# Power Systems Questions & Answers

Define economic dispatch problem?

The objective of economic dispatch problem is to minimize the operating cost of active power generation.

Define incremental cost?

The rate of change of fuel cost with active power generation is called incremental cost. Write the load balance equation? Pg-pd-pl=0.

Define base point?

The present operating point of the system is called base point.

Define participation factor?

The change in generation required to meet power demand is called as participation factor.

Define hydrothermal scheduling problem?

The objective is to minimize the thermal generation cost with the constraints of water availability.

Define Uncommitment?

Commitment of minmum generator to meet the required demand.

Define spinning reserve?

It is the term describe the total amount of generation availability from all units synchronized on the system.

What is meant by scheduled reserve?

These include quick start diesel turbine units as well as most hydro units and pumped storage hydro units that can be brought online, synchronized and brought up to full capacity quickly.

What are the thermal unit constraint?

Minimum up time, minimum down time crew constraints.

Define minimum up time?

Once the unit is running, it should not be turned off immediately.

Define min.down time?

Once the unit is decommited, there is a minimum time before it can be recommended.

Define crew constraints?

If a plant consist of two (or) more units, all the units cannot be turned on at the same time since there are not enough crew members to attend both units while starting up.

What are the two approaches to treat a thermal unit to operating temperature?

The first allow the unit boiler to cool down and then heat backup to operating temperature in time for a scheduled turn on. The second requires that sufficient energy be input to the boiler to just maintain operating temperature.

What are the techniques for the solution of the unit commitment problem?

Priority list method dynamic programming Lagrange relation

What are the assumptions made in dynamic programming problem?

A state consists of an array of units with specified units operating and the rest of the time. The startup cost of a unit is independent of the time it has been offline. There are no costs for shutting down the units.

Define long range hydro scheduling problem?

The problem involves the long range of water availability and scheduling of reservoir water releases. For an interval of time that depends on the reservoir capacities.

What are the optimization technique for long range hydro scheduling problem?

Dynamic programming composite hydraulic simulation methods statistical production cost.

Define short range hydro scheduling problem?

It involves the hour by hour scheduling of all generators on a system to achieve minimum production condition for the given time period.

Define system blackout problem?

If any event occurs on a system that leaves it operating with limits violated, the event may be followed by a series of further actions that switch other equipment out of service. If the process of cascading failures continues, the entire system of it may completely collapse. This is referred as system blackout.

What is meant by cascading outages?

If one of the remaining lines is now too heavily loaded, it may open due to relay action, thereby causing even more load on the remaining lines. This type of process is often termed as cascading outage.

What are the functions of control center?

System monitoring contingency analysis security constrained optimal power flow.

What is the function of system monitoring?

System monitoring provides upto date information about the power system.

It stands for supervisory control and data acquisition system, allows a few operators to monitor the generation and high voltage transmission systems and to take action to correct overloads.

What are the states of power system?

Normal state alert mode contingency mode emergency mode. Define normal mode? The system is in secure even the occurrence of all possible outages has been simulated the system remain secure is called normal mode.

The occurrence of all possible outages the system does not remain in the secure is called alert mode.

What are the distribution factors?

Line outage distribution factor, generation outage distribution factor.

Define state estimation?

State estimation is the process of assigning a value to an unknown system state variable based on measurements from that system according to some criteria.

Define max. likelihood criterion?

The objective is to maximize the probability that estimate the state variable x, is the true value of the state variable vector (i.e, to maximize the P(x)=x).

Define weighted least-squares criterion?

The objective is to minimize the sum of the squares of the weighted deviations of the estimated measurements z, from the actual measurement.

Define minimum variance criterion?

The objective is to minimize the expected value of the squares of the deviations of the estimated components of the state variable vector from the corresponding components of the true state variable vector.

Define must run constraint?

Some units are given a must run status during certain times of the year for reason of voltage support on the transmission network.

Define fuel constraints?

A system in which some units have limited fuel or else have constraints that require them to burn aspecified amount of fuel in a given time.