2011/09/09 at 2:10 pm #10624Vidhyut S.Participant
I am final year student.
We are going to do a project based on Substation design but
we don't know what to do something new..
We will just analyse various substations and will make simply one report….
Please help me to do some innovative work…..2011/09/10 at 4:59 pm #12492adminKeymaster
Electricity is generated in bulk at power
stations, located at remote places. Location of power stations is governed by
various factors, such as economy of generation, safety availability of
resources. Electricity is to be continuously generated to meet the demand and
is to be transmitted over long distances to load centres. For this purpose, a
complicated power system has been developed. The modern electrical system forms
a large interconnected network and covers a vast geographical area. This
interconnected transmission and distribution network is divided into three
hierarchical levels as shown in Figure 1.
At generating stations, voltage level of power
generated at 3.3 kV, 6.6 kV, 11 kV or 33 kV is stepped up and it is fed to the
main transmission network, operating at 400 kV or above. The main transmission
network forms a mesh or ring and is interconnected with neighbouring networks.
This network delivers power to sub-stations where the voltage level is stepped
down to 220 or 132 kV and the power is fed to the sub-transmission network.
Power from local generating stations is also received at this level. This
network transmits power to other sub-stations, where the voltage level is
brought down to 33 kV and is delivered to the distribution network. The distribution
network feeds directly to 33 kV consumers and delivers power to 33 kV
sub-stations. At these sub-stations, the voltage level is further reduced to 11
kV and consumers are supplied through 11 kV feeders. For medium and low voltage
consumers, pole-mounted or indoor 11/0.4 kV sub-stations are installed on these
feeders. The sole aim of this highly complicated and large-interconnected
network is, to supply continuous, safe, reliable and good quality electricity
to consumers. These aspects are considered separately as follows:
Frequency of occurrence of electrical accidents, gives an idea about the safety
aspect of supply system. Table 1 gives number of electrical accidents occurred
in last few years in Uttar Pradesh.
It is seen from the above that nearly 750
electrical accidents are being reported every year and about three-fourth of
these are fatal, causing loss of human or animal lives. The Section 44A of
Indian Electricity Rules, 1956, provides the details regarding the intimation of
accidents which is described below.
If any accident occurs in connection with
generation, transmission, supply or use of energy in or in connection with, any
part of the electrical supply lines or other works of any person and the
accident results in or is likely to have resulted in loss of human or animal
life or in any injury to a human being or an animal, such person or any
authorised person of the State Electricity Board/Supplier, not below the rank
of a Junior Engineer or equivalent shall send to the inspector a telegraphic
report within 24 hours of the knowledge of the occurrence of the fatal and a
written report within 48 hours of the knowledge of occurrence of fatal and all
other accidents. Where practicable a telephonic message should also be given to
the Inspector immediately the accident comes to the knowledge of the authorised
officer of the State Electricity Board/Supplier or other person concerned.
Unfortunately, public is not aware of this rule
and it is frequently breached by the board’s of supplier’s officials. As a
result, most of the electrical accidents remain unreported. Even though, the
data shown in Table 1, clearly indicate that the supply of electricity is not
Table 1 Number of electrical accidents occurred
in Uttar Pradesh
Year Number of Accidents 1989-90 719 1990-91 941 1991-92 786 1992-93 689 1993-94 691 1994-95 741 1995-96 738
Continuous and Reliable Supply of Good Quality
Presently, continuous supply of electricity to all the consumers is not
feasible because of a large gap between demand and generation. To bridge this
gap, high level planning is required which involves central as well as state
governments. This is a well known fact and generally the consumers are not
bothered about it. However, they are most seriously involved with the
uninterrupted supply of available energy. Inability of the distribution system
to ensure reliable supply of good quality power, during scheduled hours, has
become a major concern and it has received considerable attention of various
sections of society, such as politicians, professionals, businessmen and common
people. Interruption during supply hours is caused mainly due to breakdowns,
which occur frequently. Also the quality of power supplied, especially in rural
areas, is not good, i.e., voltage and frequency vary beyond permissible limits.
As a result, performance of appliances and equipments is adversely affected and
damage to them is caused.
Taking inspiration from the problems discussed
above, a survey was conducted about the defects and shortcomings of 33 kV
distribution sub-stations of UP Power Corporation Ltd. (previously the UP State
Electricity Board), located in the Ghazipur district. Purpose of these
sub-stations is voltage transformation, switching, metering and monitoring the
condition of the system. In the survey, 20 sub-stations were covered during the
period from September to December, 1999. The survey was conducted in the light of
Indian Electricity Rules, 1956, made to regulate the generation, transmission,
supply and use of electricity.
Section 29(1) of Indian
Electricity Rules, 1956 reads as: all electric supply lines and apparatus shall
be of sufficient ratings for power, insulation and estimated fault current and
of sufficient mechanical strength, for the duty which they may be required to
perform under the environmental conditions of installation, and shall be
constructed, installed, protected, worked and maintained in such a manner as to
ensure safety of personnel and property. In general, observations are made on
the basis of this Section, but wherever necessary, specific Sections of the
said Rules are referred. Findings of the survey are as follows:
- Proper danger notices
[Section 35], fire buckets filled with clean dry sand and fire extinguishers
ready to use for dealing with electric fires [Section 43(1)], and first-aid box
[Section 43(2)], were not found at any of the sub-stations. Also, instructions
for restoration of persons suffering from electric shock [Section 44(1)], were
not affixed in any of the centre. Further, acquaintance of authorised persons
with these instructions and their competency to apply them [Section 44(3)] were
not ensured. The situation worsens with the fact that these sub-stations do not
have tools and accessories, such as handle for charging the oil
circuit-breakers (OCBs), earthing chains, rubber mats, hand gloves, safety
belts, etc. for proper working. Thus, safety of personnel and property is the
most neglected concern at these sub-stations.
- At 17 of the
sub-stations, the number of working oil circuit breakers (OCBs) were found to
be less than the required ones [Section 50(1)(c)]. Thus, instead of proper
connections of Figure 2(a), they were found connected as shown in Figure 2(b).
Also, 19 of the sub-stations do not have load breaking isolators or TPMOs on
all the outgoing feeders. Connection of two or more feeders to some of the
OCBs, as shown in Figure 2(b), results in power cut for twice or more larger
area in case of breakdown or during period of maintenance. Thus, supply to a
large number of consumers is unnecessarily interrupted. Further, burden of
these OCBs has increased considerably as they have to make or break twice or
larger amount of current than they were intended for. As a result, melting,
pitting or fusion of their contacts occur frequently. From the safety point of
view, it is never advised to work on the feeders with only opening the circuit
breaker contacts. But it is not always possible to follow the guidelines as
TPMOs are not provided on most of the feeders. Further, at 8 of the
sub-stations, some of the working OCBs have mechanical defects and at 17 of
them, their mechanisms were found bare. Thus, persons on duty do not take
interest in operating them unless there is an utmost urgency. In this way,
during abnormal conditions, maximum damage to the system is caused. Clearly,
switching operations are not being performed satisfactorily at these
- At 6 of the sub-stations,
most of relays were found either removed or defective. Even the condition of
the rest of the relays could not be judged as at none of the sub-stations
periodical testing of them is being carried out and records thereof are being
Consider the feeder A in Figure 2(a), assuming
its full load current as 100% let its two over-current relays are set at 135%.
When two more feeders are connected with the same OCB as shown in Figure 2(b),
the full load current becomes 300% and for proper working of the OCB, the
relays must be set at about 400%. Thus, even the healthy over-current relays
will not be able to sense the abnormal conditions unless the current increases
to a much larger extent.
As far as earth fault relay is concerned, it is
not expected to operate the OCB for earth faults occuring on the line as none
of the overhead lines has continuous earth wire or proper earthing of
non-current carrying metallic parts [Section 90]. Thus, even a healthy earth
fault relay will be able to sense the earth fault occuring inside the control
room and the switchyard only. Also, even this may not happen as at 4
substations, earthing system inside the switchyard [Section 67] was found
defective. Further, periodical testing of the earthing system is not being
carried out and records thereof are not being maintained at any sub-station
[Section 67(5)(b)]. In this way, neither the over-current not the earth fault
relays are able to provide effective protection to the system. The problem is
so severe that at some of the sub-stations, fuses on the 33 kV side of the
transformers were found as the only effective means of protection.
The situation worsens with the fact that at some
of the sub-stations, all the outgoing feeders were found connected with a
single OCB, as OCB of feeder A in Figure 2(b). In this case the OCB of the
feeder, with settings of the relays changed accordingly, is in series with the
OCB of the incoming feeder. Thus, one of the OCBs becomes redundant.
One of the important functions of these sub-stations
is that of metering the energy, but unfortunately none of them has the required
number of energy meters in working order. Some of them were found either
removed or defective. Also, periodical testing of energy meter is not being
carried out regularly and records thereof are not being maintained. At some of
the sub-stations, some of the energy meters have not been connected because of
non-availability of current or/and potential transformers. Thus, proper
metering of energy is not being performed at these sub-stations. Instead of
metering the energy supplied, it is being allocated to different feeders,
depending on the ingenuity and experience of the person involved. In this way,
the actual data of energy supplied by these sub-stations is not available which
results in failure of the schemes and damage to the system, designed on the
basis of erroneous data, and makes it difficult to estimate the losses in the
system due to theft. Thus, the energy theft is encouraged and preventative
measures are inhibited.
Another aspect of not metering the energy
properly is the fact that it permits the manipulation by the officials
responsible for the collection of corporation’s revenue. They lessen their
burden by allocating maximum amount of energy to the sectors with unmetered
supply and minimum tariff, such as agriculture sector, Kutir Jyoti scheme,
Harizan Basti, and show a large amount of energy as losses in the distribution
system. As a result, the revenue of the corporation is reduced considerably.
Further, the state exchequer is adversely affected as the amount of electricity
duty is significantly reduced.
- Indicators on the panel
in the control room, such as ammeters, voltmeters, power factor meters, were
found defective at 17 sub-stations. Also at 11 of them, indicators on the
transformers were defective. Further, 19 sub-stations have defective alarm
system. Thus, even a healthy Buchholz relay and oil temperature indicator will
not be able to give remote warning of development of incipient faults or leakage
of transformer oil and abnormally high oil temperature. So the operator would
not be able to take preventive action. Thus, proper monitoring of the system
condition is not feasible at all. The situation worsens with the fact that at 2
sub-stations, unauthorised persons were on duty and logsheets were not being
- As far as maintenance of
transformers is concerned, their bushings were found broken at 2 sub-stations
and oil leakage was seen at 8 of them. At 10 of the sub-stations, silica gel of
the transformers was found old and ineffective. Also, at all the sub-stations,
periodical testing of the transformer oil is not being carried out and records
thereof are not being maintained.
- At 15 of the
sub-stations, wiring inside the control room was found defective. Also, at 2
sub-stations, unused or damaged cables were found in the cable trench and at 6
of them, cable trenches were found not properly filled with sand and covered.
Further, unused materials or defective equipments were found stored inside the
control room at 7 sub-stations. Even spacing behind the panel was found
improper at one sub-station, indicating flaw at the planning and designing
- At 11 sub-stations, some
insulators were found broken in the switchyard and isolators were found
defective at 11 of them. Also unused installations were found dangerously
connected to the supply mains at 5 sub-stations and unused materials or
defective equipments were stored inside the switchyard of 7 of them. Further,
at 14 sub-stations, fencing of the switchyard was found either broken or
ineffective, allowing entrance to unauthorized persons and animals. Even
connections inside the switchyard and on the double poles and lines of the
outgoing feeders were not found proper at 17 of the sub-stations.
- At 18 of the
sub-stations, some or all the surge or lightning arresters were found broken or
removed. The situation is so worse that at some of these sub-stations, healthy
ones are provided on unused installations while installations in use do not have
proper protection. Thus, temporary power frequency over voltages, lightning and
switching surges are likely to damage the main 33/11 kV transformer, the
costliest and inevitable equipment of the sub-station.
- Section 54 provides that
the supplier shall not permit the voltage, at the point of commencement of
supply, to vary from the declared voltage.
in the case low and
medium voltage, by more than 6%, or;
in the case of high
voltage, by more than 6% on the higher side or by more than 9% on the lower
To maintain the voltage of supply within permissible limits, capacitor banks
are provided for reactive power injection at these sub-stations, but at none of
them these were found operational. Surprisingly, a consumer using energy at low
power factor, is penalized with surcharge but the Corporation is completely
negligent to its responsibility of providing good quality power. As a result,
performance of equipments and appliances suffers and their life is also
Parallel operation of transformers is not being
used at any sub-station, having two transformers. Also, none of them is
provided with OCB on the 33 kV side. Further, at one of the sub-stations,
auto-reclosing circuit breakers were provided but the Corporation has failed to
maintain them. Thus, better techniques, to improve system’s performance, are
not being used and it seems that the Corporation doesn’t have sufficient
expertise to cope up with these at this level.
The survey indicates that the safety of personnel and property is the most
neglected concern at these sub-stations, resulting in increase in occurrence of
electrical accidents. It is found that the Corporation’s officials, instead of
investigating the cause of accidents and taking precautions to avoid them in
future, rely on hiding the facts. As far as switching is concerned, most of the
sub-stations have defective OCBs and improper connection of feeders. Also,
protective relays have rarely been found working properly. Thus, proper
switching is not being performed at these sub-stations. Further, energy meters
and indicators are defective at most of the sub-station, so the metering and
condition monitoring are also not being performed satisfactorily. In this way,
except the voltage transformation, these sub-stations have failed to perform
effective and satisfactorily switching, metering or condition monitoring. In
short, they have lost much of the purpose they were meant for. Thus, the
Corporation has failed to maintain these sub-stations based on age-old
technologies, and has not attempted seriously the incorporation of better
techniques to improve the system’s performance at this level.2011/09/12 at 3:55 pm #12476Vidhyut S.Participant
Thanks for giving such a nice information.
Your main concentration is on safety measures.
It is right that accidents occur due to lack of technology but
I live in ‘Gujarat’.We have very less chances of accidents.
Rarely two or three accidents occur in a year.
Can you suggest another idea..?
- Proper danger notices
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