Fuse and Types of different Fuses

Fuse and Types of Fuses

What is a Fuse:

The fuse is an electronic device, which is used to protect circuits from over current, overload and make sure the protection of the circuit. There are many types of fuses available in the market, but function of all these fuses is same.

SELECTION OF MCCB / MCB (LESSON-3)

SELECTION OF MCCB / MCB (LESSON-3)

(E) Others:

 (1) Frequency:

• MCB is designed and used in AC power system of 50 to 60Hz.
• Electromagnetic force of magnetic release is related with power supply frequency so If Frequency is changed than electromagnetic fore of Magnetic element is changed hence MCCB tripping current will be different.
• If we used MCCB for protection in DC circuits than specially design DC circuit MCCB should be used rather than normal type of MCCB.

SELECTION OF MCB / MCCB ( LESSON-2)

 HOW TO SELECT  MCB / MCCB  

A. Utilization category / Characteristic (B, C, D, K, Z curve):

• Characteristic of Trip curves of MCCB tell about the trip current rating of MCCB.
• MCB will trip instantaneously according to their Tripping Characteristic at 0.1 sec.
• There are various type of MCCB
• Type B MCCB
• Type C MCCB
• Type D MCCB
• Type K MCCB
• Type Z MCCB

SELECTION OF MCB / MCCB ( LESSON-1)

SELECTION OF MCB / MCCB

Introduction

MCB or MCCB are widely used in electrical distribution system for ON/OFF Electrical supply and it also gives over current and short circuit protection. Selection of MCB or MCCB involved technical, Mechanical parameters. Some parameters are important but some parameters are confusing and mislead to wrong selection of MCCB. Some parameters are directly affected on cost of MCCB.  

Specification / Name Plate Details of MCB/MCCB:

 Following specifications are required to select appropriate MCB or MCCB.

(A) Current Related:

• Frame Size (Inm): Amp
• Rated current (In/ Ie): Amp
• Ultimate short circuit breaking capacity (Icu): KA
• Rated short-circuit breaking capacity (Ics): % of Icu

(B) Voltage Related:

• Rated voltage (Ue): Volt
• Rated Insulation voltage (Ui): Volt
• Rated impulse withstand voltage(Uimp): KV
• No’s of Pole : SP,DP,TP,TPN,FP

(C) Application Type:

• Utilization Category/ Characteristic : B,C or D curve

(D) Accessories:

• Rotary Handle: Extended/ Direct
• Alarm Contact:
• Shunt Trip:
• Under voltage Trip:
• Mechanical interlocking:
• Manual /Auto operation
• Motorized Operation:

(E) Protection Type:

• Protection : Over current / Short circuit
• Trip Mechanism: Thermal / Magnetic / Solid / Microprocessor
• Trip Mechanism adjustment : Fixed / Adjustable

(F) Others:

• Frequency;
• Reference temperature: (if different from 30°C)
• Pollution degree:
• Suitability for isolation:
• Type of Mounting arrangement
• Electrical Life Cycles:
• Mechanical Life Cycles:
• Dimension: mm
• Weight: Kg
• Reference Standard: IEC: 60947-1/2, IS: 13947-1/2

 (A) Current Related:

  (1) Frame Size (Inm): 

• Breaker Frame Size indicates the basic framework of the Plastic shell of MCCB that can hold the biggest rated current.
• It is the maximum current value for which the MCCB is designed (upper limit of the adjustable trip current range) and it also determines the physical dimensions of the device.
• There are varieties current ratings MCCB for the same series frame Size.
• For example, DX100 Frame Size MCCB for rated current of 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A.
• Same DX225 Frame Size MCCB for rated current of 100A, 125A, 160A, 180A, 200A, 225A.
• In above DX100 and DX225 has two Type of frame Size for rated current of 100A, but the shape and size of breaking capacity of circuit breakers is not the same.

 (2) Rated Current (In /Ie):

• It is the current value above which overload protection is tripped.
• For MCB it is fixed while in MCCB the rated current is an adjustable range instead of a fixed value.
• Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.

(B) Voltage Related:

 (3) Ultimate short-circuit breaking capacity (Icu):

• Breaking capacity can be defined as the maximum level of fault current which can be safely cleared.
• It is the highest fault current that the MCCB can trip without being damaged permanently.
• The MCCB will be reusable after interrupting a fault, as long as it doesn’t exceed this value.
• It is indicate operation reliability of MCCB
• This parameter may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application fault level may be 10kA.

(4) Operating short-circuit breaking capacity (Ics):

• It is expressed as a percentage ratio of Icu and tells you the maximum short-circuit current if a circuit breaker can break three times and still resume normal service.
• The higher the lcs, the more reliable the circuit breaker
• It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds this value, the MCCB will be unable to trip and another protection mechanism must operate.
• If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
• The Main difference between Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) that Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterwards.
• For example, if a circuit breaker has an Ics of 25,000 Amperes and an Icu of 40,000 Amperes:
• Any fault below 25kA will be cleared with no problem.
• A fault between 25kA and 40kA will cause permanent damage when cleared.
• Any current exceeding 40 kA can’t be cleared by this breaker.

 (5) Rated working voltage (Ue):

• It is the continuous operation voltage for which the MCCB is designed.
• This value is typically equivalent or close to a standard system voltage.
• In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V.

(6) Rated Insulation voltage (Ui):

• It is the maximum voltage that the MCCB can resist according to laboratory tests.
• It is higher than the rated working voltage, in order to provide a margin of safety during field operation.

(7) Rated impulse withstands voltage (Uimp):

• It is the value of transient peak voltage the circuit-breaker can withstand from switching surges or lighting strikes imposed on the supply.
• This value characterizes the ability of the device to withstand transient over voltages such as lightning (standard impulse 1.2/50 μs).
• Uimp = 8kV means Tested at 8 kV peak with 1.2/50μs impulse wave.

(8) Number of Poles:

• No of Pole for MCCB depends on Single Phase & Three Phase Power Controlling /Protection
• Single Pole (SP) MCB: 
• A single pole MCB provides switching and protection for one single phase of a circuit.
• Used: for Single Phase circuit
• Double Pole (DP) MCB: 
• A two Pole MCB provides switching and protection both for a phase and the neutral.
• Used: for Single Phase circuit
• Triple Pole (TP) MCB: 
• A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral.
• Used: for Three Phase circuit
• 3 Pole with Neutral (TPN (3P+N) MCB): 
• A TPN MCB, has switching and protection to all three phases of circuit and additionally Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any protection and can only be switched.
• Used: for Three Phase circuit with Neutral
• 4 Pole (4P) MCB: 
• A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit.
• Used: for Three Phase circuit with Neutral

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PROTECTION SETTING OF MCCB (LESSON-2)

 Over load , Shirt circuit & Ground Fault Protection (LESSON-2) 

(2) For Short Circuit Protection (Magnetic Setting):

  (C) Short Time pickup Current Setting (Im):

• Short time protection is time-independent.
• It is determines or sets the level of fault current at which the short-time trip delay countdown is actuated.
• Short Time Pick up Value (Im) (multiplied by the ampere rating) sets the short circuit current level at which the circuit breaker will trip after the set time delay.
• The short-time pickup (Isd) sets current level (below instantaneous trip level) at which circuit breaker will trip after the preset time delay.
• Standard Practice for Setting:
• No trip for a current below 80% of the short time setting
• Trip for a current equal to 120% of the short time setting
• The trip time is Less than 0.2 s for a short time protection with no time delay and equal to the value of the time delay tsd for a protection with time delay

PROTECTION SETTING OF MCCB (LESSON-1)

Protection setting of  MCCB ( Over load , Shirt circuit & Ground Fault Protection (LESSON-1)

Introduction:

• There are various types of protections setting in MCCB, which define various protection of Electrical Network.
• In MCCB we can set most of protection are adjustable according to Electrical Load profile.
• The main adjustable Setting in MCCB are
• Over current Setting
• Short Circuit Setting
• Ground Fault Setting

Meaning of each selector switches of MCCB

• As Per Standard IEC 60947-2 defines the names of the selector switches.

Setting	Adjustment	Protection For
Ir	Long time Pick up Current Setting (or thermal Setting). This is a multiplication coefficient of the rating of the device. (Ir=xIn)	Protection against overloads
tr	Long time delay Setting in seconds, enabling in particular the starting current of a motor to be tolerated. (tr=Sec)	Protection against overloads
Im / Isd	Short time (Magnetic Setting). This is a multiplier of the Ir setting, often 1.5 to 10 times the Ir current (im=xIr)	Protection against short circuits.
tm / tsd	Short time delay Setting, enabling in particular the discrimination (time) to be increased with downstream feeders and the magnetization peaks of a transformer or a motor to be tolerated. It is recommended that the I²t selector switch is set to the ON position.(tm=Sec)	Protection against short circuits.
Ii	Instantaneous current Setting. Protecting the installation against strong short circuits (dead short circuits) by instantaneous tripping without Time Delay and self-protection of the circuit breaker. The Ii > Isd.	Protection against Dead Short circuits.
Ig	for monitoring the earth fault current circulating in the Phase and Earth conductor in TNS systems	Earth protection
tg	Earth protection time delay	Earth protection
I delta n	Adjustment of the sensitivity of the earth leakage protection	Earth leakage protection
delta t	Earth leakage protection delay.	Earth leakage protection

  Setting of each Protection switch of MCCB

 (1) For Low level Fault / Over Current Protection (Thermal Setting):

  (A) Long-Pickup Current Setting (Ir):

• It is determines the continuous ampere rating of the breaker.
• Long time protection is time-dependent.
• Long Pickup (Ir) value (multiplied by the ampere rating (In) of MCCB) sets the maximum current level which the circuit breaker will carry continuously.
• If MCB is 1000A Rating but Full Load current is 800A than MCCB Rating can be changed from 1000A to 800A by setting it 0.8, Now Ir=0.8XIn =0.8×1000=800Amp
• If the current exceeds this value for longer than the circuit breaker will trip at the set delay time.
• Long time protection is inverse time type (with I2t constant)
• The long-time pickup (Ir) is adjustable from 4 to 1.0 times the sensor plug rating (In)
  

• Standard Practice for Setting:
• No trip for a current below 105% of Ir
• Trip in less than two hours for a current equal to for
• 120% of Ir for an electronic trip unit and for
• 130% of Ir for a thermal-magnetic trip unit
• For a higher fault current, the trip time is inversely proportional to the fault current value.

(B) Long-Time delay Setting (tr):

• Long time delay (tr) sets length of time that the circuit breaker will carry a sustained overload before tripping.
• The delay bands are labeled in seconds of over current at six times the ampere rating.
• Long-time delay is an inverse time characteristic in that the tripping time decreases as the current increases.
• The long-time delay (tr) sets the length of the time that the circuit breaker will carry an over current (below the short-time or instantaneous pickup current level) before tripping.
• The Long time delay can be set to I2t On and I2t OFF settings.
• (A) I2t Response:I2t Out ,For coordination with other circuit breakers with electronic trip devices and for coordination with thermal-magnetic circuit breakers.
• (B) I2t Response: I2t In ,For coordination with fuses and upstream transformer