A64-Transformers for Wind Turbine Power Projects
1.0 When we consider renewable power projects, wind turbine power farms are the major type after the solar power parks. In wind farms, there will be several wind turbines with dedicated asynchronous generators, producing AC power at low voltages from each turbine. Wind turbine transformers, installed near or on the turbine tower, steps up the generated power voltage to MV levels. Power from several turbine transformers is pooled and fed to a collector transformer for stepping up to transmission level voltages. Farm may also require grounding transformers, auxiliary transformers and voltages regulators in addition to turbine and collector transformers.
?1.1 Typical wind turbine ratings now in use are 1-3 MW, with unit rating reaching a maximum around 10MW. Offshore wind turbines of capacity up to 20 MW are in the anvil. The step-up transformer (wind turbine transformer) can be put at ground level, inside or outside of turbine tower or up inside the nacelle platform of the tower. Off-shore installed turbines are also common. Wind turbine transformers are to be compact and are to be cooled within a constrained space. Both oil-filled and dry type transformers are used as step-up transformers. Collector transformers are fed by several turbine -transformers and they step up power from 33 kV to 66-400 kV for connecting to the power grid.
???????????????????????????????
1.2 Specifications.
?
???1.3 Constructional Features:
Fire resistant insulating fluid (silicon oil, esters) filled -F class or 115 C K or H class.
Hermetically sealed with corrugated tank for fluid expansion
Oil Filled Wind Turbine Transformer ( Top)
Dry Cast Resin Wind Turbine Transformer ( Bottom)
??1.4 The following are some of the special technical parameters to be considered while selecting/ designing wind turbine transformers:
?????????1) Ambient temperature inside the enclosure, where transformer is installed, will be higher than normal. Transformer design shall take into account this higher ambient temperature. Enclosure openings for natural and forced ventilation can be calculated as per appendix A1 of IEC 60076-16.
领英推荐
?????????2) Transformer will be fed from turbine -generator with currents having non -sinusoidal content. Magnitude and frequency of these harmonics shall be considered while conducting temperature rise test for an equivalent higher rated power due to harmonic current heating. Select appropriate K level. (Appendix A2 of IEC standard) In effect, a higher rating than the nominal rating shall be considered to take care of the harmonics in the generator current.
?????????3) While selecting the core flux density under the rated voltage and frequency, consider the maximum V/f from the generator.
?????????4) Depending on the magnitude and frequency of the harmonic voltage on LV side, core magnetic flux density may increase. This will result in increased core temperature, no-load losses, excitation current and noise level. (Appendix 3 of IEC standard)
??????????5) Due to frequent energization of the transformers during wind farm operation, transformers are frequently exposed to mechanical and thermal effects of inrush currents.?Frequency of energization (number of energizations per year) shall be given at enquiry stage.
???Unless otherwise specified, switching is done from the HV (grid) side. The method of switching and synchronization shall be described in case of generator side energization.
????System inrush current limitations (maximum value, duration) shall be given at enquiry ????stage by the purchaser.
6) Effect of turbine structure vibrations on transformer shall be considered during the design stage. Special consideration shall be given to the stress transferred to the bushing terminals from the connecting leads. The purchaser shall specify vibration spectrum at the enquiry stage. (IEC 68-2-6/59-EN 60068). The procedure of vibration test if any, should be agreed at enquiry stage between purchaser and manufacturer.
7)The risk of wind turbine transformer failures is higher due to the repeated transient over and under voltages on each side of transformer. Several solutions are available to increase the reliability of transformers against these fast-transient interactions:
Evaluate the insulation level of the transformer and if necessary, apply one or more of the following solutions. This can be done by modelling or measuring the system using high frequency resonance analysis. The resonance frequency test is a special test for this purpose. Test method shall be agreed between manufacturer and purchaser. One test method is described in A.4 of IEC standard
Install standard protection techniques such as surge arresters (HV, LV), or RC circuit (snubber) or surge capacitor.
Adopt one step higher BIL for windings (see list 3 of table 1 of IEC 60076-16). For Um ≤ 1,1 kV, A C withstand voltage should be 10 kV.
8)???High frequency steep voltage surges can be generated by the switching operation on LV or HV side. These surges are transferred by cables to the terminals of the transformer. Transformer windings have different values of internal resonance frequency. See the measurement method as per Annexure A4 of IEC standard. If the high frequency steep surges generated by switching operation coincide with the internal frequency of the winding, these surges can resonate with the winding internal frequencies and cause higher voltages and consequent electric stresses than the nominal dielectric withstand strength of the windings.
?1.5 Special Test
-???????110% (of BIL) chopped impulse test as type test
-???????Environmental Tests for dry and off-shore transformers
-???????High Frequency resonance analysis (Appendix A4 of IEC 60076-16)
?1.6 Typical Failure Modes from site
- ?????Failure from overheating of dry type transformers- enclosure design issues; shifting of cooling fan direction
-????Oil filled transformers - High hydrogen gas generation (20,000 ppm) with small amounts of ethane, ethylene and methane due to PD in small oil film between thin core laminations of 5 limbed wound core- Solution: provide core shield or grounding from the inside surface of wound core.
-????When a group of transformers are switched from remote by MV side VCB, last or first transformer in the group is most vulnerable from over voltages. Due to the current chopping and reignition transients from VCB, windings may fail (at line end or tap sections). Shielded cables amplify resonances with reflected waves and voltage doubling. Solution: Provide resistor-capacitor snubbers for protection. Dry type, 36 kV class transformers are more vulnerable to this type of over voltages.
?
??????????
Electrical Engineer SAP
2 年Do you have any thoughts on the method of earthing the MV Cable Surge Arrestors? The ABB Tx shown, clearly earths the Surge arrestor to the tank body, rather than to WTG earth bar. I feel the earth return path should be as direct as possible.
Specialist, Power Transformers
2 年Let me point out couple of errors that I am correcting in the article.( Thanks to Dr K R M Nair for pointing it out. 1) Clause 1.2 Specifications- Connection is Dyn as per IEC 60076-16 instead of Dy 2) Clause 1.3 Constructional Features - Fire resistance class is F1 instead of F2. There is no F2 class as per IEC 60076-11
Chief Operating Officer
2 年This is a very handy reference material primarily for the transformer designers. I feel that collaborative study between transformer designers and the wind power system designers will be necessary to identify the possible problems and finding practical solutions.
Placas inoxidável gravadas em profundidade reflecte a imagem com textura.
2 年Bom dia quero fazer parte desses transformador com as minhas placas identificadas em alumínio ou a?o inoxidável 316 que têm anticorrossao as intempéries com inscri??es em baixo relevo pintado com duas camadas de tinta, uma de primário e outra de selulosso para n?o destacar. Estou disponível a propostas para sua execu??o. Cumprimentos. [email protected]