What are the levels of SF6 gas in 220 kV breaker and their significance?

1 Answer

Answer :

7 kg/cm2 - normal pressure

5.2 bar - alarm

5.0 bar - closing/tripping operation blocked. 

Related questions

Description : What is the type of 220 kV circuit breaker? 

Last Answer : 220 kV, SF6 breaker, single pole, puffer type. 

Description : What are the main parts of 220 kV Circuit Breaker? 

Last Answer : Pole column filled with SF6 Pneumatic drive system with compressed air circuit Control cubicle unit 

Description : What is the significance of SF6 gas pressure in 6.6kV breakers?

Last Answer : Density gauge Green – correct SF6 pressure (3 –3.5bar) Yellow – pressure for breaking system fault current (refilling should be done) Red – SF6 pressure less than 2 bar, which indicates leak in the system. 

Description : What Is Sf6 Circuit Breaker?

Last Answer : SF6 is Sulpher hexa Flouride gas.. if this gas is used as arc quenching medium in a Circuitbreaker me SF6 CB.

Description : What is the purpose of compressed air in SF6 breaker?

Last Answer : This used for drive for opening and closing of the contacts. (Arc quenching is taken care by SF6 gas) 

Description : For interrupting capacitive currents which Circuit Breaker (CB) is used a) SF6 CB b) Oil CB c) Vacuum CB d) Air blast CB

Last Answer : Ans: Vacuum CB

Description : Which of the following circuit breakers has high reliability and minimum maintenance ? (a) Air blast circuit breakers (b) Circuit breaker with SF6 gas (c) Vacuum circuit breakers (d) Oil circuit breakers

Last Answer : (b) Circuit breaker with SF6 gas

Description : Give the details of switchyard 220 kV CB, Isolator, CT, CVT and lightning arrestor.  

Last Answer : 220 kV SF6 Circuit Breaker 1. Make - ABB 2. Air pressure blocking a. Close Block - 17.3 bar. b. Open block - 16.7 bar. c. Auto reclose block - 19 bar. 3. SF6 pressure block a. Alarm - 5. ... , storage and erection. Rated voltage : 216 kV rms. Operating voltage : 184 kV rms. 

Description : In 220 kV switchyard why lightning arrestor should be properly grounded?

Last Answer : a. During lightning, surges should be discharged to ground, otherwise it will puncture the equipment insulation and it is possible only when lightning arrestor is grounded properly.  b. In order to make it effective ... kV. Soil resistivity a should be minimum and may be it is 3.5 ohm per meter.  

Description : What is the difference in action of lock out pressure signal on 6.6 kV and 220 kV breakers?

Last Answer : When lock out signal comes to 6.6 kV breakers the breaker will trip. Where as in case of 220 kV breakers the breaker will not trip. If the breaker is open it will be open only and can not be closed. If it is in closed condition it will be closed.

Description : What are the protections provided for 220 kV lines and bus bars? 

Last Answer : a. Bus bar differential protection. b. Distance protection. c. Over current protection. d. Earth fault protection. 

Description : Why earth switches are provided in 220 kV bays?  

Last Answer : When bay CB trips, both end (station and grid) CB will trip. The earth switches are provided because the grid will always be alive so to prevent any shocks to the operator or maintenance personnel who is working on the line or bay due to accidental energizing of the bus.  

Description : Cables for 220 kV lines are invariably (a) mica insulated (b) paper insulated (c) compressed oil or compressed gas insulated (d) rubber insulated (e) none of the above

Last Answer : (c) compressed oil or compressed gas insulated

Description : Which of the following medium is employed for extinction of arc in air circuit breaker ? (a) Water (b) Oil (c) Air (d) SF6

Last Answer : (c) Air

Description : Describe the construction of SF6 circuit breaker with neat diagram.

Last Answer : Construction of SF6 Circuit Breaker : A sulphur hexafluoride (SF6) circuit breaker consists of fixed and moving contacts enclosed in a chamber. The chamber is called arc interruption ... contact, moving contact and arcing horn are coated with a copper-tungsten arc-resistant material. 

Description : Explain construction and working of SF6 circuit breaker.

Last Answer : Construction: A sulphur hexafluoride (SF6) circuit breaker consists of fixed and moving contacts enclosed in a chamber. The chamber is called arc interruption chamber, which contains the ... arc being extinguished. Finally the gas enters the contact space increasing the dielectric strength.

Description : what is SF6 circuit breaker?

Last Answer : SF6 is Sulpher hexa Fluoride gas. If this gas is used as arc quenching medium in a Circuit breaker means SF6 CB.

Description : The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Last Answer : (c) 7.0 m

Description : For transmission of power over a distance of 500 km, the transmission voltage should be in the range (a) 150 to 220 kV (b) 100 to 120 kV (c) 60 to 100 kV (d) 20 to 50 kV

Last Answer : (a) 150 to 220 kV

Description : The spacing between phase conductors of a 220 kV line is approximately equal to (a) 2 m (b) 3.5 m (c) 6 m (d) 8.5 m

Last Answer : (c) 6 m

Description : The minimum clearance between the ground and a 220 kV line is about (a) 4.3 m (b) 5.5 m (c) 7.0 m (d) 10.5 m

Last Answer : (c) 7.0 m

Description : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is (A) 28.2 mm (B) 26.4 mm (C) 24.4 mm (D) 22.0 mm

Last Answer : A single core cable is designed to work for a single phase system with a peak voltage of 220 kV. The maximum permissible stress in the dielectric is not to exceed 20 kV/mm. For economical size, the overall core diameter of the cable is 22.0 mm

Description : The X:R ratio of 220 kV line as compared to 400 kV line is?

Last Answer : The X:R ratio of 220 kV line as compared to 400 kV line is smaller.

Description : What are the characteristic of SF6 gas?

Last Answer : It has good dielectric strength and excellent arc quenching property. It is inert, non-toxic, noninflammable and heavy. At atmospheric pressure, its dielectric strength is 2.5 times that of air. At three times atmospheric pressure, its dielectric strength is equal to that of the transformer oil.

Description : What is meant by electro negativity of SF6 gas?

Last Answer : SF6 has high affinity for electrons. When a free electron comes and collides with a neutral gas molecule, the electron is absorbed by the neutral gas molecule and negative ion is formed. This is called as electro negativity of SF6 gas.

Description : What are the properties of SF6 gas?  

Last Answer : This is inert gas. Odorless, non-toxic, colourless, stable, non-inflammable and density is more hence high dielectric strength. The special property of this gas is Electro negativity. This gas ... more slow in conduction, so that resistance in medium is increases and get arc get extinguishes. 

Description : What are the properties of SF6 gas?  

Last Answer : Physical properties 1. Colourless 2. Odorless 3. Non-toxic. Pure SF6 gas is not harmful to the health. 4. Non-inflammable. 5. Density- more gas density, 5 times ... advantages offer increased safety, reduction in size, weight, noiseless operation, easy installation, handling and maintenance. 

Description : A three-phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3 s. The symmetrical breaking current is  (A) 1200 A (B) 3600 A (C) 35 kA (D) 104.8 kA

Last Answer : A three-phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3 s. The symmetrical breaking current is 35 kA 

Description : A 3-phase circuit breaker is rated at 1250 A, 2000 MVA, 33 kV, 4s. Its making current capacity will be   (a) 35 kA (b) 89 kA (c) 79 kA (d) 69 kA

Last Answer : 89

Description : SF6 gas (a) is yellow in colour (b) is lighter than air (c) is nontoxic (d) has pungent small (e) none of the above

Last Answer : (c) is nontoxic

Description : Which of the following is not a greenhouse gas ? a) CFCs b) SO2 c) PFC d) SF6

Last Answer : b) SO2

Last Answer : SF6 gas is nontoxic.

Description : The dielectric strength of a vacuum or dry air is approximately ________________. A. 450 volts/inch B. 1000 volts/inch C. 20-kv/inch D. 50-kv/inch

Last Answer : Answer: C

Description : If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

Last Answer : A. As we know the Voltage & current relation for transformer-V1/V2 = I2/I1 We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps. By putting these value on Relation540/11000= I2/2334 So,I2 = 114.5 Amps

Description : Why 1.1 kV grade cables used for 415V?

Last Answer : To take care of the both earthed / unearthed systems.  

Description : What are the types of cables used in 6.6 kV and 415 V system voltages? 

Last Answer : In 6.6 kV system AC (unearthed) grade having stranded aluminium conductors cables are used. Their insulation's are as follows. 1. XLPE - Crossed linked polyethylene insulation. 2. FRLS PVC - Fire ... V grade copper or aluminium stranded cables are used. Their insulations are HR PVC and FS type. 

Description : What are the interlocks between 415 V and 6.6 kV switch gear? 

Last Answer : 6.6 kV Breaker closed cannot rack in or out. Service lever cannot move while breaker closed. Breaker cannot be closed in in-between position. 415 V Breaker door cannot be opened when breaker is ... . Breaker cannot be closed in in-between position. Breaker closed cannot be rack in or out. 

Description : What is the difference between lockout of 6.6 kV and 415 V CB’s?

Last Answer : Voltage levels. Manual / auto reset. Lockout relays of 415 V breakers are all Electro-magnetic type. There is no mechanical latch. But in 6.6 kV it is of mechanical latch type relays.

Description : What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?

Last Answer : Closing coil and Trip coil 2 supply from one source. Trip coil 1 supply from one source. Protections supply from one source. 

Description : How 6.6 kV-bus supply was chosen?

Last Answer : 11 kV was rejected in view of the high insulation cost with 11 kV motors. 3.3 kV was rejected, since max motor size with 3.3 kV bus is limited to 2 MW. But we are having the motors having rating more than 2 MW, which cannot suit to 3.3 kV bus. 6.6 kV bus we can start upto 5 mw size motor. 

Description : Why resistance grounding preferred for less than 33 kV and more than 415 V?

Last Answer : a) To limit the earth fault current for equipment safety else, high short ckt forces dislocate in windings/bus bars etc, b) Over voltage due to arcing ground reduced c) Permits earth fault protection (not possible in ungrounded system)

Description : Why neutrals are solid grounded above 33 kV? 

Last Answer : a) Less transient over voltage due to arcing grounds. b) Voltage of phases are limited to phase to ground voltage. (No neutral shifting) c) Allows graded insulation of transformer (low cost) d) Fast E/F protection. 

Description : Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Last Answer : a) To avoid relay mal-operation due to CT saturation b) Better sensitivity is got. c) High pickup and TMS avoided in IDMT earth fault relay. 

Description : Why 2 types of earth fault relays in 6.6 kV side of transformers?

Last Answer : I – Trips 6.6 kV breakers only. It gives primary protection for 6.6 kV bus bars. I1 – Trips the both HT and LT breakers. It acts as a backup to ref and also acts as backup to bus bar earthfault relay. 

Description : What is the design basis of 6.6 kV aluminium bus bars?  

Last Answer : a) Temperature rises not exceed 90 ºC. b) Withstand short ckt stresses. c) Take care of thermal expansion. 

Description : During unit operation can we have one UT feeding both unit 6.6 kV loads? 

Last Answer : No, logically prevented.  

Description : Why 6.6 kV transformer is resistance grounded by 10 ohms and current limited to 400 A?

Last Answer : a) To reduce burning and melting in faulted switchgear or machine. b) To reduce mechanical stresses in equipment. c) To reduce the electrical hazards by stray ground fault currents in the ground ... screen in 6.6 kV XLPE (cross-linked polyethylene). Therefore the cost of the cable decreases. 

Description : Why the earthing transformer primary voltage is 16.5 kV rated in main generator even though actual voltage during the E/F is root 3 times less?

Last Answer : The transformer should not saturate during E/F otherwise it will cause ferroresonance with the GT winding capacitance. Dangerous O/V and neutral shifting will occur. During loss of load or field ... saturation. Saturation can also occur due to point on wave of application causing flux doubling. 

Description : What type breakers are provided in 6.6 kV buses?

Last Answer : ABB. Make, SF6 gas, 1250A and 2000A capacity circuit breakers are provided in 6.6 kV buses. 

Description : List some important loads to 6.6 kV buses. 

Last Answer : a. Auxiliary transformers. b. PHT motors. c. BFP motors.  d. CEP motors. e. CCW motors. f. Chiller motors. g. Pressuring pump motors.