Load Flow Analysis

The Load Flow Analysis is done to determine the voltage, current, real and reactive power in a particular point in a power system as well as the flow from one point to another.

The Load Flow Analysis helps understand the operation and behaviour of the system when a generator trips or when a big load is suddenly cut off. Load Flow Analysis also helps identify routes to transfer power when a transmission line has to be isolated due to a fault. This ensures reliable power supply and ensures quick restoration in the event of blackouts.

Load Flow Analysis is done during the design of the power system. It should also be done before any modification of the power system such as the addition of loads or generating units.

Components and Structure of a Power System

A Power system has three main components:

• The Generating System
• The Transmission System
• The Distribution System

Generating System

The Generating System is the source of the power. The generation can be from generators, solar panels, etc. Power can be generated from different sources such as hydropower, wind turbines, nuclear plants,etc.

Components: Synchronous Generators, induction generators, solar panels, Transmission System

The transmission system transmits the generated power over large distances to the distribution centres such as industries and cities. The distribution areas can be thousands of kilometres away from the generating stations. The voltage is stepped up to high values to minimize the losses using transformers. The power is then transmitted through the power lines to the distribution areas.

Transmission systems can be categorized into

• Primary Transmission Systems, which transfer power at voltage of 110 kV and above. These lines are hundreds of miles long. They are connected to secondary receiving substations
• Secondary Tranmission Systems, which receive the power from the primary transmission system send it to the distribution systems. The voltage levels in the secondary transmission systems are about 33kv to 66kV

Components: Transformers, Circuit Breakers, Overhead Transmission Lines, Underground Cables.

Distribution Systems

The distribution system receives power from the transmission system and distributes the power to the individual customers at the required voltage. The industrial supply voltage can be 33kV or 11kV. The domestic supply voltage is 440 or 220V

Components: Transformers, underground and overhead transmission lines.

Transient Stability and Steady State Stability

Transient Stability

Transient Stability is the ability of a power system to return to its normal state after a major disturbance, such as a fault or a disconnection or connection of a large load.

When there is a disturbance in the system, there are oscillations. These oscillations are called swings. Transient stability analysis is concerned with the response of the power system to such oscillations. A power system with proper response will bring the system back to steady state operations within a short period of time.

Steady State Stability

Steady State Stability is the ability of a power system to respond to slow or gradual changes in its operating parameters. When a number of power sources and loads are connected to a system, there will be gradual shifting of loads from one generator to another. These oscillations, if not properly controlled, can develop into large oscillations which can cause bigger disturbances.

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