2 January 2011 - Northern Regional Grid of India Collapse

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MEL 414 Power Plant Technologies SMMEE, IIT Ropar

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MEL414PowerPlantTechnologies

Term Paper

2 Jan 2001 Northern Grid collapsePrashant Pratap Singh (P2008ME1119)

ABSTRACT:

For a modern economy, the electric power system is an axiomatic need. The woes of the power sector aregenerally seen as arising in generation or distribution. However, the collapse of the northern grid on 2 January

2001 is ominous. Over 1500 MW of generation was lost and the entire region plunged into darkness,

subjecting public at large to immense inconvenience and a loss to the tune of 7 billion rupees. It took 1620

hours for the system to limp back to near normalcy. The last major grid disturbance in the region was in

January 1997.

BACKGROUND:

Northern Regional Grid

The Northern Regional Grid covers Uttar Pradesh, Delhi, Punjab, Haryana, Rajasthan, Himachal Pradesh, and

Jammu and Kashmir. It is the second largest interconnected network in the country with an installed capacity

of over 27 000 MW and a plant mix of 31% hydro, 65% thermal, and 4% nuclear. The Region has major therma

power stations located at the pit-heads of coal mines at Singrauli, Rihand, Obra, and Anpara. Major

hydroelectric power stations are located in the Himalayas such as Bhakra, Dehar, Pong, Chamera, Baira-Siul,

Salal, Uri, and the hydro-power stations on Yamuna River in Uttar Pradesh (UP). The large coal-using pit-head

thermal power stations are located in the extreme south-eastern part of the Region. Therefore, there is a large

flow of power from the south-eastern part to the central and western parts of the grid throughout the year.

The following major links connect the large generation stations (total capacity > 6 GW) in the south-eastern

part of the grid to the load centres in Western UP and Delhi.I. Rihand Dadri (500 kV, 1500 MW) HVDC link. Power is transmitted on 2 wires which are 500 kV with

respect to the ground (this is commonly known as a bipole configuration).

II. 400 kV (AC) Singrauli- Kanpur-Ballabhgarh-DadriIII. 400 kV (AC) Singrauli-Lucknow-Moradabad-Muradnagar-DadriIV. 400 kV (AC) Singrauli-Vindhyachal-Kanpur-Agra-BallabhgarhV. 400 kV (AC) Obra-Panki-Muradnagar


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Northern Region Power Grid Map


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Why Does the Grid Collapse?

The distinguishing feature of electricity transport is that electricity cannot be stored: the supply of electricity

should be matched by its demand. If supply tends to exceed demand, the generating stations are asked to

back down. Conversely, when demand tends to exceed supply, load has to be shed. Three specific reasons can

cause a grid to trip:

I. Overdrawal of power by states above the day-to-day directive of the RLDCs. When several states turnerrant the frequency dips. If frequency falls below 47.5 Hz. (the desirable frequency is 50 Hz.), the grid

trips. Cascading effects are possible, if the grid operator does not quickly isolate portions of the grid.

II. Refusal of generating stations to back down. RLDCs determine demand and advise plants to generatepower accordingly. If generation is more than demand the grid frequency rises. If it rises above a

critical value the grid trips. High frequency is experienced mainly during the monsoon months when

the agricultural and air-conditioning and fans load crash due to widespread rains and fall in

temperature. Load collapse to the extent of 4000 MW due to rains, in the Northern Regional Grid, is

common during the monsoon season. During the winter rains, similar load collapse is observed.

III. Faulty equipment/poor maintenance leading to non-functional/under-performing transmission linescan also affect grid frequency. Grid frequency increases in generation-surplus regions and decreases in

generation-deficit regions.

IV. Other major causes of the blackout can be summarised as follows: Long duration of equipment (converter transformer) outage in the HVDC link Heavy pollution and fog causing insulation flashovers Inadequate preventive control Inadequate emergency control

Build up to collapse

In the early hours of 2 January 2001, the demand was much less than the availability, following idespread

rains, and a few thermal machines had been closed down to contain the frequency. However, there was aconstraint in the transmission capability in the eastwest corridor due to outage of one of the HVDC bi-poles

and a reduction of the power capability of the other pole to 500 MW. This reduced further when parts of the

two 400-kV links owned by the STU tripped in quick succession due to insulator flashovers. This in turn led to

heavy loading of the remaining links, with power flow touching 800 MW in one of the 400-kV lines, and

cascade tripping of the remaining lin ks. Eventually the grid split into two. In the western part, the frequency

dropped due to shortfall in generation and the subsystem collapsed, while in the eastern part the frequency

shot up to about 53 Hz, tripping all the running machines and leading to the eventual collapse of the

subsystem. Only a few gas turbine units in Delhi and one nuclear unit survived on local load. All other nuclear

units tripped and were poisoned out.

THE COLLAPSE

Following widespread rains on 1 January 2001, the demand in the Northern Region had reduced. A few

thermal units in Punjab and Haryana had been closed due to low demand. After 10 p.m. of 1 January 2001, the

frequency started rising and backing down had to be resorted to at a number of thermal power stations. The

salient events that led to the collapse of the Northern Region Grid (NRG) are brought out below:


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Time (Hrs.) Event

1st Jan, 2001 1st Jan, 2001

23:21, 23:33 and 23:41 Transient faults on the operating pole-1 of HVDC Rihand-Dadri

(POWERGRID) line. The line continued in operation with

successful auto-re-starts.

23:49 Singrauli and Rihand Stations were asked to back down from

1840 MW to 1620 MW and from 910 MW to 810 MW

respectively.2nd Jan,2001 2nd Jan,2001

00:02

Transient faults on the operating pole-1 of HVDC Rihand-Dadri

line. The line continued in operation with successful auto-re-

starts.

00:17 Pole-1 of HVDC bi-pole was put on reduced voltage mode of

operation thereby reducing power flow on this line from 750

MW to 500 MW.

01:05 400 kV Obra-Panki S/C (UPPCL) line tripped on fault and

remained under breakdown.

01:07 Frequency goes above 51.0 Hz, NRLDC asked Singrauli and

Rihand Stations to back down from 1620 MW to 1540 MW and

from 810 MW to 730 MW respectively.

02:45

02:47

03:26

03:41

04:31

400 kV Agra Ballabhgarh line tripped on Y-phase earth fault

and auto reclosed.

03:11 400 kV Panki Muradnagar developed fault. Circuit Breaker at

Panki end did not operate resulting in back-up protection

operation of Main bus A. 400 kV Panki Kanpur II and ICT -II

(inter-connecting transformer) at Panki connected to this busalso tripped.

03:12 400 kV Unnao Agra line also tripped on fault.

03:18 System frequency rose to 51.2 Hz.

03:31 220 kV Narora Atomic Power Plant Muradabad tripped on

fault.

03:35 220 kV Panki Fatehpur tripped on fault.

03:33

03:54

400 kV Agra Kanpur line also tripped on B-phase earth fault

and auto reclosed.

03:50 Load dispatcher asked Singrauli Generators to further

backdown from 1480 to 1320 MW. At 04:38 hrs, 220 kV Panki-Fatehpur line tripped on fault. With all these outages, the system could not be kept in synchronism and the following lines

tripped (as a consequence of relay response to an out of step situation) and the system

separated naturally into 2 subsystems.

04:38 400 kV Lucknow Moradabad, 400 kV Kanpur Agra, 400 kV Kanpur Ballabhgarh, East West separation of Northern Grid took place. The separation of the system into 2 islands need not have led to a complete blackout.


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Since one island had excess generation, quick tripping of a few generators or govenor actioncould have stabilised frequency. In the under-generated island, under-frequency load

shedding would have stabilised the frequency. However neither of these emergency

measures were in place. Therefore,

04:40 Frequency of western part dipped and sub-system collapsed.

04:40 04:44

Frequency of eastern part shot up to more than 52.5 Hz. All

running machines in eastern part tripped on over frequency

and sub-system collapsed

Practically, whole of North India was plunged into darkness. A few generators survived by separating

themselves from the rest of the grid and kept running supplying only their "house load". After the blackout, it

took almost 16 hours to fully recover and reconnect the grid.

RESTORATION:

If a blackout (a near total loss of generation and load) takes place, efforts have to be taken to bring back the

system to a normal state at the earliest. It may surprise you to know that this (black starting!) is not an easy

task. We shall see why in this lecture.

Once a generator is tripped, restarting it requires a significant amount of power. Power is required for 2 types

of activities:

Survival Power: For emergency lighting, battery chargers etc. Usually the requirement is 0.3% of thegenerator capacity.

Startup Power: For starting power plant auxiliaries (pumps etc.) Interestingly, nuclear and thermalunits require approximately 8 % of the unit capacity for auxiliaries alone! Therefore, a 500 MW

generator requires approximately 40 MW for running its auxiliaries.

Hydro and Gas units, on the other hand, require only about 0.5-2% of unit capacity for auxiliaries and can be

started usually from in-house DG sets.

MAJOR STEPS REQUIRED FOR RESTORATION:

Islands which have survived need to be stabilised for frequency and need to be used for starting otherunits

Hydro/Gas units which require less startup power need to be started using in-house DG sets. Larger thermal units need to be fed "startup power" from: 1) Islands which have survived 2)

Blackstarted generators 3) Other synchronous grids (temporarily)

Started units are synchronised with one another. Loads and Generation have to be matched as much as possible to avoid large frequency variations.

Governors have a major role in stabilizing frequency in an island.


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Problems in Restoration

a) Securing Islands

After a blackout a few islands may survive due to separation of the system in time. A few hydro or gas

generators could be blackstarted using in-house D-G sets. Therefore some small pockets will be there in the

otherwise blacked out grid wherein generators are supplying some loads. However, the situation in these

islands is usually precarious due to the small number of generators within the island (having very littlecumulative inertia).

Recall that the initial rate of change of frequency is determined by cumulative machine inertia and the initial

load-generation imbalance, while the final settling frequency is determined by the governor and load

frequency characteristics (see Module 3).

Therefore if the load in the island is fluctuating (for instance, traction loads), the rate of change of frequency

within the island due to fluctuating loads may be quite large -- large enough for the island to collapse due to

excessive frequency variations - causing generators to trip. Therefore control of generated power (by

governors) and frequency based tripping or energisation of load is important.

Black-starting of large generators is done by availing startup power from other started generators or islands.

Startup power may also be availed from neighboring synchronous grids if an AC transmission link exists

(normally disabled). Unfortunately, startup power cannot be availed via DC links (which use AC line voltagesfor commutating thyristors), because AC voltages are not available in the system which is blacked out.

Therefore a generator at Vindyachal (near the border of the western region and northern region grid of India,

which are not synchronized but exchange power through DC asynchronous links during normal conditions) can

avail startup power through an AC line from the northern grid.


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b) Extending Power to Loads from Generators which are black-started

The next step in power system restoration is to supply loads from black-started generators. Some of these

loads may be in the form of the startup (auxiliary) loads of other larger generating plants which need to be

black-started.

These loads are supplied via transmission lines. Enregising a transmission line initially without any load can

cause over-voltages. This is avoided by:

Energizing fewer high voltage lines Operating generators at minimum voltage levels (by keeping filed excitation low) Deactivating switchable capacitors


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Connecting shunt reactors and tertiary reactors Adjusting of transformer taps Pick up loads with lagging power factor Charging more transformers Charging shorter lines Operating synchronous condensers / SVCs where available Avoiding charging lines with series capacitors

c) Re-integrating the grid

As mentioned before, some islands which have been secured should be connected with each other so that the

system cumulative inertia increases, a better generation-load balance can be achieved by encompassing a

larger set of loads and generators, and better redundancy in transmission and generation is achieved.

Note that an important step in reconnecting islands to one another is "synchronisation". While each generator

has synchronising facilities, the interconnection of two islands may have to be done at some bus in the

network wherein such facilities are available. The basic requirements for successful synchronisation of two

systems are the same as those for an individual generator connected to a large grid (see Module 2). In

particular, the frequencies should be practically the same and phase angular difference at the instant of

connection should be small. If two systems are connected at an inappropriate instant, then the generators in

both islands will not synchronize, and the situation will be akin to an out-of-step scenario; the link will have to

be disconnected.


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ACTUAL RESTORATION OF THE NORTHERN GRID

The sequence of actual restorative actions which were taken after the Northern Grid Collapsed in January

2001 is given below

The system was restored in two parts.

The south-eastern part was restored by taking power from Western Region (a neighbouring grid)through an AC line which runs parallel to the HVDC back-to-back station at Vindhyachal.

The western part was restored after starting Bhakra (hydro) machines.


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Chronology of restoration process of Eastern and Western parts is given below:

a. RestorationofEasternPart(2ndJanuary2001)Time (Hrs.) Event

04:59 OnemachineofRihand(Hydrogeneration)wasstarted.

05:10

StartuppowerfromWesternRegion(WR)wasextendedto

SingrauligeneratorsthroughACbypassofHVDCback-to-

backstationatVindhyachal.

05:38

WRpowerwasfurtherextendedtoRihandGeneratorsby

charging400kVSingrauliRihandI.

06:32 Powerwas also extended to Kanpur by charging 400 kV

VindhyachalKanpurline.

07:01 400kVKanpurPankiwascharged.

07.42 Rihand(H)-Anpara132kVlinecharged

08.15 Anparaunitclearedforlightup.

12.38 ThepowerwasextendedtoMainpuri

Between09:11and11:20

Followingunitsweresynchronized:

Singrauliunit(500MW)at09:11hrs Rihandunit(500MW)at09:54hrs. Singrauliunit(210MW)at10:48hrs Singrauliunit(210MW)at11:20hrs

11:44 WRPowerwasextendedfromKanpurtoAgraat11:44hrs

bycharging400kVKanpurAgraline,and

11:57 furthertoBallabhgarhand

12:01 Dadri

12:17 400kVBallabhgarhDadritrippedonovervoltage

12:18 BallabhgarhInterconnectingTransformer(ICT)waschargedtoextendpowertoBallabhgarh

12:39 400kVAgraBallabgarhlinetripped

12.50 Anparaunit-synchronised

b. Restoration of Western PartAs specified in Black Start Procedures, immediately after the grid failure Bhakra hydro station

attempted two times to revive the system at 05:05 hrs. and 05:40 hrs. but the machines could not be

stabilized.

Time Event06:00 Unit 4 at Bhakra (L) started 07:07 Power was extended to Panipat by charging 220 kV Bhakra

Ganguwal Dhulkote Panipat sections.


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07:28 Panipat Dadri line was charged. This line however, tripped on overvoltage.

07:33 The line was again charged but tripped immediately on over voltage.

08:47 The line was again charged from Panipat end utilizing an opencircuited 220/400 kV transformer at Dadri as a reactor to limit overvoltage.

09:08 Dadri Ballabhgarh was charged but tripped immediately along withPanipat line on over voltage.

09:19 Panipat Dadri line was again charged. Dadri Gas Turbine generatorssynchronized and started generating 200 MW.

Between 09:29 to 09:54

The following 400 kV lines were charged from Dadri end

09:29 hrs Dadri Ballabhgarh,

09:39 hrs Dadri Murad Nagar (tripped at 10:10 hrs),

09:48 hrs Ballabgarh - Agra

09:54 hrs Dadri Mandola I

10:00 hrs Agra Auraiya

10:16 Bhakra island collapsed due to under frequency.

10:33

1st unit at Bhakra(R) station started but tripped at 10:42 dueto large fluctuations in loads.

It was again started at 10:46 hrs but again tripped at 10:52due to same reasons as above.

The unit was again started at 11:00 with manual regulation ofload by locking the load limiter in steps.

11:14 Power was extended to Panipat

12:04 220/400 kV Inter-Connecting Transformer 2 was charged.

13:08

Power to Badarpur was extended from Bhakra system through

Panipat - Charkhi Dadri - Ballabhgarh. Bhakra power was not

extended to Dadri as it received WR power from Ballabhgarh.

13:32 The eastern and western parts of the grid were synchronizedANALYSIS

The enquiry carried out by the CEA committee and the submission made during the public hearing held by the

CERC reveal the following.

i. There was a general lack of grid discipline. For example, (1) the generators had not been on free-governor mode operation although this was required by the IEGC (Indian Electricity Grid Code), (2)

instructions given from the RLDC (regional load dispatch centre) were not promptly acted upon, and (3)

under frequency relay schemes were not fully operational.

ii. The role played by the RLDC was not adequate or effective. Its orders for backing down, for example,did not reflect the urgency or the gravity of the situation. Also, it does not appear to have considered

other options for congestion management like increase in hydro generation in the western part,

coupled with load shedding. This might have helped avert the incident as it was not triggered by a

sudden event and the system depletion was gradual.

iii. The maintenance and performance of the transmission system was not adequate. The insulator flash -overs and the resultant tripping of the two important links in the eastwest corridor occurred due to

the poor maintenance of the 400-kV lines owned by the STU, which pass through the polluted areas


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near Panki. Similarly, the performance of the HVDC link, especially of the convertor transformers

manufactured by BHEL (Bharat Heavy Electricals Ltd), was not satisfactory and affected the

transmission capability in the corridor. Such lapses could jeopardize the security of the grid since the

system is planned to an n-1 contingency criterion. There were also inadequacies in the switchgear and

reactive power compensation devices at some locations, as the restoration process revealed.

iv. The load dispatch and communication facilities are not adequate. Lack of time synchronizationbetween recording instruments installed at different locations makes it difficult to correctly establish

the sequence of events.

v. The restoration procedure was slow. Extending supply and build up of load was difficult due toequipment problems, delays in providing start-up power, lack of coordination, etc. The black start

procedure and the grid protection scheme must be reviewed.

vi. There is need for better training and capacity building for grid operators.THE CERC ORDER

The CERC has looked into the incident primarily as part of its function to regulate interstate transmission. The

ambit of its enquiry was restricted to the role of various functionaries in ensuring compliance of the provisions

of IEGC.

In its order, the CERC noted that there was blatant violation in operating the grid as per the IEGC. While it has

not taken action against the erring bodies, it has warned the concerned functionaries of penalties in case of

future noncompliance. It has severely criticized the CTU/RLDC for not implementing the grid code with ful

commitment and for not managing the grid efficiently. It has directed the CTU to see if it is necessary for the

RLDC to control the state level generation as well if it has to have adequate control over the grid and maintain

its security.

ACTION PLAN OF MINISTRY

The Ministry of Power has decided to adopt a time-bound action plan for various organizations to take

remedial measures to prevent the recurrence of such events. This covers tuning of governors, provision of

self-start facilities at gas turbine stations, implementation of revised under frequency relay scheme, review of

schemes for protection, islanding, and black start, simulator training for dispatch engineers, etc. A close follow

up of the action plan is proposed.

REFORM AND REGULATORY ISSUES

The collapse of the Northern Grid and the similar incident in the Eastern Region recently have brought to fore

certain reform and regulatory issues. These include the delineation of the interstate transmission system and

the responsibility of the CTU for STU-owned lines; command hierarchy in grid operation; desirability of

CTU/STU looking after the load dispatch functions; overlaps in roles, if any, of CERC, CEA, regional electricityboard, and the state regulatory commissions in enforcing grid code; and urgency for putting in place suitable

commercial mechanisms to promote grid discipline.

The collapse of the grid highlighted once again that integrated operation of large grid systems is a complex

task requiring orchestrated functioning of all agencies connected to the grid (generators, transmission

companies, and generation companies), a well-equipped hierarchical load dispatch system manned by trained

professionals, and a comprehensive grid code.


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REFERENCES:1. http://www.cdeep.iitb.ac.in/nptel/Electrical%20Engineering/Power%20System%20Operation%20and%20Contro

l/Course_home_L30.html

2. http://nrldc.org/nrldc/powermaps.asp3. http://www.nrldc.org/4. http://www.teriin.org/index.php?option=com_publication&task=details&sid=258

2 January 2011 - Northern Regional Grid of India Collapse

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