Page 65 - Mathematical Models and Algorithms for Power System Optimization

Optimization of Annual Generator Maintenance Scheduling 55

3.2.4 Way of Processing the Variable Settings and Constraints

After analyzing the GMS, the maintenance period of each unit is identified as the core variable,
because the sum of power generation output of each unit in each period needs to maximize the
reserve margin. Once the unit enters the maintenance period, the output of the unit is zero.

Based on the analysis on GMS, all constraints are determined, which should be satisfied in the
actual operation, specifically the balance constraints among the maintenance reserve, plus
system output and the forecasting load in each period for an annual load of 360h, the earliest
and latest maintenance start time constraints of units, the capacity constraint of the maintained
units simultaneously in the area, as well as the human maintenance constraints of the
power plant.
As previously mentioned, the most important variable is the maintenance period of each unit.
As long as the definition of each unit involves the identification of its own affiliated area and
power plant, the output of the generator units in different regions under different time periods
can be separately summed. On the basis of setting the maintenance period of all units as the
kernel variable, and to make the system’s power generation capacity meet the load demand with
a certain reserve margin, the GMS should satisfy the following constraints related to system
operation characteristics, geographical distribution, and some practical situations:

(1) General constraints.
1. Maintenance window interval constraint, which specifies the earliest and latest start
times of the generating equipment for maintenance. The specific maintenance interval
of generating equipment should be in accordance with relevant regulations.
2. Reserve capacity constraint, which will ensure a secure reserve capacity in the unit
maintenance phase. If there is any conflict between the unit maintenance and
minimum reserve, the schedule should be rearranged or a load adjustment measure
taken. Otherwise the system cannot operate in a secure and reliable way.
3. Maintenance manpower constraint, which limits the number of units maintainable at
the same time. This constraint is not significant for an old power plant staffed with
full-time maintenance personnel, but it is meaningful for new power plants that do not
have full-time maintenance personnel. The full-time maintenance team not only
guarantees maintenance quality but also saves maintenance costs. It is better to have a
unified, full-time maintenance team for all power plants.
(2) Special constraints.
1. Area maintenance capacity, which reflects a requirement to balance the generating
capacity and load demand in the area as much as possible. If the area in which the unit
is scheduled to be maintained requires a distant generator to compensate the regional
power demand, the system transmission loss will be increased, even if such an
arrangement can satisfy the reserve constraint of the whole system. More importantly,