16-05-2013, 03:01 PM
WIDE AREA BLACKOUT
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INTRODUCTION:
Power Systems are characterized as a large complex system covering vast areas, connecting National/continental grids, highly nonlinear and high order systems. In general, a power system network comprises of generators, loads, buses and transmission lines. All generators and loads are connected to the buses. The transmission lines are the link between all the buses which were connected to the generators and the loads. The power flows from the generators through the transmission lines reaching the loads at various points. The flow of power through each transmission line is controlled by controllers namely transformers, capacitors and others. In order to obtain a stable power system network, all generators rotational speed is required to be synchronized. Failure to meet synchronization will cause the system to go into an unstable state and power outages.
WHAT IS BLACKOUT?
A blackout refers to the total loss of power to an area and is the most severe form of power outage that can occur in a power system. Blackouts which results in power stations tripping are particularly difficult to recover quickly.
Outages may last from a few minutes to a few weeks depending on
1. The nature of the blackout and
2. 2.The configuration of the electrical network
Blackout in a power system would result the entire high voltage transmission grid to force out of service, thereby isolating the load it would normally serve. Grid failure also results almost simultaneous loss of multiple generating units or plants.
JULY 2012 INDIA BLACKOUT:
It is considered as the largest power outage in history as number of people affected.
Occurred as two separate events on 30th and 31st July 2012 and affected over 620 million people, half of India's population and about 9% of the population. Spread across 22 states in Northern, Eastern, and Northeast India, and estimated 32 giga watts of generating capacity was taken offline
Sequence of events:
At 02:35 IST (on 30th July), the 400 kV Bina-Gwalior line tripped. As this line fed into the Agra-Bareilly transmission section, the station also tripped, and power failures cascaded through the grid. All major power stations were shut down in the affected states, causing an estimated shortage of 32 GW.
On the day of the collapse, some states had attempted to draw more power than permitted due to the higher consumption. Spokesperson of PGCIL and the Northern Regional Load Dispatch Centre (NRLDC) stated that Uttar Pradesh, Punjab and Haryana were the states responsible for the overdraw.
A senior director for an Indian power company described the outage as "a fairly large breakdown that exposed major technical faults in India’s grid system. Something went terribly wrong which caused the backup safety systems to fail."
Synchrophasors
Synchrophasors (fig shown below) are fast sub-second rate power system measurements such as three-phase voltages and currents, frequency, and rate of change of frequency.
These measurements are time-stamped to a common global time reference. This provides synchronized real-time monitoring of multiple remote points on the electrical grid and also provides monitoring of fast dynamic grid behavior.
Synchrophasors are measured by Phasor Measurement Units (PMUs). A PMU can be a dedicated device, a meter, or any measuring device that can accept a global time reference and properly time-stamp the power system measurements.
Because Synchrophasors provide an instantaneous synchronized view of the grid’s state, we can identify and locate abnormal behaviors more quickly. They also monitor the fast dynamic behavior of the grid. The control center has a snapshot of the grid with fast sub-second measurements that are synchronized. This allows for introduction of a new generation of innovative Energy Management System (EMS) software to analyze abnormal as well as dynamic behavior and to take corrective action automatically without operator intervention.