underground transmission lines PPT

2. SUMMER TRAINING REPORT NDMC , NEW DELHI
Submitted To: - Submitted By: -
Mr. TARUNJEET SINGH PRINCE KUMAR
(Asst. Professor) 8614304@apiit.edu.in
Dept. of Electrical & Electronics Electrical & Electronics
Engineering Engineering

3. As per office order No.146/EE(T-II)/2016 dated 24/05/2016 ,vocational training (summer
training ) of student of Elect Engg ( Degree ) ,it has been completed successfully his
vocational training .

4. NDMC ,NEW DELHI
 New delhi municipal council (NDMC) is the municipal council of the city of
new delhi ,India and area under its administration is referred to as area of
43.7 km sq.
 NDMC has its origins in the Imperial Delhi Committee which was constituted
on 25 March 1913 to overlook the construction of the new capital of India.
Thereafter in February 1916 the Chief Commissioner, Delhi, created the
Raisina Municipal Committee, which was upgraded to a 2nd class
Municipality under the Punjab Municipal Act on 7 April 1925. Then on 22
February 1927, the Committee passed a resolution adopting the name "New
Delhi" giving it the name, "New Delhi Municipal Committee", approved by
Chief Commissioner on 16 March 1927. In May 1994, the NDMC Act 1994,
replaced the Punjab Municipal Act 1911, and the Committee was renamed as
the New Delhi Municipal Council.

5. NDMC's headquarters building, known
as Palika Kendra, was built in 1984, and
was the tallest building

6. NDMC has 28 departments:-
 Architecture Dept.
 Audit Dept.
 Accounts Dept.
 Civil Engineering Dept.
 Commercial Dept.
 Council Secretariat Dept.
 Fire Dept.
 Finance Dept.
 Information Technology Dept.
 Horticulture Dept.

7. NDMC has 28 departments:-
 Electricity Dept.
 Enforcement Dept.
 Public Health Dept.
 Project Dept.
 General Admn.Dept.
 Security Dept.
 Law Dept.
 Enforcement (B.R) Dept.
 Estate I Dept.
 Estate II Dept.
 Public Relations Dept

8. NDMC has 28 departments:-
 Municipal Housing.
 Personnel Dept.
 Vigilance Dept.
 Welfare Dept.
 Education Dept.
 Medical Services Dept.
 Property Tax Dept

9. ELECTRICAL DEPARTMENT
 Electricity Department is responsible for distribution of electricity to all
consumers coming underits jurisdiction including all government buildings. It
is fulfilling the responsibility of providing andmaintaining reliable and quality
supply of electricity round the clock to all its consumers. Besides above the
street lightings and electric maintenance of NDMC offices (Commercial
building, Schools, Hospitals) and NDMC residential flats.
 The Zone-I of electricity department is responsible for electrical planning &
major procurement of electrical equipments through stores, maintenance of
electrical installation works in NDMC office buildings, NDMC commercial
buildings, hospitals, and dispensaries, NDMC schools etc. etc.. along with
operation & maintenance of Road lighting system, Installation of grid
Interacted solar PV and CCTV for surveillance and monitoring in NDMC
buildings, Schools, Hospitals etc.

10. Transformer
 “A Transformer is a static electromagnetic energy conversion device, which
transfers electrical energy from one electrical circuit to another electrical
circuit, without any change in supply frequency”.

11. Working …..
 When an alternating voltage V1 is applied to the primary, an alternating flux
φ is set up in the core. This alternating flux links both the windings and
induces e.m.f.s E1 and E 2 in them according to Faraday’s laws of
electromagnetic induction. The e.m.f. E1 is termed as primary e.m.f. and
e.m.f. E2 is termed as secondary e.m.f.
 Note that magnitudes of E2 and E 1 depend upon the number of turns on the
secondary and primary respectively. If N2 > N1, then E2 > E1 (or V2 > V1) and
we get a step-up transformer. On the other hand, if N2 < N1, then E2 < E1 (or
V2 < V 1) and we get a step-down transformer. If load is connected across the
secondary winding, the secondary e.m.f. E2 will cause a current I2 to flow
through the load. Thus, a transformer enables us to transfer a.c. power from
one circuit to another with a change in voltage level.

12. Working…

13. ….
 The following points may be noted carefully:
 The transformer action is based on the laws of electromagnetic induction.
 There is no electrical connection between the primary and secondary. The
a.c. power is transferred from primary to secondary through magnetic flux.
 There is no change in frequency i.e., output power has the same frequency
as the input power.
 The losses that occur in a transformer are:
 (a) core losses—eddy current and hysteresis losses
 (b) copper losses—in the resistance of the windings.
 In practice, these losses are very small so that output power is nearly equal to
the input primary power. In other words, a transformer has very high
efficiency.

14. Type of transformer
 There are many type of transformer as following.
 Power transformer.
A power transformer is a static piece of apparatus with two or more windings
which, by electromagnetic induction, transforms a system of alternating voltage
and current into another system of voltage and current for the purpose of
transmitting electrical power .

15. Distribution transformer
 A distribution transformer or service transformer is a transformer that
provides the final voltage transformation in the electric power
distribution system, stepping down the voltage used in the distribution lines
to the level used by the customer. Distribution transformer divided by two
type:
 Oil type transformer
 Dry type transformer

16. Oil type transformer
 Single-phase and three-phase transformers for the range above 16 kVA and up
to 72.5 kV. These units are designed for power centres, substations and
networks; also for pad-mounts. They are used in public distribution systems,
commercial buildings and industrial complexes. The unique core and coil
designs and the use of special turn insulating materials make these units
extremely compact, reliable and durable. A wide range of transformer fluids
is available including BIOTEMP™, which is biodegradable, less flammable and
thermally efficient – ideal for densely populated or environmentally sensitive
areas.

17. Dry Type Transformers
 For the range 30 kVA to 30 MVA with primary operating voltages up to 41.5 kV
and secondary operating voltages up to 36 kV. These units are designed for
operation in difficult conditions – environmental contamination, fire hazard,
high humidity or extreme climates. They provide high level security and are
found in hospitals and other public areas, on oil platforms, in ships,
underground railways and mines. They are extremely tough and resilient and
are resistant to the effects of vibration. They should be considered for
earthquake prone areas. RESIBLOC® transformers have a special resin-
encapsulated construction which is unique to ABB. This construction provides
great strength and flexible design dimensions.
 Figure- (Dry type transformer)

18. Current transformer
 The Current Transformer ( C.T. ), is a type of “instrument transformer” that
is designed to produce an alternating current in its secondary winding which
is proportional to the current being measured in its primary.
 Current transformers reduce high voltage currents to a much lower value and
provide a convenient way of safely monitoring the actual electrical current
flowing in an AC transmission line using a standard ammeter. The principal of
operation of a current transformer is no different from that of an ordinary
transformer.
 Figure- (current transformer)

19. Potential transformer
 Voltage transformers (VT), also called potential transformers (PT), are a
parallel connected type of instrument transformer. They are designed to
present negligible load to the supply being measured and have an
accurate voltage ratio and phase relationship to enable accurate secondary
connected metering
 Figure-(potential transformer)

20. Cooling of transformer and type of cooling.
 No transformer is truly an 'ideal transformer' and hence each will incur
some losses, most of which get converted into heat. If this heat is not
dissipated properly, the excess temperature in transformer may cause serious
problems like insulation failure. It is obvious that transformer needs a cooling
system. Transformers can be divided in two types as (i) dry type transformers
and (ii) oil immersed transformers. Different cooling methods of
transformers are
 For dry type transformers
Air Natural (AN)
Air Blast (AB)

21. ……
 For oil immersed transformers
Oil Natural Air Natural (ONAN)
Oil Natural Air Forced (ONAF)
Oil Forced Air Forced (OFAF)
Oil Forced Water Forced (OFWF)

22. Cooling Methods For Dry Type Transformers
 Air Natural Or Self Air Cooled Transformer
 This method of transformer cooling is generally used in
small transformers (upto 3 MVA). In this method the transformer is allowed to
cool by natural air flow surrounding it.
 Air Blast
 For transformers rated more than 3 MVA, cooling by natural air method is
inadequate. In this method, air is forced on the core and windings with the
help of fans or blowers. The air supply must be filtered to prevent the
accumulation of dust particles in ventilation ducts. This method can be
used for transformers upto 15 MVA.

23. Cooling Methods For Oil Immersed
Transformers
 Oil Natural Air Natural (ONAN)
 This method is used for oil immersed transformers. In this method, the heat
generated in the core and winding is transferred to the oil. According to the
principle of convection, the heated oil flows in the upward direction and then
in the radiator. The vacant place is filled up by cooled oil from the radiator.
The heat from the oil will dissipate in the atmosphere due to the natural air
flow around the transformer. In this way, the oil in transformer keeps
circulating due to natural convection and dissipating heat in atmosphere due
to natural conduction. This method can be used for transformers upto about
30 MVA.

24. Oil Natural Air Forced (ONAF)
 The heat dissipation can be improved further by applying forced air on the
dissipating surface. Forced air provides faster heat dissipation than natural air
flow. In this method, fans are mounted near the radiator and may be provided
with an automatic starting arrangement, which turns on when temperature
increases beyond certain value. This transformer cooling method is generally
used for large transformers upto about 60 MVA

25. Oil Forced Air Forced (OFAF)
 In this method, oil is circulated with the help of a pump. The oil circulation is
forced through the heat exchangers. Then compressed air is forced to flow on
the heat exchanger with the help of fans. The heat exchangers may be
mounted separately from the transformer tank and connected through pipes
at top and bottom as shown in the figure. This type of cooling is provided for
higher rating transformers at substations or power stations.

26. Oil Forced Water Forced (OFWF)
 This method is similar to OFWF method, but here forced water flow is used to
dissipate hear from the heat exchangers. The oil is forced to flow through the
heat exchanger with the help of a pump, where the heat is dissipated in the
water which is also forced to flow. The heated water is taken away to cool in
separate coolers. This type of cooling is used in very large transformers
having rating of several 100 MVA.

27. Underground cable
 The Underground cable employed for transmission of power at high voltage
consists of one central core.
 Requirements of cable
 The conductor used in cable should be stranded one in order to provide
flexibility to the cable and should be of such X – section area that it may carry
the desired load current without overheating and causing voltage drop.
 The insulation provided should be of such thickness that it may give high
degree of safety and reliability at the working voltage for which for it is
designed.
 The cable should be provided with a mechanical protection so that it may
withstand the rough usage in laying it.
 Material used in manufacture of cable should be such as to give complete
chemical and physical stability throughout.

28. Insulating material for cables
 The main requirements of the insulating materials used for cables are :
High insulation resistance to avoid leakage current.
High dielectric strength to avoid electrical breakdown cable.
Low permittivity’
Immune to attacks by acids and alkalies , over a range of temperature of
about -18c
To 94c
Good mechanical properties.

29. Classification of cables
 Usually the operating voltage determines the type of insulation and the cable
are placed in various categories depending upon voltage for which they are
designed .According to voltage, the cable are classified as:
 Low voltage (LT) cables for operating voltage upto 1,000V.
 High voltage (HT) cables for operating voltage upto 11,000V.
 Super -tension (ST) cables for operating voltage upto 33,000V.
 Extra high tension (EHT) cables for operating voltage upto 66,000V.
 Extra super voltage cable for operating voltage beyond 1,33,000V.
 A cable may be a single core or multi –core depending upon the type of
service.

30. Low tension (LT) cables:
 The lt cable are of two type viz single core and multi core cable. The former
type has the advantage of simplicity of construction and availability of larger
conductor section. The various size of LT cable are given below:
Single core cable with aluminium conductors : 1.5-625 mm sqr.
Two , three , three and a half and four core
Cable with aluminium conductors : 1.5-625 mm sqr.
Control cable upto 61 cores with copper
Conductor : 1.5 and 2.5 mm sqr.

31. Extra high tension (EHT) cables
 the cable considered up till now are called solid type and in such cables it
was assumed that the dielectric is homogeneous and there are no voids in the
this assumption it is necessary to stick to maximum safe dielectric stress of
about 4 or 5 KV per mm.in order to meet the increased voltage demand the
extra high tension and extra super – voltage power cable ,useful for 132 KV
and above ,have been developed. In all such cables, the voids have
eliminated by increasing the pressure of the compound and that is why such
cable are called pressure cables.
 Pressure cables are of two type
 Oil – filled cable
 Gas – pressure cable

32. Underground transmision line
 Undergrounding is the replacement of overhead cables providing electrical
power or telecommunications, with underground cables. This is typically
performed for aesthetic purposes, but also serves the additional significant
purpose of making the power lines less susceptible to outages during high
wind thunderstorms or heavy snow or ice storms. Undergrounding can
increase the initial costs of electric power transmission and distribution but
may decrease operational costs over the lifetime of the cables.

33. Advantages….
 Less subject to damage from severe weather conditions (mainly lightning,
wind and freezing)
 Reduced range of electromagnetic fields (EMF) emission, into the surrounding
area. However depending on the depth of the underground cable, greater emf
may be experienced. The electric current in the cable conductor produces a
magnetic field, but the closer grouping of underground power cables reduces
the resultant external magnetic field and further magnetic shielding may be
provided.
 Underground cables need a narrower surrounding strip of about 1–10
meters to install (up to 30 m for 400 kV cables during construction),
whereas an overhead line requires a surrounding strip of about 20–200
meters wide to be kept permanently clear for safety, maintenance and
repair.

34. …..
 Underground cables pose no hazard to low flying aircraft or to wildlife.
 Much less subject to conductor theft, illegal connections sabotage, and
damage from armed conflict.
 Burying utility lines makes room for more large trees on sidewalks which
convey environmental benefits and increase property values

35. Disadvantages
 Undergrounding is more expensive, since the cost of burying cables at
transmission voltages is several times greater than overhead power lines, and
the life-cycle cost of an underground power cable is two to four times the
cost of an overhead power line.
 Whereas finding and repairing overhead wire breaks can be accomplished in
hours, underground repairs can take days or weeks and for this reason
redundant lines are run.
 Underground cable locations are not always obvious, which can lead to
unwary diggers damaging cables or being electrocuted.
 Operations are more difficult since the high reactive power of underground
cables produces large charging currents and so makes voltage control more
difficult.

36. …..
 Whereas overhead lines can easily be uprated by modifying line clearances
and power poles to carry more power, underground cables cannot be uprated
and must be supplemented or replaced to increase capacity. Transmission and
distribution companies generally future-proof underground lines by installing
the highest-rated cables while being still cost-effective.
 Underground cables are more subject to damage by ground movement.

37. Methods of laying of underground cables
 There are three method of laying underground cable:
 Direct laying .this method of laying underground cable is simple and cheap
.in this method of laying underground cable a treach about 1.2m deep and 0.5
m wide.
 as recommended in ISI specification the minimum depth of trench from the
ground level or from the upper surface of the street pavement are given
below:
 For cable below 1.1 KV rating – 0.45 m plus radius of complete cable.
 For cable between 3.3 and 11 KV rating – 0.75 m plus radius of complete
cable.
 For cable between 22 and 33 KV rating – 1.0 m plus radius of complete
cable.
 Though this method of laying underground cable is simple , clean , safe and
cheap and provides better condition for heat dissipation resulting In higher
current carrying capacity cable.

38. Joining of underground cable
T- type joint y- type joint
Straight joint

39. Cable fault
 Cables are generally laid directly in the ground or in ducts in the underground
distribution system. , 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 :
a) Open-circuit fault. 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 a megger.
The megger will indicate zero resistance in the circuit of the conductor that is
not broken
b) Short-circuit fault. 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. . If the megger gives zero reading, it indicates shortcircuit
fault between these conductors

40. Causes of failure of underground cable
a) The cable may be also get damaged due to vibration fatigue or overheating.
a) The most common Point of failure is at the cable sealing box mostly due to
the cable jointer when the end was sealed.

41. Thank You All….. !!!

Special thanks to
Mr. TARUNJEET SINGH
(Asst. Professor) APIIT SD INDIA
Dept. of Electrical & Electronics Engineering