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Posts Tagged ‘arc chutes’

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.

Arc Blast Damaged Westinghouse PC32000 Molded Case Circuit Breaker

December 29th, 2011 9 comments
Arc Damaged Westinghouse PC32000 Circuit Breaker

Arc Damaged Westinghouse PC32000 Circuit Breaker

If you want to see a good picture of a large circuit breaker that has been damaged by an arc blast, look at the pictures with this blog. The breaker was a Westinghouse PC32000 molded case circuit breaker. It was a 2000 amp circuit breaker that failed to interrupt a fault and blasted the inside of the breaker until it actually blew a hole through the side of the circuit breaker frame. If you look closely, you will see where a MIDWESTswitchgear service technician actually stuck a screwdriver through the hole. The close up picture shows the hole and shows the extensive arcing damage to the moveable arcing and main contacts. The phase barriers, arc chutes, pretty much the whole Westinghouse PC32000 circuit breaker, was arc blasted beyond repair. One picture shows the destroyed circuit breaker next to a MIDWEST inventory stock PC32000 circuit breaker. This is a tough Westinghouse molded case circuit breaker. It wouldn’t make any difference whether the breaker was Square D or GE General Electric. If the breaker contacts begin to open, but fail to interrupt the current, arc damage will quickly occur. If the breaker is trying to interrupt fault current, extensive arc damage occurs very fast and will quickly expand into a phase to phase fault with catastrophic destruction. The arcing fault may explode outside the case of the circuit breaker.  This is one of the reasons for wearing protective clothing and following safe work practices when operation circuit breakers. Bad things can happen very fast. Too fast for you to get out of the way.  We suggest being paranoid about safety when working around electrical power equipment.

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

Another View of a Arc Damanged Westinghouse PC32000 Circuit Breaker

15 Kv Power Circuit Breaker, Perfect Scrap

September 16th, 2011 No comments

15 KV Vacuum Circuit Breaker

For an Electrical Power Engineer, it may seem strange to see someone tearing apart a 15 Kv GE magna blast circuit breaker for scrap. They are one of many work horse high voltage air circuit breakers used successfully for decades in manufacturing plants across the Country. But they have been replaced with 15 kv vacuum circuit breakers. Vacuum breakers are reliable, fast acting, low maintenance devices. Many air circuit breakers have been retrofitted with vacuum circuit breakers. The old air circuit breakers are being scrapped because there are just so many on the secondary market and many are not in good condition. They might look great, be in good mechanical condition, but the arc chutes may have serious damage or dielectric deterioration. These things are not noticeable to most people, but MIDWEST tests high voltage circuit breakers and looks can be extremely deceiving. In addition, the cost to recondition an air circuit breaker is very high. It’s not just the mechanics of the circuit breaker, but the dielectrics can be far more costly. The old GE General Electric and Westinghouse high voltage air circuit breakers are everywhere in the secondary market and they sit for years on the storage shelves. If we have 40 GE General Electric 1200 amp magna blast circuit breakers and we sell 5 a year and we can buy as many more as we need, at little cost, then their value today may be greatest as scrap.  This is especially true with the value of scrap metal, like copper, being so high. It’s not 1970 any more.  

Noisy Circuit Breaker is a Warning

August 12th, 2011 1 comment
HKD3400F Westinghouse 400 Amp Circuit Breakers For Sale at www.swgr.com

HKD3400F Westinghouse 400 Amp Circuit Breakers For Sale at www.swgr.com

A contractor called MIDWEST for a little free advice. His customer had a 400 amp molded case circuit breaker. This happened to be a 400 amp Westinghouse circuit breaker, but it could just as well have been Square D or General Electric. He was very worried because his customer’s 400 amp circuit breaker was rattling, making a terrible humming and rattling noise. He had never heard this before and didn’t know if the circuit breaker was going to blow up, fall apart or what. He said this was a very old breaker, 1960s. We recommended he measure the load on the feeder cables from the breaker, but to do this very safely. Measure the current at the load end of the feeder, if possible, not at the circuit breaker. It is not totally unusual for an old circuit breaker to rattle and hum away when the load is near or over the rating of the over current device. When the breaker’s internal over current device is picking up because of the load. It depends on the breaker. The noise might be an indication the over current device is picking up and may trip the circuit breaker if the load doesn’t drop down below pickup soon enough. Either way, it may be a good idea to replace the circuit breaker. Sometimes these breakers will nuisance trip at less than the pickup current level. If possible retrofit the old circuit breaker with a newer replacement model. Sometimes the rattling is from the metal arc dividers in the circuit breaker arc chutes. Either way, it is not a noise you want to hear. Check the load. If that is not the problem, change the circuit breaker. Safely.

Removing Cover from an Energized Breaker

November 19th, 2010 No comments

 

MIDWEST had a customer call and ask if it was okay to remove the cover from an old 400 amp circuit breaker, live. Our Infrared Scan indicated the load side connection was overheating. They wanted to repair it, but didn’t want to turn the power off to the whole panel board. They needed to remove the cover of the circuit breaker to make the repair and thought they could just remove the four screws holding the cover on and carefully remove the cover. We explained politely that they were crazy to try such a thing. This was an old molded case circuit breaker and the arc chutes for this breaker were not fastened in place as they are in some breakers. In addition, the arc dividers were metal and they were held together with an insulated band. On some of these breakers we have to tape the band to hold the arc dividers together or they just fall apart. So the danger would be that you remove the cover with the line side still hot and one of the arc chutes falls out and the metal arc dividers fall apart. It would be almost certain that one of the metal arc dividers would short a stationary contact to a moveable contact and cause a horrific arcing blast, arcing fault.  Depending on the instantaneous, ie fault, setting of the main breaker, the fault might last for seconds and result in tremendous damage to the equipment and expose anyone nearby to serious injury or death from an arc blast. Because the fault is on the line side of the breaker, it wouldn’t take much to create a panel board bus fault. This is a good way to get someone seriously injured or killed and a good way to destroy a whole panel board. To remove the cover off any circuit breaker with the line side hot is a very bad idea. But to remove the cover of some of the older circuit breakers, with the line side hot, is just crazy because of the construction of the breaker. Inside molded case circuit breakers there are other devices that may fall out when you remove the cover. Besides all this, there may be something defective inside the breaker, just waiting there, for the first unfortunate person to take the cover off, and then it falls apart or breaks completely. You could get very unlucky. We call these things incipient failures and they can be some of the most nasty and dangerous defects in electrical equipment, because you are not expecting them. This is true whether it’s a Square D, Cutler Hammer, Westinghouse, GE General Electric, or Siemens circuit breaker or any other breaker manufacturer. Turn the main power off!

How Circuit Breaker Arc Chutes Work

June 16th, 2010 1 comment

Buy EHD3070 Westinghouse Molded Case Circuit Breaker

Buy EHD3070 Westinghouse Molded Case Circuit Breaker

The arc chutes for molded case circuit breakers and old power breakers look simple enough, but they actually are a complex design and perform extremely important functions.  For excitement, read the patent application for an old circuit breaker arc chute, if you can stay awake.  MIDWEST sometimes is asked to explain what an arc chute does. We always go for the short version.  Basically an old or new circuit breaker arc chute stretches the arcing that takes place when a circuit breaker opens, such that the arc is too long for the voltage to keep it going.  Arc chutes have arc dividers in the form of flat segments stacked one above the other, with an air gap between them.  When the arc occurs, it is expelled into the arc chute and into the arc dividers, such that it wraps back and further between the arc dividers. The wrapping back and forth around the arc dividers effectively stretches the length of the arc until it is just too long for the voltage to keep it going.  When this happens, the arcing stops.  The arc has been extinguished.  When the circuit breaker opens, the main current carrying contacts open first and a different set of contacts, the arcing contacts, open second, such that the arcing contacts endure limited damage from the arcing, until the arc chutes interrupt the arc. So the combination of the arc chutes and the arcing contacts protect the main contacts from arcing damage when the circuit breaker opens and when it closes.  When a circuit breaker is closed, the arcing contacts close first, again taking on the arc such that the main contacts are protected from arcing damage when closed.  This is especially important when the circuit breaker interrupts a high current fault and there is a real blast in the arc chutes.  Each phase, ie pole, of a circuit breaker has a separate arc chute. This is pretty much how the arc chutes of obsolete, old, and new replacement circuit breakers operate.  So the arc chutes perform an extremely important function.