Additional Agenda for the 90th Meeting of PCSC scheduled to be
held on 27th May, 2020 (through VC/Online) Page 1
Southern Regional Power Committee Bengaluru
Additional Agenda for the 90th Meeting of Protection
Coordination
Sub-Committee of SRPC to be held on 27th May, 2020 through
VC/Online
1. Grid Disturbance
Sl.N
o
Details of Event Date &
Time
Reason Remarks Category
1 Complete Outage
of 220kV
Shimoga Station
of KPTCL
19-03-2020
at 17:08 Hr.
During antecedent conditions,
all the elements were
connected to Bus-1 North bus
at 220kV Shimoga SS.
Triggering incident was R –N
fault in 220 kV Shimoga-
Varahi line-2 due to insulator
decapping. At the same time,
220 kV Bus-1 BBP
maloperated at 220kV Shimoga
SS. Since all the elements were
connected to Bus-1, this
resulted in the complete loss of
supply at 220kV Shimoga SS
160 MW GD-1
PGCIL (SR-1) had given the following Agenda items for discussion
in PCSC-90:
2. Resonance problem in over compensated 765kV & 400kV
lines
Problem of resonance during tripping of 400kV NPKunta - Hindupur
line-2 was observed at
18:14 Hr. on 09-06-2019. R-phase to earth fault occurred in line
& line tripped due to
operation of over-voltage stg-2. Voltage swell was observed in
DR (Rph to earth voltage-
462kV and DR, EL attached) and this tripping was also discussed
in 85th PCSC.
PGCIL referred the issue was to their CC/AM & CC/Engg and
they have opined that
resonance in the 400kV NP Kunta – Hindupur Lines during Single
Phase Earth Faults may be
due to Line Reactor at Hindupur end and advised to extend trip
signal to Switchable Line
Reactors for Single Phase E/Fs.
In view of above, PGCIL proposes to extend trip signal to
Switchable Line Reactors in 400kV
NP Kunta – Hindupur – 1 & 2 lines at Hindupur end after
study by SRPC/SRLDC. For other
Line Reactors extending trip signal shall be decided on SOS.
The issue may be discussed is meeting
3. Implementation of A/R of 220kV Lines through under voltage
interlock with 0.85
PU pickup at Warangal and NP Kunta Substations
Additional Agenda for the 90th Meeting of PCSC scheduled to be
held on 27th May, 2020 (through VC/Online) Page 2
DGA gases in 315 MVA Warangal ICT-1 is observed to be increasing
due to frequent faults in 220kV Lines. To avoid further stress on
ICTs and Circuit Breakers, PGCIL (SR-1) is proposing to implement
A/R reclose at POWERGRID end only after successful A/R at SEB end.
A/R scheme shall be implemented using under voltage interlock with
0.85 PU setting.
The issue may be discussed in meeting for concurrence.
4. Frequent Failure of PLCC Link of 400kV Warangal –
Bhoopalapalli – 1 and 220kV
Warangal – Nagaram D/C
The PLCC link of 400kV Warangal – Bhoopalapalli – 1 and 220kV
Warangal – Nagaram D/C is frequently failing. This may cause
delayed clearance of line faults, if any. To avoid delayed
clearance of line faults during PLCC failures, PGCIL (SR-1) is
proposing to reduce Zone- 2 timer to 200 msec. The issue may be
discussed is meeting for concurrence.
5. Providing additional O/C Protection in Bus Sectionaliser at
400kV Nellore
Substation
At 400 kV Nellore Substation, 400 kV Bus is connected to 400 kV
Bus of Nellore-AP station through Bus-Sectionaliser. In case of any
un-cleared fault in SEB portion, all the feeders connected to 400
kV Nellore shall be isolated on operation of Remote end Zone-2
protections. To avoid black-out of station for un-cleared faults in
other section, PGCIL (SR-1) proposes to provide additional O/C
protection in Bus-Sectionaliser. The issue may be discussed is
meeting for concurrence.
6. Providing additional Backup Impedance Protection for ICTs
At present back-up protection of Transformers is being provided
by installing Directional over Current and Earth-fault protection.
This back-up protection is being coordinated with the downstream
and upstream lines distance protection zones. The co-ordination of
overcurrent protection requires exact information of the station
fault level and the in-feed values. In the evolving Indian Power
system, with the addition of new generation and transmission, these
values vary with time. Further complications arise in cases where
several parallel transformers are connected at a substation and
zone-3 reach of line encroaching beyond transformer into the next
lower voltage level. In view of constraints being observed in
co-ordination of overcurrent relays, POWERGRID is installing
Impedance Relays for back-up protection of 400/220kV ICTs on HV
side and for 765/400kV ICTs on both HV & IV sides. The CBIP
manual of protection system mentions that under impedance relays
can be used as back-up protection for the transformer. It shall
consist of multi-zone impedance relay on the HV side or on LV side
of the transformer looking into transformer. In the CEA technical
standard also for connectivity to Grid Part-III, Sec-4, Para-2 d,
it has been mentioned that the back-up protection to transformer
could be provided through either back-up overcurrent relay or
impedance relay.
