This document discusses bulk oil and minimum oil circuit breakers. It defines circuit breakers and explains their need to protect electrical equipment from faults. It describes how bulk oil circuit breakers use oil as both an insulating and interrupting medium, while minimum oil circuit breakers only use a small amount of oil in the interrupting chamber. The document outlines the operation of both types of oil circuit breakers and compares their advantages and disadvantages. Maintenance of oil circuit breakers is also briefly discussed.

1. Bulk Oil And Minimum Oil Circuit Breaker
Presented by
SAURABH DAYAL SINGH (130050109106)
YASH PATEL (130050109088)
Semester – VII
ELECTRICAL ENGINEERING DEPARTMENT
BABARIA INSITUTE OF TECHNOLOGY
VARNAMA
SWITCHGEAR AND PROTECTION

2.  WHAT IS CIRCUIT BREAKER ?
 NEED OF CIRCUIT BREAKER ?
 WHERE IT IS USED ?
 HOW IT OPERATES ?

3. WHAT IS A CIRCUIT BREAKER
 A circuit breaker is an equipment that breaks a circuit either manually or
automatically under all conditions at no load, full load or short circuit.
A circuit breaker is an automatically-operated electrical switch designed to protect
an electrical circuit from damage caused by overload or short circuit.
 Its basic function is to detect a fault condition and by interrupting continuity, to
immediately discontinue electrical flow.

4. NEED OF CIRCUIT BREAKER
 During short circuit fault or any other types of electrical fault these equipment as
well as the power network suffer a high stress of fault current in them which may
damage the equipment and networks permanently.
For saving these equipments and the power networks the fault current should be
cleared from the system as quickly as possible.

5.  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.
HOW IT OPERATES

6. ARC PHENOMENON
 The arc provides the low resistance path to the current and the current in the
circuit remains uninterrupted.
 When a short circuit occurs, the contacts of circuit breaker begin to separate
 The p.d between the contacts is sufficient to ionize the air or oil or gas.
 This ionized air acts as conductor and arc is struck between them even though
contacts of breaker are opened

8. The arc resistance depends upon the following factors.
1. Degree of ionization
2. Length of the arc
3. Cross Section of the arc

9. METHODS OF ARC EXTINCTION
 HIGH RESISTANCE METHOD
 LOW RESISTANCE METHOD

10. High Resistance Method
The resistance of arc is increased by
1. Lengthening the arc
2. Cooling the arc
3. Reducing cross section of
arc
4. Splitting the arc
Low Resistance Method
1.Lengthening of the gap
2. High pressure
3.Cooling
4.Blast effect
If rate of heat generation is greater than rate of
heat dissipation between the contacts arc will be
extinguished.
If the dielectric strength increases more rapidly
than the restricking voltage arc is extinguished.
ARC INTERRUPTION METHOD

11. RATING, SELECTION OF BREAKERS
 Rated voltage:12 KV to 765KV
 Rated current: 200,400,630,800,1000,1250,1600,2000, 2500,3150,4000A
 Rated frequency: 50 or 60Hz
 Short circuit breaking current:12.5,16,20,25,31.5,40,50,63,80 KA
 Rated short time withstand current: 1s

12. BREAKER COMPARISON
Functions performed Protections
Isolation Control
Switchgear Overloads Short-circuit
Fuse Yes Yes No No
Disconnector No No Yes No
Switch No No Yes Yes
Disconnector – fuse Yes Yes Yes No
Switch – fuse Yes Yes Yes Yes
Contactor No No No Yes
Circuit-breaker Yes Yes Yes Yes

15. SELECTION OF SWITCHING DEVICES
LOW VOLTAGE
 FUSE
 MCB
 ELCB
 MCCB
 ISOLATOR
 CONTACTOR
HIGH VOLTAGE
 ACB
 LOCB
 VCB
 SF6 BREAKER
 HT FUSE

16.  Mineral oil has better insulating property than air.
 In oil circuit breaker the fixed contact and moving contact are immerged inside the
insulating oil.
 Whenever there is a separation of current carrying contacts in the oil, the arc in
circuit breaker is initialized at the moment of separation of contacts.
 Due to this arc the oil is vaporized and decomposed in mostly hydrogen gas and
ultimately creates a hydrogen bubble around the arc.
 This highly compressed gas bubble around the arc prevents re-striking of the arc
after current reaches zero crossing of the cycle.
 The oil circuit breaker is the one of the oldest type of circuit breakers.
OIL CIRCUIT BREAKER

17. TYPES OF OIL CIRCUIT BREAKERS
1. Bulk oil circuit breakers:
(a)Plain break oil circuit breakers
(b) Arc control oil circuit breakers
(b.1) Self-blast oil circuit breakers—in which arc control is provided by internal
means. The arc itself is employed for its own extinction efficiently.
We have to common types ----
(i) Plain explosion pot.
(ii) Cross jet explosion pot.
(iii) Self-compensated explosion pot.
(b.2) Forced-blast oil circuit breakers—in which arc control is provided by mechanical
means external to the circuit breaker.
2. Low Oil Circuit Breaker

18.  Bulk oil circuit breaker or BOCB is such types of circuit breakers where oil is
used as arc quenching media as well as insulating media between current carrying
contacts and earthed parts of the breaker.
 The oil used here is same as transformer insulating oil .
 The circuit breaker which uses more oil or which is bulky is called bulk oil circuit
breaker.
 The construction is simple and it consists of fixed and moving contacts enclosed in
a strong weather –tight earthed tank containing oil up to a certain level and an air
cushion above the oil level.
BULK OIL CIRCUIT BREAKER

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OPERATION

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1. Oil has high dielectric strength
2. Oil absorbs arc energy while
decomposing
3. Good cooling property of the gas
formed due to decomposition
4. It acts as an insulator between
the live parts and earth
DISADVANTAGES
1. Long arcing time
2. Do not permit high speed of
interruption
3. Arc interruption control can be
obtained only by increasing the
length of arc
ADVANTAGES

21. MINIMUM OIL CIRCUIT BREAKER
 These types of circuit breakers utilize oil as the
interrupting media.
 A minimum oil circuit breaker places the
interrupting unit in insulating chamber at live
potential. The insulating oil is available only in
interrupting chamber.
 The features of designing MOCB is to reduce
requirement of oil, and hence these breaker are
called minimum oil circuit breaker.

22.  When the contacts are separated in
oil arc is formed.
 The heat of arc decomposes oil and
gases are formed.
 These gases expand due to heating
of the arc.
 The gas flowing near the contact
zone cause cooling and splitting of
the arc and the arc gets
extinguished.
OPERATION

23. 1. Requires less quantity of oil
2. Requires smaller space
3. Maintenance is less
4. Cost per breaking capacity in
MVA is less
5. Suitable for both manual and
automatic operation
1. Possibility of fire and explosion.
2. Difficult to remove gases from
the space between contacts.
3. Oil deteriorates rapidly due to
carbonization
4. Smaller quantity of oil, so
carbonization increases.
DISADVANTAGESADVANTAGES

24. MAINTANAINCE OF OIL CIRCUIT BREAKERS
During inspection of the breaker, the following points should be kept in view :
1. Check the current carrying parts and arcing contacts. If the burning is severe,
the contacts should be replaced.
2. Check the dielectric strength of the oil. If the oil is badly discolored, it should
be changed or reconditioned. The oil in good condition should withstand 30
kV for one minute in a standard oil testing cup with 4 mm gap between
electrodes.
3. Check the insulation for possible damage. Clean the surface and remove
carbon deposits with a strong and dry fabric.
4. Check the oil level.

25. CONCLUSION
• Therefore, we conclude that circuit breaker is the most essential part of the
electrical networks as it protects every device from damage. It helps us to
detect the fault and area affected by it.
• Nowadays vacuum and SF6 circuit breakers are widely used due to their
reliable and fast operations.