How A Blackout Can Occur

HOW A BLACKOUT CAN OCCUR 1.0 TITLE

: Describe in detail and by deriving the necessary equation, the operation of a generator connected to a grid in terms of its terminal voltage and frequency. Using these facts and a simple discussion, describe how a blackout can occur.

2.0 INTRODUCTION :

A Grid system is essentially an infrastructure that allows location independent access to the resources and services that are provided by geographically distributed machines and networks. One of the fundamental operations needed to support location-independent computing is resource discovery. Generally, resource discovery schemes maintain and query a resource status database. Dissemination of the resource status information is one of the key operations required to keep the resource status databases consistent. The deployment of faster networking infrastructures and the availability of powerful microprocessors have positioned network computing as a cost-effective alternative to the traditional computing approaches. The Grid is defined as a generalized, large-scale network computing system that is formed by aggregating the services provided several distributed resources. A Grid can potentially provide pervasive, dependable, consistent, and cost-effective access to the diverse services provided by the distributed resources and support problem solving environments that may be constructed using such resources. One of the key motivations for constructing Grids is to provide application-level connectivity among the various machines so that resources and services supported by the individual systems can be shared in a Global fashion. To enable such sharing, it is necessary for the Grid architecture to support several services and resource discovery is one of them. In a Grid system, the resource discovery service may operate in conjunction with the resource management service. When a client requests service, along with the request it presents a set of attributes that should be satisfied by a candidate resource. The resource discovery process may be responsible for generating a set of best possible candidates for the given set of attributes. The scheduling heuristics that are part of the resource management mechanism may allocate the best resource(s) from the set based on the some criterion. For example, the resource management may solicit bids from the potential candidates and select the resource with the highest bid to serve the request. Along with other services, resource discovery is necessary to support resources going off-line and coming on-line. Further, the cascaded operation of resource discovery followed by resource allocation can be efficient in an heterogeneous dynamic system such as the Grid. 3.0 GRID CONNECTION The electrical grid (also known as the electrical power network) in the grandest sense consists of three distinct operations: 3.1. Electricity generation 3.2. Electric power transmission 3.3. Electricity distribution Generating plants are usually located near a source of water, and away from heavily populated areas. The electric power which is generated is stepped up to a higher voltage at which it connects to the transmission network. The transmission network will move the power long distances often across state lines, and sometimes across international boundaries until it reaches its wholesale customer. Upon arrival at the substation, the power will be stepped down in voltage from a transmission level voltage to a distribution level voltage. As it exits the substation, it enters the

distribution wiring. Finally, upon arrival at the service location, the power is stepped down again from the distribution voltage to the required service voltage. 4.0 THE OPERATION OF A GENERATOR CONNECTED TO A GRID (In terms of its terminal voltage and frequency) The electrical grid provide maximum reliability and operating flexibility. These networks are te most economical and effective method in serving the high density loads in metropolitan cities. The grid is simultaneously supplied from several feeders. In the grid network, no consumer outage is caused by switching off the primary feeder for scheduled maintenance. Voltage regulation is improved since power flow to the consumer is through several transformers operating in parallel. The grid can handle abrupt load change and disturbances associated with large motor starting, without severe voltage dips or surge. A strong grid network is sufficiently stiff and a fault in one unit does not disrupt voltage outside the sensitive load tolerance limits. Regardless of where power plants are located, their power must be brought from the plant to the users, and that's the purpose of the electricity grid. The grid consists of two infrastructures: the high-voltage transmission systems, which carry electricity from the power plants and transmit it hundreds of miles away, and the lower-voltage distribution systems, which draw electricity from the transmission lines and distribute it to individual customers. High voltage is used for transmission lines to minimize electrical losses; however, high voltage is impractical for distribution lines. The interface between the two is the electrical substation, which features transformers that "step down" the transmission voltages—ranging from 138 kV to 765 kV—to lower voltages for the distribution systems. Transformers located along the distribution lines further step down the voltage to 120 V or 240 V for household use. Substations also include electrical switchgear and circuit breakers to protect the transformers and the transmission system from electrical failures on the distribution lines. Circuit breakers are also located along the distribution lines to locally isolate electrical problems (such as short circuits caused by downed power lines). A node in the Grid has several attributes that can be categorized as rate-based attributes and non rate-based attributes. Examples of rate-based attributes include CPU speed, FLOP rating, sustained memory access rate, and sustained disk access rate. A node in a Grid can be characterized by a vector where each element of the vector is an attribute-value pair. The Grid potential is based on the computing power or operating rate of a node. Therefore, to characterize a node for deriving the Grid potential only rate-based attributes are considered. Let X = á x0 = a0 , x1 = a1,... xN -1 = a N-1ñ , where xi = rate-based attribute of the system ai = its value at a given time. Let F be a set of functions { f0, f1,K, fk-1} , where fi operates on the set X to return a scalar value li = fi (x0, x1,... xN -1) . Depending on the system, different functions may be defined for it. The functions essentially form weighted sums of the attributes that can be interpreted as different types of potentials.

For example, the function lc = fc (x0 , x1,... xN-1) may be interpreted as the compute potential of the system and another function ls = fs (x0 , x1,... xN-1) may be interpreted as the secondary storage potential. While the compute potential fc may be based on attributes that relate to the processing rate of the node the storage potential fs may be based on attributes that relate to the performance of the storage subsystem. Further, we could have functions that compute application specific potentials that could be useful if the Grid is used exclusively for particular sets of applications. 5.0 HOW A BLACKOUT CAN OCCUR The term "blackout" can bring to mind several different images, depending upon your past experiences. For sometime it can be mean of the lights going out for a short period of time during a thunderstorm. A blackout is a complete interruption of power in a given service area. Blackout is where power is lost completely. "Load shedding" or a rolling blackout is a common term for a controlled way of rotating available generation capacity between various districts or customers, thus avoiding wide area total blackouts.Rolling blackouts are controlled and usually preplanned interruptions of service. A brownout is a partial, temporary reduction in system voltage or total system capacity. Blackouts come without warning, last for indeterminate periods, and are typically caused by catastrophic equipment failure or severe weather. The nature and cause of the blackout determines who is affected. Blackouts occur for a number of reasons. Although most are associated with weather, the impact can be wide ranging. Weather can blow down a single distribution feeder affecting a small region, or an ice storm can take out a major portion of a transmission grid affecting millions of people for days. 6.0 CONCLUSIONS The grid always comes from a diversity of power sources, which may include coal, nuclear, natural gas, oil, and renewable energy sources such as hydropower, biomass, wind, and solar power. This is often referred to as "system power" because it is the standard power mixture that supplies the transmission system. There are financial and contractual means of tying an individual generating source, such as a wind farm, with an individual user in a meaningful way, but it is still true that the electricity one draws from the grid is always system power. 7.0 REFERENCES : 1. 2. 3. 4. 5. 6.

Electric Power Distribution, A. S. Pabla, McGraw-Hill Professional Engineering, 2004. System Of Electrical Supply And Distribution, C Duncan,E G Stocks, Stam Press Ltd, 1990. Direct Current Transmission, Edward Wilson Kimbark, Wiley-Interscience, 1971. Guide To Electrical Power Distribution Systems, Anthony J. Pansini, Prentice Hall, 1992 http://en.wikipedia.org/wiki/Electric_power_transmission http://www.cs.umanitoba.ca/~anrl/PUBS/grid2000_gp.pdf