CIRCUIT BREAKER
• Give circuit breaker nameplate details of 6.6 kV, and 415 V.
6.6 kV (SF6 circuit Breaker) 415 V (Air Circuit Breaker)
Type HPA12/1240C(Tr./ PM) 812 (MCC/UPS)
HPA12/2040C(Tr./ PM) 610 (Tie/PM/MCC)
3037 (B/c, Incomer)
Standard IEC 56
Rated voltage 12 kV (6.6 kV) 415 V
Insulation level 28 / 75 kV 660 V
Rated current 1250A/2000A 1600A/1000A/3750A
Breaking current 40 kA 50 kA (rms.)
Making current 100 kA 105 kA (peak)
Short ckt withstand 40 kA/sec 50 kA/sec
Closing time 52 milli sec 60 sec (III/IV) & 30 sec (II)
Opening time 75 milli sec 35 sec (III/IV) & 40 sec (II)
SF6 pressure 2.3 - 2.8 bar (2.2 alarm) at 20°C
Sliding contact Copper with silver of 10 microns
• What are the difference between DCCB and ACCB?
DCCB
Two poles seriesed for one side.
Breaker is adequately de-rated for use in dc circuits.
Only DINF, DIRS provided. DIT 5 will not work for dc.
In GFB, magnetic blowout coils used to increase the speed of rise of arc into the arc
chutes for effective quenching.
ACCB
The inherent current zero of sine wave helps arc quenching. For DCCB arc
quenching is difficult, since current zero is not existing naturally.
• What are the indications used in 415V and 6.6 kV breakers panel?
415 V Breaker 6.6 kV Breaker
Open Green Green
Close Red Red
Test White
Service Blue
Auto trip Yellow White
Spring charge Blue
Gas pressure Yellow
Voltage (RYB) Red
• What are the advantages and disadvantages of 415V English Electric breaker?
Advantages
1. Auto reclosing shutters.
2. Proven wiping contacts.
3. Sturdy rugged mechanism.
4. Reliable aux. Switches contacts.
5. Slow closing facility independent of closing spring.
Disadvantages
Bulky, more space, spring charge motor 5A. , Spring charging time 14 sec 4 sec at
timing, trip extends in test position also. No neutral bus bar link, we cannot finger
contact resistance since fixed on bus side.
• Type of closing spring is compression type.(415V)
• Why parallel operations of classIII buses are not permitted?
Fault on one side affects the other buses, switchgear fault level rating is exceeded.
• Why auto transfer is blocked for back up protection?
Because Backup protection operates normally for bus faults. All main protections are
generally operating for internal faults therefore there is no point in restoring the
power supply through auto transfer when there is a bus fault existing.
• What decides the control transformer VA rating?
Contactor coil VA rating.
• Can we use AC contactor in DC circuit?
Yes, but with adequate de-rating.
• Can we use ac coils in dc circuit?
Yes with economy resistor in series.
• Why shading rings provided in armature core of ac contactor. Why not for dc
contactor?
Because the force developed is not steady in ac therefore contacts will chatter but if
shading ring is used force developed becomes steady due to splitting of phases of
flux, therefore contacts becomes bounce free and humming sound reduces.
• Why copper contact are not used in contactor?
Because corrosion rate increases. Poor surface property , large closing force
required.
• Why pure silver is not used in contactor?
Affected by sulphur, mechanical or arcing damages (adv. Lower voltage drop)
• What are the types of contactors?
Type Contacts Rating Use
3 TB 41 2 NO + 2 NC 12 A 0 – 5.5 kW
3 TA 22 2 NO + 2 NC 30 A 7.5 – 11 kW
3 TA 13 2 NO + 2 NC 38 A 15 kW
3 TA 24 4 NO + 2 NC 70 A 18 – 38 kW
3 TA 16 4 NO + 2 NC 105 A 40 – 48 kW
3 TA 28 4 NO + 2 NC 170 A 55 – 80 kW
3 TA 28 3 NO + 3 NC 170 A 55 – 80 kW
3 TB 56 4 NO + 2 NC 400 A 93 kW for F/M supply PM.
3 TD 11 2 NO + 2 NC 12 A 0 – 1.5 kW for valve motors.
3 T I 22 2 NO + 2 NC 30 A 1.6 – 7.5 kW for valve motors.
• What material used for contactor?
Silver-nickel for <100A
Silver-cadmium oxide for large currents.
• Why pick up voltage is more than drop out voltage?
Initially air gap is more. Large force is required to overcome the high reluctance
initially. After closing air gap is reduced. Hence drop voltage is reduced.
• Can we file the pitted contacts of contactor?
No, use emery paper and etc.
• How the contact resistance can increase?
Humidity + salty air, dust, poor contact pressure
• Fusing current- the current at which the fuse element melts depends upon the
material, length and diameter.
• Fusing factor- fusing current /rated current (1.25 -1.75)
• Prospective fault current – first loop of fault current
• Cut off current - actual peak value of current reached due to interruption by fuse
blowing.
• What is rated current and short circuit current?
Rated current = VA / √3 * V Amps.
Short circuit current = VA * 100 / %Z * √3 * V Amps.
• What is the advantage of lower cut off current?
Less electromagnetic forces on contactor / CB’s
• How two fuses in-series are discriminated?
Total I2t of minor fuse should be less than pre-arcing I2t of major fuse.
Major fuse should be greater than 1.5 times the minor fuse.
• Why OLR time set high for belt driven fans?
Because acceleration time is high.
• What is the safety reason to keep the contactor / MCC remote from motor?
Contactor = sparking equipment. Not suiting for hazardous location.
• Where wound type CT used and where not used?
Used where low CT ratio req.
Not used where high short ckt. Current exists.
• What is advantage of cast resin CT’s?
Can withstand bursting forces under short ckt, protect damages against external
causes impervious to moisture.
• Why fuses with fusing factor more than 1.5 is not allowed in PVC cables?
Because PVC cables have low thermal capacity than paper cables. Full loading of
PVC only possible if it has close excess current protection (i.e.) Fusing Factor = 1.5
• What are the advantages of HRC fuses re-wirable fuses? What are the characteristics
of HRC fuse?
1. Consistent and stable characteristics for accuracy of discrimination. Capacity
to break at high and low current. It is inverse time characteristics, as the
current is high the time taken to break the circuit is less.
2. Arc quenching is reliable. Chemical action between quartz and arc gas gives
high resistance to the arc. Quartz does not produce more gas after observing
heat as its sand powder observes more heat of the arc.
3. Non deteriorating since it is sealed. No maintenance, Cheap and indication is
available.
Characteristics
1. I2t characteristics. This determines the energy that element can pass and to
determine the cut off characteristics.
105 Total I2t
104
103
102 Pre-arcing I2t
10
10 50 100 150 200
Fuse rating
2. Inverse time characteristics, which is useful for selection of the fuse for motor.
75
50
Current
20
10
0.2 0.5 0.7 0.9 1 sec
Time
Inverse time characteristics
Current
Fuse characteristics
Margin to avoid fuse operation
During starting
Minimum fusing current
Staring current
Running current
Time
Motor selection characteristics
• What is the advantage of CMM relay over normal Inv. O/C current relay?
Inv. O/C relay under protects at low current and over protects at high currents.
CMM: accounts for both +ve and –ve sequence currents i.e. Single phasing /
unbalance supply conditions and gives three times more weightage for the –ve phase
sequence current heating than + ve sequence current heating. i.e. Net rotor heating =
I1
2 + 3 I2
2.
Therefore CMM relay protection characteristic is closely matched to motor heating
characteristic. So it is better than thermal overload relay also.
• What is the purpose of anti-pumping relay?
When closing signal is continuously existing even after the closing of the breaker the
anti-pumping relay will be picked up and it will not allow the breaker to close back
in case of tripping of the breaker.
• Why breaker tripping is prohibited on very low pressure?
The efficiency with which the arc quenching is taking place in the breaker depends
on the air pressure. So if the air pressure is low effective arc quenching will not take
place which will result in damage of CB. Hence the tripping of the breaker at very
low air pressure is prevented.
• Why neutral breaker used in DG neutral grounding?
In case of high earth fault currents it is therefore normal practice to install a circuit
breaker in the neutral of the generator in order to reduce the total fault clearance
time.
• What are the protections used in Class III & Class IV 415 V LV side?
Class III 415 V LV side
1. 51 (inverse over current)
2. 50 (instantaneous over current)
3. 27 (under voltage)
4. 51N (earth fault)
5. 64 (REF)
Class IV 415 V LV side
1. 51 RYB (inverse over current)
2. 51N (earth fault)
• What are the protections used in 415 V Class II side?
LV to UPS
1. CTZM
2. 50 (instantaneous over current)
3. short circuit
UPS to PMCC S & T
1. 51 RYB (inverse over current)
2. 27 (under voltage)
3. 51N (earth fault)
From Class III to Class II tie
CTZM at Class III and 51, 51N at Class II.
• Define the followings.
Insulation level – it is the combination of rated voltage, the corresponding impulse
withstand voltage, which together characterize the insulation of the equipment as
regards its ability to withstand the electrical stresses.
Rated short circuit breaking current – it is the highest RMS value of short circuit
current which the circuit breaker is capable of breaking the circuit in safe.
Making current – it is the peak value of first loop of current of short circuit current
which the circuit breaker is capable of making at the rated voltage.
Rated making current = 2.5 times rated breaking current.
Short time rating – it is the RMS value of current that the circuit breaker can carry in
a fully closed position during a specified time.
Impulse withstand voltage – it is the amplitude of the standard voltage wave with the
insulation of equipment can withstand.
Power frequency withstand voltage – it is RMS value of alternating voltage wave of
power frequency (50 Hz) which the insulation of equipment should withstand.
• What is switchgear?
Equipment which is used for switching, controlling and protecting an electrical
circuit.
• Bus bar specifications of 6.6kV and 415 V.
415V
Aluminium 200 X 12mm
2 nos. per phase, 1 no. for neutral
Bus bar joints – silver plated to 5 micron thick (tightness 50 NM)
6.6kV
Copper
Silver coated joints
Insulation level – 27kV
Fault level estimated – 27kA Designed – 40kA
• What is the type of arc extinction in switchgears?
415V – resistance method (through arc splitter)
6.6kV – single puffer principle
• How Arc quenching is done?
When fault occurs depending on design element melts at one point and arc starts and
a transient current is super imposed on prospective current. When the sum of two is
zeroing the arc is quenching.
• What is lock out relay?
It is the relay to prevent the closing of circuit breaker after tripping (protection)
without attention of the operator.
• What is the significance of SF6 gas pressure in 6.6kV breakers?
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.
• What is the measure of atmospheric pressure and PSI?
1 Atmospheric pressure = 1.033 kg/cm2.
1 PSI = 0.07031 kg/cm2.
• What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?
Closing coil and Trip coil 2 supply from one source.
Trip coil 1 supply from one source.
Protections supply from one source.
• Why 86.1 and 86.2 relays are used?
All electrical protection is wired to 86.1 and under voltage protection is wired to 86.2
relay for automatic restoration in EMTR.
• What is the difference between lockout of 6.6 kV and 415 V CB’s?
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.
• If breaker contact resistance is more what action to be taken?
In 6.6 kV breakers 1250 A breaker contact resistance is <100 μς.
2000 A breaker contact resistance is <50 μς.
If contact resistance is found more than this value should be sent to the manufacturer
for repair.
• What are the interlocks between 415 V and 6.6 kV switch gear?
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 in service.
Breaker cannot be closed in in-between position.
Breaker closed cannot be rack in or out.
• Where are the provision of GR-A and GR-B tie possibilities?
Bus D1-D2 to E1-E2 (CL III 6.6 kV)
Bus X to Bus Y (CL III 415V)
Bus S to Bus T (CL II 415 V)
• What are the properties of SF6 gas?
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 attracts electrons to form –ve ions and –ve ion are havier
than electrons and more slow in conduction, so that resistance in medium is increases
and get arc get extinguishes.
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
• Give circuit breaker nameplate details of 6.6 kV, and 415 V.
6.6 kV (SF6 circuit Breaker) 415 V (Air Circuit Breaker)
Type HPA12/1240C(Tr./ PM) 812 (MCC/UPS)
HPA12/2040C(Tr./ PM) 610 (Tie/PM/MCC)
3037 (B/c, Incomer)
Standard IEC 56
Rated voltage 12 kV (6.6 kV) 415 V
Insulation level 28 / 75 kV 660 V
Rated current 1250A/2000A 1600A/1000A/3750A
Breaking current 40 kA 50 kA (rms.)
Making current 100 kA 105 kA (peak)
Short ckt withstand 40 kA/sec 50 kA/sec
Closing time 52 milli sec 60 sec (III/IV) & 30 sec (II)
Opening time 75 milli sec 35 sec (III/IV) & 40 sec (II)
SF6 pressure 2.3 - 2.8 bar (2.2 alarm) at 20°C
Sliding contact Copper with silver of 10 microns
• What are the difference between DCCB and ACCB?
DCCB
Two poles seriesed for one side.
Breaker is adequately de-rated for use in dc circuits.
Only DINF, DIRS provided. DIT 5 will not work for dc.
In GFB, magnetic blowout coils used to increase the speed of rise of arc into the arc
chutes for effective quenching.
ACCB
The inherent current zero of sine wave helps arc quenching. For DCCB arc
quenching is difficult, since current zero is not existing naturally.
• What are the indications used in 415V and 6.6 kV breakers panel?
415 V Breaker 6.6 kV Breaker
Open Green Green
Close Red Red
Test White
Service Blue
Auto trip Yellow White
Spring charge Blue
Gas pressure Yellow
Voltage (RYB) Red
• What are the advantages and disadvantages of 415V English Electric breaker?
Advantages
1. Auto reclosing shutters.
2. Proven wiping contacts.
3. Sturdy rugged mechanism.
4. Reliable aux. Switches contacts.
5. Slow closing facility independent of closing spring.
Disadvantages
Bulky, more space, spring charge motor 5A. , Spring charging time 14 sec 4 sec at
timing, trip extends in test position also. No neutral bus bar link, we cannot finger
contact resistance since fixed on bus side.
• Type of closing spring is compression type.(415V)
• Why parallel operations of classIII buses are not permitted?
Fault on one side affects the other buses, switchgear fault level rating is exceeded.
• Why auto transfer is blocked for back up protection?
Because Backup protection operates normally for bus faults. All main protections are
generally operating for internal faults therefore there is no point in restoring the
power supply through auto transfer when there is a bus fault existing.
• What decides the control transformer VA rating?
Contactor coil VA rating.
• Can we use AC contactor in DC circuit?
Yes, but with adequate de-rating.
• Can we use ac coils in dc circuit?
Yes with economy resistor in series.
• Why shading rings provided in armature core of ac contactor. Why not for dc
contactor?
Because the force developed is not steady in ac therefore contacts will chatter but if
shading ring is used force developed becomes steady due to splitting of phases of
flux, therefore contacts becomes bounce free and humming sound reduces.
• Why copper contact are not used in contactor?
Because corrosion rate increases. Poor surface property , large closing force
required.
• Why pure silver is not used in contactor?
Affected by sulphur, mechanical or arcing damages (adv. Lower voltage drop)
• What are the types of contactors?
Type Contacts Rating Use
3 TB 41 2 NO + 2 NC 12 A 0 – 5.5 kW
3 TA 22 2 NO + 2 NC 30 A 7.5 – 11 kW
3 TA 13 2 NO + 2 NC 38 A 15 kW
3 TA 24 4 NO + 2 NC 70 A 18 – 38 kW
3 TA 16 4 NO + 2 NC 105 A 40 – 48 kW
3 TA 28 4 NO + 2 NC 170 A 55 – 80 kW
3 TA 28 3 NO + 3 NC 170 A 55 – 80 kW
3 TB 56 4 NO + 2 NC 400 A 93 kW for F/M supply PM.
3 TD 11 2 NO + 2 NC 12 A 0 – 1.5 kW for valve motors.
3 T I 22 2 NO + 2 NC 30 A 1.6 – 7.5 kW for valve motors.
• What material used for contactor?
Silver-nickel for <100A
Silver-cadmium oxide for large currents.
• Why pick up voltage is more than drop out voltage?
Initially air gap is more. Large force is required to overcome the high reluctance
initially. After closing air gap is reduced. Hence drop voltage is reduced.
• Can we file the pitted contacts of contactor?
No, use emery paper and etc.
• How the contact resistance can increase?
Humidity + salty air, dust, poor contact pressure
• Fusing current- the current at which the fuse element melts depends upon the
material, length and diameter.
• Fusing factor- fusing current /rated current (1.25 -1.75)
• Prospective fault current – first loop of fault current
• Cut off current - actual peak value of current reached due to interruption by fuse
blowing.
• What is rated current and short circuit current?
Rated current = VA / √3 * V Amps.
Short circuit current = VA * 100 / %Z * √3 * V Amps.
• What is the advantage of lower cut off current?
Less electromagnetic forces on contactor / CB’s
• How two fuses in-series are discriminated?
Total I2t of minor fuse should be less than pre-arcing I2t of major fuse.
Major fuse should be greater than 1.5 times the minor fuse.
• Why OLR time set high for belt driven fans?
Because acceleration time is high.
• What is the safety reason to keep the contactor / MCC remote from motor?
Contactor = sparking equipment. Not suiting for hazardous location.
• Where wound type CT used and where not used?
Used where low CT ratio req.
Not used where high short ckt. Current exists.
• What is advantage of cast resin CT’s?
Can withstand bursting forces under short ckt, protect damages against external
causes impervious to moisture.
• Why fuses with fusing factor more than 1.5 is not allowed in PVC cables?
Because PVC cables have low thermal capacity than paper cables. Full loading of
PVC only possible if it has close excess current protection (i.e.) Fusing Factor = 1.5
• What are the advantages of HRC fuses re-wirable fuses? What are the characteristics
of HRC fuse?
1. Consistent and stable characteristics for accuracy of discrimination. Capacity
to break at high and low current. It is inverse time characteristics, as the
current is high the time taken to break the circuit is less.
2. Arc quenching is reliable. Chemical action between quartz and arc gas gives
high resistance to the arc. Quartz does not produce more gas after observing
heat as its sand powder observes more heat of the arc.
3. Non deteriorating since it is sealed. No maintenance, Cheap and indication is
available.
Characteristics
1. I2t characteristics. This determines the energy that element can pass and to
determine the cut off characteristics.
105 Total I2t
104
103
102 Pre-arcing I2t
10
10 50 100 150 200
Fuse rating
2. Inverse time characteristics, which is useful for selection of the fuse for motor.
75
50
Current
20
10
0.2 0.5 0.7 0.9 1 sec
Time
Inverse time characteristics
Current
Fuse characteristics
Margin to avoid fuse operation
During starting
Minimum fusing current
Staring current
Running current
Time
Motor selection characteristics
• What is the advantage of CMM relay over normal Inv. O/C current relay?
Inv. O/C relay under protects at low current and over protects at high currents.
CMM: accounts for both +ve and –ve sequence currents i.e. Single phasing /
unbalance supply conditions and gives three times more weightage for the –ve phase
sequence current heating than + ve sequence current heating. i.e. Net rotor heating =
I1
2 + 3 I2
2.
Therefore CMM relay protection characteristic is closely matched to motor heating
characteristic. So it is better than thermal overload relay also.
• What is the purpose of anti-pumping relay?
When closing signal is continuously existing even after the closing of the breaker the
anti-pumping relay will be picked up and it will not allow the breaker to close back
in case of tripping of the breaker.
• Why breaker tripping is prohibited on very low pressure?
The efficiency with which the arc quenching is taking place in the breaker depends
on the air pressure. So if the air pressure is low effective arc quenching will not take
place which will result in damage of CB. Hence the tripping of the breaker at very
low air pressure is prevented.
• Why neutral breaker used in DG neutral grounding?
In case of high earth fault currents it is therefore normal practice to install a circuit
breaker in the neutral of the generator in order to reduce the total fault clearance
time.
• What are the protections used in Class III & Class IV 415 V LV side?
Class III 415 V LV side
1. 51 (inverse over current)
2. 50 (instantaneous over current)
3. 27 (under voltage)
4. 51N (earth fault)
5. 64 (REF)
Class IV 415 V LV side
1. 51 RYB (inverse over current)
2. 51N (earth fault)
• What are the protections used in 415 V Class II side?
LV to UPS
1. CTZM
2. 50 (instantaneous over current)
3. short circuit
UPS to PMCC S & T
1. 51 RYB (inverse over current)
2. 27 (under voltage)
3. 51N (earth fault)
From Class III to Class II tie
CTZM at Class III and 51, 51N at Class II.
• Define the followings.
Insulation level – it is the combination of rated voltage, the corresponding impulse
withstand voltage, which together characterize the insulation of the equipment as
regards its ability to withstand the electrical stresses.
Rated short circuit breaking current – it is the highest RMS value of short circuit
current which the circuit breaker is capable of breaking the circuit in safe.
Making current – it is the peak value of first loop of current of short circuit current
which the circuit breaker is capable of making at the rated voltage.
Rated making current = 2.5 times rated breaking current.
Short time rating – it is the RMS value of current that the circuit breaker can carry in
a fully closed position during a specified time.
Impulse withstand voltage – it is the amplitude of the standard voltage wave with the
insulation of equipment can withstand.
Power frequency withstand voltage – it is RMS value of alternating voltage wave of
power frequency (50 Hz) which the insulation of equipment should withstand.
• What is switchgear?
Equipment which is used for switching, controlling and protecting an electrical
circuit.
• Bus bar specifications of 6.6kV and 415 V.
415V
Aluminium 200 X 12mm
2 nos. per phase, 1 no. for neutral
Bus bar joints – silver plated to 5 micron thick (tightness 50 NM)
6.6kV
Copper
Silver coated joints
Insulation level – 27kV
Fault level estimated – 27kA Designed – 40kA
• What is the type of arc extinction in switchgears?
415V – resistance method (through arc splitter)
6.6kV – single puffer principle
• How Arc quenching is done?
When fault occurs depending on design element melts at one point and arc starts and
a transient current is super imposed on prospective current. When the sum of two is
zeroing the arc is quenching.
• What is lock out relay?
It is the relay to prevent the closing of circuit breaker after tripping (protection)
without attention of the operator.
• What is the significance of SF6 gas pressure in 6.6kV breakers?
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.
• What is the measure of atmospheric pressure and PSI?
1 Atmospheric pressure = 1.033 kg/cm2.
1 PSI = 0.07031 kg/cm2.
• What is the distribution of DC control supply in CL IV, III, II- 415V and 6.6 kV?
Closing coil and Trip coil 2 supply from one source.
Trip coil 1 supply from one source.
Protections supply from one source.
• Why 86.1 and 86.2 relays are used?
All electrical protection is wired to 86.1 and under voltage protection is wired to 86.2
relay for automatic restoration in EMTR.
• What is the difference between lockout of 6.6 kV and 415 V CB’s?
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.
• If breaker contact resistance is more what action to be taken?
In 6.6 kV breakers 1250 A breaker contact resistance is <100 μς.
2000 A breaker contact resistance is <50 μς.
If contact resistance is found more than this value should be sent to the manufacturer
for repair.
• What are the interlocks between 415 V and 6.6 kV switch gear?
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 in service.
Breaker cannot be closed in in-between position.
Breaker closed cannot be rack in or out.
• Where are the provision of GR-A and GR-B tie possibilities?
Bus D1-D2 to E1-E2 (CL III 6.6 kV)
Bus X to Bus Y (CL III 415V)
Bus S to Bus T (CL II 415 V)
• What are the properties of SF6 gas?
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 attracts electrons to form –ve ions and –ve ion are havier
than electrons and more slow in conduction, so that resistance in medium is increases
and get arc get extinguishes.
https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg https://www.youtube.com/channel/UC4_D50vMu1wbQrPaLFYo6Eg RRB JE, SSC AE/JE UPSSSC JE, SSC JE, CIVIL ENGINEERING MCQs, ELECTICAL ENGINEERING MCQs, preavious year quesion papers, dmrc, lmrc, drdo,rrb ntpc, ntpc, pgcil, dsssb, states board, GATE IES EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA https://t.me/pravendrarajpoot Daily news & current affairs in hindi & english fully updated Daily current affairs https://t.me/newsdailypkr Engineering Discussion group for your upcoming exams, you can ask your any query regarding your problem,👇👇👇 https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA PKR ELECTRICAL ENGINEERING I am sure this is the best place for you guys subscribe and get success IF YOU WANT TO JOIN ME ON TELEGRAM FOR PDF @newsdailypkr AE/JE EE, ESE, ECE, ME, CE, IT & CS EXAM MATERIALS & OLD PAPERS Electrical Engineering https://t.me/pravendrarajpoot facebook page:- Pravendra Kumar Rajpoot https://t.me/newsdailypkr https://chat.whatsapp.com/5AS7dNFTP4H4vVsiWsqHrT https://t.me/srk50 https://t.me/pravendrarajpoot https://t.me/joinchat/JObxeA7n6S4qvnegrGhTgA
No comments:
Post a Comment