Since the loads having the trends towards growing density. This requires the better appearance, rugged construction, greater service reliability and increased safety. An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. The interference from external disturbances like storms, lightening, ice, trees etc. should be reduced to achieve trouble free service. The cables may be buried directly in the ground, or may be installed in ducts buried in the ground.
This Presentation is about l.v switch gear design, presented during the graduation project final discussion 15/7/2018.
It presented a good summary of switch gear components and types and practicing on AL.HAMOOL W.T.P M.D.B design using SIEMENS SIVACON S8
This Presentation is about l.v switch gear design, presented during the graduation project final discussion 15/7/2018.
It presented a good summary of switch gear components and types and practicing on AL.HAMOOL W.T.P M.D.B design using SIEMENS SIVACON S8
Modern underground power cables are sophisticated assemblies of insulators, conductors and protective materials. Within these components are sensors, which enable cable operators to monitor conditions along the cable in real time.
The condition of the cable insulation is usually monitored through the following two main methods:
Loss tangent measurements
Partial discharge (PD) measurements
About Transmission Line.
Transmission Lines
Classification Of Transmission Lines
Overhead Power Line
Advantages Of Overhead Transmission Lines
Disadvantages Of Overhead Transmission Lines
Nominal “T” Method
Nominal “Pi” Model of a Medium Transmission Line
Underground Transmission Lines
Classification Of Underground Cables
Advantages Of Underground Cables
Disadvantages Of Underground Cables
Underground cables are used for power applications where it is impractical, difficult, or dangerous to use the overhead lines. They are widely used in densely populated urban areas, in factories, and even to supply power from the overhead posts to the consumer premises.
The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs. However, they are more expensive to manufacture, and their cost may vary depending on the construction as well as the voltage rating.
The underground cables are classified in two ways; by the voltage capacity, or by the construction.
By Voltage
LT cables: Low-tension cables with a maximum capacity of 1000 V
HT Cables: High-tension cables with a maximum of 11KV
ST cables: Super-tension cables with a rating of between 22 KV and 33 KV
EHT cables: Extra high-tension cables with a rating of between 33 KV and 66 KV
Extra super voltage cables: with maximum voltage ratings beyond 132 KV
By Construction
Belted cables: Maximum voltage of 11KVA
Screened cables: Maximum voltage of 66 KVA
Pressure cables: the Maximum voltage of more than 66KVA
Construction of cables
Parts of a cable
Properties of cable insulators
Properties of conductors
Types of cables
Underground cables
Methods of laying underground cables
Types of cable faults
Comparison between overhead and underground cables
Insulation resistance measurements are performed to verify that the state of dryness of the insulation of the various Winding , Bushings and the core are of acceptable values. In these presentation we will discuss about basic Insulation resistance test carried out in a two winding transformer.
Modern underground power cables are sophisticated assemblies of insulators, conductors and protective materials. Within these components are sensors, which enable cable operators to monitor conditions along the cable in real time.
The condition of the cable insulation is usually monitored through the following two main methods:
Loss tangent measurements
Partial discharge (PD) measurements
About Transmission Line.
Transmission Lines
Classification Of Transmission Lines
Overhead Power Line
Advantages Of Overhead Transmission Lines
Disadvantages Of Overhead Transmission Lines
Nominal “T” Method
Nominal “Pi” Model of a Medium Transmission Line
Underground Transmission Lines
Classification Of Underground Cables
Advantages Of Underground Cables
Disadvantages Of Underground Cables
Underground cables are used for power applications where it is impractical, difficult, or dangerous to use the overhead lines. They are widely used in densely populated urban areas, in factories, and even to supply power from the overhead posts to the consumer premises.
The underground cables have several advantages over the overhead lines; they have smaller voltage drops, low chances of developing faults and have low maintenance costs. However, they are more expensive to manufacture, and their cost may vary depending on the construction as well as the voltage rating.
The underground cables are classified in two ways; by the voltage capacity, or by the construction.
By Voltage
LT cables: Low-tension cables with a maximum capacity of 1000 V
HT Cables: High-tension cables with a maximum of 11KV
ST cables: Super-tension cables with a rating of between 22 KV and 33 KV
EHT cables: Extra high-tension cables with a rating of between 33 KV and 66 KV
Extra super voltage cables: with maximum voltage ratings beyond 132 KV
By Construction
Belted cables: Maximum voltage of 11KVA
Screened cables: Maximum voltage of 66 KVA
Pressure cables: the Maximum voltage of more than 66KVA
Construction of cables
Parts of a cable
Properties of cable insulators
Properties of conductors
Types of cables
Underground cables
Methods of laying underground cables
Types of cable faults
Comparison between overhead and underground cables
Insulation resistance measurements are performed to verify that the state of dryness of the insulation of the various Winding , Bushings and the core are of acceptable values. In these presentation we will discuss about basic Insulation resistance test carried out in a two winding transformer.
This is the simple ppt explaining about the main components of the power systems. especially we are determining the insulators and its types with real time pictures which are attractive,
A Presentation based on Underground Cables Used In the Transmission And Distribution System.It is a topic covered in the syllabus of B.E. in Electrical Engineering in 5th semester Subject named "Electrical Power System" For more detail you can check the book "Electrical Power System" by Author V.K.Mehta and S.Chand Publication.
Underground transmission line:
The aim of this unit are to: Analyze the resistance,inductance and capacitance of underground transmission lines
t the end of this unit, you will be able to:
explain where Underground Cables are applicable and the Requirements of choosing underground cables in electrical networks
determine the values of C,L and R per unit length in underground electrical line
Select the right type of cable for a particular system based on the voltage to deliver
estimate the right parameters for a single core for a given transmission line
determine the current rating for a given network and also know how underground cables are installed
explain the method of testing, locating, confirming, and troubleshooting any fault in the underground cables for a given electrical network
Indicative resources:
Principles of power systems, by Mehta and Mehta
A_Textbook_of_Electrical_Technology_Volume_III
Electrical Power systems by Wadhwa
Power system Analysis by Weedy and Cory
Power system by Grainger and Stevenson
this ppt is base on construction of under ground cable. in this ppt i gave information the all type of insulation and its specification. and is advantages.
8 step-by-step processes of manufacturing of electrical cableDevanshVarma1
The manufacturing process of electrical wires and cables is complicated. If the manufacturers don’t provide good quality products, the wires will not be the perfect conductor to produce electricity.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
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The field of Information retrieval (IR) is currently undergoing a transformative shift, at least partly due to the emerging applications of generative AI to information access. In this talk, we will deliberate on the sociotechnical implications of generative AI for information access. We will argue that there is both a critical necessity and an exciting opportunity for the IR community to re-center our research agendas on societal needs while dismantling the artificial separation between the work on fairness, accountability, transparency, and ethics in IR and the rest of IR research. Instead of adopting a reactionary strategy of trying to mitigate potential social harms from emerging technologies, the community should aim to proactively set the research agenda for the kinds of systems we should build inspired by diverse explicitly stated sociotechnical imaginaries. The sociotechnical imaginaries that underpin the design and development of information access technologies needs to be explicitly articulated, and we need to develop theories of change in context of these diverse perspectives. Our guiding future imaginaries must be informed by other academic fields, such as democratic theory and critical theory, and should be co-developed with social science scholars, legal scholars, civil rights and social justice activists, and artists, among others.
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Essentials of Automations: Optimizing FME Workflows with ParametersSafe Software
Are you looking to streamline your workflows and boost your projects’ efficiency? Do you find yourself searching for ways to add flexibility and control over your FME workflows? If so, you’re in the right place.
Join us for an insightful dive into the world of FME parameters, a critical element in optimizing workflow efficiency. This webinar marks the beginning of our three-part “Essentials of Automation” series. This first webinar is designed to equip you with the knowledge and skills to utilize parameters effectively: enhancing the flexibility, maintainability, and user control of your FME projects.
Here’s what you’ll gain:
- Essentials of FME Parameters: Understand the pivotal role of parameters, including Reader/Writer, Transformer, User, and FME Flow categories. Discover how they are the key to unlocking automation and optimization within your workflows.
- Practical Applications in FME Form: Delve into key user parameter types including choice, connections, and file URLs. Allow users to control how a workflow runs, making your workflows more reusable. Learn to import values and deliver the best user experience for your workflows while enhancing accuracy.
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- Pro Tips for Success: Gain insights on parameterizing connections and leveraging new features like Conditional Visibility for clarity and simplicity.
We’ll wrap up with a glimpse into future webinars, followed by a Q&A session to address your specific questions surrounding this topic.
Don’t miss this opportunity to elevate your FME expertise and drive your projects to new heights of efficiency.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
JMeter webinar - integration with InfluxDB and GrafanaRTTS
Watch this recorded webinar about real-time monitoring of application performance. See how to integrate Apache JMeter, the open-source leader in performance testing, with InfluxDB, the open-source time-series database, and Grafana, the open-source analytics and visualization application.
In this webinar, we will review the benefits of leveraging InfluxDB and Grafana when executing load tests and demonstrate how these tools are used to visualize performance metrics.
Length: 30 minutes
Session Overview
-------------------------------------------
During this webinar, we will cover the following topics while demonstrating the integrations of JMeter, InfluxDB and Grafana:
- What out-of-the-box solutions are available for real-time monitoring JMeter tests?
- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
- Which features are provided by Grafana?
- Demonstration of InfluxDB and Grafana using a practice web application
To view the webinar recording, go to:
https://www.rttsweb.com/jmeter-integration-webinar
UiPath Test Automation using UiPath Test Suite series, part 3DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 3. In this session, we will cover desktop automation along with UI automation.
Topics covered:
UI automation Introduction,
UI automation Sample
Desktop automation flow
Pradeep Chinnala, Senior Consultant Automation Developer @WonderBotz and UiPath MVP
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
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Dev Dives: Train smarter, not harder – active learning and UiPath LLMs for do...UiPathCommunity
💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
See how to accelerate model training and optimize model performance with active learning
Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
This is a hands-on session specifically designed for automation developers and AI enthusiasts seeking to enhance their knowledge in leveraging the latest intelligent document processing capabilities offered by UiPath.
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👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
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Charlie Greenberg, Host
State of ICS and IoT Cyber Threat Landscape Report 2024 previewPrayukth K V
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State of global ICS asset and network exposure
Sectoral targets and attacks as well as the cost of ransom
Global APT activity, AI usage, actor and tactic profiles, and implications
Rise in volumes of AI-powered cyberattacks
Major cyber events in 2024
Malware and malicious payload trends
Cyberattack types and targets
Vulnerability exploit attempts on CVEs
Attacks on counties – USA
Expansion of bot farms – how, where, and why
In-depth analysis of the cyber threat landscape across North America, South America, Europe, APAC, and the Middle East
Why are attacks on smart factories rising?
Cyber risk predictions
Axis of attacks – Europe
Systemic attacks in the Middle East
Download the full report from here:
https://sectrio.com/resources/ot-threat-landscape-reports/sectrio-releases-ot-ics-and-iot-security-threat-landscape-report-2024/
1. Underground Cables
Presented By:
Engr.Mafijur Rahman
Electrical and Electronic Engineer
Professional Associates Limited.
Engr.razu.powergen@gmail.com
+8801675453088
1Professional Associates Limited.
2. Introduction
• Since the loads having the trends towards
growing density. This requires the better
appearance, rugged construction, greater service
reliability and increased safety. An underground
cable essentially consists of one or more
conductors covered with suitable insulation and
surrounded by a protecting cover. The
interference from external disturbances like
storms, lightening, ice, trees etc. should be
reduced to achieve trouble free service. The
cables may be buried directly in the ground, or
may be installed in ducts buried in the ground.
2Professional Associates Limited.
5. Advantages & Disadvantages
Advantages
– Better general appearance
– Less liable to damage through storms or lighting
– Low maintenance cost
– Less chances of faults
– Small voltage drops
Disadvantages
– The major drawback is that they have greater installation cost and
introduce insulation problems at high voltages compared with
equivalent overhead system.
5Professional Associates Limited.
6. Construction of Cables
• Core or Conductor
A cable may have one or more than one core
depending upon the type of service for which it
is intended. The conductor could be of
aluminum or copper and is stranded in order to
provide flexibility to the cable.
• Insulation
The core is provided with suitable thickness of
insulation, depending upon the voltage to be
withstood by the cable.
The commonly used material for insulation are
impregnated paper, varnished cambric or
rubber mineral compound.
6Professional Associates Limited.
7. Construction of Cables
• Metallic Sheath
A metallic sheath of lead or aluminum is provided
over the insulation to protect the cable from
moisture, gases or others damaging liquids
• Bedding
Bedding is provided to protect the metallic
sheath from corrosion and from mechanical
damage due to armoring. It is a fibrous material
like jute or hessian tape.
7Professional Associates Limited.
8. • Armouring
Its purpose is to protect the cable from
mechanical injury while laying it or during the
course of handling. It consists of one or two
layers of galvanized steel wire or steel tape.
• Serving
To protect armouring from atmospheric
conditions, a layer of fibrous material is provided.
Construction of Cables
8Professional Associates Limited.
10. Properties of Insulating Material
High resistivity.
High dielectric strength.
Low thermal co-efficient.
Low water absorption.
Low permittivity.
Non – inflammable.
Chemical stability.
High mechanical strength.
High viscosity at impregnation temperature.
Capability to with stand high rupturing voltage.
High tensile strength and plasticity.
10Professional Associates Limited.
12. Insulating Materials for Cables
• Rubber
It can be obtained from milky sap of tropical trees or from oil
products.
It has the dielectric strength of 30 KV/mm.
Insulation resistivity of 10 exp 17 ohm.cm
Relative permittivity varying between 2 and 3.
They readily absorbs moisture, soft and liable to damage due to
rough handling and ages when exposed to light.
Maximum safe temperature is very low about 38 C
12Professional Associates Limited.
13. • Vulcanized India Rubber
It can be obtained from mixing pure rubber with mineral compounds i-e
zinc oxide, red lead and sulphur and heated upto 150 C.
It has greater mechanical strength, durability and wear resistant property.
The sulphur reacts quickly with copper so tinned copper conductors are
used.
It is suitable for low and moderate voltage cables.
Insulating Materials for Cables
13Professional Associates Limited.
14. • Impregnated Paper
This material has superseded the rubber, consists of chemically pulped
paper impregnated with napthenic and paraffinic materials.
It has low cost, low capacitance, high dielectric strength and high
insulation resistance.
The only disadvantage is the paper is hygroscopic, for this reason
paper insulation is always provided protective covering.
• Varnished Cambric
This is simply the cotton cloth impregnated and coated with varnish.
As the varnish cambric is also hygroscopic so need some protection.
Its dielectric strength is about 4KV / mm and permittivity is 2.5 to 3.8.
Insulating Materials for Cables
14Professional Associates Limited.
15. • Polyvinyl chloride (PVC)
This material has good dielectric strength, high insulation resistance and high
melting temperatures.
These have not so good mechanical properties as those of rubber.
It is inert to oxygen and almost inert to many alkalis and acids.
• XLPE Cables (Cross Linked Poly-ethene)
This material has temperature range beyond 250 – 300 C
This material gives good insulating properties
It is light in weight, small overall dimensions, low dielectric constant and high
mechanical strength, low water absorption.
These cables permit conductor temperature of 90 C and 250 C under normal
and short circuit conditions.
These cables are suitable up to voltages of 33 KV.
Insulating Materials for Cables
15Professional Associates Limited.
17. CLSSIFICATION OF CABLES
• Low tension (L.T) ----- up to 1000V
• High tension (H.T) ----- up to 11, 000V
• Super tension (S.T) ---- from 22KV to 33KV
• Extra high tension (E.H.T) cables --- from 33KV to 66KV
• Extra super voltage cables ------beyond 132KV
17Professional Associates Limited.
20. 3- Core Cables
Belted Cables
In these cables the conductors are wrapped with oil
impregnated paper, and then cores are assembled with filler
material. The assembly is enclosed by paper insulating belt.
These can be used for voltages up to 11KV or in some cases
can be used up to 22KV.
High voltages beyond 22KV, the tangential stresses becomes
an important consideration.
As the insulation resistance of paper is quite small along the
layer, therefore tangential stress set up, hence, leakage
current along the layer of the paper insulation.
This leakage current causes local heating, resulting breaking
of insulation at any moment
20Professional Associates Limited.
22. • Screened Cables
• These can be used up to 33kv but in certain
cases can be extended up to 66kv.
• These are mainly of two types
H-type and
S.L type cables
3- Core Cables
22Professional Associates Limited.
23. 3- Core Cables
H-TYPE Cables:
• Designed by H. Hochstadter.
• Each core is insulated by layer of impregnated paper.
• The insulation on each core is covered with a metallic
screen which is usually of perforated aluminum foil.
• The cores are laid in such a way that metallic screen
make contact with one another.
• Basic advantage of H-TYPE is that the perforation in the
metallic screen assists in the complete impregnation of
the cable with the compound and thus the possibility
of air pockets or voids in the dielectric is eliminated.
• The metallic screen increase the heat dissipation power
of the cable.
23Professional Associates Limited.
25. S.L - Type: (Separate Lead)
• Each core insulation is covered by its own lead
sheath.
• It has two main advantages, firstly the separate
sheath minimize the possibility of core-to-core
breakdown. Secondly the, bending of cables
become easy due to the elimination of over all
sheath.
• The disadvantage is that the lead sheaths of S.L
is much thinner as compared to H-Type
cables, therefore for greater care is required in
manufacturing.
3- Core Cables
25Professional Associates Limited.
27. • Pressurized Type Cables
• In these cables, pressure is maintained
above atmosphere either by oil or by gas.
• Gas pressure cables are used up to 275KV.
• Oil filled cables are used up to 500KV.
3- Core Cables
27Professional Associates Limited.
29. • Oil Filled Cables
• Low viscosity oil is kept under pressure and
fills the voids in oil impregnated paper under
all conditions of varying load.
• There are three main types of oil filled cables
a. Self-contained circular type
b. Self-contained flat type
c. Pipe Type cables
3- Core Cables
29Professional Associates Limited.
31. Advantages of Oil Filled Cables
• Greater operating dielectric stresses
• Greater working temperature and current
carrying capacity
• Better impregnation
• Impregnation is possible after sheath
• No void formation
• Smaller size of cable due to reduced dielectric
thickness
• Defect can easily be detected by oil leakage
31Professional Associates Limited.
32. Gas Pressure Cables
In these cables an inert gas like nitrogen is used to exert
pressure on paper dielectric to prevent void formation.
These are also termed as Compression cables
They insulated cores similar to solid type
The cable is inserted in a pressure vessel which may be a
rigid steel pipe, commonly known as pipe line
compression cable.
The nitrogen gas is filled in vessel at nominal pressure of
1.38 * 10 exp 6 N/ square meter with a maximum
pressure of 1.725 * 10 exp 6 N/ square meter.
32Professional Associates Limited.
34. Gas Insulated Cables (GIC)
• In GIC cables high pressure sulphur hexaflouride
(SF6), fills the small spaces in oil impregnated paper
insulation and suppresses the ionization.
• Most EHV and UHV lines insulated with sulphur
hexaflouride (SF6) gas are being used extensively for
voltages above 132 KV up to 1200 KV.
• These cables are very popular for short lengths, river
crossings and high way crossings.
34Professional Associates Limited.
36. Advantages of GIC
Gas Insulated Cables have several advantages
over oil filled cables,
• Efficient heat transfer hence can carry more
current.
• Low dielectric loss and low capacitance
• SF6 gas is non-toxic, chemically stable and
non-inflamable.
• Terminations of GIC cables are simpler and
cheaper.
36Professional Associates Limited.
37. Laying of Underground Cables
• The reliability of underground cable network
depends to a considerable extent upon
proper laying.
• There are three main methods of Laying
underground cables
a. Direct Laying
b. Draw in system
c. Solid system
37Professional Associates Limited.
38. Direct Laying
• This method is cheap and simple and is most
likely to be used in practice.
• A trench of about 1.5 meters deep and 45 cm
wide is dug.
• A cable is been laid inside the trench and is
covered with concrete material or bricks in
order to protect it from mechanical injury.
• This gives the best heat dissipating conditions
beneath the earth.
• It is clean and safe method
38Professional Associates Limited.
40. Disadvantages of Direct Laying
• Localization of fault is difficult
• It can be costlier in congested areas where
excavation is expensive and inconvenient.
• The maintenance cost is high
40Professional Associates Limited.
41. Draw in System
• In this conduit or duct of concrete is laid in
ground with main holes at suitable positions
along the cable route.
• The cables are then pulled into positions from
main holes.
41Professional Associates Limited.
42. • It is very high initial cost
• Heat dissipation conditions are not good
• This method is suitable for congested areas
where excavation is expensive and
inconvenient
• This is generally used for short lengths cable
route such as in workshops, road crossings
where frequent digging is costlier and
impossible
Advantages of Draw in System
42Professional Associates Limited.
43. Solid System
• In this system the cable is laid in open pipes or
troughs dug out in earth along the cable route.
• The troughing is of cast iron or treated wood
• Troughing is filled with a bituminous after cables
is laid.
• It provides good mechanical strength
• It has poor heat dissipation conditions
• It requires skilled labour and favorable weather
conditions
• It is very much expensive system
43Professional Associates Limited.
45. Grading of Cables
• Since the stresses are maximum at surface of
the conductor or inner most part of the
dielectric.
• The stress goes on decreasing as outer most
layer is reached.
• Since the process of achieving the uniform
electrostatic stresses on the dielectric of
cables is known as Grading of cables
45Professional Associates Limited.
46. • The unequal distribution of stresses is
undesirable because,
• if dielectric is chosen according to maximum
stress the thickness of cable increases or either
this may lead to breakdown of insulation.
• The following are the two main methods of
grading
Capacitance grading
Inter sheath grading
Grading of Cables
46Professional Associates Limited.
47. Cables are generally laid in the ground or in ducts
in the underground distribution system. For this
reason, there are little chances of faults in
underground cables. However, if a fault does
occur it is difficult to locate and repair the fault
because conductors are not visible.
Nevertheless, the following are the faults most
likely to occur in underground cables
1) open circuit fault
2) short circuit fault
3)earth fault
47Professional Associates Limited.
48. • When there is a break in the conductor of a
cable, it is called open circuit fault.
• The open circuit fault can be checked by megger.
For this purpose, the three conductors of the 3-
core cable at the far end are shorted and earthed.
• The resistance between each conductor and earth
is measured by a megger and it will indicate zero
resistance in the circuit of the conductor that is
not broken.
• However, if the conductor is broken, the megger
will indicate infinite resistance in its circuit
48Professional Associates Limited.
49. • When two conductors of a multi-core cable come
in electrical contact with each other due to
insulation failure, it is called a short circuit fault.
• Again, we can seek the help of a megger to check
this fault.
• For this purpose the two terminals of the megger
are connected to any two conductors.
• If the megger gives zero reading, it indicates short
circuit fault between these conductors.
• The same steps is repeated for other conductors
taking two a time.
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50. EARTH FAULTS
• When the conductor of a cable comes in
contact with earth, it is called earth fault or
ground fault.
• To identify this fault, one terminal of the
megger is connected to the conductor and the
other terminal connected to earth.
• If the megger indicates zero reading, it means
the conductor is earthed. The same procedure
is repeated for other conductors of the cable.
50Professional Associates Limited.
51. Physical Limitations of
Underground Lines
The main argument against constructing underground
systems is usually financial. But costs are not the only
limitation.
The laws of physics limit how physically long a power line
can be.
These limits are relatively unimportant on overhead lines
but will severely limit high voltage underground cable
systems
The higher the voltage the shorter the line length
must be.
The limiting effects become very important at
transmission voltages, especially 100,000 Volts and
above.
Limiting effects may also be important for
subtransmission voltages, 69,000 Volts and 35,000
Volts.
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52. Physical Limitations: The Effect
of Capacitance
o Capacitance causes current to flow even when no load is
connected to the cable. This is called “line charging
current”.
o Underground line capacitance for power cables is far
higher than overhead line capacitance.
o Wires are closer to each other
o Wires are closer to the earth (within a few inches).
o Underground lines have 20-75 times the line charging
current that an overhead line has (depending on line
voltage).
o If a line is long enough the charging current could be
equal to the total amount of current the line can carry.
This will severely limit its ability to deliver power.
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53. Summary of Costs: Overhead
vs. Underground
• Transmission: Underground may be 4-20 times
Overhead.
• Sub transmission: Underground may be 4-20
times Overhead
• Distribution: Underground may be 2-10 times
Overhead
• New underground may be cheaper than
overhead in special conditions and costs vary
greatly from utility to utility and place to place.
53Professional Associates Limited.