1. Issues for discussion ON INTERTRIP SCHEME AT TALCHER II Present Scheme has worked satisfactorily as per the Logic designed On number of occasions unit(s) at Talcher stage II has tripped even though the net extra injection to Central grid is less than 500MW Since commissioning of the scheme at no time the tripping of Talcher Kolar HVDC scheme has resulted in the disturbance of central Grid Deficiencies in the present scheme are –Scheme does not consider ground return mode operation –Units are tripping even though the extra injection to Central grid is less than 450 MW –The scheme envisage tripping of a designated unit and may pose problems during outage of the designated unit Southern constituents suggested some modification to overcome the above deficiencies in the scheme and consider enhancing the quantity of power injection in to central grid during the Special TCC meeting held in September 2005.It was agreed in the meeting that the suggestions will be considered during the review of the Scheme after Commissioning of the Tala system The new system proposed should also consider the enhancement of the capacity of HVDC system to 2500 MW by Southern region has implemented a System protection scheme to take care of contingency of tripping of one/both poles of Talcher HVDC Scheme.

2. Talcher schedule Talcher –Kolar Power flows EXISTING SCHEME Talcher inter trip Present measurement Talcher inter trip Scheme Suggestion Talcher inter trip proposed Measurement DETAILS OF TALCHER UNIT TRIPPING TCC MINUTES DETAILS OF TALCHER Kolar HVDC tripping NTPC LETTER (PROPOSAL) CEA MINUTES Talcher inter trip EXISTING & PROPOSED Talcher inter trip suggestion Table CEA LETTER REG. THE PROPOSAL PROPOSED SCHEME SRLDC COMMENTS NTPC LETTER 28 TH DEC 2006

3. DETAILS TRIPPING OF NTPC UNITS DUE TO TALCHER INTERTRIP Pole Norm alisati on Talcher II Generation Before Tripping SL NO DATE TIM EFROMTODETAILS OF TRIPPINGTAL INTERTRIP 1 28-Nov- 05 13:1 01409150Pole I tripped, pole II to GR modeU 6 TRIPPED13:43 500 /500 /503 /500 2 4-Apr-06 21:4 61625 123 3 Pole I tripped,Loss was only 392 MWU 6 TRIPPED23:27 512 /509 /502 /517 3 6-Apr-06 16:0 11559145Pole II tripped,Pole I to GR modeU 6 TRIPPED20:11 500 /504 /515 /506 4 12-Apr-06 17:1 71595 118 8 Pole II tripped,Loss was only 407 MWU 6 TRIPPED17:42 5 31-May- 066:3410500Pole I tripped.Pole I was S/D U 4 & U5 TRIPPED6:45 501 /498 /504 /503 6 13-Jul-06 17:0 71520 120 0 Pole II tripped,Loss was only 320 MWU 6 TRIPPED17:36 497 /507 /509 /511 7 29-Jul-06 15:4 01600350Pole I tripped, pole II to MR modeU 6 TRIPPED21:24 500 /497 / 500 /500 8 15-Sep- 06 16:5 118870Pole I & II tripped U 4,U 5 & U 6 TRIPPED 17:32 17:36 500/ 503/ 500/ 504 9 14-Oct-06 10:1 08800Pole II tripped.Pole I was S/DU4 & U5 TRIPPED20:24

4. Other alternatives –Automatic ramp up through HVDC Gajuwaks link at high Ramprate by Signal through optical fiber to Gajuwaka from Talcher Sencing of df/dt at Gajuwaka Issues involved –Quantum of power to be ramped up – ramp up rate –Loading of ER system Design of the control system complicated but possible –Central control system to be located at Talcher II –Information from Gajuwaka and possible overloading system elements of ER system to be transmitted to Talcher II through wide band –Control system should take a decision considering all aspects of the system and decide to trip/reduce generation at Talcher stage II RTN