostics and control at the common house. The action of suitable control is extended by the signal called BI or DI (Binary or Digital Output)

Modern Applications:

Digital technologies are also being embedded by technology providers in different type of transformers, be it oil type or dry type. More relevant for the dry-type transformers, designed to work without oil, where the core and the coil are cooled by natural or forced air and non-flammable high grade solid insulation material. This makes them safer and more environmental friendly. Such transformers are ideally suited for high-risk applications such as in offshore and densely populated areas, and in sensitive ecosystems. In digitally enabled dry-type transformers, smart sensors collect data and combine them to provide powerful analytics. For the higher rating transformers, these sensors embedded digital response transformers could also be the best solution to monitor for proactive action towards its control and necessary action.

Digital technologies embedded robots now have reached to the field application for submersible transformer inspection which perform fast, safe and cost-effective internal inspection, reducing personnel risk and lesser down time with cost effective solution. Another advantage is that this could also be controlled wireless from remote center, maintaining point to point security control. Many other applications include like RTCC bank controller, Cooler Kiosk Controller by MCU (Motor Controller Unit), ON line DGA, Piezo-electric camera controller, On line condition monitoring etc... (Fig 1.)

DIGITAL SUBSTATION ARCHITECTURE.

This Digital Substation has a three level architect (fig 2):

• Process Level: The first is the process level, interfacing with the primary equipment in the switchyard.

• Bay Level: Second is the protection and control level, including IEDs (protection, measurement devices, bay controller, recorders, etc.).

• Station Level: Third, the station control level handles communication within the substation and control system, coordination with the substation operational functions and station-level support.

Fig 2: Parts of Digital Substation

PROCESS BUS

a. Electronic Fibre Optic CT and VT

A growing trend in the digital substation is the use of optical current and voltage transducers (called as non-conventional instrument transformers - NCIT). These devices operate by measuring changes in the optical performance of fibres in the presence of electric and magnetic fields. The transducers are able to measure both current and voltage. The Optical CT is composed of two parts, one in the switchyard, the optical primary sensor that senses the current in the HV line or the bar and the 2nd part is the secondary converter which is placed in the substation control room.The secondary converter comprises of the light source, sends light to primary sensor and processes the optical signal returned and then converts it into the appropriate output in order to interface with the connected IEDs. The link between the primary optical sensor and Secondary converter is fibre optics which may be as long as 1000 meters.

b. Merging Unit MU

The Merging Unit (MU) is the interface between physical analogue world to the digital, using secure and dependable communication network. The analogue signal from conventional Current Transformer and Voltage Transformer are converted in to digital signal and transmitted via Sample Value network communication protocol(IEC61850-9-2). Analogue Merging Unit (AMU) for converting only CT and VT information or Integrated Merging Unit (IMU) for converting both Analogue and digital information can be used.(fig-3)

c. Switchgear Control Unit (SCU):

Switchgear Control Unit brings forward the complete digital substation. It has been designed to be placed near primary equipment such as switching devices and helps minimize the cabling. It manages a remote set of extra binary input/output boards for the substation computer and other IEC 61850-8-1- compatible IEDs, such as protection IEDs for instance. It acquires binary values from primary devices such as switchgear and forwards them to the substation computer and/or IEDs over the Ethernet Process Bus.

BAY LEVEL

In the digital substation, bay level devices are IEDs (intelligent electronic devices), interacting with the field via the process bus, and with other peer devices in the bay, to other bays, and the digital control system via the station bus. In a fully-digital architecture, protection relays receive currents and voltages as IEC 61850-9-2 sampled values, and issue trip or alarm signals using IEC 61850-8-1 GOOSE. The protection relay should have following qualities in a digital substation[13-17].

TIME SYNCHRONISATION;

Accurate timekeeping is a critical need of the digital substation. This not only guarantees that the protection functions are activated at the appropriate times, but it also synchronises substations at different places so that event and operation records can be compared and trip events can be analyzed.

COMMUNICATION:

The back bone of this digital project is Ethernet communication over TCP/IP as per standard IEC 61850. The IEC61850 international standard for communications in substations has brought a new era in the development of substations. It affects not only the design of the substation protection, monitoring and control system, but also the design of the substation secondary circuits. IEC61850 is a part of the International Electrotechnical Commission (IEC) Technical Committee 57 (TC57) architecture for electric power systems.

ETHERNET SWITCH:

The switch for digital substation must connect all the elements needed for the IEC 61850 substation. It must be modular, flexible and robust to work satisfactory in substation environments.

STATION BUS COMMUNICATION:

The station bus digital substation has manifold tasks, it permits multiple clients to exchange data, supports peer-to-peer device communication, and links to gateways for inter-substation wide-area communication. GOOSE (Generic Object Oriented Substation Event) is used as high-speed exchange of binary status information/commands.

Digital Control System (DCS)

The Digital Control System DCS is the intelligence which binds together the digital substation. It is central to the flow, management and presentation of all components in the digital substation.

DIGITAL SUBSTATION PILOT PROJECT IN OPTCL (ODISHA POWER TRANSMISSION CORPORATION LIMITED)

One digital substation pilot project has been implemented in three numbers of 33kV bays of 220/33kV Grid [18-19]Substation Chandaka. The project has been done by Alstom T & D, India. Following digital technology are used. Fig 4

• OPTICAL Current transformer in one bay.

• Conventional CT with Analogue merging unit in two number bays.

• Time synchronization using Precision Time Protocol (IEEE 1588 v2)

• Process bus technology (Sampled Value) using networked connection.

• Conversion of optical signal of Optical CT to analogue signal for measurement in conventional of energy meter.

The system was successfully commissioned on 30th August’2016.

Acknowledgement:

Authors would like to extend their hearty gratitude to AICTE to carry out this research

against grant of National conference (OEOGP-2021), vide F.No.-67/IDC/GOC/POLICY -

/2020-21, (AQIS ID-1-9345546836) to the Department of EE, GITA, Bhubaneswar.

Conclusion

The transmission utility face increasing challenges from evolving energy markets, aging infrastructure, transmission bottlenecks, renewable integration, cyber security threats, tighter regulatory oversight, and complexities of modern transmission equipment. When coping with unanticipated outages, utility companies find themselves in a race against time and a struggle against data – to restore safe, dependable, and efficient electricity to their consumers as well as key buildings and infrastructures. Fortunately, technical advancements like the ones mentioned above, when correctly applied, can assist in maintaining grid reliability, stability, and security at a reasonable cost.

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