1. Electrical Engineers Meet ‘ Oct-05
KNOW YOUR FUSE

2. Topics Introduction Definitions Fuse Characteristics
Construction of Fuse
Fuse Link Operation
Types of Fuse Links
Fuse Standards
Parameters For Selection of Fuse
Effect of Temperature on Fuse
Conclusion

3. Introduction :
A Fuse Link is a device with a strip or element of easily melted metal placed in an electric circuit so as to interrupt an excessive current by melting.
The Weakest Link :
All electrical equipment that we use; together with the cables connecting them, are designed to operate safely provided that only the normal current flows. Occasionally things can go wrong: The immediate effect of any such incident is for the current to rise to a value far above what is safe for the rest of the system to carry. The consequence is usually overheating which can lead to fire or even explosion. This is when the Fuse Link comes to the rescue- it is the specially designed weak link in the chain.

4. Definitions :
Fusing Current : It is the minimum current at which the fuse element melts and thus disconnects the circuit protected by it.
Fusing Factor : It is the ratio of the minimum fusing current to the current rating.
F.F = Min Fusing Current
Fuse Rating

5. Definitions :
Current corresponding to fusing factor which if passed through the fuse it shall blow in a conventional time as follows.
According to IS:9224 Part II minimum non fusing current for a given fuse is 1.2 times the fuse rating.
Fuse Rating
Conventional Current
63 > X
1 Hr.
63 < X < 160
2 Hr.
160 < X < 400
3 Hr.
X > 400
4 Hr.

6. Definitions :
Cut–off Current : It is the maximum value of fault current actually reached before the fuse melts.
Prospective Current : The r.m.s value of the first loop of the fault current is known as prospective current.

7. Definitions :
Rated Breaking Capacity : The highest value of fault current that the Fuse Link has been tested to interrupt e.g. 80 kA. The standard values of breaking capacity are 80kA for voltages of 415V ac. and above, 40kA for dc.applications. The 240V ac. designs have a breaking capacity of 50kA.
HRC or HBC : High Rupturing Capacity or High Breaking Capacity denotes the ability of the Fuse Link to interrupt extremely high fault currents

8. Definitions :
Let Through Energy : It is the integral of square of current for a given time interval. X1
I2t = ∫ i2 dt X0
It is the integral of square of current and time which gives area under the curve covered by pre-arcing and arcing time

9. Fuse Characteristics :
Fuse Links are used in a variety of applications, each having its own special requirements. Fuse Link operation depends on three different conditions.
1) Normal running conditions.
2) Small sustained overload conditions.
3) Heavy overload or short circuit conditions.
Therefore selection of a Fuse Link for a particular application, the operating characteristics are the most important consideration.

10. Time-Current Characteristic :
A characteristic of all Fuse Links is that the speed at which they operate is directly linked to the level of the fault current.
A graph plotting the operating time of a Fuse Link against fault current is called a Time - Current graph.
Time - Current curves are produced according to BS or IEC Standards, which are termed average curves. This average allows for manufacturing tolerances on a given type of Fuse Link.

11. Cut-off Current Characteristic :
When a Fuse Link interrupts a high value of fault current, it chops off the current before it has time to reach its full value, in other words the Fuse Link current - limits.
The rate at which the Fuse Link chops off the potential fault current is shown on the cut-off current graph.
Current limiting is the most important feature of Fuse Link operation as it ensures that cables, motors, transformers and other equipment are protected from the potentially catastrophic effects of many thousands of amps of fault current which could otherwise flow.

12. I2t or Joule - Integrated Data:
A calculation of energy which is controlled or cuts off through the Fuse Link, by convention this energy is sometimes referred to as the Joule-integral.
These values represent the total operating and pre-arcing times of the Fuse Link under onerous conditions of maximum arc energy.
Cont…

13. I2t or Joule - Integrated Data:
Two values or curves are always given for each Fuse Link:
1) Minimum pre-melting I2t
2) Maximum clearing I2t
The first represents the amount of energy let through by the Fuse Link from the start of the fault up until the time the Fuse Link actually begins to operate.
The second represents the total package of energy let through by the Fuse Link until the instant when the Fuse Link Finally interrupts the fault current.

14. Construction of Fuse : Main Parts: 1) The Fuse Link Body.
2) The Element.
3) Filler.
4) Inner Caps.
5) Discs.
6) Connectors & Outer Caps.

15. Construction of Fuse : The Fuse Link Body :
This is produced to very precise dimensions from high grade ceramic or fiber material which must be able to withstand the high thermal and mechanical stresses which occur when the Fuse Link operates.

16. Construction of Fuse : The Element :
Materials used for the Fuse Element are Lead, Tin, Copper, Zink & Silver.
For the small currents up to 10 Amps. Tin or an alloy of Lead & Tin ( Lead 37% & Tin 63%) is used as the Element.
For the large currents Silver plated Copper or Silver is used as the Element.
Cont….

17. Construction of Fuse : The Element :
Other Types of Fuse Elements :
Quick-Acting Element :
Quick-acting components are typically used in circuits exhibiting little or no inrush currents or where high over currents or short-circuit currents must be quickly interrupted. Resistive loads such as a heater element is one example where a quick-acting component is applied.
Cont..

18. Construction of Fuse : The Element :
Other Types of Fuse Elements :
Time – Lag Element ( Slow acting) :
Time-lag components are used where high starting inrush currents occur and decay gradually. Examples are high switch-on currents of a loaded motor (inductive loads) or a battery charger (capacitive loads). Zinc (in the strip form) is one which acts as a time lag fuse element.

19. Construction of Fuse : Filler & Inner Caps:
Filler : A quartz filler of controlled size, free from organic and metallic impurities and in a moisture free form, is compacted into the ceramic body.
Inner Caps : These are made of copper or brass and electro-tinned. They are interference fitted to the ends of the ceramic body and the outer caps are then pressed on to them ensuring a good mechanical fit and sound electrical connection.

20. Construction of Fuse : Discs, Connectors & Outer Caps :
Discs : These are used to provide resilience between the inner and outer caps and act as an arc barrier.
Connectors & Outer Caps : These are of copper or brass, the connectors (tags) being fixed to the end caps by welding and soldering or by riveting and soldering. The whole component is electro-tinned.

21. Operation of Fuse - Link
A) During the normal load current , the elements get quite hot but the heat is carried away by the sand and the metal connections so the elements don't reach their melting temperature.
B) If the current flow rises above the rated current of the Fuse Link, the elements get much hotter and the excess heat cannot be carried away quickly enough. The element therefore reaches melting temperature and breaks.

22. Types of Fuses : 1) Low Voltage Fuse a) HN type Fuse
b) D/Do Type fuses ( Screw Type)
c) Cylindrical fuse Link
d) Semiconductor Protection Fuses
2) High Voltage Fuse
a) Cartridge Type Fuse
b) Liquid Type Fuse
c) Metal Clad Fuses

23. Fuse Utilisation Categories :
gG : Full Range breaking capability, General Application
gM : Full Range breaking capability, Motor Application
aM : Partial Range breaking capability, Motor Application
aR / gR : Semiconductor Protection, Fast Acting (Superflink)
gTr : Transformer Protection

24. Fuse Standards :
IEC Standard : (International Electrotechnical Commission) is now accepted by most countries world-wide, and many countries have altered their own National Standards to comply with IEC
IEC : General Requirements.
IEC : Additional Requirements for Industrial Fuse Links (bolted tag).
IEC269 – 3 : Additional Requirements for Household Fuse Links(domestic).
IEC269 – 4 : Additional Requirements for Semiconductor Protection Fuse Links.
Cont…

25. Fuse Standards :
VDE Standard : ( Verband Deutscher Elektrotechniker ) In Germany, VDE 0660 for Low Voltage Fuses has been aligned with the relevant IEC Standard. The dimensions of German Fuse Links are specified to Din for Low Voltage Fuse Links. Note: Din (Deutsche Industries Norm) is a dimensional standard only.
UL Standard : (Underwriters Laboratories) In the USA, standards are quite different from those adopted in Europe. Electrical tests are specified in standards written by UL. Low Voltage Fuse Links have dimensions according to NEMA (National Electrical Manufacturers Association).

26. Fuse Standards :
CSA Standard : ( Canadian Standards Authority ) In Canada, Low Voltage Fuses have to comply with CSA, which is a mixture of UK and USA practice.

27. Parameters for selection of Fuse :
Parameters include :
Intended market of the end device or product
Required safety approvals
Mounting method - solderable or replaceable
Maximum operating voltage
Maximum effective operating current
Maximum fault current (prospective current of a circuit)

28. Parameters for selection of Fuse :
Parameters include :
Application type – short-circuit protection or fault current limitation
Description of inrush pulse current waveform including pulse amplitude, pulse duration, and waveform shape
Expected number of pulses over the product life span
Anticipated fault currents and required blowing times
Ambient temperature in proximity to the fuse

29. Effect of Temperature on Fuse Operation :
Fuse Links are thermal devices and as such may require some de-rating when used at elevated ambient temperatures. A de-rating in terms of current of 0.5% per degree centigrade above an ambient of 35 degrees C is recommended.
For e.g. If the fuse is rated for 250 Amps. and if the proximate temperature is 100 deg. C. Then the realistic rating of the fuse is only 169 Amps.

30. Conclusion :
Fuses are the one of the most popular & best available device to give protection against short circuit currents.
Flashovers, damaged to associated switchgears, equipments and loss of production can be avoided by the proper selection, Installation, Condition monitoring and maintenance of the Fuse .

31. CONCLUSION……
Journey Towards TQM continues…
THANK YOU !!!

32. HN Type Fuses :

33. Screw Type Fuses :

34. Cylindrical Fuse Link :

35. Element for Semiconductor Application :

36. THERMOGRAPH SURVEY - CRACKER OFFSITE
90KW MOTOR FEEDER ---- FUSE CONNECTION
BEFORE – 13/08/04
AFTER – 07/10/04
 TEMPERATURE AT FUSE OUTOGOING  
R-ph 112*C
Y-ph 118*C
B-ph 164*C
LOAD CURRENT A
 TEMPERATURE AT FUSE OUTOGOING  
R-ph 76*C
Y-ph 80*C
B-ph 112*C
LOAD CURRENT A

37. 90KW MOTOR FEEDER MODULE – FUSE UNIT DIGITAL IMAGE

38. Cut Off Characteristics For Fuse : Cut Off Current

39. Cut Off Characteristics For Fuse : Prospective Current

40. Cut Off Characteristics For Fuse : Let Through Energyx0 X1

41. Time-Current Characteristic :

42. Cut-off Current Characteristic :

43. I2t or Joule - Integrated Data:

44. Construction Of Fuse :

45. Operation of Fuse Link :
A - Arc burning away ends of element
B – Hot ionised gas carries current
between broken element ends
C – Sand grains are molten to form
glass ‘tube’
D – Sand grains stick together to form
pumice stone like mass called
‘fulgurite’
E – Element wire or Strip
F – Fuse body
G – Sand filler