PRACTICES ADOPTED IN NLDC & RLDCs
These are in addition to S.O.P
S. No.
Function
Frequency control
management
ERLDC
High frequency

Purulia Pump storage hydro units can be run into pump mode, in consultation with SLDC, West Bengal

The Hydro stations of Bhutan power system exporting power to India are not covered commercially under
ABT mechanism. Backing down advice on account of high frequency conditions may be issued to stations
at Tala, Chukha and Kiruchu of Bhutan system only after all possible remedial measures are exhausted.
However, in case the stations are noticed generating extra with respect to schedule issued , ERLDC shall
attempt revising the generation schedule with due revision of constituents drawal schedule.
Low frequency

If any unit of Purulia Pump storage is operating in pump mode and if the concerned beneficiary is over
drawing, ERLDC shall advise the concerned SLDC for discontinuing the pump operation.

The Actual receipt from the Hydro stations from Bhutan is less than the schedule, because of some
technical reasons like low inflow etc., ERLDC may suo motto revise the generation schedule downwards
with corresponding downward revision of drawal schedules of the respective constituents who have share
on such stations. Such downward revision shall be duly informed to the concerned beneficiaries with an
advise to curtail their drawal from the grid.
Power flow management
Power Flow which will critically load a circuit during probable N-1 outage needs regulation in addition to
deterioration of other grid parameters like voltage etc.
 Hvdc power number is changed in consultation with NLDC
 Generation Rescheduling vide IEGC regulation 6.4.12, 6.5.5, and 6.5.16 .In case of criticality in North
Bengal , liquid power is indented from Bhutan/NHPC HEPs. In case of congestion in ER-NR corridor , PPSP
plant of WBSEB can be run into pump mode.
 Curtailment of Scheduled Transactions vide 6.4.12, 6.5.28, 6.5.30 and 6.5.31 of IEGC the transactions shall
generally be curtailed in the following sequence
1
2
a. Deviation from schedule
b. Short term bilateral transactions
c. Short term collective transactions
d. Medium term transactions
e. Long-term transactions
 Pre studied congested nodes like violation of Flow gates , 220 kv jaypore-jaynagar d/c , 400 kv FstppBerhampur , 400 kv MPL-Maithon D/C etc are closely monitored.
Contingency handling
3
3)
4)
5)
Voltage control and
reactive power
management
4
1)
2)
CONTROL ROOM should not be used for management information system.
Immediate Fault analysis should be done with pmu and relay details .Test charging should be based on
that.
Restoration manual should be present in control room.
Necessary revision in schedule should be carried out.
Flash report should be prepared.
Eastern Region Grid has a very good spatial distribution of generation rendering a better voltage
profile across 400 kV and 220kV network. However, in some pockets of system where radial loads
are fed, occasional low voltage is experienced. With commissioning of HVDC Bheramera (Bangladesh) and export
of approx. 500MW , nodes in south Bengal like Jeerat & Subhasgram witness extremely low voltges . 400kV stations
at Jeypore occasionally experience low or high voltages due to the low fault MVA of these stations. As the HVDC
station Gajuwaka is also connected to Jeypore having low fault MVA, any power flow change associated with
switching of filter banks operation render at times wide fluctuations in voltage at 400kV level.
Posts commissioning of Tala Transmission system exhaustive 400kV networks have been laid. This part of the
network is essentially used to evacuate the hydro power from Bhutan system, generation of Teesta-V HPS and
surplus hydro power of North Eastern Grid during monsoon. But during low hydro of winter season , several lines
have to be kept in this corridor to control voltages.
ERLDC examines the pattern of VARh drawal by regional entities at various ISTS interconnection points at HIGH/LOW
voltage from the weekly special energy meter data. Effort shall be made to identify such ISTS points where regular
VARh charge payment to regional pool takes place. Necessary measure shall be initiated to set optimum ICT taps so
as to minimise such payment to pool.
ERLDC monitors the generation/absorption of reactive power of all generating units on bar up to the limits of their
respective capability curves during high/low voltage conditions.
Deviation control
5
ERLDC may direct any SLDC/ SEB/distribution licensee or bulk consumer connected to the ISTS to decrease drawal of
its control area by a certain quantum (ACE is taken into account) in case of overdrawal. In case repeated warning
messages from ERLDC to curb over drawal does not yield any results, ERLDC will instruct the defaulting constituents
to disconnect identified radial feeders within their respective systems for reduction of over drawl. Concerned
constituents should send compliance report to ERLDC in this regard after taking necessary action .
If any ISGS is under-generating, it may be reminded to generate as per schedule. If such generation increase is not
possible due to any technical constraints, the concerned ISGS may be advised to reduce its Declared Capability.
ERLDC would then correspondingly reduce the drawal schedules of all concerned beneficiaries (including outside
regions) and advise them to maintain their net exchanges as per their respective revised schedules.
Congestion management
6
Eastern Region being strategically located, is connected to all the other regions. The typical generation dispatch
pattern during monsoon and winter, demand scenarios within the region as well as of the other regions results in
congestion in some corridors of the Eastern Network. These congestions are well identified. The anticipated power
flow pattern along these flow gates has a direct impact on the Total Transfer Capability in different seasons. While
carrying out the system studies for arriving at the TTC and ATC figures anticipated flow pattern along these flow
gates need to be checked under and in real time require to be monitored for a secured operation. The various flow
gates and their characteristics and actions required to be taken by ERLDC operators during congestions in these flow
gates are :
Flow gate –I ( allowable limit≈ 4000MW) 400kV Kahalgaon-Banka-Biharsariff D/C
400 kV Kahalgaon-Lakhisarai-Biharsariff S/C
400 kV Kalgaon-Biharsariff S/C
400kV Kahalgaon-Barh D/C
Scenarios:
•
High drawl by NR
•
Injection from WR and SR
Flow gate –II ( allowable limit≈ 1200 MW or less)
400kV Farakka-Malda D/C
Scenarios:
Winter ( period Dec to Mid Feb)
Low Hydro Availability at Bhutan( Tala and Chukha), Teesta, and NE Region
High winter Demand in Northern Region
•
•
•
Defence mechanism
7




Automatic Under Frequency Load Shedding Scheme
Special Protection scheme a ) SPS for power transfer to Bangladesh b Special protection system at SEL c)
Power Demand Over (PDO) ride at Gazuwaka and Talcher
Special protection system at HVDC Talcher( SPS 450 and SPS 1000) . Modification in Talcher-Kolar SPS in ER
Region due to Synchronisation of SR grid with NEW grid (Additional 600MW Gen Reduction)
Islanding Scheme

8
Scheduling
Reporting system
Real Time Event Information : any of the following events require reporting by ERLDC/ Regional
Entity Vide clause 5.9.5
i)
ii)
iii)
iv)
v)
vi)
vii)
viii)
ix)
9
Violation of security standards
Grid indiscipline
Non compliance of RLDC’s instructions
System islanding / system split
Regional blackout / partial system blackout
Protection failure on any element of ISTS and or any item on the agreed list of the intra-state systems
Power system instability
Tripping of any element of the regional grid
Sudden load rejection in regional entity’s control area
Mandatory information to ERLDC by Regional Entity

Any tripping of an element under the list of important elements of regional grid, whether manual or
automatic, shall be intimated by the control centre of the regional entity to ERLDC in a reasonable time
say within 10 minutes of the incident. Along with the tripping intimation, the reasons for tripping (to the
extent known) and the likely time of restoration shall also be intimated. Such information can be on
telephone, fax or e-mail.

Any operation planned to be carried by a regional entity which may have an impact on the regional grid or
on any of the important element, shall be reported by the concerned SLDC to ERLDC in advance.

Any operation planned to be carried out on the instructions of ERLDC which may have an impact on the
system of a regional entity shall be reported by ERLDC to the concerned SLDC in advance.

The intimation and the exact time of revival of any element under the category of important events will
be furnished to ERLDC as early as possible.
Reporting system
The details of event reports and periodic reports to be prepared and issued by regional entities / ERLDC are as
follows:


Operational security




10



System restoration
procedures
11

•
•
•
•
•
•
All regional entities would endeavor to operate the connected generation and reactive power management
devices such as Capacitors, Reactors, Synchronous Condensers, Fixed Series Capacitors (FSCs), Static Var
Compensators (SVCs) etc in a manner which enables stable voltage behavior at various points of the grid under
different operating conditions
All regional entities would also maintain in good operating conditions of all control measures such as defence
mechanism, SPS, U/F & U/V load shedding, AVRs, PSS, FGMO, Operating reserves, emergency back-up power
supplies etc
In order to damp out the low frequency oscillations in the system, the power system stabilizers on the
generating units would be tuned as per the programme drawn at ERPC forum in consultation with the
constituents.
In case of a 2 main & transfer bus system at any sub-station, it must be ensured that the segregation of feeders
on the different buses is uniform. It would help in minimizing the effect on the system in case of a bus fault.
In 400kV substations having one and half breaker scheme, it must be ensured that each feeder remains
connected to both the buses so that any bus fault does not result in inadvertent outage of feeders. In case any
element, say a line or an ICT or a bus reactor, is expected to remain out for a prolonged period at such
substation, the main and tie breakers of such elements should be closed after opening the line side isolator.
This should be done after taking all suitable precautions to avert inadvertent tripping.
The substation operators must ensure the above condition even when any lightly loaded line is opened to
control over voltage. Such opening of lines is generally superimposed over other line outages on account of
faults created by adverse weather conditions resulting in reduced security of the system.
Single pole auto reclose facility on 400kV lines should always be in service. Approval of ERLDC would be
required for taking this facility out of service. Likewise, in case any transfer breaker at any 400kV substations
having two main and transfer bus scheme is engaged, the same would be informed to ERLDC.
Secure generation
Secure transmission
Restore interconnection with neighbours
Avoid utility plant damage
Avoid consumer plant damage
Restore demand
Reparallel islands taking into account the available facilities / constraints.
Shutdown & outage
procedure
Procedure for Availing the Outage in Real Time


12
In the event of tripping of any important elements, the preliminary event report with possible
details shall be sent by the SLDC of the concerned regional entity to ERLDC within a period of three hours
of the occurrence of the event and the detailed event report in the form detailed under the section
5.9.6(C) of IEGC (contents vide Annexure XII) shall be sent within the next day.
Such report shall follow the telephonic / flash reporting by the concerned SLDC say within a
reasonable time say within 10 minutes of the occurrence of the event
The agencies involved shall ensure availing of outages as per the approved schedule time.
Request for outages which are approved by OCC must be sent by the owner of the transmission asset at
least 3 days in advance to ERLDC by 10:00 hours.

In case the owner is not availing the OCC approved outage, the same shall be intimated to the
ERLDC at least 3 days in advance.

On the day of outage, the outage availing agency shall seek the code for availing outage from
ERLDC/NLDC (wherever applicable). The agencies involved shall endeavour to avail the outage with in
15mintues of availing the code but not later than 30 minutes. In case, due to any contingency, the outage
could not be availed within 30 minutes, a fresh code needs to be obtained by all concerned agencies
stating the reason there of Record of scheduled and actual time of outage and restoration shall be
maintained at ERLDC/NLDC.

i)
ii)
iii)
iv)
v)
vi)
vii)
viii)
13
14
15
Suomoto action & feeder
opening
SCADA/PMU displays
Data Exchange/
Communication System/It
Tools
While issuing clearance of the shutdown ERLDC shall clearly mention the following( vide format at
Annexure IX)
Message no.
Name of the element /elements which shall remain under outage.
Name of the agency /agencies availing the outage.
Date and duration of the outage
Nature of the outage
Reason for availing the shutdown
Specific network /system conditions to be maintained including impact of the outage
Sequence of switching instruction if any