40220140505009

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
ISSN 0976 – 6553(Online) Volume 5, Issue 5, May (2014), pp. 89-99 © IAEME
89
FAULT ANALYSIS IN HYDRO POWER PLANTS USING
MATLAB/SIMULINK
P Sridhar1
, K Bhanu Prasad2
1
Professor, Department of EEE, Institute of Aeronautical Engineering, Hyderabad
2
Department of EEE, Institute of Aeronautical Engineering, Hyderabad
ABSTRACT
Scarcity of electrical power is the key problem in developing countries, needs are to be
addressed. Due to the depletion of fossil fuel, their usage as a conventional source for production of
electrical power is not adequate. Hydro power plant is a possible environment friendly solution in
developing, hilly countries where rivers are available, for rural electrification. Hydro power plants
are advantageous because of their low administrative and executive costs, possibility of using water
for drinking and irrigation purposes, suitability for rural areas and low environmental pollutions.
Hydro is a flexible source of electricity since plants can be ramped up and down very quickly to
adapt to changing energy demands. Hydro turbines have a start-up time of the order of few minutes.
Hydro power plant constructed at a remote area is capable of supplying electrical power to local
consumers through an isolated transmission line. In the present study an attempt has been made to
develop a Hydro power plant model and study the suitability of different controllers in a governor
model for a fault occurrence in a transmission line by means of carrying out a MATLAB based
simulation. With MATLAB/SIMULINK, the models of the proposed simulation system are all
modularized and visualized, and can be reused easily [1]. Simulation results performed on the
proposed control scheme have demonstrated the efficiency of proposed virtual model.
Keywords: Hydro-Power Plant, Hydraulic Turbine, Governor, Excitation System, Line Fault,
Controllers.
1. INTRODUCTION
Excessive usage of fossil fuels has led to global climatic changes and warming. It is believed
that attention must be drawn towards the application of renewable energy sources which possesses
the potential to be the most suitable future fuel. With the increase in the demand for electrical
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
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ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 5, Issue 5, May (2014), pp. 89-99
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IJEET
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90
energy, hydro power plants have assumed importance [2]. Hydro power plants have been identified
as a very appropriate alternative to conventional electricity generation for several developing
countries around the world. However, these are affected by various technical and economic
challenges. Hydropower is emerging as a major contributor to the world energy requirement [3]. It is
inexhaustible and clean in nature and answers the problem of environmental pollution [4]. On the
other hand it requires a large area and initial investment is very high.
This paper describes the dynamic model of one of the main components of hydro power
plants i.e. the hydro turbine governor. The detailed mathematical representation of the hydraulic
turbine-penstock also presented in this paper. The dynamic performance of the hydraulic system is
studied using time domain method. The introduced mathematical representation of a hydraulic
system is including both turbine-penstock and the governing system. The primary source for the
electrical power provided by utilities is the kinetic energy of water which is converted into
mechanical energy by the prime movers. The electrical energy to be supplied to the end users is then
transformed from mechanical energy by the synchronous generators. The speed governing system
adjusts the generator speed based on the input signals of the deviations of both system frequency and
interchanged power with respect to the reference settings. This is to ensure that the generator
operates at or near nominal speed at all times. Simulation of the three-phase synchronous machine
and hydro turbines is well documented in the literature and a digital computer solution can be
performed using various methods. This paper discusses the use of SIMULINK software of
MATLAB, in the dynamic modeling of the hydro plant components. The main advantage of
SIMULINK over other programming software is that, instead of compilation of program code, the
simulation model is built up systematically by means of basic function blocks. To be able to model
the dynamics of the hydro power plant, dynamic behavior or differential equations of the
synchronous machine as well as hydro turbine need to be considered.
The Simulation of hydropower plant including its various components viz. Penstock and
Turbine, PID Governor, PI Governor and Exciter etc., have been carried out in this work. The
developed software demonstrates the dynamic behavior of the hydro power plants by changing load,
speed, voltage etc. The type of exciter considered in this paper is a standard IEEE type1 exciter
system.
A fault is an electrical system is defined as a defect in the electrical circuit due to which
current is diverted from the intended path. The nature of fault simply implies any abnormal
condition which causes a reduction in the basic insulation strength between phase conductors or
between phase conductors and earth. The most common and dangerous fault, that occurs in a power
system is the short circuit or shunt fault. They occur as a result of breakdown of the insulation of the
current carrying phase conductors relative to earth or in the insulation between phases.
The short circuit fault can be classified as
1. Single Phase to ground (L-G).
2. Phase to Phase (L-L).
3. Two Phase to Ground (L-L-G).
4. Phase to Phase and Third Phase to Ground.
5. All Three Phases to Ground (L-L-L-G).
6. All Three Phases Short Circuited (L-L-L).
The Line to ground fault occurs most commonly in overhead line practice. The balanced
three phase fault is very rare in occurrence, accounting for only about 5% of the total, but is the
severest of all types of faults and imposes the most severe duty on the circuit breakers and is used in

91
the determination of circuit breaker rating. Faults sustained on the system and duration of the faults
can be minimized by improving the system design. The type of fault simulated is L-L-L-G fault.
2. HYDRAULIC TURBINE MODELING
Power system performance is acted by dynamic characteristics of hydraulic governor-turbines
during and followed by any disturbance, such as occurrence of a fault, loss of a transmission line or a
rapid change of load. Accurate modeling of hydraulic governor-turbines is essential to characterize
and diagnose the system response during an emergency. Simple hydraulic systems governed by
proportional-integral-derivative and proportional-integral controllers are modeled. This model
examines their transient responses to disturbances through simulation in Matlab/Simulink
The linear model of the hydraulic turbine is inadequate for studies involving large variations
in power output and frequency. The block diagram shown in Fig.1 represents the dynamic
characteristics of the turbine [5]. Fig.3 shows a block diagram of the hydraulic governor-turbine
system connected to a power system network. The primary source for the electrical power provided
by utilities is the kinetic energy of water which is converted into mechanical energy by the prime
movers. The electrical energy to be supplied to the end users is then transformed from mechanical
energy by the synchronous generators. The speed governing system adjusts the generator speed
based on the input signals of the deviations of both system frequency and interchanged power with
respect to the reference settings. This is to ensure that the generator operates at or near nominal speed
at all times.
Figure 1: Block Diagram of Non-Linear Turbine Model
The mathematical equation representing dynamic behavior of the penstock-turbine is given
as:
[ ]








−





−=
2
10
2
1010
1
1
Xf
Gate
X
Tdt
dX
p
w
--- (1)

92
Mechanical power output is given by:
[ ] WGateDQX
Gate
X
AP nltmech ∆−−





= ..10
2
10
--- (2)
Where,
‘Tw’ is the water starting time constant
‘fp’ is the frictional loss coefficient
‘Pmech’ is the mechanical power
‘Qnl’ is the no-load water flow-rate.
‘At’ is the turbine gain constant
‘ωr’ is the rotor speed
‘D’ is the turbine damping constant.
3. SPEED GOVERNOR
3.1. PID Governor Model
PID controllers are commonly used to regulate the time-domain behavior of many different
types of dynamic plants. These controllers are extremely popular because they can usually provide
good closed-loop response characteristics, can be tuned using relatively simple design rules, and are
easy to construct using either analog or digital components. In modern hydroelectric power plants,
the conventional PID control law is applied to control the hydraulic turbine speed, where the control
signal ‘u’ is the sum of three elements of proportional, integral, and differential gain of hydraulic
turbine speed deviation. The transfer function of a PID controller is given below:
x
sT
sK
s
K
Ku
n
di
p )
1
(
+
++−= --- (3)
Where,
‘Kp’ proportional gain,
‘Ki’ integral gain,
‘Kd’ derivative gain,
‘Tn’ derivative filter time constant (in sec).
Some of the electro-hydraulic governors are provided with three-term controllers with
proportional-integral-derivative (PID) action. These governors provide higher response speeds by
providing both transient gain decrement and transient gain increment. The proportional and integral
gains can be adjusted to obtain desired temporary droop and reset-time. The derivative action is
beneficial for isolated operation. Fig.2 shows the SIMULINK block diagram of the PID governor
with head controller [6].

93
Figure 2: Simulink model of PID Governor
3.2. PI Governor Model
PI governor does not have a derivation action; hence it is equivalent to a hydraulic governor.
Fig. 3 shows the PI governor SIMULINK model.
Figure 3: Simulink model of PI Governor
Similarly other governor models such as PD governor model and Fuzzy controlled governor
model have been implemented.
4. EXCITATION SYSTEM
An excitation system model is described [7] - Type DC excitation system, without the
exciter's saturation, which utilize a direct current generator with a commutator as the source of
excitation system power.

94
This model, described by the block diagram of Fig.4, is used to represent field controlled dc
commutator exciters with continuously acting voltage regulators.
Figure 4: Exciter system model
The exciter is represented by the following transfer function between the exciter voltage Vfd
and the regulator’s output ef :
eef
fd
sTKe
V
+
=
1
--- (4)
A signal derived from field voltage is normally used to provide excitation system
stabilization, ef, via the rate feedback with gain, Ke, and time constant, Te.
5. HYDRO POWER PLANT MODELING
The theoretical study of the behavior and stability of hydro power plants is complex and
highly difficult due to the large number of variables, to the fact that hydro units cannot be
standardized (each of them depending on the geographical situation of the area where it is placed)
and to the non-linearity of the hydro power system. The entire simulation system for the analysis of
three-phase to Ground fault on hydroelectric power plant has been developed in a
MATLAB/Simulink based software environment. Subsystems have been utilized in the
simplification of a system diagram and the creation of reusable systems. Further, a subsystem is a
group of blocks that is represented by a subsystem block. The entire simulation system contains three
subsystems: first, the speed governor and servomechanism, in which turbine speed, dead zone, valve
saturation, and limitation are all considered; second: the hydrodynamics system (HS), which consists
of tunnels, penstock, and surge tanks; and third, the turbine generator and network, which has a
generator unit operating in isolation.
In order to be able to analyze the stability of a hydro power plant, this should be theoretically
divided into two subsystems: the hydro subsystem (from the reservoir to the turbine) and the electro-
mechanical one (comprising the admission valves control system and speed governor. The general
block diagram for a hydro power plant [8] is shown in Fig.5. The Simulation Model of Power Plant
is shown in Fig.6.
We have selected synchronous machine with active power 150 MW, Terminal voltage
(Vrms) = 13.8 kV. Pmech = 150.32 MW. Field voltage Ef = 1.291 p u.

95
Figure 5: Basic Block diagram of a Hydro Power Plant
Figure 6: Simulation Model of Power Plant

96
6. SIMULATION RESULTS
The SIMULINK models for different types of governors have been simulated and their
effectiveness against a LLLG fault has been studied. The model is considering of regulator
servomotor, turbine and generator and servomotor type governor is regulated depending on the signal
come from controller. Results are observed which show parameters such as generator terminal
voltage, excitation voltage, stator current, rotors speed and rotor angular position. In this case,
synchronous generator is connected to the load through a transmission line as shown in Fig.6.
Initially the load is 15MW on the generator. At 10 seconds, disturbance is created by creating phase-
phase fault for 0.2seconds. The values of the governor, exciter, synchronous generator and hydraulic
turbine are same as given before. The simulation time for all models is 50 sec. The following
observations can be made from the simulation results.
PID Controller PI Controller
Time Time
Figure 7: Rotor Speed Deviation VS Time
Time Time
Figure 8: Stator Current Vs Time
Time Time
Figure 9: Mechanical Power Vs Time
RotorSpeedDeviation
RotorSpeedDeviation
StatorCurrent
StatorCurrent
MechanicalPower
MechanicalPower

97
Time Time
Figure 10: Speed Vs Time
Time Time
Figure 11: Field Voltage Vs Time
Time Time
Figure 12: Rotor Angle Deviation Vs Time
Fig.7 shows the deviations in the rotor speed for individual controllers. For a PID controller
the rotor speed deviates at the time of fault at t= 10 sec and reaches the magnitude of 0.35
(p.u) and takes t= 37 sec for entering stable state.
For a PI controller the rotor speed deviates at the time of fault at t= 10 sec and reaches the
magnitude of -0.35 (p.u) and takes t= 29 sec for entering stable state.
Fig.8 depicts the stator current variations for PID and PI Controllers. For a PID controller the
stator current increases dramatically as expected at the time of fault i.e. at t=10 sec and enters
a transient region at t=20 sec when the fault is cleared and stabilizes at t= 38.2 sec. For a PI
controller the stator current increases dramatically as expected at the time of fault i.e. at t=10
sec and enters a transient range at t=20 sec when the fault is cleared and stabilizes at t= 30
sec.
Fig.9 explains the variations in the mechanical power. For a PID controller the mechanical
power takes a dip at t=10 sec and keeps climbing up till t=50 sec. For a PI controller the
Speed
Speed
FieldVoltage
FieldVoltage
RotorAngleDeviation
RotorAngleDeviation

98
mechanical power starts climbing at t=10 sec and keeps climbing up till t=24 sec and dips till
t= 28.5 sec before its starts climbing till t=50 sec.
Fig.10 shows the speed of the alternator variations, a PID controller, the speed of the
alternator rises at t= 10 sec to reach a peak value of 1.54 pu and stabilizes at t= 36.5 sec. For
a PI controller the speed of the alternator dips at t= 10 sec to reach a peak value of 0.652 and
stabilizes at t= 28.5 sec.
Fig.11 exhibits the field voltage variations. For a PID controller the field voltage rises
drastically at t= 10 sec and stabilizes at t= 37.5 sec. For a PI controller the field voltage rises
drastically at t= 10 sec and stabilizes at t= 30 sec.
Fig.12 reveals the rotor angle deviations. For a PID controller the rotor angle deviation
increases from t =10 sec till it stabilizes at t =32 sec. For a PI controller the rotor angle
deviation decreases from t =10 sec till it stabilizes at t =24 sec.
CONCLUSION
SIMULINK is a powerful software package for the study of dynamic and nonlinear systems.
Using SIMULINK, the simulation model can be built up systematically starting from simple sub-
models. The hydro power plant model developed. Several tests and operating conditions can be
applied on the model. In this paper a three phase fault to ground case was shown, many other faults
or operating conditions as over load conditions can be applied and examined by this model.
The significance of controllers in Hydro power plant control system is to implement the
system operator knowledge to higher degree. A PI based turbine governor was proposed. It maintains
the frequency constant in spite of changing user load at any operating point. According to the
simulation results PI controller has proven to be the most suited controller for governing mechanism.
The values of Proportional gain and Integral gain play an important role in determining the
stabilizing time hence their optimization is absolutely necessary. The Simulation results prove that PI
based turbine governor has good performances. Moreover, good transient and steady state responses
for different operating points of the processes can be achieved.
9. ACKNOWLEDGEMENTS
The authors would like to acknowledge gratefully the constant encouragement and
continuous support by the Management, Principal and staff members of Electrical & Electronics
Engineering Department of Institute of Aeronautical Engineering, Hyderabad.
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99
[4] Ghanashyam Ranjitkar, Jinxing Huang and Tony Tung (2006): Application of Micro-
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