A fuse used has a story to tell. Find the breaker open, with no signs of trouble on the line, can be frustrating for linemen. A fuse removed and examined visually Shorting is sometimes listed as if it had fallen off, the fuse could actually operate because there was a failure and fuse reacted to it. Observing certain characteristics of the fuse LUHFSER brand, you can determine when the fuse has operated and how current levels.
Construction of a fuse
To analyze the wastes of a fuse must first know its construction. Different materials such as thread lift, punched joints, coils and solder joints are all used in fuses to control the speeds of operation. These performances are shown in time-current curves shown in Figure 1.
Construction Type T Fuse
Fuses 1, 2 and 3 Amp, have a thread alloy Fe - Cr - Al, punching in the terminal and the cap. The fuses of 6 to 100 amps, have a thread tensioner stainless steel, which acts mainly to absorb mechanical stress at the time of closing (Photo 1). The current is carried mainly by a tin or lead wire in parallel, which is stamped and welded on both the terminal and in the bush. Fuses 140 and 200 Amp, have a tin plate which is welded into the terminal and in the bush (photo 2).
Construction of Type K fuse
The construction of the fuse 1 to 100 Amp, is equal to that of type T. (photo 3), fuses 140 and 200 Amp, have a thread of silver-copper alloy which is stamped on both the terminal and in the bush (photo 4).
Slow Fuse Construction Type - RAPID
RAPID SLOW-Fuse has two sections (photo 5). Slow section has a coil wound on a yarn tensioner isolated, both in parallel are punched in the terminal and the other end to a small copper junction.
The fast section is shunted by a wire tensioning steel and copper wire, similar to a type K These last two are punched into the bushing and the small joints of copper.
The two sections, slow and fast are joined by a weld.
Construction Type Fuse VS
VS fuse as RAPID SLOW-fuse has two sections (Photo 6).
The slow section is 2-wire copper nickel alloy in parallel. Punching in the terminal, and the fast section as the slow copper alloy wire has two parallel nickel punched into the socket.
The two sections are joined by a welding seam.
Fuses type K, T, H and VS 1.2 and 3 Amp., Are designed to withstand a force of 14 lbs. This is 1.4 times the requirements of ANSI (10 Lbs). 6 Amp fuses. hereinafter resist traction of 20 lbs. and more. The RAPID AND SLOW fuses VS resist traction up to 35 Lbs.
Function of a fuse
High fault currents, 1000 amps and more, are easy to recognize. The auxiliary tube is completely destroyed fuse and the fuse wire is consumed. When faults are in the range of 500 to 1000 amps, the auxiliary tube is reached to burn but remains intact. In such cases the majority of the fuse wires are consumed depending on the size of the fuse.
Unlike the failure of high currents, low fault currents are difficult to accept since the damage is not noticeable. In a low power failure, the auxiliary tube does not deteriorate and the fuse wire is practically over. Knowing the characteristics of what remains of a fuse wire after a failure, one can recognize that type of failure has occurred. These characteristics vary with the type of fuse.
Fault current fuses Low Type T
T-type fuses 1 to 140 Amp., Which have operated with low-fault current or overload currents, have auxiliary pipes which do not rupture. The fuse wire will melt tin or lead somewhere between terminal and socket, transferred all power to the thread tension, which in turn melt near the center of its size.
After the interruption, the fuse wire tin or lead retains the original smooth surface. The die-cut parts remain unchanged. (Photos 7 and 8).
Detachment of type T
T fuses from 6 to 100 Amp., Which have been mechanically overloaded and detached have a fuse wire elongated tin or le
The surface of the fuse wire will be uneven, rough and have a bottom section where the break. The thread tensioner also be dislodged from the terminal or cap, recognized by the curvature at the thread end or break just at one end (photo 9). T-type fuses 2 and 3 Amp, having a fusible thread which simultaneously functions as a tensioner. If they emerge from their appearance will be the thread lift of the fuses from 6 to 100 Amp. (Photo 10). Fuses 140 and 200 Amp, are robust and indifferent to this kind of traction.
T-type fuses 1 Amp, have a fuse wire spring and in series connected by a bushing, the fuse wire is apparent from the cap and the spring is stretched (picture 11)
Fault current fuses Low Type K
As the T type, the thread tensioner and melt the fuse wire located somewhere between the terminal and the bushing, and the punched parts remain unaffected.
The amount of thread consumed tensor and fuse wire is proportional to the ratio of the fault current and the rated current.
A failure of 15 times the rated current consume more thread tension and thread fuse failure than 3 times the rated current (photos 12a and 12b).
Detachment of the type K
K-type fuses from 6 to 100 Amp., Which have been overloaded mechanically detached, will behave like the type T.
Fuse Low Fault Currents Slow-RAPID
RAPID SLOW fuses have two sections that can operate at currents of 500 amps or less. The fast section is similar to that of a K-type fuse operates when the fault current is below 4 seconds of minimum melting curve (Figure 2).
In this type of failure, the yarn tension and melt the fuse wire located somewhere between the joint and the bushing.
What remains will be similar to that shown in photo 13. A fuse SLOW-RAPID operating in the slow section as shown in photo 14, is sometimes regarded wrongly as a detachment, with fault currents down or overload the heating coil transmits enough heat to the ceramic and this in time to the junction to cause fusion.
Detachment SLOW RAPID Fuses
When a fuse SLOW-RAPID is mechanically overloaded and detached, separates the fast section, this section is constructed similarly to K and T (picture 15).
Fault current fuses Low VS Type
In VS type fuses, the fuse wire will melt somewhere between the cap and the welding seam when operating with high fault currents (photo 16). A fuse VS operating low fault currents or overload (photo 17) transmitted by the wire hot enough to fuse weld seam to cause fusion.
Detachment Type VS
When a fuse VS is mechanically overloaded and detached, the fuse wire acting as tensor are derived from the terminal or the cap and will break just at one end (picture 18).
Knowing the above you can look at the characteristics of a low fault interruption. When the auxiliary tube has not blown look for these signs:
• K - T: fusible thread tensioning and thread are fused about half of its length, punching in the terminal and the bushing remain unchanged, the fuse wire surface remains smooth.
• Type SLOW RAPID: fuse wire and thread tension melt between the terminal and the cap, die-cut parts remain unchanged, the joint appears separate and coil insulator intact.