TECHNICAL SEMINAR TOPIC ON
UNDERGROUND POWER
TRANSMISSION
Under The Guidance Of
Mrs .N.SHANKER M.Tech
Assistant Professor , EEE Department
Submitted By
Sk.Arif
17C11A0203
Contents
1. Abstract
2. Introduction
3. Underground Transmission
4. Types of Underground Transmission Tables
5. Advantages Of Underground Electric Transmission
6. Disadvantages Of Underground Power Systems
7. Fault Location
8. Conclusion
ABSTRACT:
The transmission of electrical power can be done overhead rather than
underground using different types of transmission cables. These types
of electrical power transmissions have their own benefits, pitfalls and
also applications where it is frequently used. The selection of method
mainly depends on the factors like cost, voltage, safety, application,
etc. The overhead power transmission is cheap and the installation
process is cheap.
Whereas, underground power transmission is expensive and also
has many advantages. The applications of this transmission mainly
depend on the crowd areas as well as where the possibility of overhead
power transmission is not possible. Sometimes, due to factors like
physical, cost and environmental, the two types of cables are combined
together for electrical power transmission This Technical Seminar
topic discusses an overview of underground electric power
transmission, types, installation, features and more.
INTRODUCTION TO UNDERGROUND TRANSMISSION
The electric power transmission can be done using a method like undergrounding as an alternative to
overhead power transmission. These cables have low visibility and not affected by bad -weather. But, the
cost of these cables is high and laying process is time-consuming instead of overhead building. The
finding of faults in underground transmission lines takes much time for repairing as well as locating.
In urban areas, this type of transmission is enclosed with shielded with dielectric liquid and a
metal pipe that is either fixed or spread through pumps.
If an electric-fault breaks the underground pipe & generates
a dielectric liquid into the nearby mud, then the liquid
nitrogen trucks are assembled to fix the damaged part of the
pipe location. This kind of transmission cable can extend
the fixed period as well as the cost of repair. The stats of the
pipe and soil are monitored frequently throughout the
period of repair
TYPES OF UNDERGROUND TRANSMISSION CABLES
The most common types of underground electric power transmission cables
include the following.
HPFF (High-Pressure Fluid Filled Pipe)
HPGF (High-Pressure Gas Filled Pipe)
SCFF (Self Contained Fluid Filled)
XLPE (Solid Cable Cross-Linked Polyethylene)
High-Pressure, Fluid-Filled Pipe-Type Cable:
A high-pressure, fluid-filled (HPFF) pipe-type of underground
transmission line, consists of a steel pipe that contains three high-voltage
conductors. Figure illustrates a typical HPFF pipe-type cable. Each
conductor is made of copper or aluminum; insulated with high-quality,
oil-impregnated kraft paper insulation; and covered with metal shielding
(usually lead) and skid wires (for protection during construction).
Figure HPFF or HPGF Pipe-Type Cross Section
HPFF or HPGF Pipe-Type Cross Section
The outer steel pipe protects the
conductors from mechanical damage,
water infiltration, and minimizes the
potential for oil leaks. The pipe is
protected from the chemical and
electrical environment of the soil by
means of a coating and cathodic
protection. Problems associated with
HPFF pipe-type underground
transmission lines include maintenance
issues and possible contamination of
surrounding soils and groundwater due
to leaking oil.
High-Pressure, Gas-Filled Pipe-Type Cable:
The high-pressure, gas-filled (HPGF) pipe-type of underground transmission line is a
variation of the HPFF pipe-type, described above. Instead of a dielectric oil, pressurized
nitrogen gas is used to insulate the conductors. Nitrogen gas is less effective than dielectric
fluids at suppressing electrical discharges and cooling. To compensate for this, the
conductors’ insulation is about 20 percent thicker than the insulation in fluid-filled pipes.
Thicker insulation and a warmer pipe reduce the amount of current the line can safely and
efficiently carry. In case of a leak or break in the cable system, the nitrogen gas is easier to
deal with than the dielectric oil in the surrounding environment.
Self-Contained, Fluid-Filled Pipe-Type:
The self-contained, fluid-filled (SCFF) pipe-type of underground transmission is often used
for underwater transmission construction. The conductors are hollow and filled with an
insulating fluid that is pressurized to 25 to 50 psi. In addition, the three cables are
independent of each other. They are not placed together in a pipe. Each cable consists of a
fluid-filled conductor insulated with high-quality kraft paper and protected by a lead-bronze
or aluminum sheath and a plastic jacket. The fluid reduces the chance of electrical discharge
and line failure. The sheath helps pressurize the conductor’s fluid and the plastic jacket
keeps the water out. This type of construction reduces the risk of a total failure, but the
construction costs are much higher than the single pipe used to construct the HPFF or HPGF
systems.
Solid Cable, Cross-Linked Polyethylene:
The cross-linked polyethylene (XLPE) underground transmission line is
often called solid di-electric cable. The solid dielectric material replaces the
pressurized liquid or gas of the pipe-type cables. XLPE cable has become the
national standard for underground electric transmission lines less than 200
kV. There is less maintenance with the solid cable, but impending insulation
failures are much 4 more difficult to monitor and detect. The diameter of the
XLPE cables increase with voltage
XLPE Cable Cross-Section
For 345 kV XLPE construction, two sets of three cables (six cables) are
necessary for a number of reasons, primarily so that the capacity of the
underground system matches the capacity of the overhead line. This design
aids in limiting the scope of any cable failure and shortens restoration time
in an emergency situation. Most underground transmission requires
increased down time for the repair of operating problems or maintenance
issues compared to overhead lines. The double Cross-linked Polyethylene
Insulation Segmental Copper Conductor and Shield Outer Coverings 5 sets
of cables allows for the rerouting of the power through the backup cable
set, reducing the down time but increases the construction footprint of the
line.
ADVANTAGES OF UNDERGROUND ELECTRIC
TRANSMISSION
Safe Operation
Good General Appearance
Prone to Environmental Hazards
Less Maintenance Cost
Less Fault Occurrence
Less Voltage Drop
Disadvantages of Underground Power systems
High Capital Cost
Can’t Use for High Voltage Levels
FAULT LOCATION
Distance Fault Detection :
 Underground cables are prone to a wide variety of faults
due to underground conditions, wear and tear, rodents etc.
Also detecting fault source is difficult and entire line is to
be dug in order to check entire line and fix faults. So here
we propose an cable fault detection over IOT that detects
the exact fault position over IOT that makes repairing
work very easy. The repairmen know exactly which part
has fault and only that area is to be dug to detect the fault
source. This saves a lot of time, money and efforts and also
allows to service underground cables faster. We use IOT
technology that allows the authorities to monitor and
check faults over internet. The system detects fault with
the help of potential divider network laid across the cable.
Fault Locater using arduino micro controller
We can provide used power to the arduino board that is the 12V dc supply will
passing though the board But we are using relay to sense the fault. The relay is working
12V.dc so we have to use adopter.
The power will passing through arduino board to relay board. The relay is having
some sound because relay is shifting one line to another line. We have 3-lines i.e. RYB.
These switches are in this direction there is no fault. It any switch is in reverse
direction in the place fault occurs.
The distance network one switch to another switch is we have taken 3km to each.
It a fault occurs in any line is at any distance that will be displayed
CONCLUSION
The underground cables are convenient for distributing
power in urban and other areas where overhead cables may
be not be possible. To ensure safety and service continuity,
the underground power cabling systems must be protected
against both fault conditions as well as physical damage.
A proper protection indicates the presence of underground
power cables, prevents physical damage to the cable,
minimizes supply interruptions and reduces the risks of
accidents and personal injury.