Basics of Circuit Breakers in Layperson Terms

December 4th, 2013 No comments

Basics of Circuit Breakers in Layperson Terms

Square D KAB36225 Circuit Breaker

Square D KAB36225 Circuit Breaker

TKMA30600WL General Electric Circuit Breaker

TKMA30600WL General Electric Circuit Breaker

Equipment that needs electricity to operate doesn’t know the difference between normal electrical current and dangerous electrical current. Normal electrical current would be the normal load amperes the equipment needs to run. If there is a problem, the equipment might use too much current, which could result in over heating and even melting of the wires to the equipment. When current moves through wires, it causes the wires to get warm, depending on the size of the wires compared to the amount of current. Too much current and things get very unhappy, melt, and even burn down buildings. So a device called a circuit breaker is placed in the circuit such that the current has to go through the breaker. The breaker is selected by its voltage rating and current rating so that it protects the wires and equipment connected to it. It will “trip open” if the current is too much and lasts too long. In addition, if the electrical wires actually touch each other, a short circuit occurs and a massive amount of current can flow through the wires. An electrical arc can take place, causing an explosion and burning of anything nearby, including people. So the breaker also has a current rating at which it will “trip instantly” if there is a short circuit…an electrical arc. This assumes the breaker is sized and rated properly.

How do they actually work? The most basic breakers have two protective functions. The first is “overload protection.” In this case, especially in older breakers, an element inside is heat sensitive. As the current increases, this element heats up and eventually will cause the breaker to trip open, opening the circuit and stopping the flow of current. This internal “thermal overload” device is sized properly by the manufacturer. The second protective function is “short circuit protection,” also called fault current protection. An internal magnetic pickup device, a coil, operates instantly when there is a sudden very high current above a fixed level. So overload and fault protection is provided by a properly voltage rated, current rated, and install breaker.

Far more complicated breakers are available today, using electronic protective components, with many more protective functions, ratings, installation configurations, and interrupting designs. Using these requires professional help. Here is a list to give you some idea of the complexity. Do not use any of this information to make a decision on breaker selection. A lot of very important information is not included here.

HLA3250 Cutler Hammer Circuit Breaker

HLA3250 Cutler Hammer Circuit Breaker

Examples of Specific Breakers
• Square D – KAB36225 - 225 amp and 600 volt
• GE General Electric - TKMA31200 - 1200 amp and 600 volt
• Westinghouse - HLA3400 - 400 amp and 600 volt
• Cutler Hammer - MA36800 - 800 amp and 600 volt

General Types of breakers

• Molded case breakers rated 120 volts to 600 volts and 15 amps to 2000 amps
• Insulated case breakers rated up to 600 volts and 3000 amps
• Low voltage air breakers rated up to 600 volts and 4000 amps
• Medium voltage air breakers
• Medium voltage vacuum breakers
• Medium voltage and high voltage oil breakers
• Medium voltage and high voltage SF6 breakers

MA36800 Square D Circuit Breaker

MA36800 Square D Circuit Breaker


Basic Protective functions

• Ground fault pickup and delay
• Overload pickup and delay
• Short time pickup and delay
• Instantaneous pickup and trip.
• There are modern breakers that have many times the number of functions shown here.

Buzz Words explained
• Thermo Magnetic – Having overload and short circuit protection
• Current Limiting – Stopping current extremely fast, possibly within 1/240 second (1/4 cycle)
• Arc Chute – Part of a breaker that extinguishes the electrical arc caused when current is interrupted
• Interrupting Rating – The maximum amount of current a device can interrupt without failing

More obscure words
• Roller Smith – Very old, heavy breakers that used a tank filled with oil to interrupt current
• Tri-Pac – A basic older Westinghouse breaker with fuses inside to interrupt very high current

This is basic information about circuit breakers. Is should not be used for decision making.

Surge Suppressor Fires, Circuit Breakers, and Varistor Conduction

May 29th, 2013 2 comments

A customer called MIDWEST because some of their surge suppressor strips had caught fire underneath office workers’ desks.

The surge suppressors had integral circuit breakers in them for over current protection. However, despite the smoke and fire, the internal circuit breakers never tripped. The surge suppressors were still supplying power to the workers’ desktop computers.

Carefully taking apart the surge suppressors, MIDWEST discovered that extensive damage had been done inside the strip. The actual electronic component inside the strips that is meant to mitigate high voltage line spikes is called a metal oxide varistor. Most of these had burned up inside the strips. In addition, the heating caused massive damage to the printed circuit boards. The metal oxide varistors had greatly overheated, and both the varistors and the circuit boards had mostly been baked into carbon. This carbon was not a perfect short circuit, but had sufficient impedance to limit the current flow below the 15 amperes of the circuit breakers. But it had sufficient conductivity to generate large amounts of heat inside the strips.

From this and other evidence, MIDWEST determined the varistors had suffered an overvoltage condition, probably twice or three times the normal line voltage of 120 volts. This caused the varistors to conduct slightly, and dissipate power. It is very roughly estimated that the component dissipated between 5 and 20 times its nominal rated power dissipation of one watt, or 5 to 20 watts.

Experience has shown that power dissipations of less than roughly 5 times rated do not cause catastrophic damage. Above 5 times rated, and components begin to release the “magic smoke” that manufacturers seem to build into electrical components. Dissipations over about 20 times rated tend to cause violent disintegration of the component, accompanied by immediate flames, possible arc flash, and most noticeably, a very loud acoustic signature.

The varistors have an estimated 200 – 300 Volts RMS on them; therefore conduction currents were probably between 10 milliamperes to 100 milliamperes. Obviously, the 15 ampere circuit breakers would not trip from this conduction current. The overvoltage and the heating probably lasted several minutes.

It might seem strange to realize that the varistors never experienced any high voltage spikes, which is their usual reason for being. A sufficiently high voltage spike normally causes the varistors to explode with the sound of a gunshot, and vaporized zinc oxide and copper becomes spalled in the area around the varistor. That is, the internal bulk varistor material and copper electrodes vaporize in an arc flash, and deposit themselves in tiny balls on adjoining surfaces.

But no such spalling or deposited material was discovered upon disassembly of the melted plastic housings. Instead, the 5 to 20 watts dissipated in the 1 watt body of the varistor simply cooked itself, and everything around it into carbon. Then the carbon supported current flow.

In such a situation, surge suppressors have resulted in a number of fires throughout the US.

High Voltage Oil Circuit Breaker – A look inside the tank

January 31st, 2013 No comments

Image of Inside Oil Circuit Breaker Tank

Have you ever wondered what the inside of an old high voltage oil circuit breaker looks like? Maybe you have driven by a utility substation and saw three large round tanks hanging on a frame with high voltage wires coming into tall insulators on the top of each tank. Well, these actually are oil filled circuit breakers. The oil is a good electrical insulator, so it is used to fill the tank and protect all the energized electrical equipment inside the tank. In years past little rectangular tank oil circuit breakers where even used to protect 240 volt circuits. That was 75 years ago. But there are 5000 volt, 15,000, 25,000, 35,000 and 69,000 volt and much higher voltage oil circuit breakers still in service. Some Utilities have high voltage units still operating. In recent decades and years, high voltage oil circuit breakers have been replaced with vacuum circuit breakers and SF6 filled circuit breakers. But here is a picture of the inside of a 35,000 volt oil circuit breaker. Not a lot there, mostly oil, which has been removed in this image. The whole tank is full of oil when the unit is in service. Oil circuit breakers, or OCBs, as they are known in the trade, are just big tanks full of oil with a bit of mechanical equipment inside to interrupt the current during an overload or electrical fault. The oil does deteriorate over the years and it gets dark if the OCB has to frequently interrupt a lot of current. With new oil, you can see right through it, to the bottom of the tank. But, on some old units, the oil can get so dark you can’t see anything in the oil. Part of the maintenance services on OCBs is replacement of the oil when it deteriorates. It all sounds very crude for equipment operating at thousands of volts and hundreds of amps, but OCBs have been used reliably for many decades. General Electric oil circuit breakers or Westinghouse oil circuit breakers, they all work about the same. MIDWEST thought you might like to actually see the inside of a high voltage oil circuit breaker.

Image of Circuit Breaker Main and Arcing Contacts

July 9th, 2012 No comments

 

Circuit Breaker Main and Arcing Contacts with Copper Splatter

Circuit Breaker Main and Arcing Contacts with Copper Splatter

When discussing circuit breakers, we like to have good images to show the difference between the main contacts and the arcing contacts. When a circuit breaker opens, the main contacts should open partially first before the arcing contacts start to open. There should be no arcing damage to the main contacts because the arc interruption takes place between the arcing contacts. This protects the current carrying surfaces of the main contacts so there is minimum contact resistance at the main contacts. Good contact surface means no overheating. For the same reason, when the circuit breaker closes, the arcing contacts close first, suffering any arcing damage. After the arcing contacts are closed, the main contacts close. All this keeps the main contacts in good condition. The arcing contacts are enclosed in something called an arc chute that extends and separates the arc until it is extinguished when the circuit breaker opens. When the arc chutes are contaminated with dirt or high humidity or interrupt very high loads or fault currents, the arc chutes take a beating. Whether you’re talking about Square D circuit breakers, Cutler Hammer circuit breakers, Siemens, Westinghouse or GE General Electric circuit breakers, molded case circuit breakers, power circuit breakers, or medium voltage air circuit breakers, the function of the arc chutes is the same, take a beating to protect the main breakers. The attached image shows the damage to the stationary and movable arcing contacts and to the arc runner that extends into the arc chutes to extend and divide the arc until it is extinguished. The main contacts, the 16 curved segments across the middle of the image, are in good shape. No arcing damage what so ever. This image is from a medium voltage air circuit breaker.

Circuit Breaker – POJ with perfect test results

May 30th, 2012 No comments

Sometimes MIDWEST’s Engineering Technicians in our Switchgear Shop like to do what the Engineers call “Play.”  The technicians call it serious research.  Sometimes their adventures are quite worthwhile, even enlightening.  Recently an Engineering Technician dropped a circuit breaker test form on an Engineer’s desk and said, “Would you take a look at that and tell me if you think it’s okay.” The test results were excellent.  The contact resistance, insulation resistance, over current test results, reset tests, all the test results were excellent.  So why in the world was the Engineering Technician dropping it on the Engineer’s desk when the test results were so good?  The results looked like those for a new circuit breaker.  What they had done was test an old Westinghouse circuit breaker that had been practically crushed.  The case was broken and the arc chutes damaged.  It looked like it had been dropped from 50 feet and hit on one corner.  But, oddly enough, against all reason, it operated mechanically and the test results were all good.  But, of course, it failed the visual inspection.  When the Technician dragged the Engineer to the Switchgear Shop to evaluate the breaker, everyone had a good laugh.  This was good fun and the technical evaluation was unanimous, POJ, Piece of Junk.  One of our favorite highly technical terms.  In this case it was very obvious.  But frequently we find defects in used circuit breakers and in brand new circuit breakers, and other electrical equipment, that would never be revealed by testing alone.  That’s why the experience, training and knowledge of the Technicians and Engineers are extremely important.  There is no perfect test standard for every POJ.

Cutler Hammer Circuit Breaker Trip Indication

April 20th, 2012 1 comment

 

Cutler Hammer LD3450 Molded Case Circuit Breaker with Handle In Trip Position

Cutler Hammer LD3450 Molded Case Circuit Breaker with Handle In Trip Position

MIDWEST gets lots of phone calls from folks desperate for a little technical help. Sometimes they know very little about electrical equipment, circuit breakers for example. These are the most difficult calls because the caller may be putting themselves in harms way and not know it. We could tell them what to do, but unqualified people in the electrical power world need to hear “Hire an electrician, call a qualified person, call an electrical contractor.”  We might tell them to send us a picture of their circuit breaker and we can help them identify it, but get a qualified person to service or replace it. All too frequently the caller wants someone to tell them it is okay to just turn the breaker back on after it has tripped for no known reason. This can be very dangerous and against the code. For example, a maintenance mechanic called about a Cutler Hammer 450 amp molded case circuit breaker. This was a Cutler Hammer Catalog Number LD3450 circuit breaker. The breaker had tripped and one area of lighting in their plant was off.  He was told to “find the problem and turn the breaker back on.” Maintenance mechanics tend to be very resourceful individuals. And that is precisely what makes them dangerous around electrical equipment. They can fix mechanical problems, but most are not qualified around the dangers of electrical problems. In this case he thought the Cutler Hammer breaker was broken because the handle was in the middle and he could not close the breaker. It would have been easy to tell him how to reset the breaker so it would close. He was not overly interested in our requirement to have a qualified person investigate why a 400 amp Cutler Hammer breaker tripped. A lot of power or fault current went somewhere. The recommendation would have been the same for a GE General Electric circuit breaker, or Square D, Siemens, or old Westinghouse circuit breaker.  If the trip handle is in the middle, it tripped for a serious reason.  A qualified person has to investigate why. You can not just throw the power back on. And if you do not know how to reset a Cutler Hammer Series C industrial circuit breaker, you are not qualified.

Seeing Is Not Believing – Barrels of Junk Circuit Breakers

March 12th, 2012 No comments
Barrel of Scrap Circuit Breakers

Barrel of Scrap Circuit Breakers

This is another blog on MIDWEST’s barrels of junk circuit breakers. More specifically it is about the difficulty of not believing something you can’t see. This human factor can frequently be a challenge in our world when a customer has a perfectly good looking circuit breaker and we tell them it is no good and they need a replacement circuit breaker that will cost $3500.00. They understand the words, but their emotional pocket book says “But it looks okay.” Even after being presented with the test results or pictures of the inside of the breaker that reveal the deficiency or damage, they find it hard to believe what their brain is telling them isn’t true, “Because it looks okay.” In our world of reconditioning circuit breakers and remanufacturing circuit breakers, we frequently scrap out equipment that looks in perfectly good condition. Usually the reason for tossing out, say a Square D NA361200circuit breaker, involves deficiencies that can not

Square D NA361200 Circuit Breaker

Square D NA361200 Circuit Breaker

be seen physically, unless you remove the cover or thoroughly test the circuit breaker. Whether a reconditioned GE General Electric, Square D, Cutler Hammer or Siemens circuit breaker, if the inspection or test results say junk, out it goes. And keep in mind, some circuit breakers are not built to be happy if you remove the cover. You need to know what you’re doing. Recently we had an electrical contractor stop to pick up several reconditioned Cutler Hammer circuit breakers. He walked by the barrels labeled “Scrap Breakers” and he looked like he saw a little gold mine. He really didn’t like the idea that all those breakers were actually junk and were being scrapped. The contractor in him told him these breakers were worth a fortune. Even after showing him some of the new looking circuit breakers that had the covers off revealing visible deficiencies, all he could say was a skeptical “Hmmm.”  Even we sometimes grunt a little “Hmmm” when we toss out a $3000.00 piece of junk.