Hierarchies in Large Scale Power Systems:
Because of their complex structures
and large sizes, electric power networks are typically monitored
and controlled according to their hierarchical structures. Instead
of modeling the intricate dynamics of the entire system, the system
dynamics is modeled by deriving submodels relevant for each
particular sub-process. This is based on observing different time
scales over which sub-processes evolve under certain assumptions.
The overall system behavior can be fully portrayed by piecing
together those simpler, yet essential, elements. The theoretical
basis for this type of modeling in large electric power systems was
introduced in [8]. The basic submodels are the
(i) primary (local) model at a device level, (ii) secondary
(area-wide) level for each administrative area, and (iii) tertiary
(global) level representing the interconnected system, Figure
2-1.
The primary control level is entirely decentralized at present.
Within this level, controllers respond to the small but fast local
disturbances appearing at the terminals of each generator. The
speed governor units in electric machines maintain the control of
this level. Primary controllers stabilize system dynamics within a
very short time constant, T,, i.e., on the second scale, with the
performance specification of a minute,
or so.
The secondary control level is decentralized and is particularly
useful in analyzingand controlling the dynamic performance within
an administrative area (subsystem level). This model represents all
generators and large number of loads connected by transmission
lines in each administrative area. The secondary control is
implemented at a slower time scale, T,, than that of the primary
control (i.e., T, is typically on the several-second scale, with
the performance objective over 10 minutes, or so). The secondary
control is intended to stabilize system outputs within the
administrative area that are disturbed by changes within the area
as well as by the changes in neighboring areas. Presently
implemented AGC is based on this control structure. Seen from the
interconnected system level, each subsystem uses AGC using
decentralized
measurements at its own level only. The theoretical tertiary
control level is coordinated. The aggregate tertiary-level models
describe the inter-area dynamics among administrative areas and are
useful for regulating inter-area variables such as tie-line power
flows. These models evolve
on an even slower time constant, Tt, than the secondary level rate,
Ts, i.e., on the minute scale. This higher level structure is not
currently used in the utility industry.
However, its importance is increasing as the electric power market
is changing and becoming more competitive. It is plausible that in
the future, decentralized regulation
at the secondary-level would not be sufficient to respond to
intense interactions among the areas under an open access
environment. The later parts of this thesis provide examples
illustrating potential problems of this sort.
Hierarchical level models higher than the tertiary control level
described in this topic can also be developed. For example, in
present utility industry, the control centers reset the scheduled
values of transmission power among the areas and the phase angle of
the slack generator at a much slower rate for economic reasons. The
unit commitment procedures such as turning on- and off- the
available generators in anticipation of demand on a daily basis, is
yet another process of interest. These processes, at least in
concepts, could be regarded as evolving at hierarchies beyond the
tertiary level. However, these models are beyond the scope of this
topic.
Question 8: Using a typical frequency response illustrate the different hierarchies of frequency ...
Question 8: Using a typical frequency response illustrate the different hierarchies of frequency control in large-scale power system. Discuss and illustrate using a numerical example why governors using speed droop or speed regulation cannot alone restore the power system frequency to the pre-disturbance level. Question 9: An isolated 50 Hz synchronous generator is rated at 15 MW which is also the maximum continuous power limit of its prime mover. It is equipped with a speed governor with 5% droop. Initially,...
I need help to solve this questions about Generator Governor Droop and Transmission Line. A complete solutions with answers would be great. Thank you Generation Question 1 to 5 relate to the following grid connected generator. A governor-controlled, steam-driven 450 MW synchronous generator with 5% droop is synchronized to the 60 Hz grid and its load set-point adjusted to deliver 300 MW to the grid. Q1. (a) 000 What is the actual droop of the generating unit? 0.0225 Hz/MW (b)...
Could you please help solve this question. The following generator supplying rated load into a large grid at rated voltage (11kV) and 0.85 PF lagging Generator: 20 MVA, X = j15%. Voltage 11kV i) Determine the internal generator voltage. ii) The load suddenly drops to 50% rated power. If the rotating energy of the generator and its associated turbine is 2.0 p.u-seconds when running at its synchronous speed. It has 2 poles and system frequency is 50 Hz. Determine: (ii-a)...
solve no: 3.14 , 3.16, 3.19 please show each step and solve for beginners 120 Power System Analysis 3.12. A single-phase system similar to that shown in Figure 3.11 has two transformers A-B a B-C connected by a line B feeding a load at the receiving end C. The ratings and parame ter values of the components are 500 V/1.5 kV, 9.6 kVA. leakage reactance 5 % 1.2 kV/120 V, 7.2 kVA, leakage reactance 4 % series impedance (0.5 +...