Find out how to Calculate Temperature Rise in Copper Windings from Resistance Measurements

Find out how to Calculate Temperature Rise in Copper Windings from Resistance Measurements

Find out how to Calculate Temperature Rise in Copper Windings from Resistance Measurements

Nearly all electrical conductors exhibit a change in resistance with a change in temperature. A rise in temperature will increase the quantity of molecular agitation in a conductor impeding the motion of cost by means of the identical conductor. For an observer, the measured resistance of the conductor elevated with the change in temperature. This means that significant resistance comparisons for conductors of various sizes or supplies should be made on the similar temperature.

Experimentation has proven that for every diploma of temperature change above or beneath 20 levels C, the resistance of a pure conductor adjustments as a proportion of what it was at 20 levels C. This proportion change is a attribute of the fabric and is named the ‘temperature coefficient of resistance’. For copper at 20 levels C, the coefficient is given as 0.00393; that’s, each diploma change within the temperature of a copper wire leads to a change in resistance equal to 0.393 of 1 % of its worth at 20 deg C. For slim temperature ranges , this relationship is roughly linear and could be expressed as follows:

R2 = R [1 + a(t2 – t1)]

The place:

R2 = resistance at temperature t2

R = resistance at 20 levels C

t1 = 20 levels Celsius

a = temperature coefficient of resistance at 20 levels C

As an example:

On condition that the resistance of a size of copper wire is 3.6 ohms at 20 levels C. What’s its resistance at t2 = 80 levels C?

R2 = R [1 + a(t2 – t1)]

R2 = 3.60 [1 + 0.00393(80 – 20)]

R2 = 3.6 X 1.236 = 4.45 ohms

Utilizing the above technique, the temperature rise (levels C) in a transformer or relay winding could be precisely decided by measuring the resistance of the winding and performing the next calculation:

1) Measure the chilly winding resistance (at room temperature about 20 levels); name it R (i.e. 16 ohms).

2) Measure the ultimate resistance on the finish of a heating cycle; name it R2 (i.e. 20 ohms)

3) Calculate the resistance ratio of the new winding to that of the chilly winding: R2 / R = 20 / 16 = 1.25

4) Subtract 1 from this ratio: 1.25 – 1 = 0.25

5) Divide this quantity (0.25) by 0.00393: 0.25 / 0.00393 = 63.20 levels C

In abstract, we now have proven {that a} change in temperature will have an effect on the measured resistance of a pure conductor. We have now additionally proven that this property could be exploited to calculate the temperature rise of a winding from cold and warm resistance measurements.

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