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


Example for Setting of MCCB  for Motor Circuit

  •  When we select an MCCB for motor application, it is necessary that the instantaneous release setting in the MCCB is set to a value higher than the highest anticipated Motor magnetizing inrush current during switching-on the motor.
  • The values for magnetizing inrush current (sub transient current) are higher in case of high efficiency motors as compared to standard efficiency motors.
  • By theoretical and empirical means it is established that the maximum ratio between peak and LRC can go up to 2.5 for high efficiency motors.

Motor Starting Current:

  • Motor starting current is one of the most important electrical parameter of motor to understand its electrical characteristics.
  • It is important to note the distinction between inrush current and starting current
  • The current drawn by the motor in different phases are.
  1. Inrush Current (Sub transient phase)
  2. Starting or Lock Rotor Current (Transient phase)
  3. Steady state operation.

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Inrush Current (Sub transient phase)

  • During the initial phase of motor starting Current drawn by motor is known as inrush current or peak current.
  • Inrush current is the current drawn between switch on and when the magnetic fields are established in the motor this current is due to magnetizing inrush component of the motor starting current.
  • Inrush Current: It is generally 13 to 17 x FLA for older motors to New Motor.
  • The duration of inrush current: It is in milliseconds.
  • Motor circuits are highly inductive. Motor can be started at any point on voltage wave of the circuit. Depending on the initiation of the circuit i.e. point on the voltage wave.
  • The magnitude of the
    asymmetry is directly related to X/R ratio of the circuit.

Starting Current (Transient phase)

  • Motor starting current or Lock Rotor Current is the current drawn while Motor is accelerating to full speed.
  • Starting Current: It is depend upon Starting method of Motor
  • For DOL Starter : 6 to 8 x FLA
  • Star- Delta: 2 to 3 x FLA
  • Auto Transformer: 2 to 3 x FLA
  • Soft Starter: 3 to 5 x FLA
  • VFD: 1.5 x FLA
  • The duration of Starting current: Depend upon Load and Application (10 To 40 Sec)

The magnetic settings for Motor should be as follows:

  •  Motor Starting Current < Magnetic Setting of MCCB < Short Circuit Current
  • The MCCB should not trip during starting of the motor. Therefore setting should be 1.3 times the starting current. Normally the starting current will be 6 times the full load current of the motor. Therefore it will be 7.8 times the full load current.
  • However you have to calculate the short circuit current at the motor terminal. This depends on source fault level at the bus feeding the motor and cable impedance between the MCCB and motor. The setting on the MCCB should be less than the calculated short circuit current.
  • Motor Acceleration Time < Magnetic Time Setting of MCCB
  • Another important consideration is the acceleration time should be less than the time set on the MCCB for the magnetic setting.

Calculate ventilation for Transformer & DG Room


55

  • Calculate Heat Loss of Electrical Equipment in Electrical / DG Room.
  • Calculate Air Quantity Required for Ventilation.
  • Calculate No’s of Ventilation Fan.
  • Calculate Rating of Ventilation Fan.

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Setting of overload, Short circuit & Ground Fault Protection of MCCB (PART-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

(D) Short time delay Setting ™:

  • Short Time delay sets the amount of time the breaker will carry both a low level and high fault currents before tripping.
  • tm sets length of time the circuit breaker will carry a short circuit within the short-time pickup range.
  • Delays bands are labeled in seconds of short-circuit current at 10 times the ampere rating.
  • The short time delay can be set to I2t On and I2t OFF settings (Inverse Time Delay).
  • (A) I2t OFF: Gives Constant time delay usually in multiplication of 0.5 sec. It has not inverse-time delay Characteristic. It is used for coordination with other circuit breakers with electronic trip devices and for coordination with thermal-magnetic circuit breakers.
  • (B) I2t ON :Gives an inverse-time delay that resembles the time/current characteristics of fuse It is used for coordination with fuses and upstream transformer

(3) For Instantaneous Trip (Short Circuit Protection):

(E) Instantaneous Pickup Setting (Ii):

  • Instantaneous protection is time-independent.
  • It is determines the level of fault current that will actuate a trip with no time delay.
  • Ii value (multiplied by the ampere rating (In)) sets the short-circuit current level at which the circuit breaker will trip with no intentional time delay.
  • This protection trips to eliminate quickly high value currents and its trip times cannot be set
  • The instantaneous function will override the short-time function if the instantaneous Pickup is adjusted at the same or lower setting than the Short Time Pickup.
  • Standard Practice for Setting:
  • No trip for a current below 80% of the instantaneous setting
  • Trip for a current equal to 120% of the instantaneous setting
  • The trip time is less than 0.2 second.

 (4) For Ground Fault Protection:

(F) Ground Fault Pickup Setting (Ig):

  • It is determines the level of fault current at which the ground fault trip delay countdown is actuated.

(G) Ground Fault Delay Setting (Itg) :

  • It is determines the amount of time the breaker will carry a ground fault before tripping.
  • It 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

 Example for Settings of MCCB for Protections

Example1: We have Sub feeder MCCB Size of 2000A, Short Circuit Current is 4000A. Maximum Load Current is 1000A .What is Over current (Long Time) and Short Circuit (Short Time) and Instantaneous setting of MCCB.

  • Here In=2000A

Over current Setting:

  • Dial Setting=(Load current / MCB Rating) =1000/2000=0.5 , set Dial at 0.5
  • Over current Setting Ir=0.5xIn =0.5X2000=1000A
  • For Set Over Current Time Delay: It is necessary to overview Over current Time delay of downstream MCCB and Upper stream MCCB for better coordination otherwise for downstream fault upper stream MCCB gives tripping.
  • Downstream Over current Time Delay< Over current Time Delay< Upper stream Over current Time Delay.
  • In Our example it is last MCCB in circuit and upper stream MCCB Over current delay setting is 2 Sec so Select tr=1 Sec.

Short Circuit Current Setting:

  • Dial Setting=( Short Circuit Current/ MCB Rating) =4000/2000=2
  • Short Circuit Setting Isd=2xIn=2×2000=4000A
  • Downstream Short current Time Delay< Short  current Time Delay < Upper stream Over current Time Delay Short  current Time Delay
  • Our example it is last MCCB in circuit and upper stream MCCB Short Circuit current delay setting is 0.4 Sec so Select Isd=0.2Sec.
  • For coordination of other MCCB we need I2t ON with 0.2 Sec delay.

Instantaneous Tripping Setting:

  • Instantaneous Tripping gives instant tripping without any delay for switching or short Circuit current.
  • Instantaneous Tripping >= Short Circuit Tripping Setting
  • If We can set Ii=3xIn =3×2000=6000A , It will full fill our requirement
  • Here Ii>Isd=6000A>4000A.

 

Setting of overload, Short circuit & Ground Fault Protection of MCCB (PART-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

 

 

 

 

 

Type of Tripping Mechanism of MCB / MCCB-(Part-2)


(3) Thermal-Magnetic Trip mechanism (inverse-time & instantaneous-trip)

  • Thermal-magnetic circuit breaker (TMD) is most common use for over current and short circuit protection.
  • It is a combination of Thermal Circuit breaker and Magnetic Circuit Breaker.
  • It contain two different switching mechanisms, a bimetal switch and an electromagnet
  • The thermal Property (Bimetal Strip gets elongated when heating) is used to sense the overload and Magnetic Property (Magnetic Flux / induction) is used to sense the short circuit.
  • Characteristic:
  • In Thermal-Magnetic Circuit Breaker both Thermal element (Bimetallic Strip) and Magnetic element (Electromagnet) are connected in series with load.
  • In normal Load a bimetallic element is heated by the normal load current, the bimetallic element does not bend, and the magnetic element does not attract the trip bar.
  • If the temperature or current increases over a sustained period of time, the bimetallic element will bend, push the trip bar and release the latch. The circuit breaker will trip.
  • If the current suddenly or rapidly increases enough, the magnetic element will attract the trip bar, release the latch, and the circuit breaker will trip.
  • Thermal Trip gives inverse time characteristic and Magnetic Circuit Breaker (instantaneous-trip circuit breakers) gives instantaneous-tripping.
  • MCCB Rating: 10 A to 1600A
  • Operating Time: 4mili sec.
  • Application:
  • For residential Load
  • For to heavy industrial loads.
  • For higher level (short circuit) over currents,
  • For motor-circuit protection.
  • AC/DC power distribution.
  • Electrical machines
  • Protection for transformers, motors, generators.
  • For Protection of capacitor.
  • Protection Range:
  • The adjustable overload protection is from 70% to 100% of the nominal current (0.7 to 1xIn)
  • Short circuit setting from 5 to 10 times of the rated current is possible.
  • For example: A 100 A thermal-magnetic circuit breaker will trip within a short time if it is subjected to a current of 400 A, but a 100 A instantaneous-trip circuit breaker will carry that overload indefinitely, if the adjustable trip is set above that level.
  • Instantaneous-trip circuit breakers are circuit breakers that have a magnetic trip function but not a thermal trip function. They are designed for one very specific purpose, that being to provide branch-circuit short-circuits protection for motor circuits.
  • Advantage:
  • economical, tried and tested technology
  • Disadvantage:
  • The operating characteristics of the breaker may vary depending on the ambient temperature.
  • It needs particular time to trip ( heat up the metallic strip > open circuit the holding coil > opens the contacts
  • Provide less flexibility of adjustment than electronic releases.

  (4) Electronic (Static) Trip Mechanism:

  • A coil, placed on each conductor, continuously measures the current in each of them.
  • This information is processed by an electronic module which controls the tripping of the circuit breaker when the values of the settings are exceeded.
  • Both the overload trip action and the short-circuit trip action of breakers with electronic trip units are achieved by the use of current transformers and solid-state circuitry that monitors the current and initiates tripping through a flux shunt trip when an overload or a short circuit is present.
  • MCCB Rating: 20 A to 2500A
  • Operating Time: 4mili sec.
  • Protection Range:
  • The adjustable overload protection is from 60% to 100% of the nominal current (0.6 to 1xIn)
  • Short circuit setting from 2 to 10 times of the rated current is possible.

 

  • Advantage:
  • The operating characteristic of the breaker is independent of the ambient temperature. 
  • More accurate and more flexible settings
  • Becoming standard for larger size breakers
  • Ground fault easy to provide
  • It has wide flexibility to takes care of future increases in load capacity of an installation and ensures better planning at an optimum cost
  • Disadvantage:
  • It is costly compare to TMD Type MCCB.
  • Application:
  • Electronic trip breakers are generally applied for applications where high levels of system coordination.
  • Electronic trip breakers can provide superior protection and coordination as well as system alarms and diagnostics, monitoring and communications.

(5)  Microprocessor Trip Mechanism:

  • In Microprocessor type tripping mechanism release, sensing and tripping executed by Microprocessor by use of CT or current sensing resistor
  • It gives the very faster response than TMD Release.
  • MCCB Rating: 20 A to 2500A
  • Operating Time: 4mili sec.
  • Protection Range:
  • The adjustable overload protection is from 60% to 100% of the nominal current (0.6 to 1xIn)
  • Short circuit setting from 2 to 10 times of the rated current is possible.
  • Advantage:
  • System Diagnosis is possible as it stores the Trip history within the internal memory.
  • Trip current indication is also available for understanding of type of fault and set-up programming at site. 
  • High repeat accuracy and High reliability.
  • Provide coordination, Interlocking to other MCCB.
  • High Flexibility
  • Disadvantage:
  • It is costly compare to TMD Type MCCB.

Type of Tripping Mechanism of MCB / MCCB-(Part-1)


Introduction:

  • Moulded Case Circuit Breakers are electromechanical devices which manually / automatically protect / Open a circuit from Over current and Short Circuit. There is various type of Tripping mechanism to trip MCB/MCCB.

MCCB Tripping Mechanism:

MCCBs have following various Operating Mechanisms.

  • Thermal Trip
  • Magnetic Trip
  • Thermal- Magnetic Trip 
  • Electronic Trip 
  • Microprocessor Trip

 (1) Thermal Trip Mechanism (Inverse-time)

  • The thermal trip mechanism of MCCB works as a delay fuse.
  • It will protect a circuit against a small overload that continues for a long time.
  • In Thermal trip MCCB a bimetal strip is connected in series with the circuit load.

1

  • When normal current pass through bimetallic strip and rise temperature of bimetallic strip and it increase length of bimetallic strip but this expansion rate is not enough for bending movement of strip and the contacts will remain closed.
  • As current of MCCB increase beyond over load current. It heats enough bimetal and thus bimetallic strip bend as per current level and Close contact will be open.
  • The amount of current needed to trip the MCCB depends on the size of bimetallic Strip.
  • The time the bi-metal needs to bend and trip the circuit varies inversely with the current.
  • It has Inverse time characteristics, they allow a long-time delay on light overloads and they have a fast response on heavier overloads.
  • The thermal element will also protect the circuit against temperature increases.
  • It is Sensitive to ambient temperature
  • MCCB must carry 100% of rated current continuously at 40 deg C.
  • At 200% rated current, maximum trip times are

                              Trip Time of Thermal Element @200% current

Amp Rating Max Time @ 200%

0-30

2 min
31-50 4 min
51-100 6 min
101-150 8 min
151-225 10 min
1601-2000 28 min
  • Tripping Action: Tripping Time will depend upon Current. The larger the overload, the faster the circuit breaker will trip
  • Used For: Over Load Protection

 (2) Magnetic Trip Mechanism (Instantaneous-trip)

  • In magnetic trip MCCB an electromagnet (an iron core with a wire coil around it, forming an electromagnet) is in series with the circuit load.

2

  • With normal current, the electromagnet will not have enough electromagnetic field to attraction the trip bar for movement and the contacts will remain closed.
  • As High current (Short Circuit) current through the coil increases the strength of the magnetic field of the electromagnet. As soon as the current in the circuit becomes large enough, the trip bar is pulled toward the magnetic element (electromagnet), the contacts are opened and the current stops.
  • The amount of current needed to trip the MCCB depends on the size of the gap between the trip bar and the magnetic element.
  • On some MCCB this gap (trip current) are fixed and some MCCB are adjustable.
  • Tripping Action: A magnetic circuit breaker will trip instantly when the preset current is present.
  • Used For: Short Circuit Protection

Type of Light Bulb base & Socket:Part-2


(4) Single Pin Type Base (F):

1

  • The “F” type of lamp base is used to as a “pinned” base.
  • This Type of socket have Single Pin.
  • Type of Connection: “Pin” Type
  • Pin Configuration: (Fx):

(5) Cable connected Socket (K):

  • 2.jpgAction: “Cable” Type
  • Pin Configuration: K
  • K indicates that a cable is the power connection for a lamp.
  • The product is a wired connection to power.
  • Example: K4 , K6
  • Application:
  • with standardized connecting cable for electrically operated valves, mechanical position switches and valves with central connection

(6) Pr-focused Sockets (P):

3

  • Action: “Push” Type
  • Pin Configuration: P
  • Types:
  • LED light bulb pre-focus base types: S.C. Prefocus and D.C. Prefocus 
  • Application: Automobile

(7) Recessed Contact Base (R)

4.jpg

  • Action: “Spring Loaded”
  • Pin Configuration: (Rx):
  • Here “R” indicate recessed Type Socket.
  • Recessed Double Contact Base used for Fluorescent type lighting bulbs having high output.
  • Applications
  • For Fluorescent type lighting bulbs

(8) Flange base Sockets (F or T):

  • Action: “Push” Type
  • Pin Configuration: F or T5
  • Type of Flange Base Socket: Micro-midget flanged base, Midget flanged, Miniature midget flanged, Sub-midget flanged, and Special-midget flanged base types.
  • Application: LED light bulb, Electrical Panel, Indication Lamp, Automotive, Electronic device lighting applications. 

(9) Slide base Sockets (S):

6

  • Action: “Push” Type
  • Pin Configuration: S
  • Type:
  • There are various types like Slide#1 ,Slide#2
  • Slide base LED replacement bulb is perfect for industrial indicator lights.
  • It is also used as an LED pilot light bulb.
  • Applications
  • Indicator LED replacements
  • LED Pilot light bulb

(10) Wedge base Sockets (W):

7

  • Action: “Push” Type
  • Type: Double Side (D.F) Contactor and Single Side (SF) Contactor
  • Pin Configuration: (WX2.5x16q):
  • W =Wedge Type, Second Letter indicate the width in millimeters and third lowercase d to indicate a double-contact (single-filament) bulb or q for a quad-contact (dual-filament) one.
  • A wedge base is a type of connector used as a fitting for small light bulbs in Automobile. It is same as bi-pin connector, except that the two “pins” are the same wires that extend into the bulb (rather than being rigid), and the wires are bent up onto the sides of the base, where they make contact with the socket.
  • The wires are usually inserted into a plastic base that the bulb is mounted in, and which is often narrower at the tip than at the bulb, giving it a wedge shape and usually ensuring a tight connection.
  • The bulb is inserted and removed with straight in or out force, without turning as with a bayonet mount or Edison screw. compression is the force that holds the bulb in
  • Application: In Automobile and in low-voltage lighting used in landscape lighting.
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