Challenges of Continuous Parallel Challenges of Continuous Parallel - PowerPoint PPT Presentation

Challenges of Continuous Parallel Challenges of Continuous Parallel Operation of GTG Units in DPS A case study & Simulation Presented By: Date: 05-Dec-2014 Sri Rajib Kumar Sarmah Venue: Elect Conf Room Free Powerpoint Templates Dy.SEE(Gen)

Overview of Presentation • Existing Scheme of Duliajan Power Station. • Constraints of continuous parallel operation in existing scheme of DPS. existing scheme of DPS. • Solutions for continuous parallel operation. • Comments.

Duliajan Power Station Present Scenario with 2 x 14.45 MW Gas Turbine Units 11 KV B/C 2 B/C 1 Bus C Bus B Bus A ON ON Unit 2 ON ON Unit 1 Inter. Inter. Unit 2 Unit 1 OFF OFF Gen. Gen. Gen. Gen. Bkr Bkr GT GT Unit 1 Unit 2 NGR NGR Unit 1 Unit 2

Duliajan Power Station Operating Condition with only One Unit Running 11 KV B/C 2 B/C 1 Bus C Bus B Bus A ON ON Unit 2 ON ON Unit 1 Inter. Inter. Unit 2 Unit 1 ON OFF Gen. Gen. Gen. Gen. Bkr Bkr GT GT Unit 1 Unit 2 NGR NGR Unit 2 Unit 1

Constraints of Parallel running of DPS Units • Existing 2 x 14.45 MW GTG Units cannot be run in parallel for long duration due to circulating current (zero sequence current) and subsequent Generator Heating. • Existing scheme is of very old design (1979) Low Reactance Grounded system and this scheme is obsolete now. • In present system already fault currents are very high and will • In present system already fault currents are very high and will be more in parallel running condition. This pose safety threat. • New Units are designed with Generator-Unit Transformer configuration with High Resistance grounded system and this scheme prevents circulating current between parallel units.

Duliajan Power Station Operating Condition With Unit ������� Running in Parallel 11 KV B/C 2 B/C 1 Bus C Bus B Bus A ON ON Unit 2 ON ON Unit 1 Inter. Inter. Unit 1 Unit 2 ON ON Gen. Gen. Bkr Bkr Bkr Bkr GT GT Unit 1 Unit 2 Circulating Zero Sequence Current NGR NGR Unit 2 Unit 1

Eliminating Circulating Zero Sequence Current in Grid Connected Units of Various Capacities using Generator-Transformer Arrangement & High Impedance Neutral Grounding System 132 KV Bus A ON Unit 1Interrupter Bkr Unit 1 Unit 2 Interrupter Bkr ON Inter. 22.6 MVA, 30 MVA, 11/ 132 KV Tr 1 11/ 132 KV Tr 2 No circulating current between parallel ON ON Unit 1 Gen. Bkr Unit 2 Gen. Bkr running units GT Unit 1, GT Unit 2 , 15 MW 20 MW NGT NGT R R Unit 1 Unit 2

Option 1 : IDEAL Solution: Scheme for DPS for Eliminating Circulating Zero Sequence Current Using Unity Ratio Transformer & High Impedance Neutral Grounding System B/C 2 B/C 1 Bus B Bus A 11 KV Bus C ON ON ON Unit 1Interrupter Bkr Unit 1 Unit 2 Interrupter Bkr ON Inter. 20 MVA, 20 MVA, 11/ 11 KV Tr 2 11/ 11 KV Tr 1 There will not be any ON ON Unit 1 Gen. Bkr circulating current Unit 2 Gen. Bkr between parallel running units GT GT Unit 1 Unit 2 NGT NGT to be designed NGT R R Unit 1 for Gen Stator Earth Unit 2 Fault < 20 A)

Challenges of Parallel Operation of DPS Units � To mitigate circulating current between parallel running units, NGR Auto switching is required and the scheme has to be fail safe design ; so that if one of the parallel running unit trips on fault, the system with the healthy unit does not remain ungrounded. � During islanding running of two units, NGRs of all the running units to be connected to ground automatically to prevent ungrounded operation of any unit. � Automatic Changeover of Droop/ Isoch mode between parallel running units is required so that only one unit remains in Isoch mode and all other units stays in droops mode. � Automatic load shedding scheme (Unit based & Frequency based) is required so that if one of the parallel running unit trips on fault, some non-priority feeders can be segregated automatically & quickly to prevent under frequency trip of the healthy unit. (If the 20 MW unit trips then more load to be segregate corresponding to tripping of any one of 14.45 MW units).

Option 2 : Practicable Solution: Eliminating Circulating Zero Sequence Current Using Neutral Switching Breakers B/C 2 B/C 1 11 KV Bus C Bus B Bus A ON ON Unit 2 ON ON Unit 1 Inter. Inter. Unit 1 Unit 2 ON ON Gen. Gen. Gen. Gen. Bkr Bkr GT GT Unit 1 Unit 2 ON OFF NGR NGR No Circulating Unit 1 Unit 2 Zero Sequence Current

Duliajan Power Station Switchgear Arrangement with Three Units New GT- Old GT Inter Connection 1- 3 Tie 1 11 KV B/C 2 B/C 1 Bkr Bus C Bus B Bus A 11 KV N B/C 2 N B/C 1 New Bus 3 Unit 2 Tie 3 Unit 1 Tie 4 Inter. Bkr New Bus 1 Inter. New Bus 2 Bkr Tie 2 Unit 3 Bkr Unit 2 Unit 1 Gen. Bkr Gen. Gen. Gen. Gen. Bkr Bkr URT, 31.5 MVA GT 11/ 11.5 KV NGR GT Unit 1 Bkr 3 Unit 2 GT NGR Unit 3 NGR NGR URT 3 Bkr 1 Bkr 2 NGTr. High NGR NGR Unit 3 Imp Unit 2 Unit 1 Grnd.

Path of Zero Sequence Currents with Any Combination of two units or Three Units Running Parallel Tie 1 B/C 2 B/C 1 Bus C 11 KV Bus B Bus A Bkr ON ON ON 11 KV N B/C 1 N B/C 2 NBus 3 ON ON Unit 2 ON ON ON ON Tie 3 Unit 1 NBus 1 Inter. NBus 2 Bkr Inter. Tie 4 Tie 2 ON Bkr Unit 3 Bkr ON Unit 2 Unit 1 Gen. Bkr ON ON Gen. Gen. Gen. Gen. Bkr Bkr URT ON Unit 3 GT GT Unit 1 Unit 2 GT NGR Unit 3 URT 3 Path 2 NGTr. High NGR NGR Unit 3 Imp Unit 2 Unit 1 Grnd. Path 3 Path 1

Operation with Unit #3 Running Alone New GT- Old GT Inter Connection 1-3 11 KV Tie 1 B/C 2 B/C 1 Bus C Bus B Bus A Bkr ON ON ON 11 KV N B/C 1 N B/C 2 NBus 3 ON ON Unit 2 ON ON ON ON Tie 3 Unit 1 Inter. NBus 2 Bkr Inter. NBus 1 Tie 4 Tie 2 ON Bkr Unit 3 Bkr ON Unit 2 Unit 1 Gen. Bkr OFF OFF Gen. Gen. Gen. Gen. Bkr Bkr URT ON Unit 1 Unit 3 Unit 2 Not Not Running Running GT NGR Unit 3 NGR NGR URT 3 ON ON Bkr 1 Bkr 2 NGTr. High NGR NGR Unit 3 Imp Unit 2 Unit 1 Grnd.

Operation with Unit #3 & Unit #1 Running In Parallel and Unit #3 is Selected as Master Tie 1 B/C 2 B/C 1 Bus C 11 KV Bus B Bus A Bkr ON ON ON 11 KV N B/C 1 N B/C 2 NBus 3 ON ON Unit 2 Tie 3 ON ON Unit 1 ON ON Inter. NBus 1 NBus 2 Bkr Inter. Tie 4 Tie 2 ON Bkr Unit 3 Bkr ON Unit 2 Unit 2 Unit 1 Unit 1 Gen. Bkr Gen. Bkr ON ON OFF OFF Gen. Gen. Bkr Bkr URT ON Unit 3 Unit 2 Unit 1 Not Running Running GT NGR Unit 3 NGR NGR URT 3 ON OFF Bkr 1 Bkr 2 NGTr. High NGR NGR Unit 3 Imp Unit 2 Unit 1 Grnd.

Operation with Unit #3 & Unit #1 Running In Parallel and Unit #1 is Selected as Master Tie 1 B/C 2 11 KV B/C 1 Bus C Bus B Bus A Bkr ON ON ON 11 KV N B/C 1 N B/C 2 NBus 3 ON ON Unit 2 Tie 3 ON ON Unit 1 ON ON Inter. NBus 2 Bkr Inter. NBus 1 Tie 4 Tie 2 ON Bkr Unit 3 Bkr ON Unit 2 Unit 2 Unit 1 Unit 1 Gen. Bkr Gen. Bkr ON ON OFF OFF Gen. Gen. Bkr Bkr URT OFF Unit 3 Unit 2 Unit 1 Not Running Running GT NGR Unit 3 NGR NGR URT 3 ON ON Bkr 1 Bkr 2 NGTr. High NGR NGR Unit 3 Imp Unit 2 Unit 1 Grnd.

Comments • Big challenge is to integrate old equipments with technologies. • More in depth analysis is required by in-house & external experts before going for any up-gradation/ modification. • Techno- commercial feasibility study is required whether to go • Techno- commercial feasibility study is required whether to go for up-gradation of existing system or go for replacement of old units. • At present, space constraint is there to adopt new system. • Detailed analysis of system fault levels, protection & interlock requirements is required.