Investigation Of Parallel LCC-HVDC Transmission Lines In Pakistan With Close Proximity At The Rectifier End

This paper investigates the dynamic behaviour of Parallel LCC-HVDC transmission lines in Pakistan with proximity at rectifier end under different ac fault conditions.It’s a case study of 1st HVDC project that is in the construction phase in Pakistan.The Project is Parallel±660kV LCC HVDC transmission Links to transmit Bulk amount of Power from south to north of the country.As the rectifier converter stations of two transmission lines are very close to each other,commutation failure on inverter side AC system of any transmission line causes TOV issues on rectifier side AC system of both Transmission lines.PSCAD based model is designed to study the steady states and transient states(TOV and Commutation Failure)of the system.Further,it is investigated that what is the effect of dynamic AC faults occurring at the inverter side(line 1 or line 2)on the rectifier side of both HVDC lines.The final objective is to study the,1)Transient overvoltage(TOV)issues at rectifier side of both lines due to the AC faults occurring at inverter side of anyone of the Transmission line,2)Impact of SCR on TOV issues at the rectifier side of both transmission lines,3)The proximity effect of two rectifiers on TOV issues at rectifiers of both lines.By the simulation-based study of PSCAD model,it is concluded that two LCC-HVDC lines being in-parallel affect each other.If there is any fault condition at inverter side of either line 1 or line 2 it will not only generates TOV at rectifier side of the faulty line but also at the other HVDC transmission line.And by increasing the SCR value at the rectifier side of AC system of either line 1 or 2,the TOV issues may be improved accordingly.