circuit breakers

Circuit Breakers

Electrical Fundamentals

The National Electric Code (NEC) and NEMA(AB) define a circuit breaker as:

“A device designed to open and close a circuit by non-automatic means and to open the circuit automatically on a predetermined overcurrent without damage to itself when properly applied within it’s rating”.

A circuit breaker has two simple components:Contacts that make and break electrical connections.Arc chutes dissipate and extinguish electrical arcs quickly.

A breaker is designed to provide quick isolation of a component from a voltage source.

Quick operation is required to immediately eliminate the arc that is drawn when the breaker contracts separate or just prior to closing.

Circuit Breaker selection process is based upon the use and type of Arc Control desired.

There are two types of control processes associated with a breaker:

Arc Control

Non-Arc Control

Arc Control

Non-Arc Control

• Breakers selection must be capable of showing protection during abnormal conditions, yet allow for the normal operations of its associated components.

Motor Protection Curve

Circuit Breakers-General

Circuit Breakers are selected based on their Ratings.

Voltage

• Proper voltage ensures that the breaker will not exceed it’s nominal duty (damage to components due to heat).

• Proper voltage ensures that the current carry capacity of the breaker is not exceeded.

Voltage

Voltage selection is based upon voltage class.

0 - 600 volts - Low Voltage

601 - 15,000 volts - Medium Voltage

15,001 and greater - High Voltage

Outside of the United States, the voltage class is broken down into:

0 - 1000 volts - Low Voltage

1001 and greater - High Voltage

Even though the voltage classes are different, breaker selection remains the same.


Frequency

• Frequency selection is solely based on the application that the breaker will serve.

• Operating at the improper frequency could change the characteristics of how the breaker would operate. This is primary concern for breakers that rely upon inductive trip mechanisms.

• Breakers are generally designed for 50 and 60 Hz. Other models are available based of specific applications.


Short Circuit Current Capability

• A breaker (and associated switchgear) has to show 150% protection for the worse case asymmetrical fault that could occur possibly occur within a distribution system.


What is an Asymmetrical Fault?

• This type of fault is one that has a sign wave that is unpredictable.

• The breaker has to quickly isolate and cool the subsequent arc.

• What would happen if the arc were left uncontrolled:


If a 13.8 kv distribution system experiences the worst case fault, how much power could be release instantaneously?

• A Worst Case Fault is a direct short to ground with a resistance of .01 .

• 13.8 kv is an RMS value and has to be converted to a Peak Value: Peak Volts

13.8 kv / .707 = 19,519 volts x 150%

29,278.5 volts

Ohm’s Law

Current = Voltage / Resistance

Current = 29,278.5 volts / .01

Instantaneous Current = 2.93 x 10 6 amps

Power

Power = (3) x Voltage x Current x pf

(assume that system pf is .85)

Power = (3) x (29,278.5 volts) x (2.93 x 10 6 amps) x .85

Power = 218.7 x 10 6 KW !

This number is purely theoretical but illustrates how much power a fault of this magnitude has and why a structurally

sound breaker is required.

Closing or Latching Current


• Otherwise known as “control current or control power”.

• Must be rated high enough to provide sufficient strength to overcome the mechanical forces associated with breaker but low enough to prevent damage to components due to excessive heat.


Arc Extinction

• Breakers are rated on how well and by what method an arc is extinguished.

• An arc is formed when the contacts of a breaker separate due to voltage across the contacts and current supplied to a load.

ARC Characteristics

• An arc is ionized air across a potential source.

• Arc temperatures approach 35,000 oF or more.

• No arc when breakers contacts are shut.

• Uncontrolled arcs will damage equipment and are a personnel hazard.


Arc Extinction Process

• The arc is first elongated .

• An elongated arc is cooled by air, oil, vacuum, and SF6

• Arc elongation occurs Thermally (convection) and Magnetically.

• Arcs lose energy as it is broken up and moves further from the source.



Arc Elongation Process

• Arcs are elongated through the following processes:

Thermally (through convection)

Magnetically (arc is pulled into arc chutes)


Arc Elongation Process


Types of Arc Extinction Methods

• Air

• Magnetic

• Oil

• Air-Blast

• Vacuum

• SF6

• Hybrid (combination of the above)


There are several types of circuit breakers used in the power industry:

1. Molded Case (LV)

2. Air Breakers (LV and MV)

3. Magnetic (MV)

4. Vacuum (MV)

5. Air-Blast (MV and HV)

6. SF6 (HV)

7. Oil (HV) - not used anymore

But...

Breaker Components

All breakers contain the same basic components:

• Stationary Main Line Contacts

• Moveable Mainline Contacts

• Arcing Contacts

• Auxiliary Contacts

• Arc Interrupting Device

• Closing Mechanism

• Opening Mechanism

• Control Mechanism

• Interlocks

• Frame Assembly

Breaker Components

Contacts• Contacts are used to make and break electrical connections from Line to Load.

• Contacts are designed to have the absolute lowest electrical resistance.

• There are four common types of contacts found inside a circuit breaker. Each contact has a specific function.

Breaker Components

Mainline and Arcing Contacts

• Stationary Mainline Contacts: Connected to frame assembly and does not move. Referred to as the Load.

• Moveable Mainline Contacts: Connected to a moveable armature. Referred to as the Line.

Mainline Contacts are used to transfer power from Line to Load. They are normally the largest and most expensive of all of the contacts. There is one set of contacts per phase. There are two types of Mainline Contacts:

Breaker Components

Mainline and Arcing Contacts• Mainline contacts require immense force (up to several thousand pounds) for proper contact.

• Proper contact ensures that there will no high resistance connections across the contact face.

• However, in vacuum breakers (shown), the contacts are held shut by as little at 12 psi.

Breaker Components


Arcing Contacts are cheaper and easier to replace than Mainline Contacts.

Arcing Contacts are designed to protect the Mainline Contacts from damage due to excessive arc.

Arcing Contacts close first and open last. This ensures that the arc will be drawn across the arcing contacts vice the Mainline contacts.

Breaker Components


Breaker Components

Auxiliary Contacts

• Auxiliary Contacts are smaller contacts found internal or external to a breaker.

• Used to provide 120 volts or less for control functions, interlocks, and indication.

• Normally mounted to the frame or “cradle “ along the back side of the breaker

Breaker Components

Disconnects

• The disconnect are the devices that physically engage into the switchboard.

• The disconnects are broken into two types: Primary and Secondary.

Breaker Components

Disconnects• Primary Disconnects are located on the back of the breaker cradle.

• They function to positively engage the breaker into the switchboard.

• The Load and Line sides of the circuit are connect through the disconnects.

• There are two basic types of Primary Disconnects: Finger Type and Tulip Clip.

Disconnects

Breaker Components

• Finger Type disconnects can be located on all styles of breakers.

• Spring Loaded Fingers engage metal tabs on the switchboard for positive connection.

• Made from Stainless Steel, Bronze, Plated Aluminum, and Silver

• Easier maintenance than the Tulip Clip disconnects.

Breaker Components

Disconnects

• Tulip Clip disconnects are common on all styles of breakers.

• Use Spring Loaded Wafers that form a circle. This circle is can be located on the switchboard or the breaker.

• Each phase has an associated post that will engage the wafer to complete the circuit.

Breaker Components

Disconnects

• Tulip Clips are primarily used in High Current applications over the Finger Type because of an increase in surface area and higher current densities.

CT Breaker

Breaker Components

Disconnects

• Secondary Disconnects are similar to Secondary Contacts in that they are used for control features, interlocks, and indication.

Breaker Components

Arc Interrupting Devices

• Arc Chutes are normally found on all Low Voltage air cooled breakers.

• Arc Chutes function to rapidly extinguish an arc that has been caused by separated contacts.

• Arc Chutes are located around each set of Mainline Contacts (1 per phase).


Breaker Components

• Arc Chutes are normally made of a non-conducing insulator called Melamine with a ceramic liner.

• Arc Chutes are designed for ease of removal for inspection.

• Arc Chutes normally have an additional plate that located to each side that will insulate each phase from ground.


Breaker Components

• Vacuum Interrupters found on the GE PowerVac Breakers serve the same function as Arc Chutes.

• The Arc is extinguished in a vacuum sealed container vice air.

• This type of arc interruption is found in Medium Voltage Systems

Breaker Components


• In the Magnetic System, the arc is drawn away from the contact faces my magnetic attraction.

• The arc is drawn into the arc interrupter where is it subsequently cut into smaller arcs.

• As the arc travels outward, its path is increased, thereby losing energy.

• Primarily used in Medium Voltage systems and is found in the Magna-Blast breaker design.

Breaker Components


• SF6 breakers use Sulfur-Hexaflouride gas to extinguish the arc at pressures from 70 -90 psig.

• These breakers are used in High Voltage applications.


Breaker Components

SF6 Arc Extinction


Breaker Components

• Oil Filled breakers are found on older High Voltage distribution systems.

• Oil is used instead of air or gas to extinguish an arc.

Breaker Components

Closing Devices Devices

• Closing Devices can be mechanical, electrical, or hydraulic (air or oil).

• The type of closing power depends upon breaker size, location, and use.

• Closing action can be done locally or remotely.

• Closing action may require that interlocks be met.

• Closing power (normally 450 volts or less) maybe required in some applications

Breaker Components


• Manually operated breakers are found on most lighting systems, smaller auxiliary loads, and some 480 vac distribution applications.

• These types of breakers are generally used in “on-off” applications and have very little if any automatic functions.

Breaker Components


• Electrically operated breakers are found on larger distribution systems and loads.

• These breakers are desirable for remote or automatic functions.

• May use a motor or other device.

• These types of breakers will normally have interlocked inputs.

Breaker Components


For most electrically operated breakers, interlocks and permissives must be met before the closing coil will be energized.

The Closing Coil (CC) is generally a small relay that is powered from a Control Power Source (normally 120 volts)

Breaker Components


Once the Closing Coil has energized, the Charging Motor energizes. The Charging Motor physically moves the linkages to close the breaker.

Breaker Components


• Hydraulic Systems such as air or oil are used for very large breakers.

• Oil is not used as much as air due to the potential for contact contamination from oil leaks.

• High pressure air is preferred but has limited cycling capabilities because of the need to recharge the source.

• Air-Blast breakers are used for some generator breaker applications.

Breaker Components

Interlocks Devices

• Interlocks are designed to prevent a breaker from operating during unsafe conditions.

• Interlocks maybe mechanical, electrical or a combination of both.

• Interlocks should never be overridden.

• Interlocks can be easily damage rendering them inoperative.

Breaker Components

Interlocks Devices

Mechanical Interlocks

• Positive Interlock: Mechanically couples the breaker such that the racking mechanism can only be engaged if the breaker is in the OPEN position. This interlock prevents inserting or removing a CLOSED BREAKER.

• Negative Interlock: Mechanically places the breakers trip shaft in the “tripped “ position. Prevents closing a breaker in any position other than the TEST or CONNECTED positions after the racking mechanisms have been disengaged.

Breaker Components

Interlocks Devices


• Spring Discharge Interlock: This interlock will discharge the closing springs to provide a mechanical saftey feature such that the breaker is discharged as well as open when it is removed from the equipment.

• Padlocks: Provisions can be provided to enable the breaker to be locked out during certain operations or maintenance. Padlocks can either prevent closing the breaker and/or preventing engaging the racking mechanism.

Breaker Components

Interlock Devices


• Key Interlocks: Allows the coordination between two or more deices such that certain operations must be performed in sequence on one device before proceeding to operate the next device.

The above coordination is accomplished by special locks that hold the key captive until the proper conditions are met. This allows the key to be removed and inserted into another special lock on another device in order to properly operate it.

Breaker Components

Interlock Devices


• Safety Roll-In Stop: Regardless of the position of the racking mechanism, it is impossible to manually insert the breaker into the rails beyond the Disconnect/Test position.

• Safety Roll-Out Stop: This interlock prevents the breaker from being rolled out of the equipment accidentally. This stop has to be manually released prior to breaker removal onto the transfer truck.

• Gag Spring Interlock: This breaker ensures that only breakers with freely operating closing springs can be inserted into the equipment. If the closing springs have been gagged for breaker adjustments, it would be possible to place the breaker in an operational status.

Breaker Components

Interlock Devices


• Rating Interference Interlock: This is a mechanical interlock that is coded such that the only properly rated breaker can be inserted into its designated location.

Breaker Components

Interlock Devices

Electrical Interlocks

• Interlock Switches: “Interlock Switch” is a General Term.

The basic function of these switches is to block electrical closing signals and to open the closing mechanisms charging circuit whenever a breaker is being inserted or removed. To determine which switch provide what features, electrical schematics should be referenced.

Breaker Components

Frame Assembly or “Cradle”

• The Frame Assembly or “Cradle” provides structural support for the breaker components.

• It is bolted in some fashion to the switchboard.

• May have provisions for wheels or lift truck attachments for ease of removal during maintenance or inspection.

• The Frame size will be expressed in “amps”.

• The continuous current rating of the breaker will never exceed the breaker frame size.

Breaker Applications

• Molded Case Breakers are used in systems of up to 600 volts.

• A “Molded Case Breaker” is one that is assembled as an integral unit in a supportive and enclosed housing of insulated material (NEC and NEMA defined).

Low Voltage - Molded Case Breakers


• Molded Case breakers have factory calibrated and sealed elements.

• Unauthorized modifications may render this breaker incapable of performing its intended functions and may jeopardize the manufactures warranty.


• Molded Case Breakers are extremely reliable and require very little if any maintenance.

• They are designed to be “turned on” and for the operator to be able to walk away.



• Traditional LV breakers have limited trip functions.

• Limited to Thermal and Magnetic automatic trips.

• Not used as much for power distribution because of limited protective trips and slower response times.


Spectra Series

and

Low Voltage Breakers


• WavePro and Spectra Series is GE's New Line of Low Voltage Power Circuit Breakers.

• It Builds on the Experience of the AKR Line, with Improved ReliabilityAnd Functionality

• Designed for quicker response times.

• Implements micro-processor based technology.

• Used for on all major LV distribution centers as well as some limited MV applications.

• More automatic protective trips than traditional, older molded case breakers which make them better for distribution purposes.

• System Integration of Engine Generator, UPS & Distribution Switchgear

• New Solid State Products• Power Management • System Reliability is Directly

Tied to User’s Uptime


15 Digit Catalog Number, 15 Digit Catalog Number, Ordered Via OSB GE-1-STOPOrdered Via OSB GE-1-STOP

New Robust Design, No Side New Robust Design, No Side Support RequiredSupport Required

Fully Assembled, Rigid, Fully Assembled, Rigid, Aligned Substructure (No Aligned Substructure (No Adjustments)Adjustments)

Improved Reliability & Improved Reliability & Uptime, Breaker Uptime, Breaker Maintenance VideoMaintenance Video


True Closed Door Drawout Design

Robust Metal Frame Construction

Up to 72 Secondary Disconnects

Interchangeable Escutcheon Mounted Trip Units

Integral Charging Handle on MO & EO Breakers

Breaker Position Indicator Flag

Bell Alarm w/wo Lockout (target std)

Charge After Close Mechanism

“Hidden On” Button


Engraved Metal Nameplate with 15 Digit Catalog Number.

Designed & Tested to ANSI Standards

Six Breaker Frame Sizes: 800, 1600, 2000, 3200, 4000, 5000 Amp

200,000 AIC Short Circuit Rating

Improved Packaging

Optional “Power Management Ready”

Padlock Provisions for Both Breaker & Substructure


Long Time & Inst. Protection (standard)Long Time & Inst. Protection (standard) Interchangeable Rating Plug (standard)Interchangeable Rating Plug (standard) Settings via Rotary SwitchesSettings via Rotary Switches Short Time & GF Protection (optional)Short Time & GF Protection (optional) Ground Fault Integrated into Rating PlugGround Fault Integrated into Rating Plug Switchable Ground Fault (Not UL)Switchable Ground Fault (Not UL) Optional Target Module Provides Status LED’s Optional Target Module Provides Status LED’s

for Battery Check, Trip Unit Health Monitor, for Battery Check, Trip Unit Health Monitor, Longtime Pickup, and Trip Targets (LED’s) for Longtime Pickup, and Trip Targets (LED’s) for Overload, Short Circuit, and Ground FaultOverload, Short Circuit, and Ground Fault

Interchangeable with MicroVersaTrip Plus and Interchangeable with MicroVersaTrip Plus and PM Trip UnitsPM Trip Units


9-Function Solid State Trip Unit 9-Function Solid State Trip Unit Liquid Crystal Display, 5-Button Liquid Crystal Display, 5-Button

Keypad & Non-Volatile MemoryKeypad & Non-Volatile Memory Standard Phase-Selectable Ammeter, Standard Phase-Selectable Ammeter,

+/-2% Accuracy+/-2% Accuracy Interchangeable Rating PlugsInterchangeable Rating Plugs Built-In, Long-Life Lithium Battery Built-In, Long-Life Lithium Battery

for Cold Setupfor Cold Setup Easy Upgrade to Power ManagementEasy Upgrade to Power Management Trip Targets, Trip Information, and Trip Targets, Trip Information, and

Trip Operations CountersTrip Operations Counters Optional Zone Selective InterlockingOptional Zone Selective Interlocking


All the Features of MVT Plus™ and...All the Features of MVT Plus™ and... Power Leader™ CommunicationsPower Leader™ Communications Full Function MeteringFull Function Metering

CurrentCurrent Total PowerTotal Power

VoltageVoltage FrequencyFrequency

EnergyEnergy DemandDemand

Real PowerReal Power Peak DemandPeak Demand Optional Protective RelayingOptional Protective Relaying

Under voltageUnder voltage Current Unbalance Current Unbalance

Over voltage Over voltage Power Reversal Power Reversal

Voltage UnbalanceVoltage Unbalance Power Direction Power Direction SetupSetup


Metering & Relaying CT’s Mount Metering & Relaying CT’s Mount Directly to Base. Directly to Base.

Relaying CT’s Fit in Shallow Relaying CT’s Fit in Shallow SubstructuresSubstructures

Shallow Substructure for 3200 & Shallow Substructure for 3200 & 4000A Frames 4000A Frames

Neutral & Trip Unit Disconnect Neutral & Trip Unit Disconnect Moved to Secondary Disconnect Moved to Secondary Disconnect BlockBlock

New Design Does Not Require Side New Design Does Not Require Side SupportsSupports

Padlocking Provisions Standard on All Padlocking Provisions Standard on All Sizes, Preventing Breaker InsertionSizes, Preventing Breaker Insertion

New Rail/Wheel Guidance System, New Rail/Wheel Guidance System, Improved rating rejection systemImproved rating rejection system

More Options With Shutters & More Options With Shutters & Position SwitchesPosition Switches



Medium Voltage Breakers

• Medium Voltage breakers range from 601- 15,000 volts.

• A variety of breakers can be found in the category including:

Spectra Series

WavePro Series

PowerVac Vacuum Breakers

Magna-Blast

Air-Blast



CT Breaker and 8000 Series Controller

• Magna-Blast breakers are generally used for gas and steam turbine generator breakers.

• The breakers are large and require a special housing and associated motor controller.

• Breakers must have a sound maintenance program due to the size of the breaker and mechanical stresses placed upon them during operation.



• Vacuum Breakers can be used for generator output but normally are not.

• Primarily used for medium voltage distribution centers of 13.8 kV and below.

• Experience less wear and tear because of component size.

• Normally used in indoor applications.



• PowerVac breakers located in either the top or bottom (or both) control cubicles of the GE PowerVac switchgear.



• Access to the breaker is accomplished by opening the outer cover door of the cubicle.

• The lower cubicle stores protective relays, current, and potential transformers.



• The breaker is designed with a racking bolt that will remove the breaker from the switchgear.

• Breaker can be removed completely if the provided lift truck is used.


High Voltage Breakers

• SF6 Breakers are used in applications of 15,000 volts or higher.

• They have replaced Oil breakers as industry standard.

• Normally connected directly to an isolated phase bus.

• Simple designs and construction.

• Relatively small space required for placement.



• The interrupters are mounted in a grounded tank with each phase separated.

• The interrupters are operated by a hydraulic operating mechanism

• The main contacts are connected directly to the isolated phase bus.

• SF6 gas (an insulator) is used to rapidly extinguish the arc.

• Preferred over Oil Filled Breakers



SF6 Arc Extinction



• Oil Filled Breakers were used as the earliest of the High Voltage Breakers.

• Increased Maintenance requirements makes them undesirable

• Large Contact surfaces and no arcing contacts caused excessive pitting at the contact faces.

• Still maybe found in older distribution systems.



• Mainline contacts were submerged in a oil bath.

• The oil was susceptible to moisture contamination which lowered its dielectric strength leading to flash over.



• The breakers became out dated with the advent of microprocessor technology.

• Response times where generally slow and the breaker generally had limited protective features.

Disconnect Switches


• Disconnect Switches are used for a variety of applications.

• They can be found in in all voltage classes.

• They can be manually or motor operated.

•Are used to isolate a portion of a distribution system, typically during maintenance.

Disconnect Switches


• Disconnect switches are not breakers and should never be used as one.

• In some cases they can be inserted into a breaker cubical.

• Some switches are grounded to ensure that equipment (generator stators) are safe prior to maintenance.

• Grounded disconnect switches are normally interlocked with a supply breaker to ensure that both are not shut at the same time.

Breaker Precautions

Precautions with Breakers

• Always treat a breaker as if it is SHUT and Energized.

• Only QUALIFIED personnel should ever attempt to service any type of breaker. OSHA article 1910.331 defines what a Qualified person is.

• Always completely de-energize any breaker before servicing it. Always check voltages between phases and between each phase and ground.

• Always ensure that the Control Power source has been removed prior to Racking In or Out any breaker.

• Always use a procedure when performing any type of inspection on a breaker.

Breaker Precautions


• All breakers should be kept clean of water, dirt, and metal.

• Avoid touching contact surfaces with bare hands. Oil from your finger tips will damage the contact face.

• Avoid setting a breaker on its side or back. This could damage the Secondary Disconnects, Auxiliary Contacts, or any of the control modules. Some breakers are equipped with oil filled over current devices. This oil may leak out and damage the breaker.


Breaker Precautions

• Arc Chutes should be kept clean and generally free of defects.

• Ensure that the breaker charging mechanisms is completely discharged prior to breaker disassembly.


Breaker Precautions

Breaker Precautions


• Never override an interlock.

• A breaker in the TEST position is still as dangerous as a breaker that is racked in.

• Ensure the proper lubricant is used for the right breaker. There is a difference!

• For SF6 Breakers, ensure that O2 concentrations are kept less than 18%. This will ensure that there is not a sustained arc.


Breaker Precautions


Breaker Precautions

• For Vacuum Breakers, ensure that each interrupter has the proper vacuum IAW its associated tech manual.

circuit breakers

Education