International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Demonstration of Frequency Regulation by Free
Governor Mode of Operation in Western Region
Grid System
Namrata Tiwari1, Vijay Bhuria2
1
post Graduate student,2Assistant professor
Department of Electrical Engineering, Madhav Institute of Technology & Science,
Gwalior (M.P.), India
Abstract— The electric power system must deal with two unique
requirements: the need to maintain a near real-time balance
between generation and load, and the need to adjust generation
(or load) to manage power flows through individual transmission
facilities. Frequency regulation is one of the distribution services
to be supplied by the electricity market participants. Frequency
regulation is to maintaining the balance between demand and
supply in real time. In this paper determine the stability of
western region grid through Frequency Regulation by Free
Governor Mode of Operation. Matlab and Simulink model are
proposed to use the design concept and operation of the model. A
simple model of a speed governing system of the steam turbine is
taken for exhibit the dynamic simulation.
Keywords— FGMO, frequency regulation, speed governor,
drooping.
I.
INTRODUCTION
Frequency regulation is one of the most vital
system reliability services that must be provided by
market participants and managed by the system
operator (SO). The inequality between load and
generation due to contingencies or large difference
of load causes variation in frequency and it is
required to maintain the frequency within the
normal operating band (NOB) as arranged by the
reliability requirement of different countries or
regions. To maintain or bring back the frequency
within the NOB, different approaches have been
adopted by different countries or regions by their
SOs. Frequency regulation can be achieved by
balancing mechanisms either by some regulatory
approach or through some market based approach.
The main objective of all these methods is to bring
back and maintain the frequency within the NOB as
soon as possible. [8]
In case of Indian power industry scenario, All the
regional constituents would make all possible
efforts to ensure the maintenance of grid frequency
ISSN: 2231-5381
within the normal IEGC band that is 49.5 to 50.2
Hz. Emergency unloading of a unit is available only
when frequency reaches 50.2 Hz. As a consequence
excursions in frequency are common up to 1 Hz in a
time block of 15 minutes. [13] For the sake of better
control efforts are being made to enable the
frequency governors to respond to entire range of
frequency. It is called free governor mode of
operation (FGMO). Variation in grid frequency can
be minimized by putting all the generating stations
on “free governor” mode of operation. [4]
Western region load dispatch centre (WRLDC)
grid covers the power system of the states of
Madhya Pradesh, Chhattisgarh, Maharashtra,
Gujarat and the Union Territories of Daman & Diu,
Goa, Dadra and Nagar Haveli; [1] the Central
Generating Companies such as National Thermal
Power Plant Ltd., NPCIL and Joint Venture
companies and several Independent Power
Producers (IPPs) whose generating stations
connected to the Western grid including all above
functions. The Western region electricity grid
which is a part of the synchronous ‘NEW’ grid
formed after synchronization of Northern grid with
Central grid on 26th August 2006 covering area of
951.488 sq. kms and population of 273 Million
covers nearly 30% of the country’s area and
population. It has the highest installed capacity of
64394 MW which is 32% of total installed capacity
of Indian Power system including central sector,
state sector, private sector and Independent power
plants and shares as on 31.03.2012. Per capita
expenditure of Western Region is 1116.92 kWh.
During 2011-12, 889ckt. Kms. of 765 kV, 5406
Ckt.km of 400 kV and 1667 km of 220 kV
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
transmission lines were added in Western Region
Transmission System [9]. The inter connection
mostly benefited Western regional grid which is
importing power to the tune of MW from ER and
NER grids [3].
Therefore, according to this scenario the large
scale power system is divided to some distribution
areas and the area system is modelled as a
collection of independent generator units to
supplying the area-load. In the proposed strategy
one generator unit is responsible for tracking the
load and hence performing the load frequency
control task by securing as much transmission and
generation capacity as needed. [5]
II.
speed / frequency will be oscillating which is an
indication of poor power quality. A state of fixed
system frequency and zero acceleration indicates
that the generation meets the system demand. The
governing system supplies for this regulation /
adjustment and when the turbo-generator is on bars,
by the controlling of the steam inflow to the turbine.
The regulation is predicted by various control logics
and by operating the control valves in the turbine.
Stop valves presented in the governing system
protect the turbine in case of unsafe conditions by
blocking the steam flow into the turbine. [7]
FREE GOVERNOR MODE OF OPERATION
Free governor mode operation means that the
governor is free to govern as its regulation/droop
characteristics. The governing system senses this
change in speed and adjusts steam control valve so
that mechanical power matches with the changed
load. The Governor is an important controller in the
Fig.1 [7]
power plant as it regulates the turbine speed and
power participates in the grid frequency regulation.
IV.
DROOP OR REGULATION
The steady state and dynamic response behaviour of
the turbine is influenced mainly by the
The change in frequency (Δω) can be explained
characteristics of the Governing system. [7]
by the using following equation in terms of change
in load ( Δ Pl) and a factor R called ‘speed
III.
NEED FOR THE GOVERNING SYSTEM
regulation or ‘droop’.
The governor is a device that automatically
Δω = - [Δ Pl ]( R)
adjusts the rotational speed of the turbine and the
A
20
%
change
in load (Δ Pl = 0.2 per unit)
generator output. When the generator load is
constant and the turbine is operated at a constant causes 1 % change in frequency (Δω = 0.01 p.u)
rotational speed. However, when the load changes, with a per unit (p.u) droop value of 0.05. Similarly
then the balance between the generator output and full load throw off (Δ Pl = - 1.0) causes 5 %
the load is not maintained, and the rotational speed change in speed. (Δω = + 0.05). This is explained
also changes. When the load is removed, the well known droop characteristic. [12] The
governor detects the increase of the rotational regulation can be expressed in the form of power –
speed, and then, the valve is closed rapidly so that frequency characteristic as shown in Figure 2.
an abnormal speed increase of the generator.[6] The
In thermal power plants droop value is generally
load on the turbo-generator does not remain 4 % to 5 %. The sensitivity of the governor for a
constant but vary as per the consumer (Grid) given change in load varies inversely with the
demand requirements. The presence of a continuous percentage droop. The droop of hydro turbines will
mismatch between the generation and the demand be around 2 to 3% where as that of the steam
in a larger network results into variations in turbines will be 4 to 5%. [7]
frequency and necessitates a continuous adjustment
of generation at the turbo-generators. If not, the
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
Fig.2 speed regulation characteristics [7]
V.
FREQUENCY CONTROL BY FGMO
shedding or to draw/inject Unscheduled Interchange
(UI) power responding to signals generated by the
commercial mechanism (ABT). [7] Under ABT
mechanism, grid operating frequency narrowed
down from 49.2 to 50.3 Hz to 49.5 Hz to 50.2 Hz.
and limits on UI volumes below 49.7 Hz for
overdrawal as well as under injection and UI rates
also varied. [13]
Grid disturbances over the last few years, All
constituents are requested to operate maximum
number of hydro units to provide operational
flexibility. In order to avoid any sudden load
change in the system at the time of switching on
frequency response and the frequency at the start of
the test period (between 10:15 to 10:30 hrs) shall be
maintained close to 49.5 Hz. For this purpose,
regional entities of WR are to maintain their net
exchange close to the schedule. ER and NR grid
being synchronously connected to WR shall also
endeavour to maintain their net exchanges either
WR as per their respective schedules. NLDC is
requested to the coordinate with all RLDCs to
ensure that all inter regional links are healthy and in
service, and their power flows do not pose a
constraint during the test operation. [11]
Free governor mode of operation on generating
units and tripping on high frequency could be
avoided. During grid disturbances, load generation
balance can be attained at a faster rate. [7] All
generators have some type of governor control. The
governor senses a change in speed and regulates the
energy to be delivered to the generator’s prime
mover. The change in the generator output is in
response to the change in frequency and occurs in
the 3-10 sec time frame. Primary response is
responsible for the initial arrest of frequency
variation.[10] During normal operation, tripping of
a 200 MW unit leads to frequency drop of around
one hertz due to low system stiffness as the
frequency has to be controlled only by load
damping effect in the first 20-seconds after the
tripping. FGMO would increase stiffness of system
significantly and avoid large frequency dips in the
event of unit tripping. [7]
Frequency control requires provision of primary
regulation and supplementary regulation as basic
requirement. Primary regulation is giving through
speed governors which respond to frequency
changes by varying turbine outputs. Maintaining
governors free to operate in the entire frequency
range enables smooth control of frequency
fluctuations as well as security against grid
disturbances. In India, due to wide range of
frequency fluctuations and speed governors were
prevented from responding by the utilities with
dead band configuring from49.5 Hz to 50.2 Hz with
emergency unloading available only when
frequency goes above 50.2 Hz. Efforts have been
made to enable speed governors responding in the
entire frequency range which has come to be known
as free governor mode of operation (FGMO).[2]
Availability Based Tariff (ABT) stabilized
frequency in a narrower band, the quick fluctuations
continued to occur with the frequency excursions of
0.5 Hz over a time period of 10 minutes and
frequency shooting up to 50.2 Hz and above when
sudden bulk load shedding or maximization of
generation takes place before evening peak hours.
When Dipping of frequency takes place during
onset of peak loads or unit tripping. Such frequency
fluctuations during normal operation in the grid
leads to complex counter actions by the control
centre operators at regional and state level. Further,
for the fluctuating frequency even in an interval of
15 minutes does not give out clear signals to
For example, 20000MW generation on FGMO
operators to plan generation changes and load with 5% droop in Central grid would increase
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system stiffness by 4000 MW per hertz. Consider a
system of 10000 MW at 50 Hz. Assume a droop of
5% for the entire grid system.
Case-1
If due to some reasons, a generator of 400 MW
trips and no unit is under FGMO, the dip in
frequency will be 50 X 400/20000 = 1 Hz.
Case-2
Figure-4 Speed Governing System Functional Block Diagram [7]
If FGMO is available only for 10000 MW due to
disabling of the governing action in other sets, then Each block of Figure.4 can be represented by a first
the frequency drop will be 50 X (400/10000) X order transfer function as shown below:
[Xv / Ne] = [Kg / (1 + Tg s)] (1)
5/100 = 0.1 Hz.
[Pm / Xv] = [1/ (1 + Tt s)]
(2)
Case-3
[Ns
/
Pm]
=
[1/
(Ta)
s]
(3)
If FGMO is available for all the 20000 MW, the
Ne= Nr - Ns
(4)
dip in frequency will be 50 X (400/20000) X 5/100
Where Nr, Ns, Ne = machine speed reference,
= 0.05 Hz only.
actual speed and speed error respectively
Xv = governor valve opening
Pm = mechanical power output (in per unit)
Tg, Tt = time constants of governor and time
constant of turbine respectively (in seconds)
Ta = rotor acceleration time (in sec)
Kg = Governor Gain
s = Laplace operator = [d/dt]
The above transfer functions can be transformed
into differential equations. By substituting s = (d/dt).
Letting
yn (1) = Xv
yn (2) = Pm
yn (3) = Ns
and dyn = d/dt (yn). The above block diagram is
Figure-3 Free Governor Mode o f Operation [7]
transformed into set of first order differential
equations as shown below:
From the above examples, it is clear that, more the
Ne = Nr- yn (3);
constituent units are under FGMO more is the
dyn (1) = (Kg/Tg)*Ne - (1/Tg)*yn (1);
stability of the Grid. In Western Region, by
dyn (2) = (1/Tt)*yn (1) - (1/Tt)*yn (2);
operating maximum possible number of units with
dyn (3) = (1/Ta)*yn (2);
their governors in free mode, by automatic under Typical values are:
frequency load shedding and by using special Nr = 0.01 (corresponds to a step input from 0 to
protection schemes, etc. the frequency stability is 0.01 p.u change in speed reference);
being ensured. Therefore, Free Governor Mode of Tg = 0.2; Tt = 0.5; Kg = 20 Ta=9.8;
Operation (FGMO) is the quickest way in To simulate the above equations in Matlab a
Emergency High Frequency Control, particularly function called ode23 is used. This refers to
during High Frequency regime. It is now clear that, ‘ordinary differential equation’ (ODE) solution
more the constituent units are under FGMO more is using by Runge Kutta second and third order
the stability of the Grid. [7]
methods. [7]
VI.
DISCUSSION ON SIMULATION OF SPEED
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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue5- May 2013
VII.
SIMULATION RESULTS
0.25
Speed
Valve
Controller
0.2
0.15
0.1
0.05
0
-0.05
-0.1
0
1
2
3
4
tsec
5
6
7
8
change in frequency by change in generation and is
called Free Governor Mode of Operation (FGMO).
If the requirements available in the governor and
control circuits viz., load limiter, dead band,
switching off the governor etc., are employed to
limit the FGMO, it will lead to higher swings in
frequency, instability of the grid and subsequent
pull out even so that, more the constituent units are
under FGMO more is the stability of the Grid. In
Western Region, by operating maximum possible
number of units with their governors in free mode,
by automatic under frequency load shedding and by
using special protection schemes. The frequency
stability is being ensured.
Result -1(In MATLAB Environment)
REFERENCES
[1]
[2]
[3]
[4]
[5]
Result-2(In SIMULINK Environment)
[6]
VIII.
CONCLUSION
Maintaining frequency at constant value is very
vital for the health of the power generating
equipment and the utilization equipment at the
customer end. The work of automatic frequency
regulation is managed by governing systems of
individual turbine-generators and Automatic
Generation Control or Load frequency control
system of the power system. The governors of all
machines sense the frequency.When the
turbogenerator is on bars, the governor of the
turbine, if its wings are not clipped then responds to
a change in frequency by varying the control valve
lift and so changing the generation. Droop
characteristics of the governor is depend on the
variation in generation so the change in frequency
by increasing or decreasing the generation. This
mode of governor operation compensates the
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[7]
[8]
[9]
[10]
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