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The rational selectio of fuse
Categories£ºHigh Series   

The high-Volt limit-current fuse generally is known as one protection electrical device with characteristics of simple structure,reliable protection and economical investment£¬however£¬actually though this type fuse has simple structure£¬this product with super performance only can be manufactured by means of strict technology and quality control norm, additionally,it is only
correctly using-it that can make full use of its normal protection function. this product¡¯s use regulation would be introduced briefly below, anyone needing to have more information about it please contacts us£®

¡ô The factors needing consideration in selection-use

The instalIment surrounding condition in use is very important for the fuse in that it not only affects the fuse¡¯s perfo rmance,but also takes infuence on the reIiabIe abiIity of b reaking obstacle,therefore,operator should take the use condition into account£®One common instalIment way is instalIing the fuse into case body with three-phase being sealed,at this time,thefuse should be decreased by 15 percent in capacity before used except the fuse with rated current being lower than 20A,because the fuse with smalI rated-current has Iittle heat radiated in addition to Iow-temperature,so the sealed surrounding does Iittle influence onto it£®Another instalIment way is sealing one set of fuse into one tube poured with insuIation resin,under this circumstance, the fuse should be decreased by 25£¥in capacity before used in order to prevent the fuse from being damaged because of over-heated except for the fuse with rated current being Iower than 20 A According to relevant standard regulation,the normol work the fuse temperature of fuse ranges from-250¡æ to 400¡æ,The fuse¡¯s
mechanical performabce would be affected positively provided the temperature is Iower than-25¡æ,vice versa,the fuse should be reduced by 1£¥in capacity per 1 Rise in temperature when the temperature is upper than 40¡æbefore used.


As for the fuse installed in the cupboard with th ree-phase being not sealed,for the mutual interruption between temperature-
rising of th ree-phasefuse,the fuse could be decreased by 1 0£¥in capacity before used except for fuse with rated current being
lower than 20A£®Generally, as for the fuse with rated current being lower than 10A£¬operator should do his best to make the fuse
away from landing metal support because of fuse-body¡¯s easily-aging resulted from long-term co rona discharging . For
strengthening the current grade of fuse sometime£¬user would use two or three untis of fuse device for paralleling use,at this
time,the mutual influence between fuse¡¯t emperature should be taken into account by operator,and the fuse should be decreased
by 10-20£¥in capacity for use generally.
The stem-current and 12t properties of paralleling fuses can conform to following principle Ip-total£ºn x(the lp1 of single-fuse¡¯
anticipated current beinglp/n)
In the equation£ºIp-total the stem-current climax value after paralleling n the fuse\s parallel quantity
1p valid value of anticipated current
1p1 stem-current climax value of single-fuse
l2t total£ºn x(the l2t value of single-fuse,anticipated current beinglp/n)
Noted£ºthe fuse¡¯simple series-connection is banned from being used in the one-grade higher volt circuit

¡ôInstallment and change

Before installment, operator should check out whether the fuse is complete£¯good£¯clean or not,provided the fuse has suffered
from being fallen and violent vibration, operator is supposed to examine its resistance value and whether the porcelain tube has
crack or not on surface.
During installment£¬operator should take notice of the collision device¡¯s direction marked on the fuse, after the install ment is
finished, operator should lock steel-fastener(or fastened bolt)on bottom base tightly to prevent from loosely contact.
In the th ree-phase system, the common fuse device should be changed after one unit fuse happen motion except for that
operator could ascertain that only one fuse device is electrified with obstacle current£¬because although another two hasn¡¯t
happened motion, there maybe exist serious impairment on them.
Ope rator should be very careful at the time of changing fuse device, for the limit-current fuse has one reliable motion scope during operation£¬but it can¡¯t be guaranteed that every obstacle condition is within its reliable scope(such as some wrong with the switch appliance trip, or fuse conducts motion in case of being lower than its minimum brokencurrent)£®consequently,for the sake of security£¬operator couldn¡¯t conduct changing until the fuse¡¯s motion has last fo r 10minutes or longer and the ci rcuit has been isolated from other electric devices, in a word£®the fuse should be changed under the circumstance of being without any electricity.


In the common electrical system£¬the fuse should conduct motion in low frequency if it is selected suitably,Besides this case above,it is far more likely that it has some wrong with system selection compatible problem£¬calculation selection or wire connection£®So if the frequency is high£¬operator is supposed to check out and compute further
As for the fuse of normal operation£¬during examining and repairing equipment, operator could check out whether the appliailce is aging or not by means of measu ring fuse¡¯s internal resistance£¬and the fluctuation scope of internal resistance should be within¡À10£¥.

¡ô The selection of fuse for protecting electric motor

The rated current selection of fuse for directl starting should confo rm to following equation£º
1y=¦Ä N1n
In the equation£º¦Ä comprehensive coefficient(refer to form)
N¡ªthe ratio of start current and motor¡¯s fuIly-loaded current
General ly£¬N-equals 6
1n¡ªmotor¡®s fuIly-loaded current
1y¡ªthe current value in the start-time
Finding the ly value-point corresponding with start-time on time-current characte ristic curve£¬the curve corresponding with point or on right side of point is the selected fuse£¬the fuse¡¯s rated current should be bigger than 1.3 times of fully-Ioadedcurrent of motor

Start-times per hour 2 4 6 8
  1.7 1.9 2.1 2.3