Types of "Fuses"

Hi everybody,

Can somebody shed some light in this subject.

Today I came across a semiconductor fuse used inside an inverter. How does this behave, compared to normal fuse.

Thank You

is this what you're talking about?

this might be a wild goose chase but here's something interesting:

PTC Brochure

PTCs are components that utilize a unique polymer-based positive temperature coefficient material that protects electrical equipment from over-current conditions. Numerous carbon paths within the polymer allow the device to conduct electricity. As current through the device reaches its rated threshold, the polymer material begins to heat causing the polymer to expand. The resulting expansion breaks the carbon chains to reduce the current through the circuit to a small leakage current. When the fault is removed from the circuit, the device will reset itself thereby allowing current to flow through the circuit again.

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if this isn't exactly what you're talking about, try starting at the homepage of the Littelfuse (note: not Littlefuse) website ... lots of material about fuses there ...

Littelfuse homepage

I can tell you that they behave violently when they blow, at least in some cases!

I was next to a 400 hp VFD a few years ago when a bank of those solid state fuses let loose. Fortunately there was a scatter shield in place, or the ceramic fragments would have taken the poor service man's head off - literally. As it was, the flash and subsequent total blackout made me think I was either blind or dead!

Needless to say, it was time for K-Mart and a new set of Hanes.

(And this, boys and girls, is why you NEVER stand in front of ANY control system when the breaker is thrown closed for the first time!)

Tom

And this... is why you NEVER stand in front of ANY control system when the breaker is thrown closed for the first time!

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Even though this topic is a liitle off base for this forum I'm glad you made the statement above. Any time I am training someone I always teach them to stand to the side of any breaker ANY time they throw it on or off. I also show them how to get off the breaker when they throw so their hands don't remain directly in front of the panel. It only takes one bad breaker to make a believer out of you.

Tom-
Are you referring to 'semiconductor fuses' or 'solid state fuses' in that drive application? I didn't know anyone used solid state fusing in that power class.

To tell the truth I'm not sure. By the time I saw them they were mostly little white and black (charred) bits of ceramic embedded in the aluminum scatter shield. The drives were not in my scope of supply, so I made it a point to not be around during the repair and testing process.

Semi-conductor fuses are designed to protect SCR's and power diodes from heavy short circuit currents and the like.

The fast action of "current limiting" semiconductor fuses comes from a silver link with a small link section joining a substantial size sheet of silver. Silver provides a maximum of thermal conductivity, and short-circuit protection is provided when the rate of rise of heat in the small link exceeds the rate of thermal conduction away from the link. As the link melts, the voltage across it rises and arcing begins. Arc quenching is aided by silica sand crystals which effectively lengthen the arc path.

Normal fuse have a metal alloy link, thus they act slower than the semi-conductor type.

One thing to take note of:- THESE FUSES CONTAIN SILVER and good quality silver at that! Don't just throw the fuse away, break it open and recover the silver, store it in a nice liitle self sealing bag until you have enough to sell it on!! A perk of the job you might say.

Paul

Thank you PLucas, Ron and the rest for the info.

Now I understand why it cost us about US$35 for a 50A semiconductor fuse from Bussman over here. It was mounted inside a 7.5KW Yaskawa inverter.

ceramic fuses

hello plcs users,
i 'm the new kid on the bloc, i'm not an expert but i like getting into things and the latest thing is a computer(s) , simple problem the fuse in the power supply is blown due to an" overvoltage supply from a generator" the fuse is labeled as 6.3 A (H)250V IT'S ALSO CERAMIC, what is the "H" referring to, and also what is the difference in ceramic and glass fuses from a protection point, in living in haiti and i have managed to get 7A 250V glass fuses is it safe to use these, there are 12 computers with this problem and there is a possibility that this could happen again, i'm working as a volunteer mainteance person with an NGO NON PROFIT ORG in haiti, its a computer class in our school that this happened to , so i am anxious to get them working asap, looking forward to hearing from the experts,
regards pat.

I have seen the SCR power bridge blocks blow in order to save the high-dollar semi-conductor fuses. I used to work in a drive repair shop - fun to watch a 50HP motor run away.

YES!!! on standing aside upon first power-up! I never stand in front of live plasma-artillery. I do leave the door open just 'cause I might see where the blast orginated from (like the scorching wont show where)

ALWAYS have a safety man on the breaker at power-up - and bring the machine up in stages if possible - DUH!

There! I got 'block' in the post so it's legal.


Rod(The CNC dude)

Re: ceramic fuses

pat mollaghan said:

what is the "H" referring to, and also what is the difference in ceramic and glass fuses from a protection point,

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Hi Pat,

Rather than claim to be an expert on fuses, which I am not.

click here for a description of the various fuse classes that are available.

pat mollaghan said:

what is the difference in ceramic and glass fuses from a protection point

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I believe that this is do do with their interrupt capacity, a ceramic fuse has a higher rating than it's glass equivalent.

If I am wrong on this I am sure someone will put me right.

Paul

A HRC (high rupturing capacity fuse) works on the basis of limiting the I squared T value (current versus time). Thus with a standard BS88 type fuse the I squared T (how do I put in a squared sign?) is far less than a circuit breaker for example.

With a semiconductor fuse, the I squared T value is far less. With an IEC fuse is is slifghtly greater. Thge value of I squared T is usually shown on a bar graph. The bar graph shows the extremeties of the value for each fuse. This makes it very easy to plan discrimination in your plant.

Circuit breakers are harder. BS88 fuses typically blow in the first quarter of the cycle. Semiconductor in the first eighth or less. Circuit breakers are often 1 1/2 cycles or more and are no where near as good for short circuit protection. Circuit breakers are generally better for overload due to the thermal part of the circuit.

Here is a link to a page at Alstom that has lots of good information about various types of HRC fuese sold by that company. This is the product line from the old GEC and English Electric companies. Download and learn heaps about fuses. Fuse Data

By the way, I sold fusegear for 15 years.

By the way Paul, you are correct about glass fuses. They are, basically, very dangerous. I WILL NOT USE THEM FOR ANYTHING given a choice. Ceramics disintegrate as well but are far more resillient.

BobB said:

how do I put in a squared sign?

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Use the [sup] and [/sup] tags for superscript.

I[sup]2[/sup]T produces I²T.

Probably easier to just type 'squared'...

By the way, great info about fuses, Bob...

beerchug

-Eric

Spent a few years with them Eric. Got to love them but found the greatest problem I had selling them was nobody bothered with the I<sup>2T curves and blew the fuse up the line. Discrimination is invariably ignored by electricians and quite often by board builders.

banghead mddr

It was always a faulty fuse of course!</sup>