- (1.) DURING the course of hearing of the petition on 16.10.2007, it came to light that a major grid disturbance occurred in Northern Region on 12.10.2007 resulting in black-out in the western part of the Region for a few hours. The preliminary investigations into causes of grid disturbance by the petitioner revealed that the disturbance was triggered by uncalled for tripping of circuits of 400 kV D/C Mandola-Bawana and Ballabgarh-Bamnauli transmission lines owned by the sixth respondent, Delhi Transco Limited, while they were carrying power much below their capacity. Considering the seriousness of the matter, it was considered necessary to investigate the reasons and the corrective measures needed. Accordingly, by order dated 7.11.2007, Delhi Transmission Limited was directed to submit the following details. (a) Relay operations on 12.10.2007 in respect of the above noted lines; (b) Relay settings along with CT/VT ratio; and (c) Result of investigations by Delhi Transmission Ltd into the causes of these trippings.
(2.) Delhi Transmission Limited has submitted the details of relay operation and relay setting records as also copy of the preliminary report relating to the grid disturbance. It has apprised the Commission of the corrective measures taken based on its investigations, which are summarised as under: (i) On 400 kV ring, all the CT ratios have been changed from 1000/1 to 2000/1, being connected on Quad Bersimis Conductor having capacity of more than 2000 Amp. (ii) Over load protection on 400 kV Bamnauli circuits has been blocked at Ballabgarh. (iii) ABB Engineers have been called for investigation and rectification to avoid carrier mal-operation at Mandola. We have also noted that an enquiry committee has been constituted by CEA to look into the grid disturbance on 12.10.2007 in totality, and report its findings within two months.
(3.) ON consideration of the report submitted by Delhi Transmission Ltd, it appears that the required corrective action has been taken by the respondent and as such no further action is considered necessary. Accordingly, this matter is to be treated as closed.;