7/31/2019 The Importance of Short Circuit Studies

1/1

1. The importance of short circuit studiesa. It is used in sizing in of equipmentb. For protection coordinationc. For establishing Stiffness of a network, which determines the extent of voltage fluation

of a network when subjected to intermittent and fluctuating load demand e.g. when a

steel mill is connected to a network at a point

2. Functions of Operational Planning is closely related to System Operation and Control Functionsin the area of System Load Schedule and Generating Units Dispatch; Operational Planning will

normally carry out a day ahead and week ahead load forecasting (active and reactive loads) with

due consideration to extant environmental conditions and then use the forecasted loads and

proceed to simulate various scenarios in order to determine the feasible ones that can then be

communicated to Control Center for implementation on the Grid.

3. Various Classes of Load Forecasting:a. Short Term Load Forecast Used for operational Planning; Timeframe hour by hour

load forecast for 1 to 7 days (used for generation dispatch/Unit commitment)

b. Medium Term involves daily peaks predicted for 1 week to several months; Used formaintenance scheduling

c. Long Term Timeframe : Seasonal or monthly peak demand forecast for 1 year to 10years - Used for System Expansion(Transmission and Generation Networks Planning)

and Reinforcement Planning

4. Relationship btw Spinning Reserve and Power System frequency:a. Active Power Flow to any node is directly proportional to the power angle between the

two connecting nodes upto a theoretical max of 90 degrees;

b. In a Synchronous Machine (Generator) amount of active power generated is alsodirectly proportional to the rotating or angular speed of the shaft of the prime mover.

So Any increase in load will produce a decelerating torque which will slow down the

shaft and hence the speed which implies lower frequency; The Governor reacts by

opening valves to increase the speed and hence restore the Frequency of the system.

This opening of valves and increasing of speed implies generating more power. Each

Generating Unit has its limit of Power Generation. Hence there is a limit to the amount

of power that can be made up in response to increase in load or shortfall of generation.

The difference between present scheduled generation and the aggregate of the

Maximum Power that all Operating Generators as well as unloaded Generators that are

spinning and ready to be connected to the grid The more the available spinning

reserve the more the system reliability is and the less likely is that the system frequency

will fall beyond the ability of the system reserve to stabilize the frequency.

c. For practical Systems the max pwer angle is around 40 degrees. In terms of the Gridwhen System Loading outstrips Generation the