Reduction in Load (Copper) loss Due to Overhauling of Power Transformer or OLTC

Transcription

1 Reduction in Load (Copper) loss Due to Overhauling of Power Transformer or OLTC by Neeraj Khare BSES RAJDHANI POWER LTD.

2 BSES Rajdhani Power Limited BSES Rajdhani Power Limited is a Joint Venture of Government of Delhi and Reliance Infrastructure Limited with effect from July BSES Rajdhani Power Limited is the largest of the private discoms in Delhi and distribute power to to an area spread over 750 sq. km- 55% of Delhi s geographical area, with a population density of 2200 per sq km. It s over 22 lakh customers are spread in 9 districts across South and West of Delhi 2

3 Transformation in BRPL area AT&C loss reduction : The company has reduced AT&C by a record 39 % from a high of 5.54% in July 2002 to.9 % as on 3 st March 206. Power Demand : Successfully met the maximum power demand of 2778 MW during the summer of 206 a 20 % increase over the maximum demand of 259 MW in Being biggest of the three discoms, BRPL has a 42 % share in Delhi s electricity pie. System Reliability : Increased to % in 206 from 65% in

4 Overhauling of Power Transformer or OLTC With the passage of time condition of cellulose, oil and contacts of OLTC s of transformer deteriorates and hence overhauling is required for utilizing max. life of transformers. Depending upon the condition of cellulose, oil and no. of operation of OLTC s, Power transformers and OLTC s are overhauled as per standards available and maintenance practices of utilities. 4

5 Overhauling of Power Transformer or OLTC During overhauling process, along with ( i) moisture removal, (ii) oil filteration/replacement, (iii) replacement of gaskets etc., re-tightening of all connections of (a) core coil assembly, (b) metal parts /bushings of both HT & LT side & (c) OLTC also takes place. Re-tightening of all connections during overhauling, results into change in over all winding resistance, if we go through tests results before and after overhauling. 5

6 Winding Resistance Conductor used in transformers have some resistance which depends upon length and area of conductor used for coil winding. But over all winding resistance of assembled transformer is a result of conductor resistance plus contact resistance of following connections,. Tap changer contacts 2. Metal parts 3. Bushings Winding resistance plays an important role in load (copper ) as mathematically, copper loss in a transformer is given by I² R. 6

7 Winding Resistance With the passage of time, because of connections getting loose, contact resistance increases resulting into increase in winding resistance which further increases copper or load of a transformer. Because of re-tightening of all connections during overhauling, a good amount of change takes place in winding resistance, if we go through results before and after overhauling. As reduction on winding resistance will lead to reduction in I² R, hence it can be concluded that overhauling of Power transformers and OLTC S results into loss reduction also. For establishing this fact, we will see test results of winding resistance before and after overhauling of power trf. s and OLTC s. 7

8 Overhauling of OLTC s Case : 20 MVA, 66/KV, NGEF make trf. at JNU Grid Test results of winding resistance before Overhauling of OLTC Resistance/phase R at rated tap no. 5 = ( ( )*/3)*3/2 =.762 Ω Phase Current I of HV side = 0.02 Amp. Assuming 60 % annual average loading of transformer Copper = 3 (I*60/00)²*R = 3(0.02*0.6)²*.762 = W () 8

9 Overhauling of OLTC s Test results of winding resistance after Overhauling of OLTC Resistance/phase R at rated tap no. 5 = ( ( )*/3)*3/2 =.68 Ω Phase Current I of HV side = 0.02 Amp. Assuming 60 % annual average loading of transformer Copper = 3 (I*60/00)²*R = 3(0.02*0.6)²*.68 = W (2) Loss reduction = () (2) = ( ) W = W MU gain = (Loss reduction*24*365)/.00e+09 = ( *24*365)/.00E+09 =

10 Overhauling of OLTC s Case 2 : 6 MVA, 33/KV, Bharat Bijlee make trf. at Siri Fort Grid Test results of winding resistance before Overhauling of OLTC Resistance/phase R at rated tap no. 5 = ( ( )*/3)*3/2 = Ω Phase Current I of HV side = 6.66 Amp. Assuming 60 % annual average loading of transformer Copper = 3 (I*60/00)²*R = 3(6.66*0.6)²* = W () 0

11 Overhauling of OLTC s Test results of winding resistance after Overhauling of OLTC Resistance/phase R at rated tap no. 5 = ( ( )*/3)*3/2 = Ω Phase Current I of HV side = 6.66 Amp Assuming 60 % annual average loading of transformer Copper = 3 (I*60/00)²*R = 3(6.66*0.6)²* = W (2) Loss reduction = () (2) = ( ) W = W MU gain = (Loss reduction*24*365)/.00e+09 = ( *24*365)/.00E+09 =

12 Overhauling of Transformer Case : 6 MVA, 33/KV, Pushp Vihar Grid Test results of winding resistance before Overhauling of Transformer Resistance/phase R of HV side at rated tap no. 5 = ( ( )*/3)*3/2 = Ω Phase Current I of HV side = 6.66 Amp. Resistance/phase r of LV side = ( ( )*/3) = Ω Phase Current i of LV side = Amp Assuming 60 % annual average loading of transformer Copper = 3 ( (I*60/00)²*R + ( i*60/00)²*r ) ) = 3( (6.66*0.6)²* ( 839.8*0.6)² ) ) = W () 2

13 Overhauling of Transformer Test results of winding resistance after Overhauling of Transformer Resistance/phase R of HV side at rated tap no. 5 = ( ( )*/3)*3/2 = Ω Phase Current I of HV side = 6.66Amp. Resistance/phase r of LV side = ( ( )*/3) = Ω Phase Current i of LV side = Amp Assuming 60 % annual average loading of transformer Copper = 3 ( (I*60/00)²*R + ( i*60/00)²*r )) = 3 ( (6.66*0.6)²* ( 839.8*0.6)² 0.024) ) = W (2) Loss reduction = () (2) = ( ) W = W MU gain = (Loss reduction*24*365)/.00e+09 = ( *24*365)/.00E+09 =

14 Overhauling of Transformer Case 2 : 20 MVA, 66/KV, Okhla I Grid Test results of winding resistance before Overhauling of Transformer Resistance/phase R of HV side at rated tap no. 5 = ( ( )*/3)*3/2 =.305 Ω Phase Current I of HV side = 0.02 Amp. Resistance/phase r of LV side = ( )*/3 = Ω Phase Current i of LV side = Amp Assuming 60 % annual average loading of transformer Copper = 3 ( (I*60/00)²*R + ( i*60/00)²*r ) ) = 3 ( (0.02*0.6)²* ( *0.6)² ) ) = W () 4

15 Overhauling of Transformer Test results of winding resistance after Overhauling of Transformer Resistance/phase R of HV side at rated tap no. 5 = ( ( )*/3)*3/2 =.23 Ω Phase Current I of HV side = 0.02 Amp. Resistance/phase r of LV side = ( )*/3 = Ω Phase Current i of LV side = Amp Assuming 60 % annual average loading of transformer Copper = 3 ( (I*60/00)²*R + ( i*60/00)²*r ) ) = 3 ( (0.02*0.6)²*.23 + ( *0.6)² 0.022)) = W (2) Loss reduction = () (2) = ( ) W = W MU gain = (Loss reduction*24*365)/.00e+09 = ( *24*365)/.00E+09 =

16 Case 6th International Conference on Large Power Transformers Modern Trends in Summary of loss Reduction of the four cases Rated Ph current I (amp) i (amp) Results before overhauling R (ohm) r (Ohm) HV LV Overhauling of OLTC Total Results before overhauling R (ohm) r (Ohm) HV LV Total Reduction in MU gain Revenue gain (Rs) , ,025.6 Case Rated Ph current Results before overhauling Overhauling of Transformer Results before overhauling 2 I (amp) i (amp) R (ohm) r (Ohm) HV LV Total R (ohm) r (Ohm) HV LV Total Reductio n in MU gain Revenue gain (Rs) ,44, ,95,299. Note: Annual average loading of transformer is taken 60 %. 2 Revenue gain is Rs 5.75 /unit. 6

17 Conclusion From the 4 cases, 2 each of transformer overhauling and of OLTC, it is established that there is reduction in HV and LV winding resistance after overhauling of trf. s and OLTC s. Reduction in winding resistance leads to reduction in I² R, resulting in revenue gain, along with improvement of insulation condition of trf., enhancing its life due to overhauling. Revenue gain due to loss reduction, results into pay back period of Cost of overhauling in couple of years. 7

18 Thank you 8