In this tutorial, we demonstrate how to use several of harmonics analysis features in EasyPower Spectrum™. Three features are covered in particular:
To perform an arc flash analysis, you must be in the Harmonics focus.
Tip: If you are viewing the Start Page, you can click Open One-line instead.
Click Summation. Total harmonic distortion values are displayed on the one-line as shown in the figure below.
Figure 1: Harmonic Distortion Calculations
By default, Current Total Harmonic Distortion and Voltage Total Harmonic Distortion are selected. The vertical and horizontal numbers on the one-line indicate I THD and the diagonal numbers on the buses indicate V THD.
In the example above, the I THD through the capacitor on BUS-2 is 10.692 amps. The V THD on BUS-2 is 0.427%. (The current and voltage units can be modified in the Harmonics Options > One-line Output tab.)
Current Root-Sum-Squared and Voltage Root-Sum-Squared display I RSS and V RSS values on the one-line. These currents and voltages, which include fundamental and harmonics, are equivalent to I RMS and V RMS. In the Harmonics focus, the fundamental voltage at each bus is assumed to be 1 per-unit. (This can be modified in Harmonics Options > Control.) The fundamental currents for each equipment item are assumed to be either the full load current rating of the equipment or the calculated current at 1 per-unit voltage.
Additional summation information is also available for one-line display:
Figure 2: Frequency Scan
This frequency scan, by default, is based on a 1.0 per-unit current injection on BUS-2. The scan displays the BUS-2 per-unit voltage with respect to the harmonic frequency of this injected current. This per-unit voltage can also be considered a per-unit impedance as long as the current injection remains 1.0 per-unit.
This opens a bar chart that displays the different harmonics present in the buses (voltage) or branches (current).
Figure 3: Harmonics Bar Chart Example
There are two distinct methods for harmonic current flow solutions:
The Single Source Current Flow displays currents and voltages throughout the system based on a single harmonic current injection at a bus. In the case above, 1.0 per-unit (or 481 amps) of 5 th harmonic current are injected into BUS-2. The resultant 5 th harmonic current (in amps) and voltage (in system per-unit) are displayed on the one-line. (The units and injection current can be modified in the Harmonics Options dialog.) This information is useful for determining how a particular harmonic current will flow and what equipment will be affected.
Figure 4: Fifth Harmonic Current Flow Based on BUS-2 Injection
Figure 5: Fifth Harmonic Current Flow Based On All Source Injections
The motors under bus “SWG-12” represent an 18-pulse drive. Each motor injects a spectrum of harmonics. (The injected harmonic spectrum is specified in each Motor Data database dialog box. The EasyPower device library also contains typical harmonic spectra which can be imported.) The currents and voltages are based on all the fifth harmonic injections from the sources in the system. This specified harmonic can be modified in the Harmonics Options dialog box. Notice that the fifth harmonic currents cancel on transformer TX-12 due to phase cancellation. The All Source Current Flow feature determines flows in a network with all sources contributing.
Harmonics Reports enables you to create harmonics text reports. When the report check boxes are selected in the Harmonics Options dialog box, tabulated text report information is created during each harmonics Summation All or Current Flow operation. These text reports can be opened after they have been created by selecting the appropriate report from under the Window button.
Figure 6: Harmonics Text Report Example
This has been a brief overview of EasyPower’s harmonics program. Features such as IEEE 519 verification, filter modeling, zero sequence and triplen harmonics calculations, multiple Y-axes for plots, harmonics bar charts, power flow link, and others are also available. The EasyPower Help topics cover this and other features in greater depth. To open Help, click Help in the upper-right corner of the EasyPower window or press F1.