Bulk oil and min oil circuit breaker

Bulk oil and min oil circuit breaker defiinition ,operation and application.

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

7. The arc resistance depends upon the following factors. Degree of ionization Length of the arc Cross Section of the arc

8. METHODS OF ARC EXTINCTION HIGH RESISTANCE METHOD LOW RESISTANCE METHOD

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

10. 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

11. 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

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

13. 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

14. TYPES OF OIL CIRCUIT BREAKERS 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. T he 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

15. 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

16. 25 December 2017 19 OPERATION

17. 25 December 2017 20 O il has high dielectric strength Oil absorbs arc energy while decomposing Good cooling property of the gas formed due to decomposition It acts as an insulator between the live parts and earth DISADVANTAGES Long arcing time Do not permit high speed of interruption Arc interruption control can be obtained only by increasing the length of arc ADVANTAGES

18. 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.

19. 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

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

21. MAINTANAINCE OF OIL CIRCUIT BREAKERS During inspection of the breaker, the following points should be kept in view : Check the current carrying parts and arcing contacts. If the burning is severe, the contacts should be replaced. 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. Check the insulation for possible damage. Clean the surface and remove carbon deposits with a strong and dry fabric. Check the oil level.

22. 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.