university of engineering & management,Jaipur Electrical Engg

1. Protective
Device
Co-ordination
SHIBARAM MAZUMDER
12013002002039
EE
UEM, Jaipur

2. INTRODUCTION
• Power system is subjected to fault & transients. These will result in over
current & over voltages that can causes damages to conductor or
insulation. That result in equipment damages & system failure.
• Most electrical power distribution systems are not planned with protective
device coordination in mind, and can fail miserably in the proper
coordination of the protective devices.
• In distribution system Fuse & Circuit breaker are the main device for fault
current or over current protection. They pay a very important role in the
system design for good quality & reliability.

3. What is Protective device co-ordination
• If a failure occurs, it would be desirable that a short circuit would affect
only the portion of the electrical system where the failure occurs, instead
of the entire system. A circuit breaker coordination study is used to
analyse the tripping times for the series of overcurrent devices being
compared.
• The methodology is to optimize the selectivity of the devices. Selectivity
is the isolation of a faulted circuit to the point of fault without disturbing
any of the other protective devices in the system. A properly coordinated
system has each of its protective devices adjusted as to minimize the
negative impact of equipment failures.

4. E-tap simulation for Protective device
Sequence-of-operation
Star Sequence-of-
Operation (SQOP)
verifies, and confirms
the operation and
selectivity of the
protective devices for
various types of faults
for any location directly
from the one-line
diagram and via
normalized Time
Current Characteristic
Curve (TCC) views.

5. Time Current Characteristic Curve (TCC)
• If a fuse or CB has
been selected, the
designer can use the
curve for that fuse or
CB to check its
opening time versus a
given overcurrent or
fault current.

6. Devices for co-ordination
FUSE
• A fuse is a type of low resistance resistor that act
as a sacrificial device to provide over current
protection of either the load or the source circuit.
• Its essential components is a metallic wire or strip
that melts when too much current flows through it,
interrupting the circuit that it connects.
• The fuse elements is generally made of material
having low melting point, high conductivity and least
deterioration due to oxidation. E.g. Silver, Copper
etc.

7. MCB(miniature circuit breaker)
• Nowadays we use more commonly
miniature circuit breaker or MCB in low
voltage electrical network instead of fuse.
• It automatically switches off the electrical
circuit during abnormal condition of the
network means in over load condition as
well as faulty condition. MCB is much
more sensitive to over current than fuse.
• The ratings usually end up to 100. A
miniature circuit breaker which is used to
break small currents. Like in domestic LT
circuits.

8. MCCB(Molded case circuit breaker)
• A moulded case circuit breaker, abbreviated
MCCB, is a type of electrical protection device
that can be used for a wide range of voltages,
and frequencies of both 50 Hz and 60 Hz. The
main distinctions between moulded-case and
miniature circuit breaker are that the MCCB can
have current ratings of up to 2,500 amperes,
and its trip settings are normally adjustable.
• MCCB has two main functions:
Protection against overload & electrical fault –
currents above the rated value can’t last longer
than what is normal for the application.
During a fault such as a short circuit or line fault,
there are extremely high currents that must be
interrupted immediately.

9. Objectives of co-ordination
• Minimize the extent of fault in order to reduce the number of customer
affected.
• Minimize the service interruption due to fault.
• Minimize the duration of the service outages to identify the location of the
fault.

10. Thank you