Fundamentals Ckt Prot Color

1Fundamentals of Circuit Protection101 Basics

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Fundamentals of Circuit Protection101 Basics

What are the 101 Basics?These modules provide an introduction to various products and services available in the electrical control, distribution and power quality categories.

The modules are organized by market segment and you can link here to view a planning page to help select the modules that meet your product and service knowledge needs.

What will you learn from this module?You will learn:

The types of circuit protection available. Codes and Standards for circuit breakers. The five main components of circuit breakers. The functionality of those five main components.

Included in this Module

Audio Option This module has an audio option if you would like to listen to the material. You can turn off your speakers without missing any of the key module concepts.

Printed MaterialsPrintable reference material is included in the module attachments in case you want to take notes while working though this material.

Knowledge ChecksThe knowledge check questions located throughout the module are not included in your final module score.

AssessmentAn assessment is used to evaluate learning effectiveness and will be your final module score.


2Do you know the Fundamentals of Circuit Protection? Test your knowledge. An 80% or better is required to pass this module.

Assessment

Welcome to Fundamentals of Circuit Protection. This module is designed to increase your technical knowledge of circuit protection.

Learn


The primary purpose of circuit protection is to protect the wire from overheating in an

overcurrent situation, therefore limiting damage to the equipment downstream of the protective

device.

Introduction

Exampleofaprotectivedevicethatfailed

Fundamentals of Circuit Protection101 Basics - Learn

What is Circuit Protection?

Circuit protection devices, also known as circuit breakers and fuses, protect the wire and electrical equipment from fault conditions including:

Overload FaultsShort Circuit FaultsSpecialty Faults (Ground Fault and Arc Fault)

These protective devices were developed out of a need for safe resettable devices that would be used as a means of disconnect in facilities.


Objectives

By the end of this section, you will understand:

1. The purpose of circuit protection.

2. The types of circuit protection available in the market.

3. Difference between circuit breakers and fuses.

4. Codes and Standards for circuit breakers.

3MoldedCase

MediumVoltageVacuumBreaker

Miniature

SupplementaryProtector

MediumVoltageFuse

LowVoltagePowerBreaker

PicturedisarepresentationofEatonscircuit

protectionoffering,inorderofincreasingvoltagecapacity.Types of Circuit Protection


Fuse Protection

The purpose of a fuse is to protect the wire from overheating in an overcurrent situation, therefore limiting damage to the equipment downstream of the protective device.

Fuses are manufactured for low voltage through high voltage applications and can be either current limiting or expulsion type.


Eaton manufactures medium voltage fuses for use in medium voltage assemblies. Eaton does manufacture devices that require low voltage fuses (such as safety switches), however the low voltage fuses are sourced from other manufacturers.

For more information on medium voltage fuses, see the Medium Voltage Circuit Protection module.

Fuse Protection

As was defined previously, the purpose of a fuse is to protect the wire from overheating in an overcurrent situation, therefore limiting damage to the equipment downstream of the protective device.

Fuses are manufactured for applications from low voltage through high voltage and can be either current limiting or expulsion type.

Eaton manufactures medium voltage fuses for use in medium voltage assemblies. Eaton does manufacture devices that require low voltage fuses (such as safety switches), however these are sourced from other manufacturers.

For more information on fuses, see the following modules: Medium Voltage Circuit Protection and Safety Switches.

Current Limiting FuseA fuse that when its current

responsive element is melted by a current within the fuses specified

current limiting range, abruptly introduces a high resistance to reduce

current magnitude and duration, resulting in subsequent current

interruption.

Expulsion FuseA vented fuse in which the expulsion

effect of the gases produced by internal arcing, either alone or aided

by other mechanisms, results in current interruption.

An expulsion fuse limits the duration of a fault on the electrical system, not

the magnitude.

Eaton manufactures both current limiting and expulsion type medium voltage fuses. More information can be found in the Medium Voltage Circuit Protection module.


4While the purpose of circuit breakers and fuses is the same, there are fundamental differences to their designs, which are important to understand when making selections for a system or assembly.

Circuit Breaker

Resettable after a fault causes the circuit breaker to trip Generally have a higher cost of initial investment Require regular maintenance (specifically for low voltage power circuit and medium voltage vacuum circuit breakers) Optional protective features (such as ground fault)

Circuit Breakers vs. Fuses

Fuse

Must replace a fuse that is blown while interrupting a fault Less initial cost of investment No maintenance required Only sense overcurrent and do not have capability for optional protective features


Codes and Standards

The electrical industry requires that circuit breakers are designed and manufactured to meet codes and standards in order to minimize the possibility and effects of fire and other risks.

These codes and standards can vary by country or by region. For example, in the United States, the National Electrical Code can be adopted, rejected or modified down to the state or municipal level.

While standards can vary around the world, the impact that standards have on the design and application of circuit breakers worldwide is profound, and helps to ensure that the product is safe for use in electrical systems.

Example of circuit breaker label meeting UL standards


United States Domestic Standards:Molded case circuit breakers are designed, built, and tested in accordance with the NEMA and/or Underwriters' Laboratories, Inc. (UL) standards.

Low voltage power circuit breakers are designed, built and tested in accordance with the ANSI and/or Underwriters Laboratories, Inc. (UL) standards. In addition, these breakers are designed to be applied in accordance with the requirements of the National Electrical Code (NEC).

Medium voltage vacuum circuit breakers are also certified to the ANSI standard for North America.

International Standards:In addition to the above domestic standards, international standards must be complied with in order to sell products to world markets. There are many individual country standards on circuit breakers, along with the International Electrotechnical Commission (IEC) standards.

Additional details on standards can be found in Eatons catalogs and Consulting Application Guide.

Codes and Standards


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Although low and medium voltage circuit breakers have unique designs that are specific to amperage, voltage and application, there are five main components that are universal across the different types of circuit breakers.

Key Components of Circuit Breakers

FrameProtects internal parts of

circuit breaker from outside materials

Operating MechanismProvides a means of opening and closing the circuit breaker

ContactsAllow current to flow

through the circuit breaker when closed

Arc ExtinguisherExtinguishes arc when circuit

breaker interrupts a fault

Trip UnitOpens operating mechanism in the event of a prolonged

overload or short circuit

Fundamentals of Circuit Protection101 Basics - Learn Objectives

By the end of this section, you will understand:

1. The five main components of circuit breakers.

2. The functionality of the main components.

This section will provide information on each component, its functionality, and purpose.

Fast FactsThe interrupting rating of the circuit breaker is the maximum amount of fault current it can interrupt without damaging itself. The interrupting capacity of the circuit breaker must be equal to or greater than the amount of fault current that can be delivered at the point in the system where the circuit breaker is applied.

The circuit breaker frame provides the rigidity and strength required to successfully deal with the interruption process and achieve the desired interrupting ratings.

It insulates and isolates the electrical current in order to protect people and equipment during use or operation.

Frame

Metal Frame Molded Insulating Material


Click each frame to learn more:

6Fast Facts

Theprimarypurposeofacircuitbreakeristoprotectthewirefromoverheating.

Provides the rigidity and strength required to successfully deal with the interruption process and achieve the desired Interrupting Ratings.

Provides for insulation and isolation of the current path, offering personnel protection near the equipment during operation.

Two Types of Frames:

Frame


Metal FrameAssembled from precise metal pieces that are bolted and welded together to form the frame.

Some low voltage power circuit breakers and all medium voltage vacuum circuit breakers are of the metal frame design.

Eaton offers the following circuit breakers in metal frames:

Low Voltage Power Circuit BreakersMedium Voltage Vacuum Circuit Breakers


Fast Facts

Theprimarypurposeofacircuitbreakeristoprotectthewirefromoverheating.

Provides the rigidity and strength required to successfully deal with the interruption process and achieve the desired Interrupting Ratings.

Provides for insulation and isolation of the current path, offering personnel protection near the equipment during operation.

Two Types of Frames:

Frame


Molded Insulated Frame (aka Molded Case)Molded case frames are made from strong insulating materials, such as glass-polyester or thermoset composite resins (i.e. plastic frames).

Sizes vary according to the Ampere Rating of the circuit breaker. Molded insulated material frames are primarily associated with miniature, molded case and insulated case circuit breakers (low voltage power circuit breakers designed to meet molded case circuit breaker standards)

Eaton offers the following circuit breakers in molded case frames:

Miniature Circuit BreakersMolded Case Circuit BreakersInsulated Case Circuit BreakersLow Voltage Power Circuit Breakers


Operating Mechanism


Click each type of operating mechanism to learn more.

7Operating MechanismOver Toggle Operating Mechanism

The function of the operating mechanism is to provide a means of opening and closing the circuit breaker.

This toggle mechanism is the quick-make, quick-break type, meaning that the speed with which the contacts snap open or close is independent of how fast the handle is moved.

In addition to indicating whether the breaker is ON or OFF, the operating mechanism handle indicates when the breaker is tripped by moving to a position midway between the ON and OFF.

Eatons residential, miniature and molded case circuit breakers utilize over-toggle mechanisms.


Operating MechanismTwo Step Stored Energy Operating MechanismThe two-step stored energy mechanism is used when a large amount of energy is required to close the circuit breaker and when it needs to close rapidly.

The major advantages of this mechanism are rapid reclosing and safety. Rapid reclosing is achieved by storing charged energy in a separate closing spring. Safety is achieved by providing remote charging of the spring.


The two-step stored energy process is designed to charge the closing spring and release energy to close the circuit breaker. It uses separate opening and closing springs. This is important because it permits the closing spring to be charged independently of the opening process. This allows for an open-close-open duty cycle. The closing spring can be charged (or recharged) manually via a charging handle or electrically via a motor. The motor can be operated remotely, allowing maximum safety for the operator.

Eatons low voltage power circuit breakers and medium voltage vacuum circuit breakers utilize two-step stored energy mechanisms.

Contacts are found in the arc interruption chamber (in low voltage circuit breakers) and in the vacuum interrupter (in medium voltage vacuum circuit breakers)

The contact assembly consists of the movable contact, the movable contact arm, the stationary contact and the stationary conductor (as pictured).

Contacts

As the circuit breaker opens or closes, the fixed contact maintains its position while the movable contact moves to close (make) or open (break) the circuit.

The contacts are designed to protect against two fault conditions:- Overcurrent (thermal overload)- Short Circuit (magnetic)

Movable contact arm

Stationary contact arm


8An arc extinguisher is the component of the circuit breaker that extinguishes an arc when the contacts are opened.

An arc is a discharge of electric current crossing a gap between two contacts. Circuit breakers must be designed to control them because arcs cannot be prevented.

Arc Extinguisher

The next section will cover what an arc is and methods to extinguish the arc in a circuit breaker.

Real World Example of an Arc:Have you ever pulled a plug out of an electrical socket while the appliance is still turned on and seen what appeared to be sparks? What you were observing, on a very small scale, was an attempt at arc formation between the wall contacts and the plug contacts in your hand.


Arcs are formed when the contacts of a circuit breaker open due to larger than normal current.

The size of the arc depends on the amount of current present when the contacts are pulled apart. Because arcs cannot be prevented, circuit breakers must be designed to control them.

What is an Arc?

The heat associated with an arc creates an ionized gas environment. The more ionization, the better the conditions for an arc to be maintained and grow. The bigger the arc, the greater the potential for damage to the circuit breaker and electrical distribution system.

Arcing is a condition that must be dealt with quickly and effectively by a circuit breaker. The ability of the circuit breaker to control the arc is key to its short circuit interrupting capability.


Listed below are the six methods used in the electrical industry to manage electrical arcs:

Arc ChuteVacuum InterrupterSF6Minimum OilMagnetic CoilPuffer

Eaton manufactures circuit breakers using Arc Chute and Vacuum Interrupter technologies. The next slides will go into more detail on these two types of technologies.

Arc Control Methods


9Listed below are the six methods used in the industry to deal with arc control:


Eaton manufactures circuit breakers using Arc Chute (for low voltage breakers) and Vacuum Interrupter (for medium voltage breakers) technology. Those two methods will be covered in this course.

Arc Control Methods

Click the pictures to learn more about the two methods

Arc Chute Technology (also known as Arc Extinguisher)The function of the arc chute is to confine, quench, split, and extinguish the arc drawn between the circuit breaker contacts each time a circuit breaker interrupts current.

In order to interrupt high, short circuit faults, and dissipate the large amount of energy, the arc chute consists of specially shaped steel plates isolated from each other and supported by an insulating housing (as pictured).

When the contacts are opened, the arc induces a magnetic field in the steel plates which, together with other magnetic forces and gas flow, draws the arc into the plates. For an arc with current below about 6000 amperes, the arc usually splits into a series of smaller arcs by the plates and is extinguished rapidly.

Arc Chutes

Eaton uses arc chute technology in residential, miniature, molded case and low voltage power circuit breakers. Note Not all residential and miniature circuit breakers utilize an arc chute.


Listed below are the six methods used in the industry to deal with arc control:



Arc Control Methods


Shown is an animation of an arc chute extinguishing an arc during an overload.


Listed below are the six methods used in the industry to deal with arc control:



Arc Control Methods


Vacuum Interrupter TechnologyVacuum interrupter technology uses enclosed contacts to extinguish arcs.

The vacuum interrupter is a pair of contacts (primary contacts) enclosed in a vacuum-tight envelope (also known as bottle). The bottle itself is a ceramic material with a metal end plate brazed to each end. The metal plates seal the ends and provide support for the parts inside.

Because the environment inside the interrupter bottle is a vacuum, an arc cannot be easily sustained and is extinguished within the bottle.

One vacuum interrupter is provided for each pole of a circuit breaker.

Eaton uses vacuum interrupter technology for medium voltage vacuum circuit breakers.

Vacuum Interrupter Bottle


10

Trip Unit

The function of a trip unit is to trip (open) the operating mechanism in the event of a prolonged overload or short circuit fault condition, such as:

Thermal OverloadShort Circuit Currents (Magnetic / Short Circuit Currents)Specialty Faults (Ground Fault, Arc Fault)

To accomplish this, an electromechanical or a solid state trip unit is provided.

The differences between these two trip units will be explored after defining the different types of fault conditions.


ThermalOverloadProtection

Magnetic/ShortCircuitProtection

SpecialtyFaultProtection

Usesacircuitbreakertoterminatepowertothe

circuitifanoverload/overcurrent

eventoccurs.

Anelectricalfaultthatiscreatedwhentwo

exposedconductorstouchorwhenaconductors

insulationfails.

Specialtyfaultprotectionis usedinspecific

applicationsbasedoncodesandstandards.ArcFaultCircuit Interrupters

andGroundFaultProtectionaretwoofthemostcommontypes.

Click on each type of fault protection to learn more

Types of Fault Protection





Thermalprotectionisachievedthroughtheuseofabimetalelement

(consistingoftwostripsofmetalbondedtogether)

heatedbytheloadcurrent.

Magneticprotectionisachievedthroughtheuseofanelectromagnetinserieswiththeload

current.




Click on each type of protection to learn more.

Types of Overload Protection Thermal Overload Protection

Thermal trip action is achieved through the use of a bimetal element heated by the load current. A bimetal element consists of two strips of metal bonded together. Each strip has a different thermal rate of heat expansion.

Heat due to excessive current will cause the bimetal to bend or deflect. The metal having the greater rate of expansion will be on the outside (longer boundary) of the bend curve.

To trip the circuit breaker because of a sustained overload, the bimetal must deflect far enough to physically push the trip bar and unlatch the contacts, as pictured.


11








current.





Types of Overload Protection Thermal Overload Protection (continued)

Deflection of the bimetal is predictable as a function of current and time.

This means that a typical 100 ampere circuit breaker might trip in 1800 seconds at 135% of rating (Point A), as shown in the picture.

Consequently, bimetals provide a long time delay on light overloads (Point A), yet have a fast response on heavier overloads (Point B).

Thermal elements are calibrated at the factory and most are not field adjustable. Typically a specific thermal element must be supplied for each current rating.

Time Current Curve









current.





Types of Overload Protection Magnetic / Short Circuit Protection

Magnetic trip action is achieved through the use of an electromagnet in series with the load current.

When a short circuit occurs, the fault current passing through the circuit causes the electromagnet in the circuit breaker to attract the armature, initiating an unlatching action, in turn causing the circuit to open.

The only delaying factor is the time it takes the contacts to physically open and extinguish the arc.









current.





Types of Overload Protection Magnetic / Short Circuit Protection (continued)

That action takes place in less than one cycle (0.016 seconds), and trips the breaker instantaneously. See top picture for a typical magnetic trip curve. The breaker will not trip until the fault current reaches or exceeds Point A.

The magnetic trip element may be fixed or adjustable, depending upon the type of breaker and frame size.

Each adjustable magnetic trip is calibrated at the factory for a specific range and is set on the high side. Knobs located on the front of the trip unit can be adjusted to specific requirements. The knobs have a high, a low, and a series of intermediate setting positions. See bottom picture for a typical set of magnetic trip curves, illustrating how the adjustment knobs move the curve from left to right as the magnetic trip is increased.

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Tim

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12








current.





Types of Overload Protection Specialty Fault Protection

Arcing faults, a common cause of many home electrical fires, can occur when insulation around cords, wires or cables is damaged or deteriorated.

Designed to prevent fires by detecting a non-working (i.e., non-intended/non-useful) electrical arc and disconnecting the power before the arc starts a fire.

The National Electrical Code (NEC) requires the installation of combination-type AFCIs in all 15 and 20 ampere residential circuits with the exception of the laundry room, kitchen, bathrooms, garage and unfinished basement.

Arc Fault Circuit Interrupter Ground Fault Circuit Protection

Designed to protect against electrical shock, in cases where one phase goes to ground.

National Electrical Code (NEC) requires ground fault protection in applications such as:

Residential: Anywhere electricity can come into contact with water, i.e. bathrooms, laundry room, kitchen Industrial: Any assembly where there may be phase to ground loss

Ground fault circuit protection is not available in an electromagnetic trip unit and must be included in a separate device.

Can be included as an option in an electronic trip unit.


Electromechanical (Thermal Magnetic) Trip Units

Electromechanical trip units are commonly used in low voltage circuit breakers.

They utilize bimetals and electromagnets to provide overload and short circuit protection and are commonly referred to as thermal magnetic trip units.

Thermal Magnetic trip units do not include any specialty protection, such as ground fault. If ground fault protection is required, you may need to select an electronic trip unit or include separate ground fault protection within the system.

Fixed Trip Unit

Interchange-able

Trip Unit

Eatons Thermal Magnetic Circuit Breaker offering is as follows:Miniature, Residential, Supplementary Protectors Fixed (can not be replaced) Trip UnitMolded Case Circuit Breakers - Fixed or Interchangeable (replaceable) Trip Unit


Electromechanical (Thermal Magnetic) Trip Units

Thermal magnetic trip units include the features of both the thermal and magnetic protection, as pictured top.

Points A and B on the trip curve, bottom picture, illustrate both the thermal and magnetic action on a typical 100 ampere circuit breaker. A 250% overload would take 60 seconds before the bimetal would deflect far enough to hit the trip bar and open the circuit (Point A).

However, if instead of an overload there was a short circuit that was 4000% (40 times) the circuit breaker rating, the electromagnet in the circuit breaker would attract the armature and trip the circuit breaker in approximately one cycle (0.016 seconds)(Point B).


13

Electronic Trip Units

Electronic trip units offer capabilities such as programming, monitoring, diagnostics, communications, system coordination and testing that are not available on thermal magnetic trip units.

Thus, we are seeing more electronic trip units and electronic protective relays specified over conventional electromechanical and thermal magnetic trip units for circuit breakers.

The result being increased accuracy, repeatability, discrimination, temperature independence and built-in ground fault protection for the electrical system.

Clickforexamplesof

EatonsElectronicTripUnits

Almost all electronic trip units employ microprocessor based technology that provides true RMS current sensing for correlation with thermal capacity of conductors and equipment, as opposed to bimetals that are used in thermal magnetic trip units.



Electronic trip units offer capabilities such as programming, monitoring, diagnostics, communications, system coordination and testing that are not available on thermal magnetic trip units.



Clickforexamplesof




Eatons molded case circuit breakers and low voltage power circuit breakers utilize Electronic Trip Units (ETU).

Molded Case ETULow VoltagePower Breaker ETU

Protective Relays

Clickforexamplesof

EatonsProtectiveRelays

Medium voltage vacuum circuit breakers do not have an integrated trip unit, differentiating them from low voltage circuit breakers.

In this case, the circuit breaker handles the power flow and the overcurrent protection requirements are handled by external protective relays.

Overcurrent, undervoltage, differential, lockout, and timing relays are just a few different types of functions that exist.


14


Electronic trip units offers capabilities such as programming, monitoring, diagnostics, communication, system coordination and testing that are not available on thermal magnetic trip units.



Clickforexamplesof



Eatons medium voltage vacuum circuit breakers utilize external protective relays.

Example of switchgear and medium voltage vacuum circuit breaker


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Now that the five main components of circuit breakers have been defined, we will identify those components on Eaton circuit breakers. Note These are examples and not to scale. Not all circuit breakers are designed the same.

Click each type of circuit breaker for a closer look at its components.

Identifying Components on Circuit Breakers

MiniatureCircuit Breaker

Molded CaseCircuit Breaker

Low VoltagePower

Circuit Breaker

Medium VoltageVacuum

Circuit Breaker


15

Now that the four main components of circuit breakers have been defined, we will identify those components on Eaton circuit breakers. Click each type of circuit breaker for a closer look at its components.

Introduction



Low VoltagePower

Circuit Breaker


Interrupter

Miniature Circuit Breaker

Molded Frame

Operating Mechanism

Contacts

Trip Element

Remember Not all residential and miniature circuit breakers utilize an arc chute.



Introduction



Low VoltagePower

Circuit Breaker


Interrupter

Molded Case Circuit Breaker

Molded Frame

Operating Mechanism

Arc Extinguisher

Contacts

Trip Unit



Introduction



Low VoltagePower

Circuit Breaker


Interrupter

Low Voltage Power Circuit Breaker

FrameNote - Arc

Extinguisher and Contacts are located behind the interface.

Operating Mechanism (Charging Handle)

Trip Unit


16


Introduction



Low VoltagePower

Circuit Breaker


Interrupter

Medium Voltage Vacuum Circuit Breaker

Metal Frame

Vacuum Bottle (includes arc

extinguishing function and contacts)

Operating Mechanism

Remember These circuit breakers utilize external protective relays.


Module Summary

After reviewing the material in this module, you should now understand:

The purpose of circuit protection. The types of circuit protection available in the market. The difference between circuit breakers and fuses. Codes and Standards for circuit breakers. The five main components of circuit breakers. The functionality of the main components.


Assessment

This is the final section of this module. If you have any comments or suggestions about this module please email [email protected]

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Fundamentals of Circuit Protection101 Basics - Assessment

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