EE 1401 POWER SYSTEM OPERATION AND CONROL(2 marks)

UNIT- IV UNIT COMMITMENT – ECONOMIC DISPATCH CONTROL

1. What is the need for unit commitment?
Need for unit commitments are:
 Enough units will be committed to supply the system load.
 To reduce the loss or fuel cost.
 By running the most economic unit, the load can be supplied by that unit operating closer to its best efficiency.
2. What a re the difficulties to find unit commitment solution?
 Time consuming process
 If the number of units is more, the number of combinations is more in a complex bus system.
 If ‘n’ be the number of units, then the number of combinations will be (2n - 1)
3. List he constraints that are accounted in unit commitment problem.
• Spinning reserve
• Thermal Constraints
o Minimum downtime
o Minimum uptime
o Crew constraint
• Other constraints
o Hydro constraint
o Must run constraint
o Fuel constraint
4. What is the constraint for blue force technique? Is it possible to get an optimum solution with this technique and explain how?
i. Spinning reserve
ii. Thermal Constraints
1. Minimum downtime
2. Minimum uptime
3. Crew constraint
iii. Other constraints
1. Hydro constraint
2. Must run constraint
3. Fuel constraint
5. What is meant by priority list method?
Priority list method is the simplest unit commitment solution method which consists of creating a priority list of units. The priority list can be obtained by noting the full-load average production cost of each unit.
6. What are the assumptions for priority list method using full load average production cost?
• No load costs are zero.
• Unit input-output characteristics are linear between zero output and full load.
• Start-up costs are a fixed amount.
• Ignore minimum up time and minimum down time.
7. What are the merits and demerits of priority list method?
Merits:
 No need to go for ‘N’ combinations
 Take only one constraint.
 Ignore minimum up time and minimum down time.
 Complication reduced.
Demerits:
 Start-up costs are fixed amount.
 No load costs are not considered.
8. What are the advantages of using forward dynamic programming method?
 Reduction in the dimensionality of the problem. i.e., number of combinations to be tried is reduced in number.
 If a strict priority is imposed, the number of combinations for a 4 unit case are:
Priority 1 unit
Priority 1 unit + Priority 2 unit
Priority 1 unit + Priority 2 unit + Priority 3 unit
Priority 1 unit + Priority 2 unit + Priority 3 unit + Priority 4 unit

9. What are the assumptions involved in dynamic programming method?
• Total number of units available, their individual cost characteristic and the load cycle on the station are assumed priori (previously).
• A state consists of an array of units with specified units operating and the rest off-line.
• The Start-up cost of a unit is independent of the time it has been off-line (i.e., fixed amount)
• There are no costs for shutting down a unit.
• There is a strict priority order and in each interval a specified minimum amount of capacity must be operating