FUSE RATING is the current rating at which the fuse will blow
BREAKING CAPACITY/INTERRUPTING CAPACITY is the current that a fuse or CB is able to interrupt without being destroyed or cause an electrical arc.
Types of springs in ACB
Independent manual spring
Motor driven stored charge spring
Manual wound stored charge spring
solenoid
Types of FUSE
Fuse is used LV distrib circuits,motor circuits and portable appliances.
Adv is its fast reaction. Disadv of fuse is its insensitivity to small overcurrents. HRC fuse will blow for as low as 25% of overload current, but only after abt 4hrs.
HRC- high rupture capacity
Catridge
Kit kat type
Semi enclosed type
If one fuse blown, why all replaced
The others may be seriously weakened which makes dem unreliable.4
Fuse ratings-88
Single fuse-94
BREAKING CAPACITY/INTERRUPTING CAPACITY is the current that a fuse or CB is able to interrupt without being destroyed or cause an electrical arc.
Types of springs in ACB
Independent manual spring
Motor driven stored charge spring
Manual wound stored charge spring
solenoid
Types of FUSE
Fuse is used LV distrib circuits,motor circuits and portable appliances.
Adv is its fast reaction. Disadv of fuse is its insensitivity to small overcurrents. HRC fuse will blow for as low as 25% of overload current, but only after abt 4hrs.
HRC- high rupture capacity
Catridge
Kit kat type
Semi enclosed type
If one fuse blown, why all replaced
The others may be seriously weakened which makes dem unreliable.4
Fuse ratings-88
Single fuse-94
BHATTA
Which equipment requires both fuse and circuit breaker? >0.5Kw machine
In a motor power line OLR and HRC fuse are both used. Why?
OLR gives protectin against sustained overload current with a time delay and protects for as low as 25% overcurrent protection.
HRC fuse for instantaneous short cicuit protection.
Prop of fuse material
Less resistivity to flow of current, low melting point
Fuse material
tin-lead alloy, al, zinc, antimony
Mild steel cannot be used as it has higher melting point of abt 1400degrees. And its resistivity is higher – 15*10^(-8).
T 3.15A H 250V
1st letter – FF – very fast acting
F fast acting
M medium acting
T slow acting
TT very slow acting
3rd letter L Low breaking Capacity
H High breaking Capacity.
Which equipment requires both fuse and circuit breaker? >0.5Kw machine
In a motor power line OLR and HRC fuse are both used. Why?
OLR gives protectin against sustained overload current with a time delay and protects for as low as 25% overcurrent protection.
HRC fuse for instantaneous short cicuit protection.
Prop of fuse material
Less resistivity to flow of current, low melting point
Fuse material
tin-lead alloy, al, zinc, antimony
Mild steel cannot be used as it has higher melting point of abt 1400degrees. And its resistivity is higher – 15*10^(-8).
T 3.15A H 250V
1st letter – FF – very fast acting
F fast acting
M medium acting
T slow acting
TT very slow acting
3rd letter L Low breaking Capacity
H High breaking Capacity.
CIRCUIT BREAKERS
Material moving contacts- Copper of high conductivity and sometimes silver tipped or silver alloy coated high conductivity and low resistance at high temp
Arcing contacts – sintered silver tungsten res to heat and donot weld at high temp
Material moving contacts- Copper of high conductivity and sometimes silver tipped or silver alloy coated high conductivity and low resistance at high temp
Arcing contacts – sintered silver tungsten res to heat and donot weld at high temp
BHATTA CB
What to do if ACB not tripped?
Manual push button which has a mech linkage to disengage the latch.
ACB melted with bus bar, how to open the ACB?
Tie breaker used to isolate the affected side of the CB. The terminals are earthed and checked for no voltage.
MCB and MCCB? 201
What to do if ACB not tripped?
Manual push button which has a mech linkage to disengage the latch.
ACB melted with bus bar, how to open the ACB?
Tie breaker used to isolate the affected side of the CB. The terminals are earthed and checked for no voltage.
MCB and MCCB? 201
Moulded case CB and miniature CB are used in feeder and distribution circuits. The distribution board is supplied via a fuse or MCCB with the reqd breaking capacity. While MCB are used in final distrib boards instead of fuses.
MCCB is compact ACB fitted in a moulded plastic case. Lower NORMAL CURRENT RATING(50-1500A) and a lower breaking capacity. Can be used for generator breakers to small distribution breakers. The limited breaking capacity may demand for a back-up fuse. If fault occurs, front cover of larger rating (1000A) can be removed for visual insp and cleaning. If tripped, inspected for damage and IR checked and shud be more than 5Mohm.
MCB are very small ACB fitted in moulded plastic cases. Current ratings of 5-100A. have very limited breaking capacity of 3000A. Are used in final distribution boards in place of a fuse. MCB must be replaced if fault occurs and no maintenance.
MCCB is compact ACB fitted in a moulded plastic case. Lower NORMAL CURRENT RATING(50-1500A) and a lower breaking capacity. Can be used for generator breakers to small distribution breakers. The limited breaking capacity may demand for a back-up fuse. If fault occurs, front cover of larger rating (1000A) can be removed for visual insp and cleaning. If tripped, inspected for damage and IR checked and shud be more than 5Mohm.
MCB are very small ACB fitted in moulded plastic cases. Current ratings of 5-100A. have very limited breaking capacity of 3000A. Are used in final distribution boards in place of a fuse. MCB must be replaced if fault occurs and no maintenance.
Maintenance of ACB
The mechanical linkage in CB shud be lubricated as specified
Main contacts shud not be filed, it has to be realigned
Arcing contacts shud be filed with a smooth file. Carborundum or emery shud not be used as the hard particles can embed in the soft contacts
Splitter plates in the arc chute shud be checked for erosion and broken parts
The mechanical linkage in CB shud be lubricated as specified
Main contacts shud not be filed, it has to be realigned
Arcing contacts shud be filed with a smooth file. Carborundum or emery shud not be used as the hard particles can embed in the soft contacts
Splitter plates in the arc chute shud be checked for erosion and broken parts
MCB maintenance?
MINIAture CB is maintainence free. For freeing mechanical linkage, can be closed
MINIAture CB is maintainence free. For freeing mechanical linkage, can be closed
What are aux contacts and purpose of it in ACB, arc chutes? 189
Interruption of current causes generation of arc. Arcing not a prob under normal cond but prob under fault conditions. To prevent damage to main contacts, aux contacts are provided. Arc shud be elongated and moved up thru the arc runners/arc horns. And finally chopped by insulating and arc resisting splitter plates in arc chute.
Vacuum circuit breaker?
Interruption of current causes generation of arc. Arcing not a prob under normal cond but prob under fault conditions. To prevent damage to main contacts, aux contacts are provided. Arc shud be elongated and moved up thru the arc runners/arc horns. And finally chopped by insulating and arc resisting splitter plates in arc chute.
Vacuum circuit breaker?
MITRA CB
Safeties of MCCB and ACB?
MCCB consists of an under-voltage trip coil, an overcurrent trip of adjustable thermal or fixed/adj magnetic type.
MCB have thermal overcurrent and magnetic short circuit protection
MCB have thermal overcurrent and magnetic short circuit protection
Mechanical interlocks to MCB to prevent racking out if it is on position. Withdrawing CB causes the safety shutter to cover the live bus bar contacts.
Electrical interlock switches to prevent incorrect sequence like interlock for shore supply
Electrical interlock switches to prevent incorrect sequence like interlock for shore supply
MCB and ACB differentiate?
LV generator CB(1000V) and large distribution CB(600-6000A) use ACB which means contacts are separated by air.
HV(6.6kV,11kV) use Vacuum interrupter type VCB and gas filled breakers SF6 CB.
Operating mechanism for both are same except the medium surrounding the contacts.
VCB contacts have to move only by few mm as the insulation level of vacuum is very high. Quality of vacuum in the sealed interrupter is checked by applying a short duration of HV pulse(eg 10KV for 6.6kV) across open contacts
In the gas breaker, contacts are separated by Sulphur hexafluoride) at 5bar @20degrees.
HV(6.6kV,11kV) use Vacuum interrupter type VCB and gas filled breakers SF6 CB.
Operating mechanism for both are same except the medium surrounding the contacts.
VCB contacts have to move only by few mm as the insulation level of vacuum is very high. Quality of vacuum in the sealed interrupter is checked by applying a short duration of HV pulse(eg 10KV for 6.6kV) across open contacts
In the gas breaker, contacts are separated by Sulphur hexafluoride) at 5bar @20degrees.
BHOUMIK CB
Alternator ACB protection? 192
Type of circuit breaker in bow thruster? 196
Alternator ACB protection? 192
Type of circuit breaker in bow thruster? 196
BHATTA
What is arc horn?
What is arc horn?
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