Tinned Copper Fuse Wire

             Tinned Copper fuse wire is one of the common and simple fuse element used in semi enclosed fuses for maintaining the safety of electric equipment. The material used is Tin plated Copper. Copper is a good conductor, has good tensile strength and corrosion resistance. Hence bare copper wire is not a bad choice to use as a fuse. But, Tin plated copper fuse wires are much popular and widely used. Why ?

Tin Plating

             When Tin plating is applied over bare copper wire, it improves the strength and longevity of the copper beneath it. The corrosion resistive power of bare copper wire to humid and wet atmospheres gradually decreases when temperatures exceed especially above 100 degrees Celsius when carrying currents. In such circumstances, Tin plating on the bare Copper wire protects Copper beneath it and improves longevity and strength of the fuse wire. Tin coating does not allow oxidation easily. Tin coating on the fuse wire also makes it convenient for soldering. Even though Tin plated Copper wire is expensive than bare Copper wire, the expenditure will be prudent in the long run usage. Hence, TC fuse wires are widely used in electrical maintenance.

Advantages of TC fuse wire

  1. It is cheapest.
  2. It requires no maintenance.
  3. It requires minimum time to replace.

Disadvantages of TC fuse wire

  1. Due to prolonged exposure to atmosphere, oxidation makes the wire thin and fails.
  2. Operation is unreliable and hence cannot be used for large fault currents.
  3. There is a chance of misuse by using inappropriate rated fuse wire.
  4. Loose connections causes local heating.

 

Specification & Ratings

The common specification of TC fuse wire is Standard Wire Gauge (SWG) in the market based on the diameter of the wire which is the main parameter to decide the current carrying capacity of the fuse wire. The current carrying capacity of a TC fuse wire is usually mentioned as ‘Rated Current‘ of the wire which indicates the maximum current that the fuse can continuously conduct without interrupting the circuit and ‘Fusing Current‘ which indicates the current at which the fuse blows isolating the equipment from the circuit.

The ratings of TC fuse wires as per IEE regulations are mentioned below for reference and practise of using correct rated TC fuse wires for the electrical equipment under protection.

TINNED COPPER FUSE WIRES

I.E.E Regulation 14th edition Table A1

Approximated size of Fuse Elements Composed to Tinned Copper wire for use in semi-enclosed Fuses.

S.W.G

Diameter in inches Rated Current‘ of fuse in amperes

Approximate ‘fusing current’ in amperes

40

0.0048 1.5 3
39 1.0052 2.5

4

38

0.0060 3.0 5

37

0.0068 3.5 6

36

0.0076 4.5 7

35

0.0084 5.0

8

34 0.0092 5.5

9

33

0.0101 6.0

10

32

0.0108 7.0

11

31

0.0116 8.0

12

30

0.0124 8.5

13

29

0.0136 10.0

16

28

0.0148 12.0

18

27

0.0164 13.0

23

26

0.0180 14.0

28

25

 0.020 15.0

30

24

0.022 17.0

33

23

0.024 20.0

38

22

0.028 24.0

48

21

0.032 29.0

58

20

0.036 34.0

70

19

0.040 38.0 81
18 0.048 45.0

106

17

0.056 65.0 135

16

0.064 73.0

166

15 0.072 78.0

197

14 0.080 102.0

230

13 0.092 130.0

295

Sample look

bfw-01

 

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Why temperature degree indicator shown on the MOG of Transformer conservator tank ?

Magnetic Oil Gauge
Magnetic Oil Gauge

Magnetic Oil Gauge (MOG) is fixed to the conservator tank of the Transformer to indicate oil level in the conservator tank. The oil levels are generally indicated on the MOG dial as ‘Empty’, 1/4, 1/2, 3/4 and ‘Full’. But in between these levels usually 300C temperature indication is also shown. This is because oil level in the conservator tank changes according to the ambient temperature. The hotter the temperature, the more will be the oil level in the conservator tank due to expansion and vice versa. So, as the oil level depends on the ambient temperature, we must have an indication to what level the oil is to be filled at a certain temperature. This is why the level is indicated in temperature degrees so that the when the ambient temperature is same as the temperature indicated on that MOG dial, the oil level should reach that mark to ensure that the Transformer has sufficient oil level in the conservator. Whenever oil is to be filled in the conservator tank, the level is to be checked properly and to be set according to the ambient temperature prevailing at the time of filling the oil.

Why the Transformers are tested at double the rated frequency which never happens practically?

               DVDF (Double voltage and double frequency) test is popular test conducted on the Transformer before it is commissioned. In this test double the rated voltage and double the rated frequency is applied to the Transformer under test and observed for its withstand capability usually for 1 min. Double voltage is applied to test the Transformer withstand capability for higher voltages which are sometimes occur in the form of lightning surges and faults on the transformer. But, practically, no transformer is subjected to double the rated frequency as the frequency variations are not allowed beyond 0.5% by the power supply grid controlling authority. In such a case, is it essential to test the transformer at 200% i.e. double the rated frequency conditions?

                When alternating electrical source is applied to the primary winding of the transformer, it draws magnetizing current which produces alternating flux in the core of the transformer. This flux links both primary and secondary windings and due its alternating nature EMF is induced across both windings and Erms can be deduced by the equation.

                                              Erms= 4.44ᴓmfN volts

                                           Where      Erms is RMS voltage induced

                                                             ᴓm is maximum flux linked

                                                             f is the operating frequency

                                                             N is the number of turns in the winding.

               As per the above equation, when double the rated voltage is applied while testing the transformer, without doubling the frequency, the maximum amount of flux linked will also be doubled as the number of turns is always constant for a particular design. This causes the abnormal heating of core of the Transformer under test and the magnetizing properties of the core are disturbed permanently. Hence, to avoid this abnormal heating of the Transformer due to increase in flux, applied frequency will also be doubled along with applied voltage to test the high voltage with stand capability of the Transformer. Thus the test is named as Double Voltage Double Frequency test.