![motor winding resistance unbalance motor winding resistance unbalance](http://www.generatortech.com/Images/clip_image001.gif)
Hence calculating the zero-sequence voltage unbalance is not very useful practically.īelow is a calculator that can be used to calculate the voltage unbalance using the true definition or the IEC definition. Induction motor windings are almost always connected in delta or ungrounded wye. Why zero sequence voltage unbalance is not used? This is because, zero sequence currents cannot flow in induction motor loads that are most affected by voltage unbalance. However, the counter rotating negative sequence flux will create additional heating in the motor. The positive sequence voltage will be much larger than the negative sequence and hence the direction of rotation of motor is not affected. Negative sequence voltage rotates in the opposite direction (vectorially) from positive sequence and hence creates flux in the opposite direction. Note that positive sequence voltage creates flux in the direction that the motor is intended to rotate. Out of these we will use the negative and positive sequence voltage magnitudes to calculated the unbalance. For example, if we have an unbalanced voltage that is vectorially represented as shown below it can be separated in to its constituent positive, negative and zero sequence components as shown. It is a mathematical technique that is used extensively in power system engineering and its details can be found in many power engineering text books. Three phase voltages (or currents), balanced or unbalanced can be mathematically expressed as a sum of positive, negative and zero sequence components.
![motor winding resistance unbalance motor winding resistance unbalance](https://dam-assets.fluke.com/s3fs-public/Motor_with-drive-revised.png)
If you are wondering what negative and positive sequence voltages are, here is a simple explanation. Based on this, the percent voltage unbalance is defined as the ratio of negative sequence voltage (V2) to the positive sequence voltage (V1). True Definition: This definition of voltage unbalance is also known as ‘ True definition’, ‘IEC Definition’ or ‘Voltage Unbalance factor’. The following calculator can be used for calculation voltage unbalance based on NEMA method. As can be observed, calculating the NEMA voltage unbalance is relatively straightforward. Additionally, phase angles are not included in the equation. Line to neutral voltage should not be used as zero sequence components can give incorrect results. Phase-Phase voltages) are only used for calculation. NEMA definition is also called Line Voltage unbalance rate (LVUR) since Line voltages (i.e. NEMA definition of voltage unbalance is given by: These are: NEMA Definition: NEMA stands for National Equipment Manufacturers Association in USA. There are two commonly used definitions of Voltage Unbalance in the industry. Definition of Voltage Unbalance or Voltage Imbalance:
![motor winding resistance unbalance motor winding resistance unbalance](https://theramreview.com/wp-content/uploads/2020/07/Equations-2-and-3.png)
![motor winding resistance unbalance motor winding resistance unbalance](https://electricmotorwarehouse.com/product_images/uploaded_images/str09-f.jpg)
The above points will be discussed in detail after the definition of voltage unbalance is introduced.