3. ELECTRICAL POWER GENERATION
• POWER GENERATION- Electricity is generated various kinds of power plants by utilities and
independent power Producers . Generation is the production of electricity at power stations
or generating units where a form of primary energy is converted into electricity.
4. • The huge amount of power generated in a power station is to be transported
over a long distance to load centers to cater power to consumers with the
help of transmission line and transmission towers.
• For instance, for a power station generating 120 MW power at 10 kV line to
line voltage, current in the transmission line will be 8660 A. Instead of
choosing 10 kV transmission voltage, if transmission voltage were chosen to
be 400 kV, current value in the line would have been only 261.5 A.
• So, the sectional area of the transmission line (copper conductor) will now be
much smaller compared to 10 kV transmission voltage. The cost of conductor
will be greatly reduced if power is transmitted at higher and higher
transmission voltage.
• The cost of conductor will be greatly reduced if power is transmitted at
higher and higher transmission voltage.
5. • The use of higher voltage (hence lower current in the line) reduces voltage
drop in the line resistance and reactance. Also transmission losses are
reduced.
• Standard transmission voltages used are 132 kV or 220 kV or 400 kV or 765
kV depending upon how long the transmission lines are.
• After the generator, there is a step up transformer to change the generated
voltage (say 10 kV) to desired transmission voltage (say 400 kV) before
transmitting it over a long distance with the help of transmission lines
supported at regular intervals by transmission towers.
• While magnitude of current decides the cost of copper, level of voltage
decides the cost of insulators. The idea is, in a spree to reduce the cost of
copper one can not indefinitely increase the level of transmission voltage as
cost of insulators will offset the reduction copper cost.
6. • At the load centers voltage level should be brought down at suitable values
for supplying different types of consumers.
• Consumers can be categorized as:
• big industries such as steel plants
• medium and small industries
• offices and domestic consumers
• Electricity is purchased by different consumers at different voltage level. For
example, big industries may purchase power at 132 kV, medium and big
industries purchase power at 33 kV or 11 kV and domestic consumers at
rather low voltage of 230 V, single phase.
• Thus, 400 kV transmission voltage is to be brought down to different voltage
levels before finally delivering power to different consumers. This is done by
step down transformers.
7. • Substations
• Substations are the places where the level of voltage undergoes change with
the help of transformers. Apart from transformers a substation houses
switches (called circuit breakers), meters, relays for protection and other
control equipment.
• A big substation receives power through incoming lines at some voltage (say
400 kV) changes level of voltage (say to 132 kV) using a transformer and then
directs it out wards through outgoing lines.
• At the lowest voltage level of 400 V, generally 3-phase, 4-wire system is
adopted for domestic connections. The fourth wire is called the neutral wire
(N) which is taken out from the common point of the star connected
secondary of the 6 kV/400 V distribution transformer.
8. Regional and National Grid
• Transmission forms a critical link in the power sector value
chain. India's power generation capacities are unevenly
dispersed across the country creating an imbalance between
the distribution of power demand and supply centres.
• The country has been demarcated into five electrical Regions:
1. Northern (NR)
2. Eastern (ER)
3. Western (WR)
4. Southern (SR)
5. North Eastern (NER)
• All the regional grids are synchronously interconnected and
operating as single grid known as Central Grid or National Grid.
9. Distribution System
• Power received at a 33 kV substation is first stepped down to 6 kV and with the help of
under ground cables (called feeder lines), power flow is directed to different
directions.
• At the last level, step down transformers are used to step down the voltage form 6 kV
to 400 V. These transformers are called distribution transformers with 400 V, star
connected secondary. Such transformers are generally mounted on poles in cities
beside the roads. These are called pole mounted substations.
• From the secondary of these transformers 4 terminals (R, Y, B and N) come out. N is
called the neutral and taken out from the common point of star connected secondary.
Voltage between any two phases (i.e., R-Y, Y-B and B-R) is 400 V and between any
phase and neutral is 230 V.
• Residential consumers are supplied with single phase 230 V, 50 Hz. So individual are to
be supplied with any one of the phases and neutral.
12. Armored cable
Aluminum conductor steel-Reinforced cable (ACSR)
CABLE IN ELECTRICAL TRANSMISSION TO DISTRIBUTION
• Aluminum conductor steel –reinforced cable (ACSR) is a type
of high- Capacity , high –strength stranded conductor typically
used in overhead power line . The outer strands are high-purity
aluminum , chosen for its good conductivity ,low weight , low
cost , resistance to corrosion decent mechanical stress
resistance
• Armored cable Commonly known as SWA cable, the steel
wire armored cable is a power and auxiliary control cable,
designed for use in mains supply electricity. Used
for underground systems, cable networks, power networks,
outdoor and indoor applications, and cable ducting
Cable- An electrical cable is an assembly of one or more wires
running side by side or bundled, which is used to carry electric current
Types Of cable
• Power Cable- PVC/XLPE
• Armored cable
• Twisted Pair Cable-Telephone/Network
• Fiber optics- Data/Communication
• RG cable-for CCTV
• Co-axial Cable- TV
13. Transformer to LT panel
through air circuit
breaker(ACB).
LT Panel to building main
switch through
outgoing ACB/MCCB
POWER FLOW
Tap-off from rising main at
each floor feeds the floor
panel with incoming MCCB
and outgoing MCCB.
Outgoing from DB feeds the
load on light/power circuit.
Power load at the end of
the power circuit is
through by MCCB/MCB.
HT Panel to transformer.
HT panel with overload/
short circuit/earth
leakage protection of
transformer.
Outgoing MCCB (moulded
case circuit breaker) to feed
rising main with incoming
MCCB.
Power is received in building
main LT Panel with incoming
ACB/MCCB and outgoing
MCCB.
Outgoing MCCB of floor panel
feeds DB with incoming
MCCB/MCB (miniature circuit
breaker) and outgoing
MCCB/MCB
14. ● Electrical Power System is a highly invested area. The more reliable electricity we
want, the more is need to protect it. Protection is essential to keep equipment and
personnel safe from any kind of damage caused by an electrical unbalance or fault
condition.
● Protection devices perform their purpose by keeping a faulty section isolated from the
remaining healthy system to make it work without any disturbances. The function of a
protection system is not to prevent faults as its name suggests, rather it minimizes
repair costs as it senses fault because it only acts after a fault occurs
PROTECTION SCHEMES FOR ELECTRICAL POWER SYSTEM
15. Power system protection's main objective is to maintain the reliability of the running power system
and to save the equipment from getting damaged.
• Only the faulty part of the system is completely isolated within a minimum time so that the
remaining system operates normally.
• In the case of normal conditions, there should be no nuisance tripping.
• To isolate the system from the faulty section, fuses and circuit breakers are used and to detect
fault relays are used.
• In low voltage systems breakers perform both functions of detecting and isolating the fault.
OBJECTIVES OF POWER SYSTEM PROTECTION
16. The protection zone surrounds each power equipment. When a fault occurs in
any of the zone, then only the circuit breaker in that zone trips. Therefore, only
a faulty element is disconnected without affecting the rest of the system.
Following six categories of protection zones are possible in a system, we apply
here a concept of selective coordination.
• Generators and generator–transformer units
• Transformers
• Buses
• Lines (transmission, sub-transmission, and distribution)
• Utilization equipment (motors, static loads, or other)
• Capacitor or reactor banks (when separately protected).
PROTECTION ZONES IN POWER SYSTEM
17. PROTECTION SCHEMES
1. Over current protection scheme
An over-current protection scheme is regarded as the most obvious principle of protection as it can
detect a sudden buildup of current magnitude that is considered as an effect of fault. But, the
magnitude of the fault current is related to the type of fault and the source impedance.
The source impedance depends upon the number of generating units that are in service at a given
time and keeps changing from time to time. So, the setpoint for the distinction of fault current
magnitude from the normal current as well as the operating time of over-current protection keep
changing from fault to fault, and time to time. This has led protection engineers to think of other
principles.
2. Differential Protection Scheme
Differential protection is based on the assertion that the current leaving a protected section must be
equal to that entering it. Any difference between the two endpoints of a single section indicates a
fault. Thus, we can compare the two currents either their phase or magnitude or both
18. 3. Distance Protection Scheme
A distance protection scheme relates the voltage with the current at the same end.
This scheme computes the impedance between the protection location and the
fault point. Then it compares it with a pre-set value to make the trip decision.
4. Directional Protection Scheme
Directional protection scheme becomes functional in the case of a double-end
feed system or parallel lines or a ring main system, where a fault gets fed from
both sides. From the selection perspective, this type of protection is sensitive
enough to detect the direction of the fault power flow.
19. Switchgear
• The apparatus used for switching, controlling & protecting the
electrical circuits & equipment are known as switchgear.
• The switchgear equipment is essentially used with switching &
interrupting currents either under normal or abnormal operating
condition.
• It consists of devices such as switches, fuses, circuit breakers, relays
etc.
• Basically every electric circuit needs a switching device & a
protecting device.
• On the other hand, when a failure (e.g. short circuit) occurs on any
part of power system, a heavy current flows through the equipment,
threatening damage to the equipment and interruption of service to
the customers. However, the switchgear detects the fault and
disconnects the unhealthy section from the system. In this way,
switchgear protects the system from the damage and ensures
continuity of supply
• Switchgear is also a combination of switching devices such as :-
• - protection devices
• - switching devices
HV SWITCHGEAR
HV wire-way
HV compartment
20. Protection devices
• Circuit breakers(MCB- Miniature Circuit Breaker)
• MCCB(Moulded case circuit breaker)
• Relays
• Fuse
Switching devices
• Switches
• isolator
• Contactors
Control and sensing devices
• CT(current transformer)
• Ammeter
• Energy meter
SWITCHGEAR EQUIPMENT
21. PROTECTION DEVICES
(MINIATURE CIRCUIT BREAKER-MCB)
• Miniature Circuit Breakers are electromechanical devices
which protect an electric circuit from an over current.
• The over current, in an electrical circuit, may result from short
circuit, overload or faulty design. Miniature Circuit Breakers are
used to protect lower current circuits and have the following
Specifications :-
• Rated current not more than 100A.
• Trip characteristics normally not adjustable.
22. • MCB means miniature circuit breaker –it is used for
up to 100 amp.
• MCCB means Molded case circuit breaker –it is
used for 250 amp.
• An MCCB provides protection by combining a
temperature sensitive device with a current sensitive
electromagnetic device.
• The traditional molded-case circuit breaker uses
electromechanical (thermal magnetic) trip units that
may be fixed or interchangeable.
• Molded case circuit breakers are a type of electrical
protection device that is commonly used when load
currents exceed the capabilities of miniature circuit
breakers. They are also used in applications of any
current rating that require adjustable trip settings,
which are not available in plug-in circuit breakers and
MCB
A MCCB has three main functions:-
• Protection against overload
• Protection against electrical faults
• Switching a circuit on and off
MCCB (MEANS MOLDED CASE CIRCUIT BREAKER)
23. A circuit breaker is a device which can make or break a circuit either manually or automatically under
normal or abnormal condition.
OPERATING PRINCIPLE
• Two contacts called electrode remains closed under normal operating conditions. When fault
occurs on any part of the system, the trip coil of the circuit breaker get energized and contacts are
separated.
• A circuit breaker essentially consists of fixed and moving contacts
TYPES OF CIRCUIT BREAKER
• Oil Circuit Breaker
• Air Blast Circuit Breaker
• Sf6 Circuit Breaker
• Vacuum Circuit Breaker
CIRCUIT BREAKER
24. RELAYS
• A relay is a automatic device which senses an abnormal
condition of electric circuit and closes its contacts.
• A relay may also be called an “electromagnetic switch”
• Protective relay is a device designed to trip a circuit breaker
when fault is detected.
• It is operating on moving parts to provide detection of
abnormal condition.
There Are Two Basic Classifications Of Relays:-
• Electromechanical Relays
• Solid State Relays
• One main difference between them is electromechanical
relays have moving parts, whereas solid state relays have no
moving parts.
25. • Fuse is a device used in circuit for protecting electrical equipment against overloads and /or short
circuits. Fuse element or fuse wire is that part of the fuse device which melts when an excessive
current flows in the circuit and thus isolates the faulty device from the supply circuit.
• A fuse is a short piece of wire or thin strip which melts when excessive current flows through it for a
sufficient time.
Desirable qualities of fuse elements
• Low melting point
• Low ohmic losses
• High conductivity
• Low cost
FUSE
26. • A switch is a device which is used to open or close an electrical circuit in a convenient way.
• it can be used under full-load or no load condition but it cannot interrupt the fault current.
THE SWITCHES ARE CLASSIFIED ARE AS FOLLOW:-
• Air-break switches
• oil switches
Switches
There are wide variety of switches available differ
mechanically, electrically, and in the arrangement
of switch contacts
• Single-pole single throw switch(SPST)
• Single-pole double throw switch(SPDT)
• Double-pole single throw switch(DPST)
• Double-pole double throw switch(DPDT)
29. INDOOR SUBSTATIONS AND UNDERGROUND CABLE POWER
DISTRIBUTION:
• Outdoor substations are subject to dust, rain, storm, extreme heat and theft
leading to breakdowns and higher maintenance. During winds, cyclones and
storms, the entire distribution system including poles, and conductors
collapse taking long time to restore the power supply.
• The indoor substations work at much lower ambient, say at 28 Degree C,
when the outside temperature may be above 40 degree C. Similarly the UG
cable of power distribution is far superior to overhead system.
• Substation with DG Backup: Uninterrupted power supply is supplied by the
substation to cater to various loads based on DG Backup and UPS backup..
30. DRY V/S OIL COOLED TRANSFORMER: Oil cooled transformers are not
allowed to be located inside the building. They are allowed when the
substation is away from the main building.
However it is recommended to go for dry transformer in place of oil cooled
transformer for following reasons:
• Not prone to fire and explosion thereof.
• Practically maintenance free.
EACH DISTRIBUTION SUBSTATION TO HAVE ITS DG BACK UP: It is
recommended that each distribution substation should have its own DG
Backup so that in case of mains power failure local DG sets are available as
backup as per the normal practice.
• It is not recommended to have a centralized DG Backup to supply 11 KV DG
Power to the distribution substations. This will not allow for segregation of
essential and non-essential supply. Also in case of any fault in 11 KV feeder
cable the whole campus will have no DG Backup
31. PROVISION OF SCADA PANEL : Substation For Digital monitoring and data
logging of the substation parameters, SCADA Panel should be provided if the
additional cost is justified considering its utility.
PROVISION OF MAIN LT PANEL : conforming to IS 8623:1993 and other
relevant Indian Standards. All main LT Panels shall conform to IS 8623:1993
and other relevant Indian Standards for ensuring proper quality.
SPACE FOR FUTURE EXPANSION OF SUBSTATION: Each substation should
have provision of addition for at least one transformer and extension of LT
Panel to take care of future growth of load.
32. THE OBJECTIVE OF UNINTERRUPTED POWER SUPPLY IS ACHIEVED BY
THE FOLLOWING MEANS:
First, assess power requirement of the building/campus. Keeping
reasonable provision for future growth of power which conservatively is
about 5% growth per annum. For example, Delhi peak power demand has
increased from 4700 MW in 2010 to 7000 MW in 2018-growth of 50 % in 8
years.
This power will be received at the receiving substation (Grid substation)
from the local supply company. Depending on the quantum of power
required and local regulations, the power may be supplied at
11KV/33KV/66KV.
The campus may take about 5 to 10 years to develop the full load so have
a flexible contract with the supply company to gradually take care of the
growth of load may be explored, the provision for space for extension of
substation building during future load may be kept in layout.
33. LOCATING THE RECEIVING SUBSTATION AND DISTRIBUTION
SUBSTATIONS:
The receiving substation is to be located in consultation with the supply
company and the architect. Generally it is at the periphery of the campus.
Next to locate the various distribution substations. To reduce voltage drop
cabling cost, it is preferable that each substation feeds power up to 200
meters.
substations are independent buildings on ground floor and house supporting
services like DG Sets, UPS etc. When it is a part of the main building, it should
be located on ground floor as per CPWD specifications and NBC Code.
Basement is avoided due to likely flooding during heavy rains however in
case basement is selected, arrangements of protection if flooding and
pumping out water must be provided.
In a centrally AC building, 50% of the power is consumed by AC. Therefore
the plant room should be adjacent to the substation to reduce cost of
interconnection.
39. The design and planning of an electrical wiring installation shall take into consideration the following:
a) Type of supply, building utility, occupancy, envisaged load and the earthing arrangement available;
b) Provisioning of air conditioning systems in present and/or future loading;
c) Climatic condition, such as cooling air temperature, moisture or such other conditions which are likely
to affect the installation adversely;
d) Possible presence of inflammable or explosive dust, vapour or gas;
e) Degree of electrical and mechanical protection necessary;
f) Importance of continuity of service including the possible need for standby supply;
g) Probability of need for modification or future extension;
h) Probable operation and maintenance cost taking into account the electricity supply tariffs available;
i) Relative cost of various alternative methods;
j) Need for radio and telecommunication interference suppression;
k) Ease of maintenance;
l) Safety aspects; p) Energy conservation;
m) Importance of proper discrimination between protective devices for continuity of supply and limited
isolation of only the affected portion; and
n) eliability of power supply and redundancy (of sources and distribution paths) to cater to the needs for
emergency power and standby power for continued operation of systems as well as integration of
alternate sources of energy such as diesel generation, solar energy, wind power, etc.
PLANNING OF ELECTRICAL INSTALLATIONS
40. Layout of Substation
a) Supply company’
s meter room, generally at the periphery of the
premise with direct access from the road/outside;
b) HV isolation room, required in case the substation is away from the
meter room and is planned adjacent to meter room for
disconnecting supply in case of any repair required between meter
room and substation;
c) HV panel room/space, located adjacent to transformer;
d) Transformer room/space, separate space in case of oil-filled
transformer and combined space in case of dry type transformer;
e) MV isolation room/space, required in case MV panel is away from
transformer or on a different level for isolating supply in case of any
repair required between transformer and MV switchgear; and
f) Main MV panel room/space, required for distribution to different
facility/utility in a building
41. System of Supply
In case of connected load of 100 kVA and above, the relative advantage of high voltage three-phase supply
should be considered. Generally the supply is at 240 V single phase up to 5 kVA, 415/240 V 3-phase from 5
kVA to 100 kVA, 11 kV (or 22 kV) for loads up to 5 MVA and 33 kV or 66 kV for consumers of connected
load or contract demand more than 5 MVA.
In very large industrial buildings where heavy electric demands occur at scattered locations, the economics
of electrical distribution at high voltage from the main substation to other subsidiary transformer
substations or to certain items of plant, such as large motors and furnaces,should be considered.
Substation Equipment and Accessories
• Supply Company’
s High Voltage Meter Board
• High Voltage Switchgear
The selection of the type of high voltage switchgear for any installation inter alia depends upon the following:
a) Voltage of the supply system; b) Prospective short-circuit current at the point of supply; c) Size and layout of
electrical installation; d) Accommodation available; and e) Nature of industry.
• HV Cables
The sizing of the cable shall depend upon the method of laying cable, current to be carried, permissible
maximum temperature it shall withstand, voltage drop over the length of the cable, the prospective short-
circuit current to which the cable may be subjected, the characteristics of the overload protection gear
installed, load cycle, thermal resistivity of the soil and the operating voltage
42. • High Voltage Bus Bar Trunking/Ducting
HV bus bar system is used for transporting power between HV generators, transformers and the infeed main
switchgear of the main HV switchgear.
• Transformers
General design objective while selecting the transformer(s) for a substation should be to provide at least two or
more transformers,so that a certain amountof redundancy is built in, even if a standby system is provided. The total
installed transformer capacity shall be at least 15 to 20 percent higher than the anticipated maximum demand. With
growing emphasis on energy conservation, the system design is made for both extremes of loading. During the
periods of lowest load in the system, it would be desirable to operate only one transformer and to subsequently
switch on the additional transformers asthe load increases during the day. Total transformer capacity is generally
selected on the basis of present load, possible future load, operation and maintenance cost and other system
conditions. The selection of the maximum size (capacity) of the transformer is guided by the shortcircuit making and
breaking capacity of the switchgear used in the medium voltage distribution system.
• Medium or Low Voltage Switchgear and Controlgear and their Assemblies
• MV/LV Bus bar Trunking/Rising Mains
Where heavy loads and/or multiple distribution feeders are required to be supplied, busbar/rising main systems are
preferred. The busbars are available for continuous run from point to point or with tap offs at standard intervals and
have to be chosen as per specific requirement. Seismic supports shall be provided for bus trunking having continuous
straight lengths of more than 24 m at a single stretch.
43. SUBSTATION LOCATION AND OTHER REQUIREMENTS
1. As far as possible, avoid locating the substation in the basement.
2. If a building has just one basement, the substation room is not required to be located there. In
addition, the substation's floor level must not be the lowest point in the basement.
3. Oil-filled installation—Fire detection, protection, and suppression are all critical in substations
with oil-filled equipment.
4. Substations containing oil-filled equipment must be situated either outside or within a utility
building. They are not permitted to be situated on any floor of a utility building other than the
ground floor or the first basement. They must have direct access to the equipment from the
exterior of the building in order to operate and maintain it.
5. Dry-type Installation: If an electric substation is required to be situated within the main multi-
story structure for unavoidable reasons, it must be a dry-type installation with minimal
flammable materials. Such a substation must be on the ground floor or first basement, with
direct access from the exterior of the building for equipment operation and maintenance.
6. If two transformers (dry type or with less than 2000 litres of oil) are placed next to each other
without an intermittent 13 wall, the space between them must be at least 1500 mm for 11 kV,
minimum 2000 mm for 22 kV, and minimum 2500 mm for 33 kV. Beyond 33 kV, two transformers
must be separated by a 4 h fire-rated baffle wall. 26) The minimum height of the substation/HV
switch room/MV switch room should be determined by taking into account the 1200 mm
clearance requirement between the top of the equipment and the soffit of the beam. This will be
examined more in this research.
44. WIRING DIAGRAM FOR A TYPICAL DISTRIBUTION SCHEME IN A
RESIDENTIAL BUILDING FLAT
TYPICAL DISTRIBUTION BOARD SYSTEM
45. ⌁ The current-carrying capacity of different types of cables shall be chosen in accordance
with good practice
⌁ The current ratings of switches for domestic and similar purposes are 6 A, 16 A, 20 A and
25 A.
⌁ The current ratings of isolators and normal duty switches and composite units of switches
and fuses shall be selected from one of the following values: 16, 25, 32, 63, 100, 160, 200,
320, 400, 500, 630, 800, 1 000 and 1 250 A.
⌁ The current ratings of miniature circuit-breakers shall be chosen from the values given
below: 6, 10, 16, 20, 25, 32, 40, 50, 63, 80, 100 and 125 A
⌁ The current ratings of moulded case circuit breakers shall be chosen from the values given
below: 100, 125, 160, 200, 250, 315, 400, 630, 800, 1 000, 1 250 and 1 600A
⌁ The current ratings of air circuit-breakers shall be chosen from the values given below:
630, 800, 1 000, 1 250, 1 600, 2 000, 2 500, 3 200, 4 000A and 6 300 A
⌁ The current ratings of the distribution fuse board shall be selected from one of the
following values: 6, 16, 25, 32, 63 and 100 A
Rating of Cables and Equipment
46. INDIAN STANDARD CODES
(Part 69) : 1993/ Generation, transmission and dis-
IEC 60050 (602) : tribution of electricity — Generation
1993
(Part 70) : 1993/ Generation, transmission and dis-
IEC 60050 (604) : tribution of electricity —
1987 Operation
Part 71) : 1993/ Generation, transmission and
IEC 60050 (605) : distribution of electricity —
1983 Substations
(Part 78) : 1993/ Generation, transmission and
IEC 60050 (601) : distribution of electricity —
1985 General
(Part 79) : 1993/ Generation, transmission and
IEC 60050 (603) : distribution of electricity — Power
1986 system planning and management
