CASE:1
Analysis of the tripping at Sriprumbudur - Koyambedu feeder on 10thFeb. 2000.
Koratoor 230 kvs/s
230kv NCTPS fdr.
230kvETPS fdr.
Sriperumbudur400 kv s/s Koyambedu230kvs/s
Relay indications.
Koyambedu feeder.
Main 1. RAZFE TN
Main2. SIEMENS 7SA511 BN Z1 Observations at Sriperumbudur
Heavy flash over seen on Koyambedu feeder with jumper cut at line switch. The breaker of Koyambedu feeder tripped
AT Koratoor s/s the NCTPS fdr. And the ETPS feeders are not in service. There was a fault at KTR-SPR feeder A conductor snapped , but the line was not tripped for the fault. The KOY feeder at SPR was tripped with heavy flash over and with a jumper cut at the SPR end. There was no tripping at KOY ,the Koyambedu operator has noticed a supply failure both from Korattoor and SPR. The known fault at KTR-SPR feeder was not cleared but causes over flow of current in one single path causes the heavy flash over and the operator at SPR has opened the LV breakers of the Auto transformers.
The KTR-SPR and SPR-KOY feeders are running parallel up to some point , and the mutual compensation effect might have caused the over reaching of the setting. So, the tripping of KTR-SPR feeder might have been delayed and causing the KOY feeder jumper cut . The relays at KTR and SPR in the feeder of KTR-SPR was verified and the compensation factor was reduced to 0.7 to have the sufficient reach.
CASE:2
Deails of trippings atKortoor, NCTPS ,Sriperumbudur… on 30thJan 2000 SPK
KLPM
KDP To TVLM GDDI
MOSR TVLM TRNI KOY
Arni KTR ETS MYL NCTPS SPR TPT
Under line clear
On 30th Jan 2000 the units at NCTPS, ETPS and GMR were tripped resulting in a blackout in Chennai area. The ETS-KTR and NCTPS- KTR feeders were on line clear.
There was a line fault in NCTPS-SPR feeder 2 and tripped at both ends on BE Z1 and subsequently the feeder 1 was also tripped on same indication. At the time tripping the NCTPS units are generating 630 MW and the following feeders are in service. The NCTPS- MOSUR, NCTPS-GDDI and the NCTPS –TPT feeders. The Mylapore feeder is in radial from TondiarpetS/S.The GMR Vasavi generating machines and the TCPL unit in parallel with the 110 kV bus of Gummidipoondi were tripped.
NCTPS units trippings are Unit1 on Over voltage
Unit 2 on house load and subsequently on condensor pressure high Unit 3 on house load and subsequently on Drum level low
ETPS units tripped on Unit 2 Boiler protection Unit 1 Under Voltage
Unit 5 RH system protection
GMR Vasavi units were tripped on Under speed.
The TCPL unit tripped on ID fan tripping
CHAPTER-IX
ANALYSIS:
The tripping of generating units are unwanted for the feeder trippings which is normal. The NCTPS after tripping of SPR feeders feeding the loads in TPT feeder , MOSUR feeder and the radial load of Gummidipoondi.
The units are to be stable after the actuation of house load condition with the load of about300MW in TPT S/S.GDDIS/S and the local loads. On detailed analysis the house lead turning up for the units at NCTPS was checked and found that the valves are not func;tioning properly. After the studies conducted at Neyveli, the improvement in the terminal units are under progress. System, which is unwarranted. The feeding arrangements and the load distributions are to be studied. There are generating stations on 110kV bus system inter linking the 230 kV system, the operation of the system is in low frequency condition of about 48Hz.
Due to the operation of the system under low frequency conditions the machines are facing electromechanical thrust to move the machine to the oscillating condition and causing the tripping. The tripping are unwarranted and are to be avoided. The system has to be studied for its stability.
CASE.3
GMR SBM KTR VYD
CNPT BBGTPS
The 110 kV system links GMR private power project tripping frequently for external feeder faults. The feeders were provided with numerical distance relays of AEG make PD521. The cause for tripping of the machines on over current was found to be that they have adopted the high set value as 2.5 times with instantaneous setting and the same was corrected. For external fault conditions the feeder were tripping on over current indication. On examination of the distance relay if the measurement is not done by the relay the relay will actuate through over current if the current exceeds the setting value. The non-measurement of the distance relay was checked and found to be there is a programming error. During commissioning of the feeders it was noticed that the polarity of the CTs was wrongly selected, the relay was selected through programming for reversal of polarity. The relay is having a programming for the selection of phase rotation; it was selected for positive sequence phase rotation, which is anti clockwise.
Due to selection of polarity reversal and phase rotation the current was shifted to 180 degree causing the measurement.
CASE.4
TTPS PSQ
CKNI MYD TDLR Kundah KYR PGLR
Whenever the under frequency islanding takes place for two blocks seperation of the whole block of the system, the feeders at Chekanoorni towards Meyvadi , Pugaloor feeder and thudialoor were tripping with three phase indication. The feeders are protected with THR3PE18 relays which is having the power swing blocking removal on completion of 3rd Zone time. The power system on two block will be seperated with TTPS-KUNDAH as one block and rest of the system as one block. The TTPS-Kundah block generators are swinging and the swing settles after about 1.7 sec and so the 3rd Zone time was set at 1.7 sec . After that the tripping was not there and M/S Easun Reyrole was requested to provide a deblocking facility for 2 sec. The provision was made in Chekanoorni S/S only. The relay of MM3T also having the same problem but with de blocking time of 1 sec and the relay also requires change.
Due to the islanding conditions the electrical center of the system shifted due to outages. The ABB make relays are provided with 2 sec. Deblocking, the system with that relays are holding the condition.