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The purpose of citing the K factor to the isolation transformer

Jul. 25, 2019

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The purpose of citing the K factor to the isolation transformer shared by High Quality Rectifier Transformer supplier .

The purpose for which the K coefficient is referred to the transformer is:

Usually for K coefficient in any power supply and utilization, transmission networks and devices can be added in the reference, thus for the different types of transformer, transformer in different temperature grade, the different class of insulation in the transformer can be added in the references, the purpose is to improve the reliability of transformer, of course, the different type transformer, transformer in different temperature grade, the different working condition of transformer insulation grade in the same harmonic harmonic of tolerance ability is different, * will determine whether the transformer with the appropriate harmonic resistance depends on the transformer running average temperature rise at the design of the harmonic condition and the transformer internal * high temperature points, If it is to be in the same harmonic harmonic conditions to achieve the same tolerance ability, design and manufacturing cost difference is very big, the dry type transformer, some temperature, insulation class (such as 130 degrees under grade and class B insulation class) of transformer and some materials (low density silk covered wire insulation) manufacturing of High Quality Rectifier Transformer is tolerance cannot reach more than 7 K coefficient, thus, UPS system and data is cannot choose more transformer.

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Analysis of filtering ability and harmonic tolerance of isolating transformer:

1. Main methods to improve transformer K coefficient tolerance:

2. The transformer is specially designed to reduce or eliminate the harmonic sensitive factor of the transformer itself;

3. Select high-density insulated enameled copper wire with high temperature grade (above 180 degrees H grade);

4. Reduce transformer loss and improve transformer efficiency;

5. Choose the transformer with filtering ability, such as Dzn0 transformer, and double output transformer Dyn11d0;

6. Increase the transformer capacity appropriately when the power supply capacity allows, and reduce the load rate of the equipment.

7. Analysis and comparison of harmonic elimination ability of Dyn11, Dzn0 and Dyn11d0 isolation transformer

8. Dyn11 transformer:

9. The third harmonic of the input power supply is enclosed in the input triangle winding and will not be transmitted to the output end through electromagnetic induction. However, the third harmonic will generate additional third harmonic heat loss to the input winding and reduce the tolerance ability of the transformer's K coefficient.

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10. The third harmonic generated by the output load will pass through the output winding and generate additional third harmonic heat loss for the output winding, which will be transmitted to the input end through electromagnetic induction, and generate additional harmonic heat loss in the input winding to reduce the tolerance ability of the transformer's K coefficient.

11. Other sub-harmonics generated by input power supply or output load, mainly including 5, 7, 11, 13, 17, and 19, will be conducted with each other through electromagnetic induction, and additional harmonic heat loss will be generated in input and output windings, which will be fed back to the power grid to reduce the tolerance ability of transformer's K coefficient.

12. Dzn0 transformer:

13. The third harmonic of the input power supply of the Oil Immersed Transformer China  is enclosed in the input triangle winding and will not be transmitted to the output end through electromagnetic induction. However, the third harmonic will generate additional third harmonic heat loss to the input winding and reduce the tolerance ability of the transformer's K coefficient.

14. After the output output load of three harmonic winding, the output winding produce additional three harmonic heat loss, but because the output winding are winding connection, the output transformer in each column are two groups of opposite direction (phase) basic equal to the number three times by harmonic current, electromagnetic induction to basic offset, so that it can't be sensed input end, also won't produce additional harmonic input winding heat loss, because the UPS systems and data of load harmonic produced mainly for three harmonic percentage (about 40 or above), thus greatly improving the K coefficient of transformer tolerance ability; For example, when load balance and three-phase voltage are basically balanced, the zero sequence current detected on the zero line of transformer is much smaller than that detected on the zero line of Dyn11 transformer. Therefore, for the zero line copper row of Dzn0 transformer with the same design section, the loss of zero line copper row of Dzn0 transformer is much smaller, and the K coefficient tolerance of transformer is also greatly improved.

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15. The zero sequence impedance of Dzn0 transformer is very small, the third harmonic current is the zero sequence current, because the load imbalance and three-phase voltage imbalance, will reduce the proportion of filtering the third harmonic, so the three harmonic zero sequence current is easy to flow into the earth through the neutral point of the output winding

16. Input power or output load produced by other harmonics, modular high voltage switchgear, there are mainly five,7,17,19, five negative sequence current in 2, 7, 12 for the positive sequence current, will conduct with each other by the electromagnetic induction, and feed back to the grid, but the output transformer of each column (phase) are two groups of phase difference for 120 * n - 180 degrees, number only Dyn11 percentage 58 harmonic current through the transformer, and the percentage of electromagnetic induction vector superposition only Dyn11 transformer after eighty-two, so compared with Dyn11 transformer, this type of transformer 5,7,17,19 harmonic eliminating percentage about twenty, The experience shows that K=13Dzn0 transformer can replace K=20Dyn11 transformer, and the transformer cost can be reduced by more than 10%.

17. Dyn11d0 dual output transformer:

18. The third harmonic of the input power supply is enclosed in the input triangle winding and will not be transmitted to the output end through electromagnetic induction. However, the third harmonic will generate additional third harmonic heat loss to the input winding and reduce the tolerance ability of the transformer's K coefficient.

19. The third harmonic generated by the output load goes through the output winding, and additional third harmonic heat loss is generated to the output winding. However, because the output winding is double-winding output, one group of which is delta connection, the third harmonic is enclosed in the coil, and will not be induced to the input end. For the other wy-wire output winding, the third harmonic of the input coil is sensed by half as the load is halved. Therefore, for the Dyn11d0 double output transformer, half of the third harmonic can be eliminated when the two sets of output loads are equal.

20. Input power or output load produced by other harmonics, there are mainly five,7,17,19, five negative sequence current in 2, 7, 12 for the positive sequence current, due to the transformer output for double winding output, in two groups of equal load cases, 5 negative sequence current harmonics: each column (phase) are two groups of phase difference for 30 * n (harmonic frequency) + 30 = 180 odd multiples in the opposite direction (vector), the amount equal to the harmonic current, electromagnetic induction vector superposition offset; 7,19 negative sequence harmonic current: for each column (phase), there are two groups of phase difference of 30*n (harmonic frequency) -30 degrees =180 degrees odd multiple (vector direction is opposite), the same number of harmonic current through, electromagnetic induction vector superposition to cancel; Therefore, when the output load of Dyn11d0 double output transformer is equal to that of two groups, the 5, 7, 17, and 19 harmonics can be completely filtered out. With the increase of load unbalance degree of the two groups, the filtering effect drops sharply, so this transformer is especially suitable for 12-pulse rectifier circuit.

21. The filtering principle of multi-output transformer is the same as that of dual-output transformer. Due to its complexity, no analysis is required.


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