doc regarding indian balckout juli 30-31st.doc

7/28/2019 Doc regarding Indian Balckout Juli 30-31st.doc

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About the Indian Grid Hierarchy:Indian power system is operated as five Regional grids viz., Northern Regional grid (NR),

Western Regional grid (WR), Eastern Regional grid (ER), Southern Regional grid (SR) andNorth Eastern Regional grid (NER). The control of the grid is planned to be done at four levels

of hierarchy namely

1. National Load Despatch Center (NLDC)2. Regional Load Despatch Center (RLDC)

3. State Load Despatch Center (SLDC) and4. Area Load Despatch Center (ALDC)

http://www.desismartgrid.com/2012/08/indian-power-grid-blackout-reasons-and-future-requirements/2/

[National Load Dispatch Centre (NLDC) was formed in Delhi in 2009 to manage the inter-regional exchanges, in addition to the existing Regional Load Dispatch Centres (RLDCs) which

had been managing the intra-regional power balance. These load dispatch centres (LDCs) are

autonomous subsidiaries of the public sector Transmission System Operator (TSO) called thePower Grid Corporation of India. Their priority is to ensure generation-load balance throughout

the network.

The arteries for these cross-country flows are a network of 400 kV transmission lines.During the first wave of electricity reforms in India in the early 1990s, the plan to connect the

regional grids into a national grid was conceptualised, following which all regional grids, except

the southern region achieved interconnectivity. The synchronous operation of these regionalgrids, forming the combined grid called the North-East-West (NEW) Grid, eases the power

exchanges among these geographic regions to manage the surplus and deficit generation. A

power transmission superhighway was commissioned to tightly link these regions together.This corridor which is made up of high capacity lines connecting Agra and Gwalior in the west,

to Sasaram in Bihar in the east, allow voluminous flows of power from thermal power stations in

the east to the load centres in the west and north.

Whenever the demand in a regional grid exceeds the supply, the frequency of the grid tends to

drop.To compensate, the generators all over the interconnected system start pumping more

power into the network which then requires more power to be transmitted over the transmissionlines. Carrying power above the rated capacity of the transmission lines results in increased

thermal stresses and when the safety limits are crossed, a protective shutdown of the lines is

activated. In turn, this partial shutdown of some of the grid connectors may lead to yet morestress and the subsequent shutdown of the other lines in the network, followed by turning off of

generators and eventually causing a blackout. The sequence of events in July 2012 closely

resembled this classic spiral breakdown effect of a power system.http://esi.nus.edu.sg/publications/2013/04/24/india-s-blackouts-of-july-2012-what-happened-

and-why-]

NR-ER-NER-WR (termed as NEW grid) connected synchronously, thus maintains same

frequency

SR connected asynchronously with the NEW grid through a HVDC links

In all, there are 5 regional grids, 31 state grids and 100 plus area-wise grids in India. Further,

internal to area grids, local distribution area grids are also available. Each grid has its owndispatch center.


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The mechanism has been extended recently to intra-state level. At present the states are the

participants in the central ABT scheduling mechanism. The RLDCs issue day-ahead schedules incoordination with the states and states have to conform to these fixed schedules on the day of

operation. Any deviations are accounted for by the Unscheduled Interchange (UI) mechanism as

a part of ABT. The UI rate is a function of system frequency at the time of operation, the

definition of which is updated time to time by the Central Electricity Regulatory Commission

(CERC).

The blackout-1 on 30-July-2012 (around 2:33hrs) occurred in the NR grid followed by blackout-2 on 31-July-2012 (around 13:00 hrs) which occurred in the NEW grid, after the NR was

restored from the previous black-out and synchronized with the NEW grid. There was also some

low significance tripping events during 30-July-2012 and 31-July-2012.

Blackout-1:

Most of the media coverage on the issue of the black-out-1 cite over-drawl of power by Northern

states as the reason. The over-drawl may be due to the frequency approaching 50.46 Hz justbefore the event, which provides apparently free power to the over-drawing states as per the UI

mechanism. This happened to overload the transmission lines, resulting in line tripping andpower re-routing through the other connecting lines. This led to a cascading line trippings, thusisolating NR from the rest of the NEW grid. Whereas WR-ER-NER survived the situation, NR

failed!

Around 300 million people were affected. The blackout had spread across Nine North Indian

States, including the capital city, New Delhi.

As per NLDC report, the antecedent conditions confirm the inoperation of 400 kV Gwalior

Agra (ckt-2) and 400 kV Zerda Kankroli. As explained above, overdrawl by northern states

overloaded and thus tripped 400 kV Gwalior Agra (ckt-1), and impedance between WR and

NR suddenly increased. With no direct tie between NR and WR, the only link between the two isthrough ER. After about 3.35 seconds, the angular separation between WR and NR was

gradually increasing which is confirmed by the recorded frequency differential of about 0.14 Hz

(substantially constant) between Mumbai and Kanpur.At this point the ER NR ties would have snapped, owing to overloading with the re-routed

power to separate the NR from the rest of the system.

Blackout-2:

The reason for this black-out can be a sudden load pick-up in NR during the afternoon which

caused a overloading and subsequent cascade tripping of transmission ties with WR and ER. The

NR not learning a lesson from the previous day black-out were again the culprit, committing the

crime of overdrawing in a system which has just recovered a major black-out. Besides NRgetting isolated from the rest of the NEW grid, over-speeding of generators in the ER and NER

caused generators in these regions to trip resulting in a bigger black-out spreading across threeregions affecting 640 million people altogether.


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Why only the Northern states in the NEW grid were affected?

WR is the only region in the NEW grid which has survived. Many of the experts in the internalIndian technical forums say that the survival is mere luck. However, when we thought on

seriously for the reason, we have found some very interesting facts. We have recollected the

discussions we had with Maharashtra state load dispatch center (comes under WR) in June12.

Maharashtra is the main load center in the western region with more than 15GW load met ondaily average basis and also a participant in the central ABT/UI mechanism. All the Indian states

fall under the same model of central ABT/UI mechanism (i.e frequency linked structure) andsome have envisaged to extend it to the intra-state level for the settlement of imbalances during

the day of operation. However, the only state in the India happens to be Maharashtra in WR

which has actually implemented a marginal cost based settlement for real-time imbalances (IntraABT). Due to the marginal cost based settlement, the constituents (DISCOMS, captive power

plants, independent power producers, etc.) in the Maharashtra state are discouraged from

overdrawing the free power during the high grid frequency periods (>50.2Hz). If they overdraw

during those periods, the state will penalize them indirectly by making them pay the merit orderbased marginal cost prevailing at that point of time.

DesiSmartGrid believes that this might be the prime reason that has helped the WR not tooverdraw during those critical times of the grid and made grid remain secure. We confirmed this

outcome after studying the states UI schedule/drawl behaviour before & after the blackouts.

doc regarding indian balckout juli 30-31st.doc

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