What should be the limit of tan delta value for 10MVA 22KV/11KV transformer- standard to be referred to? swagata M.Principal Engineer at Technip KTI

Flag as Inappropriate Like Comment (23) Share Share this discussion

March 11, 2011 Close viewerCommentsKollangi M., Mingchin H. and 2 others like this 23 comments Jump to most recent comment MladenMladen B. PhD, Principal Consultant at Merit Media Int.0.5 % at 20 C acc. to FIST 3-30 Transformer Diagnostics (if FIST is applicable in your case) GopalanGopalan R. Group Manager-Design and Engineering at ETEL Transformers0.5% is for new transformers, for transformers in service up to 1% can be accepted. NandNand S. Lead Engineer - Procurement at Coastal Projects Ltd.May i know the meaning of FIST? MladenMladen B. PhD, Principal Consultant at Merit Media Int.FIST - Facilities Instructions Standards and Techniques. Here you can find their publications: http://www.usbr.gov/power/data/fist_pub.html GopalanGopalan R. Group Manager-Design and Engineering at ETEL TransformersFIST is US Government publication. As Mr Mohana has said, there are no limiting values in standards. However, for power transformers tested at the factory, Tan delta values shall normally be around 0.5%. The residual moisture content normally accepted is around 0.5% for large power transformers. It is generally believed that for small tan delta values, there is a direct correlation between moisture and tan delta values. G. MatthewG. Matthew K. Solutions Director: Enterprise and Data Technology at Doble Engineering CompanyThe upcoming replacement for IEEE 62 C57.149 (I think) will state that the limit for this size should be 0.5% when corrected to 20 C. But that is a commission testing limit. You must consider where the unit started, the bushings installed, weather conditions and rate of trend in your final analysis.

Cheers! PP R. Technical Advisor at ABB LtdThe relevant standard where limiting values for power factor for new and in service transformers are specified is in clause 6.1.6.8 of IEEE Std 62-1995( R 2005) Guide for diagnostic Field testing of oil filled transforners. The limiting values are 0.5 % and 1 % respectively at 20 C , 60 Hz. These values were established by Doble Company in early 70's after extensive field survey and US manufacturers and utilities accepted these benchmarks after some intial reservations and objections.

rohitrohit G. Asst Manager Projects SPIwhat is the correction factor temperature for tan delta value of winding??? In which standard it is referred?? MingchinMingchin H. senior engineer at TA YA co.The tan is used to assess the general aging degree of insulation. If you want to estimate the risks of deteriorated, you can compare the variation of trend of tan between temperatures and voltages. As if the variation of trend of tan with large values, then it will be in a critical condition. PP R. Technical Advisor at ABB LtdTemperature correction factor for power factor is given in Clause 10.10.5 of ANSI/IEEE Std C57.12.90 -2006_Transformer Test Code. But these factors may not be valid for all transformers or for all make.Doble, USA had suggested different values,based on their experience in that market. It is better to check this factor for different makes.In general, we can say PF variation with temperature is negligible in fully dried high voltage, oil filled transformers.If moisture content is high, naturally PF will go up drastically with increase in temperature. DimitarDimitar M. Head of High Voltage Mobile LaboratoryCorrecting the ta delta value to fixed temperature give us inexact information about the condition of oil-paper insulation. Usually I measure the insulation characteristics / tan delta, insulation resistance / at two, even three different temperatures at interval of 20 C. Thus I can calculate how tan delta value is changed per 1 C and receive the exact moisture contain of the insulation. There isn't a limit for tan delta for transformers in service. However the comparing of measured values give us useful information. For this voltage level of 22kV the transformer with old oil the attension lamp will flash at tandelta=2.5% at 20C. G. MatthewG. Matthew K. Solutions Director: Enterprise and Data Technology at Doble Engineering CompanyI couldn't agree more with P Ramachandran. IEEE openly acknowledges that the IEEE temperature correction curves provided can lead to erroneous results so should be used with care (grain of salt). You really need to rely on large statistical data groups of simliar designs to get to the true value. You can always ask the manufacturer, but they often don't have them. We use a statsical database that many call the "Doble Database" that goes back to the 1920s to develop our temperature correction factors. JoydeepJoydeep D. Testing Manager at Eurogulf Transformer FZE0.5% at 20C, this same whatever may be the kV class PP R. Technical Advisor at ABB LtdYes .0.5 % limit irrespective of voltage class. But not applicalble to dry type transformers.

swagataswagata M. Principal Engineer at Technip KTIWhat will be the value for dry type transformer? PP R. Technical Advisor at ABB LtdSince the types and designs of dry type transformers vary so much IEEE C57.94 Instllation,operation and maintenance of transformers , does not specify any limit values for dry type transformers.Doble has a large data bank for PF of dry type trfs and they may be able to give guidance. Normal values vary 1-2 % at ambient temperature. PP R. Technical Advisor at ABB LtdAs per Doble 1989 conference paper,typical PF for ventilated /open dry type trfs is 2 % ( for HV & HV-LV) and 5 % for LV.For encapsulated units overall PF is 1 %. Modern day cast coil transformers have a PF 0.8-1 %. Arun KumarArun Kumar S. NCC Project Management / National Grid SAI am not directly involved in TAN Delta testing. What I know is an equipment say a Transformer or Capacitor banks is in service. The testing guys ask for LC and we permit them. When we ask them to return the LC, they certify that the equipment is not fit to put back in to service and give some numbers. Once they said that a particular PT cannot be put into service. Since it is a critical one we superseded them and forced them to put back the PT into service. Now it is service for more than a year. There should be a clear standards. ie if it is 1 put it into service if 0 remove from service. KollangiKollangi M. Asst.C.O.O/QA & IS at Powertrans Consultants & servicesThe tan delta value is to Check the Impregnation Process (Removing Moisture & Voids if any in the Insulating paper ,oil) of the Particular Batch.If we use Oil Confirming to IS-335/IEC-296 Tan dela value to be fixed by the Designer depending upon the process the Transformer under go & Oil Used(Paraffinic or Napthanic base).Normally No standards says it shall be max this much only. When Cable,Crepe Paper along with Transformer Oil is being used the measured Tan delta value shall be 0.5%( max). KollangiKollangi M. Asst.C.O.O/QA & IS at Powertrans Consultants & servicesSo far i have tested 2MVA Transformers for about 15 Nos (Cast Resin Type) with megger make Tan delta Bridge ,the tan delta value maximum noticed is 0.5%. KollangiKollangi M. Asst.C.O.O/QA & IS at Powertrans Consultants & servicesWe can not say tan delta is not applicable for Dry Type Transformers.

RajeevRajeev A. AGM at BHELA very good discussion. The issue right now I am looking for is whether temperature correction should be applied at all for the tan delta value. Since it is mentioned in previous reply by Mr Dimitar Markov and Mr G. Matthew Kennedy that the insulation if dried properly the tan delta value will not be affected by temperature or the IEEE correction factors give erroneous results, but at the same time more important question right now facing us is whether we are right when we apply temperature correction factor on the Tan Delta value for large power transformers. Since the acceptable limit is 0.5%, it is not a very good dryout. If we want to have really good dried transformer then I think value much lower than 0.5% should be allowed, may be 0.3% or so. So I want to know whether temperature correction isacceptable for tan delta values when measured at ammbient temp range of 20 to 50 Deg C. India is having hot climate, in shop tempratures can vary from 5 Deg C to 45 Deg C.