Submitted by:
B.NAGARAJU

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ABTRACT:
The electricity sector is facing enormous challenge in most countries around the world due to deregulation and growing demand on power. Efficient supply of electricity in restricted environment conditions has added more pressure on power utilities to operate increasingly on commercial terms. Therefore, utilities must develop greater flexibility and security in terms of supply and distribution of electricity in the most effective and environment-friendly way possible. Underground cables have the potential to reduce outages, maintenance cost and transmission losses.
In general transmission losses are lower with underground cables compared to overhead lines. Additionally, new underground cable technology with its unique characteristics of low impedance and ohmic loss enables a massive increase in power transmission capacity, underground cables can also deliver economic benefits where civil works are reduced by avoiding unnecessary digging, besides a big savings in tree pruning for local councils. This paper will demonstrate the potential impact of new technologies in underground cables on power transmission and distribution networks and examine other cable influence relating to power networks.
CHAPTER-1
INTRODUCTION
Back ground of underground cables:
The beginning of power cable technology can be traced back to the 1880s, when the need for power distribution cables became pressing, following the introduction of incandescent lighting. The illumination of some of the larger cities advanced at such a quick rate that under certain circumstances it was impossible to accommodate the number and size of feeders required for distribution, using the overhead line system approach. The situation in New York City deteriorated, so notably, that apart from technical and aesthetic considerations, the overhead line system began to pose safety hazards . Due to this fast growth, by the early 1990s, underground electrification via insulated cables was on its way to become a well-established practice. Some of the more common early solid and liquid insulating materials employed in various underground cable installations were natural rubber, gutta-percha, oil and wax, rosin and asphalt, jute, hemp, and cotton.
During the period of world war I, oil-impregnated paper cables of the three
conductor belted type were used extensively. the belted cable proved to be highly partial discharge susceptible when attempts were made to extend the operating voltage range to 35 kv, due to non-uniform stress distribution in the cable construction.
Prior to and within the early 1950s various forms of rubber had been employed in the distribution-voltage cable. After hydrocarbon thermoplastic polyethylene (PE) hadbeen invented in England in 1933, it took a substantially longer time for polyethyleneinsulation to be introduced into the power cable area.
Solid-polyethylene-extruded power distribution cables were first introduced in the 1950s. In these early days of the 1950s,polyethylene, because of its intrinsically low dielectric loss characteristics, was always viewed as an attractive substitute for the more traditional solid-liquid insulating systems.In the beginning, plastic cables were manufactured using low density high-molecular weight polyethylene (HMWPE), which has been used since 1951 for distribution voltages up to 35 kV and sometimes higher
CHAPTER-2
Developments in underground cables:
The principal technology used today for long distance, high power transmission is high voltage underground lines, whether alternating current (AC) or direct current (DC). The desire to transmit large amounts of electrical energy produced from renewable resources is complicated by the large distance frequently found between renewable sources and locations of power demand. Further complicating this is the need to collect the renewable energy over a wide geographic region and to deliver it to large numbers of separate population centers.
The most commonly and for realbility ,Underground lines will be provided only in those areas higly populated region. Underground line installation will be coordinated with the in-stallation master plan to avoid conflict with construction of future facilities. Lines will normally Be installed adjacent to roadways in urban, housing, or industrial plant areas, but may be routedas required to meet the project objectives.
A careful study will be made of all underground utilities in order to ensure a minimum of interference between electrical lines and other underground utilities, whether existing, being constructed ,or proposed as a definite future construction project. Electrical lines will be atleast six feet from any steam or hot water lines ,except at crossings where a one-foot separation from such lines is adequate.
CHAPTER-3
INTEGERATION OF UNDER GROUND CABLES IN EXISTING NETWORK
A Geographic Information System (GIS) is a computer-based tool for mapping and analyzing data. Spatially enabled information provides a unique geographic dimension to the understanding and interpretation of information. GIS based solutions are playing a key role in today’s power scenario mostly in distribution system maintenance management and in efficient customerservices
The dynamic nature of the electricity distribution system causes a complicated procedure to analyze, as it includes both graphic and non-graphic data. In an underground network this becomes more challenging due to the criticality of the information . To achieve a higher level of accuracy and increased productivity in maintenance operations, an efficient system to manage the spatial and aspatial information is required. Such a system is required to operate with all existing data and also adapt to currently used workflow of operations. The system assists in choosing suitable alternatives within the limits of the design parameters, working out a precise diagram of existing network and mapping them onto actual maps of the area. Optimal allocation of resources for maintenance Can thus be ensure.
Problems with Cable Maintenance and Management Information Systems have been encountered at many places and Solutions have been sought through Customized packages linked to the GIS based information . Such Solutions are product based and hence development efforts are more inclined to product customization.
Features of integration:
 Integration of new cable systems needs detailed planning
 Quicker realization of network extansion
 There might be compensation systems needed at length longer than the 20 km.

Presented by
B.NAGA RAJU

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NEW TECHNOLOGIES USED IN THE MAINTAINENCES OF UDERGROUND CABLES
BACK GROUND OF CABLES
 Some of the more common early solid and liquid insulating materials employed in various underground cable installations were natural rubber, gutta-percha, oil and wax, rosin and asphalt, jute, hemp, and cotton.
 The operating voltage range to 35 kv, due to non-uniform stress distribution in the cable construction.
 This cables cann’t satisfies minimum requirement of more dielectric ,aging of cables and effient power transfer cabilities.
IMPACT OF UNDERGROUND CABLES IN EXISTING NETWORKS
 Integration of new cable system needs detailled planning
 Quicker realization of networkextansion
 There might be compensationsystems needed at length longer than 20 km
• New technologies of under ground cables
New technologies of under ground cables
• CROSS- LINKED POLY ETHYLENE(XPLE)
• TREE RETARDANT ACROSS-LINKED POLYENTHYENE(TR-XPLE)
• SUPERCONDUCTOR CABLES
• REAL TIME THERMAL RATING(RTTR)
• ELECTROMAGNETIC SHIELDING
CROSS- LINKED POLY ETHYLENE(XPLE)
• The cross-linked polyethylene (XLPE) underground transmission line is often called “soliddi electric”.
• This type of line relies on high-quality manufacturing controls to eliminate any contaminantsor voids in the insulation that could lead to electrical discharges and breakdown of the line from electrical stress
• The solid dielectric material replaces the pressurized liquid or gas of other types of cable. The below Figure illustrates the XLPE in cross-section.
• They are not housed together in a pipe, but are set in concrete ducts or buried side-by-side directly in specially prepared soil.
• The insulation is about twice as thick as the oil insulation used in other types of cable
 While all previous installations are AC applications, applying the technology to DC is straightforward.
TREE RETARDANT ACROSS-LINKED POLYENTHYENE(TR-XPLE)
 The use of tree retardant XLPE insulation has allowed utilities to achieve long service life under severe operating conditions.
 This has led to improved life cycle economics and has minimized social and environmental issues resulting from cable replacement activities.
 XLPE and other polymers, undergo a degradation process, called water treeing, when exposed to moisture and an electrical stress.
 Tree-retardant crosslinked polyethylene (TR-XLPE) was designed to overcome the water treeing deficiency of high molecular weight thermoplastic polyethylene and crosslinked polyethylene (XLPE)
 TR-XLPE was designed to maintain XLPE’s high dielectric strength and low electrical loss.
SUPERCONDUCTOR CABLES
 Superconductor cables utilize superconductor materials instead of the copper or aluminum traditionally used to carry electricity in underground cables.
 Superconductor materials can carry well over 100 times the current density of copper or aluminum
 when transmitting DC power, superconductors become perfect conductors with zero electrical resistance and introduce no electrical losses of their own.
 Superconductor cable systems are now operating in multiple in-gridsites around the world, demonstrating their reliability and performance, as illustrated in Figure 1
 While all previous installations are AC applications, applying the technology to DC is straightforward.