this is the presentation slide of protection scheme

1. The protection scheme of a grid
substation
Presented by
MD. Abu Jubayer Siddiqui
BSc in EEE
ID: EEE 04606760

2. Power-system protection is a branch of electrical power
engineering that deals with the protection of electrical
power systems from faults through the isolation of faulted
parts from the rest of the electrical network. The objective
of a protection scheme is to keep the power system stable
by isolating only the components that are under fault, whilst
leaving as much of the network as possible still in
operation. Thus, protection schemes must apply with very
pragmatic and pessimistic approach to clearing system
faults. The devices that are used to protect the power
systems from faults are called protection devices.
 What is protection scheme?

3. Some kind of protection scheme
 Circuit breaker
A circuit breaker is an automatically
operated electrical switch designed
to protect an electrical circuit from
damage caused by overcurrent or
overload or short circuit. Its basic
function is to interrupt current flow
after protective relays detect a fault.

4. Low-voltage circuit breakers
 The characteristics of low-voltage circuit breakers are given by
international standards such as IEC 947. These circuit breakers are
often installed in draw-out enclosures that allow removal and
interchange without dismantling the switchgear.
 Large low-voltage molded case and power circuit breakers may
have electric motor operators so they can open and close under
remote control. These may form part of an automatic transfer switch
system for standby power.
 Low-voltage circuit breakers are also made for direct-current (DC)
applications, such as DC for subway lines. Direct current requires
special breakers because the arc is continuous—unlike an AC arc,
which tends to go out on each half cycle. A direct current circuit
breaker has blow-out coils that generate a magnetic field that
rapidly stretches the arc. Small circuit breakers are either installed
directly in equipment, or are arranged in a breaker panel.

5. Magnetic circuit breakers
 Magnetic circuit breakers use a solenoid (electromagnet) whose
pulling force increases with the current. Certain designs utilize
electromagnetic forces in addition to those of the solenoid. The
circuit breaker contacts are held closed by a latch. As the current
in the solenoid increases beyond the rating of the circuit breaker,
the solenoid's pull releases the latch, which lets the contacts open
by spring action. Some magnetic breakers incorporate a hydraulic
time delay feature using a viscous fluid. A spring restrains the core
until the current exceeds the breaker rating. During an overload,
the speed of the solenoid motion is restricted by the fluid. The
delay permits brief current surges beyond normal running current
for motor starting, energizing equipment, etc. Short circuit currents
provide sufficient solenoid force to release the latch regardless of
core position thus bypassing the delay feature. Ambient
temperature affects the time delay but does not affect the current
rating of a magnetic breaker

6. Thermal magnetic circuit breakers
Thermal-magnetic circuit breakers
contain two different switching
mechanisms, a bimetal switch and
an electromagnet. The bimetal
serves as a means of handling over
currents. The bimetal typically sits
behind a trip bar and is part of the
current carrying path.

7. Common trip breakers
 When supplying a branch circuit with more
than one live conductor, each live
conductor must be protected by a breaker
pole. To ensure that all live conductors are
interrupted when any pole trips, a
"common trip" breaker must be used.
These may either contain two or three
tripping mechanisms within one case, or
for small breakers, may externally tie the
poles together via their operating handles.
Two-pole common trip breakers are
common on 120/240-volt systems where
240 volt loads (including major appliances
or further distribution boards) span the two
live wires. Three-pole common trip
breakers are typically used to supply
three-phase electric power to large motors
or further distribution boards.

8. Medium-voltage circuit breakers
Medium-voltage circuit breakers rated between 1 and 72 kV may be
assembled into metal-enclosed switchgear line ups for indoor use,
or may be individual components installed outdoors in a substation.
Air-break circuit breakers replaced oil-filled units for indoor
applications, but are now themselves being replaced by vacuum
circuit breakers (up to about 40.5 kV). Like the high voltage circuit
breakers described below, these are also operated by current
sensing protective relays operated through current transformers.
The characteristics of MV breakers are given by international
standards such as IEC 62271. Medium-voltage circuit breakers
nearly always use separate current sensors and protective relays,
instead of relying on built-in thermal or magnetic overcurrent
sensors.

9. High-voltage circuit breakers
 Electrical power transmission networks are protected
and controlled by high-voltage breakers. The definition
of high voltage varies but in power transmission work is
usually thought to be 72.5 kV or higher, according to a
recent definition by the International Electrotechnical
Commission (IEC). High-voltage breakers are nearly
always solenoid-operated, with current sensing
protective relays operated through current transformers.
In substations the protective relay scheme can be
complex, protecting equipment and buses from various
types of overload or ground/earth fault.
 High-voltage breakers are broadly classified by the
medium used to extinguish the arc.
 Bulk oil
 Minimum oil
 Air blast
 Vacuum
 SF6
 CO2

10. Sulfur hexafluoride (SF6) high-
voltage circuit breakers
 A sulfur hexafluoride circuit
breaker uses contacts
surrounded by sulfur
hexafluoride gas to quench the
arc. They are most often used
for transmission-level voltages
and may be incorporated into
compact gas-insulated
switchgear. In cold climates,
supplemental heating or de-
rating of the circuit breakers
may be required due to
liquefaction of the SF6 gas.

11. Disconnecting circuit breaker
(DCB)
 The disconnecting circuit breaker (DCB) was
introduced in 2000[11] and is a high-voltage circuit
breaker modeled after the SF6-breaker. It presents a
technical solution where the disconnecting function is
integrated in the breaking chamber, eliminating the
need for separate disconnectors. This increases the
availability, since open-air disconnecting switch main
contacts need maintenance every 2–6 years, while
modern circuit breakers have maintenance intervals of
15 years. Implementing a DCB solution also reduces
the space requirements within the substation, and
increases the reliability, due to the lack of separate
disconnectors.

12. Carbon dioxide (CO2) high-
voltage circuit breakers
 In 2012 ABB presented a 75
kV high-voltage breaker that
uses carbon dioxide as the
medium to extinguish the arc.
The carbon dioxide breaker
works on the same principles
as an SF6 breaker and can
also be produced as a
disconnecting circuit breaker.
By switching from SF6 to CO2
it is possible to reduce the
CO2 emissions by 10 tons
during the product’s life cycle.

13. MCB (Miniature Circuit Breaker)
Characteristics
 Rated current not
more than 100 A.
 Trip characteristics
normally not
adjustable.
 Thermal or thermal-
magnetic operation.

14. MCCB (Moulded Case Circuit
Breaker)
Characteristics
 Rated current up to
1000 A.
 Trip current may be
adjustable.
 Thermal or thermal-
magnetic operation.

15. Air Circuit Breaker
Characteristics
 Rated current up to 10,000 A.
 Trip characteristics often fully adjustable
including configurable trip thresholds and
delays.
 Usually electronically controlled—some
models are microprocessor controlled.
 Often used for main power distribution in large
industrial plant, where the breakers are
arranged in draw-out enclosures for ease of
maintenance.

16. Vacuum Circuit Breaker
Characteristics
 With rated current up to 3000 A,
 These breakers interrupt the arc in a
vacuum bottle.
 These can also be applied at up to 35,000
V. Vacuum circuit breakers tend to have
longer life expectancies between overhaul
than do air circuit breakers.

17. RCD (Residual Current Device /
RCCB(Residual Current Circuit
Breaker)
Characteristics
 Phase (line) and Neutral both wires
connected through RCD.
 It trips the circuit when there is earth fault
current.
 The amount of current flows through the
phase (line) should return through neutral
.
 It detects by RCD. any mismatch between
two currents flowing through phase and
neutral detect by -RCD and trip the circuit
within 30Miliseconed.
 If a house has an earth system connected
to an earth rod and not the main incoming
cable, then it must have all circuits
protected by an RCD (because u mite not
be able to get enough fault current to trip a
MCB)
 RCDs are an extremely effective form of
shock protection

18. Lightening Arrester

19. C V T

20. Wave Trap
 Wave trap is an instrument using for tripping
of the wave. The function of this trap is that it
traps the unwanted waves. Its function is of
trapping wave. Its shape is like a drum. It is
connected to the main incoming feeder so
that it can trap the waves which may be
dangerous to the instruments here in the
substation.

21. Current Transformer

22. Potential Transformer

23. Drop out fuse
 Drop-out fuse insulated
bearing, static and dynamic
contact, fuse tube composed
of three parts. The static
contact at both ends of the
insulated bearing fuse also
oxygen tube from the inner
arc tube and the outer layer
of phenolic paper tube or
glass fiber cloth tube
composition.

24. Bus Bar In electrical power distribution, a busbar
(also spelled bus bar, or sometimes as
buss bar or bussbar, with the term bus
being a contraction of the Latin omnibus,
"for all", or buss being short for buttress
is a metallic strip or bar (typically copper,
brass or aluminium) that conducts
electricity within a switchboard,
distribution board, substation, battery
bank, or other electrical apparatus. Its
main purpose is to conduct a substantial
current of electricity, and not to function
as a structural member. Busbars may or
may not be enclosed in a bus duct. Also,
busbars are important components in
electrical power grid because they can
reduce the power loss via reducing the
corona effects. This is because busbars
have bigger surface areas compared to
wires.

25. Insulators
 The metal which does not allow free
movement of electrons or electric
charge is called as an insulator.
Hence, insulators resist electricity
with their high resisting property.
There are different types of insulators
such as suspension type, strain type,
stray type, shackle, pin type and so
on. A few types of insulators are
shown in the above figure. Insulators
are used for insulation purpose while
erecting electric poles with
conductors to avoid short circuit and
for other insulation requirements.

26. Isolator
 The use of this isolator is to
protect the transformer and the
other instrument in the line. The
isolator isolates the extra
voltage to the ground and thus
any extra voltage cannot enter
the line. Thus an isolator is used
after the bus also for protection.

27. Control and Relay Panel

28. Protective Relaying
 Protective relays are used to detect defective lines or apparatus
and to initiate the operation of circuit interrupting devices to
isolate the defective equipment. Relays are also used to detect
abnormal or undesirable operating conditions other than those
caused by defective equipment and either operate an alarm or
initiate operation of circuit interrupting devices. Protective relays
protect the electrical system by causing the defective apparatus
or lines to be disconnected to minimize damage and maintain
service continuity to the rest of the system. There are different
types of relays.
 i. Over current relay
 ii. Distance relay
 iii. Differential relay
 iv. Directional over current relay

29. Capacitor banks
 A Capacitor bank is a set of many
identical capacitors connected in series
or parallel within a enclosure and is
used for the power factor correction
and basic protection of substation.
These capacitor banks are acts as a
source of reactive power, and thus, the
phase difference between voltage and
current can be reduced by the capacitor
banks. They will increase the ripple
current capacity of the supply. It avoids
undesirable characteristics in the power
system. It is the most economical
method for maintaining power factor
and of correction of the power lag
problems.

30. Conductors
 The material or object that obeys the
electrical property conductance (mostly
made of metals such as aluminum and
copper) and that allows the flow of electric
charge is called conductor. Conductors
permit free movement of the flow of
electrons through them. These are used
for the transmission of power or electrical
energy from one place (generating
station) to another place (consumer point
where power is consumed by the loads)
through substations. Conductors are of
different types and mostly aluminum
conductors are preferred in practical
power systems.

31. SCADA System
SCADA (Supervisory Control And Data
Acquisition) is a system for remote monitoring
and control that operates with coded signals
over communication channels (using typically
one communication channel per remote
station).