![]() Two tests are conducted under this caption. Now, we know all the values for the windings at 85C The general formula for calculating the voltage regulation in % of the line voltage for a given power factor is: It is admitted that with a variation in the temperature, the extra losses (CONN) vary in an inverse proportion to the variation in the resistance TRANSFORMER VOLTAGE REGULATION These extra losses (CONN) equal W cu- I 2R. In addition to the Joule losses, still other losses occur in the copper: the losses due to the skin effect and the losses due to the stray currents or losses by hysteresis. Using the above formula, we can obtain the resistance at 85 C. Where, the value T depends on the metal used. We know that the certain load losses (Joule losses) are proportional to the ohmic resistance of the windings Wcu- P2R.įor pure metals, the relation between resistance and temperature is the following One can assume that the no-load losses remain constant at temperature of between- 20 oc and + 120 ☌. Therefore, it is necessary that the load losses, the impedance voltage which are measured at ambient temperature of 29 ☌, be converted to 85 ☌. In general, the characteristics of a Transformer are guaranteed at a winding temperature of 85☌. In the last column the average value of the preceding division is given. gives the value of the resistance between phases (3 each time). Th e values are always measured between lines, no matter what system of connection is used. A 24V battery supplies the circuit with a direct current (DC) while a variable resistance R is used for limiting the current. The voltmeter is connected directly to the terminals of the Transformer. Fig.No.3 shows the schematic arrangement.įig.No.3 Measurement of Winding Resistance TRANSFORMER WINDING RESISTANCE TESTįor measuring the ohmic resistances, the Volt-Ampere meters method is used. The impedance voltage at rated current In will then be: ![]() The load losses can be measured at a current Im ≠ In.
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