Resistance winding losses

Rhodium-platinum alloys containing up to 40% Rh are used in the form of wire or ribbon in electrical resistance windings for furnaces to operate continuously at temperatures up to 1 750°C. Such windings are usually completely embedded in a layer of high-grade alumina cement or flame-sprayed alumina to prevent volatilisation losses from the metal due to the free circulation of air over its surface. Furnaces of this type are widely employed for steel analysis, ash fusions and other high-temperature analytical procedures. 

Test certificate shall be provided for resistance between windings, winding loss, and earth fault test with body of the unit. 

When the torque is determined by the above method, the voltage during the test should be so adjusted that the locked rotor current is approximately equal to the full load current. After the locked rotor test, the resistance of the stator windings should be measured and may also be considered for calculating the I R losses. 

Resistive losses are those losses associated with the resistance of the windings contained within the transformer or inductor. There are two forms of resis-... 

However, up to 30% of the power consumption of a motor can be attributed to no-load losses because of windage (by cooling fan and air drag), friction in the bearings, and core losses that comprise hysteresis and eddy current losses in the motor magnetic circuit. Load losses include stator and rotor losses (resistance of materials used in the stator, rotor bars, magnetic steel circuit) and stray load losses such as current losses in the windings.f ... 

For example, a real inductor has the basic property of inductance L, but it also has a certain non-zero dc resistance ( DCR ) term, mainly associated with the copper windings used. Similarly, any real capacitor has a capacitance C, but it also has a small equivalent series resistance ( ESR ). Each of these terms produces ohmic losses — that can all add up and become fairly significant. 

The other way to reduce losses is to decrease the thickness of the conductor. But there are several ways we can do this. If, for example, we take a winding made up of single-strand wire, and split the wire into several paralleled finer strands in such a way that the overall dc resistance does not change in the process, we will find that the ac resistance goes up first before it reduces. On the other hand, if we take a foil winding, and decrease its thickness, the ac resistance falls before it rises again. 

What about the current rating This is largely determined by the amount of heat dissipation the inductor can tolerate. But its thermal resistance (in degC/W) is not determined by the winding configuration, rather by the exposed area of the inductor, and other physical characteristics. Therefore, whether in series or in parallel configuration, we have to maintain the same total I2R loss. For example, suppose we call the current rating in parallel as Ip ,... 

Since the equivalent circuit contains two winding resistances and a core-loss resistance then power is lost as heating energy inside the transformer. Hence the conversion of power through the transformer cannot be 100%, a small loss of efficiency occurs. This is usually less then about 2% for power transformers. Assume all resistances and reactances are referred to the secondary winding. The efficiency can be expressed as,... 

The resistance R2/S represents the total power dissipated in one phase winding of the rotor. This consists of a resistive loss in the winding itself and the shaft power transmitted to the mechanical load. The resistance can be divided into two parts -... 

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