Voltage and Current Harmonics – Case Study

When the harmonic spectrum is known, or at least can be measured with a certain reliability or predicted, the additional losses can be easily calculated. The process of calculation should be made through the following steps: 1. Determination of all the components of additional losses due to the presence of harmonics. 2. Determination of the harmonic spectrum, either by measurement or by estimation, taking into account all harmonic generating equipment, in particular electronic converters. 3. Calculation of the contribution of each harmonic component and determination of total additional losses. In practice, it is important to use the real harmonic current magnitudes rather than theoretical values. Table C7.1 shows the calculated additional losses, for harmonic currents up to order 25, for two transformers at normal environmental temperature, assuming the current harmonic spectrum illustrated in Figure C7.1.