Simulation of IEEE FIRST BANCHMARK Model for SSR Studies

IJSRD - International Journal for Scientific Research & Development| Vol. 1, Issue 3, 2013 | ISSN (online): 2321-0613
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Simulation of IEEE FIRST BANCHMARK Model
for SSR Studies
K. G. Prajapati1
A. M. Upadhyay2
1
M. E. [Electrical] Student 2
Associate Professor
1, 2
Department of Electrical Engineering
1, 2
S. S. E. C., Bhavnagar, Gujarat, India
Abstract—The benchmark model for the study of
Subsynchronous resonance is presented by IEEE
Subsynchronous Resonance task force. Here, the IEEE First
Benchmark system for Subsynchronous resonance is
simulated using MATLAB for comparison. The oscillations
due to SSR are observed between turbine-generator and
between various turbine shafts. This paper mainly focuses
on the use of highly versatile software MATLAB for
analysis of Subsynchronous Resonance in power systems.
Key words: SSR, Synchronous Machine, Transient torque,
Multimass model.
I. INTRODUCTION
Electrical power generation involves interaction between the
electrical and mechanical energies coupled through the
generator. It follows that any change in the electric power
system results in a corresponding reaction/response from the
mechanical system and vice versa. Slow-changing load
translates to a slow-changing mechanical torque on the rotor
shaft, which in turn, is matched by a slow-changing rotor
angle to new steady-state angle between the rotor and the
stator along with adjustment in the mechanical power input
to the rotor through the turbines. Major disturbances such as
faults and fault clearing result in large transient torques on
the mechanical system and corresponding transient twisting
of the rotor shaft couplings between tandem turbines and
generator [1].
Worldwide series capacitors have been extensively
used for improving power transmission. While it has been
known that series capacitors can cause self-excited
oscillations at low frequencies (due to low X/R ratio) or at
Subsynchronous frequencies (due to induction generator
effect), the problem of self excited torsional frequency
oscillations (due to torsional oscillations) was first
experienced at Mohave power station in U.S.A. in
December 1970 and October 1971 [2]. The problem of self
excitation due to torsional interaction is a serious problem
and led to detailed analysis and study.
II. TYPES OF SSR INTERACTIONS
There are three types of SSR interactions which are
Induction Generator Effect, Torsional Interaction Effect and
Transient Torque Effect.
Induction generator effect is caused by self excitation of
the electrical system. Torsional interaction occurs when the
induced subsynchronous torque in the generator is close to
one of the torsional natural modes of the turbine generator
shaft[3]. Transient torques are those that result from system
disturbances. System disturbances cause sudden changes in
the network parameters, resulting in sudden changes in
currents that will tend to oscillate at the natural frequencies
of the network. Also, this can cause shaft damage as
experienced at Mohave generating station in U.S.A. [3].
Digital programs like Electromagnetic Transient Programs
(EMTP) and Simulator like RTDS (Real Time Digital
Simulator) are available to perform the studies of
Subsynchronous Resonance. SIMULINK®
, developed by
MathWorks, is a data flow graphical programming language
tool for modeling, simulating and analyzing multi domain
dynamic systems. With the use of above software, the First
Benchmark model[4] is developed and simulated.
III. THE IEEE FIRST BENCHMARK MODEL
The single line diagram of a Single Machine Infinite Bus
system given by IEEE committee for SSR study is shown in
fig. 1[4].
XT
Gen
XF
R XC
A B
XSYS
XF
Gap
XL
Infinite
Bus
Fig. 1: Single Line Diagram for First Benchmark Model for
SSR Study.
The circuit parameters are expressed in per unit on the
generator MVA rating at 60Hz. Reactances are proportional
to frequency, resistances are constant. The infinite bus is a
3-phase 60 Hz voltage source with zero impedance at all
frequencies. Two fault locations (A and B) are designated.
This network is used for both transient and self-excitation
studies.
IV. SYSTEM MODELING
First, individual mathematical models describing the
synchronous generator, turbine-generator mechanical
system, and electrical network are presented. Then, all the
equations are combined in a standard form for the analysis.
Synchronous Machine ModelingA.
For SSR analysis, experience has shown that reasonable
results may be obtained by defining two rotor circuits on

Simulation of IEEE FIRST BANCHMARK Model for SSR Studies
(IJSRD/Vol. 1/Issue 3/2013/0027)
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514
two different axes that are in space quadrature - the familiar
d and q-axes. A conventional synchronous machine
schematic diagram is shown in Fig. 2. The model shows
three-phase armature windings on the stator (a, b, and c).
The rotor of the machine carries the field fd winding and
damper windings. The damper windings are represented by
equivalent damper circuits in the direct axis (d-axis) and
quadrature axis (q-axis): 1d on d-axis, and 1q and 2q on q-
axis.
i
i
e
i
i
a e
eb
ec
i
b
c
q - axisd - axis
θ(t)
Fig. 2 : Schematic diagram of a conventional synchronous
machine.
ɑ,b,c : Stator windings
ea,eb,ec : Stator three-phase winding voltages.
ia,ib,ic : Stator three-phase winding currents.
fd : Field winding.
fed : Field voltage.
1d : d – axis damper winding.
1q : First q – axis damper winding.
2q : Second q – axis damper winding.
θ(t) : The electrical angle (in rad) by which d – axis
leads magnetic axis of phase a winding.
Two equivalent rotor circuits are represented in each axis of
the rotor - F and D in the d-axis, and G and Q in the q-axis,
with positive current direction defined as the direction
causing positive magnetization of the defined d- and q-axis
direction, respectively. Synchronous machine operation
under balanced three-phase conditions is of particular
interest for SSR analysis. The synchronous machine voltage
equations in normalized form can be written as follows.
[ ]
[
|
|
] [ ]
[ ]
[ ]
[ ]
The machine circuit equations given are usually expressed
schematically by the d and q equivalent circuits as shown in
Fig. 3
-
uF
+
iF
idrF
lF
lD
rD
LAD
+
vD
_
- ωψD +
iD
rala
iG
iqrG
lG
lQ
rQ
LAQ
+
vQ
_
- ωψQ +
iQ
rala
Fig. 3 :Equivalent circuit of machine from the voltage
equations
The Synchronous Machine block is given in MATLAB
Simpowersystems Library. The model takes into account the
dynamics of the stator, field, and damper windings. The
equivalent circuit of the model is represented in the rotor
reference frame (qd frame). All parameters and electrical
quantities are viewed from the rotor.
THP TGEN
ωH,δH
HP
DH
EXC
ωE ,δE
KEG
DE
GEN
ω,δ
KGB
DG
TIP
ωI ,δP
IP
KIH
DI
TLPA
ωA,δA
LPA
KAI
DA
TLPB
ωB,δB
LPB
KBA
DB
Fig. 4: Mechanical structure of six mass FBM system
Multi-mass model of the Turbine - Generator ShaftB.
The turbine-generator mechanical system consists of six
masses; high-pressure turbine (HP), intermediate-pressure
turbine (IP), low pressure turbine A (LPA) and low pressure
turbine B (LPB), an exciter (EXC), and a generator (GEN)
coupled to a common shaft as shown in Fig.4. The turbine
masses, generator rotor and exciter are considered as lumped
masses (rigid body) connected to each other via massless
springs.
From Fig.4, the torques acting on the generator mass are:
Generator:
Input torque
Output torque
Damping

515
Similarly, for the low pressure turbine B, the forces acting
are:
Low pressure turbine B:
Input torque
Output
Damping
Similarly all other masses torque equations can be derived.
The Steam Turbine and Governor block in MATLAB
Simpower systems library implements a complete tandem-
compound steam prime mover, including a speed governing
system, a four-stage steam turbine, and a shaft with up to
four masses. The shaft models a four-mass system, which is
coupled to the mass in the Synchronous Machine model for
a total of five masses. The exciter mass is omitted and a
static excitation system is used. Machine's mass is labeled as
mass #2. The mass in the Steam Turbine and Governor
block, which is closest to the machine's mass, is mass #3,
while the mass farthest from the machine is mass #6. The
shaft is characterized by mass inertias H, damping factors D,
and rigidity coefficients K.
V. SIMULATIONS AND RESULTS
The MATLAB Simpowersystems library components such
as multimass model of steam turbine and governor system,
Synchronous machine, exciter, a lumped parameter
transmission line and infinite source are connected as in
fig.1. and the circuit model is prepared in MATLAB
SIMULINK®
. The system is simulated for the same
operating condition as in[4]. For the transient case, three
phase fault is applied at bus B in fig.1 for duration of 75
msec from 0.01 seconds to 0.075 seconds(4.5 cycles). Fault
reactance is 0.04 p.u. and it is adjusted to produce a
capacitor transient voltage approaching the lower gap
setting.
Generator power output Po 0.9 pu
Generator power factorPF 0.9 pu (lagging)
Capacitor reactance 0.371 pu
Capacitor bypass voltage (not used)
Capacitor reinsertion voltage (not used)
Table. 1: Transient Case Description
Capacitor voltage, Generator current, Generator Electrical
Torque and Shaft Torque of LPA-LPB are plotted for the
time duration of 0.5 sec.
Fig.5(a).shows the variation of voltage across the
capacitor in per unit. The Capacitor voltage is varying up to
1 p.u. and it is settling down to a constant value after 0.3
seconds. Fig.5(b). shows the variation of the machine
current of phase A in per unit. From the graph, it is seen that
the machine phase current is oscillatory. Electrical torque of
the synchronous generator is shown Fig.5(c). It is clear that
the torque is not constant after application of fault at bus B.
That shows the electrical transmission network resonant
frequency matches one of the natural modes of the
multimass turbine.
The torque on the shaft between the LPA-LPB
turbine masses is shown in fig.5(d). There are oscillations of
frequency warring from 15Hz to 45Hz (subsynchronous).
Fig. 5: Response Curves For Transient Case
Extending the simulation for 5 seconds for the same
operating condition and applying three phase fault at bus-B
in fig.1 after 50 cycles and clearing after 4.5 cycles the
torque oscillations are as shown in fig.6. The oscillations are
growing rapidly. Fig.7 is FFT analysis window of the torque
on the shaft section LPA-LPB. It is clear from the fig. that
three torsional modes 16 Hz, 25 Hz, and 32 Hz are excited.
VI. CONCLUSION
By exciting the turbine torsional modes with three phase
fault Subsynchronous Resonance Phenomena is simulated.
The simulation is carried out for the same operating
condition as in [4]. Comparing with the reference results
except for the self-excitation case, the results obtained
(fig.5) are closely matching. The results are slight different
because of the difference in modeling of the components
and method of solving the non-linear equations. Also with
the FFT analysis tool of Power GUI the excited torsional
modes can be observed. The MATLAB model for SSR can

516
be used for the analysis of the various strategies of SSR
mitigation.
Fig. 7: FFT Analysis Of The LPA-LPB Section Torque Shown
In Fig. 6
APPENDIX
The network parameters of the system are as follows:
Generator ParametersA.
Power Factor: 0.9 lagging
Xa = 0.13 pu Xd = 1.79 pu
Xd= 0.169 pu Xl = 0.135 pu
Xq = 1.71 pu Xq= 0.228 pu
Xq pu Ra=0.002 pu
Td0 = 4.3 s Td0 = 0.032 s
Tq0 s Tq0 s
Mechanical Parameters:B.
Mass Inertia(Seconds) Torque Fraction
HP 0.0929 0.30
IP 0.1556 0.26
LPA 0.8587 0.22
LPB 0.8842 0.22
GEN 0.8686
Shaft Spring Constant (pu)
HP - IP 7277
IP - LPA 13168
LPA-LPB 19618
LPB-GEN 26713
Transformer Parameters:C.
Rated MVA: 892.4
Voltage Rating: 26/539 kV
Delta / Star grounded
R = 0.00792 pu
X = 0.14 pu
X0 = 0.14 pu
Transmission line parameters:D.
R = 0.02 pu
X = 0.50 pu
Series capacitor:E.
C = 0.371 pu
Infinite BusF.
Voltage: 500 kV RMS L-L
Phase angle: 0°
Fault ImpedanceG.
Reactance: 0.04 pu
REFERENCES
[1] N. G. Hingorani, L. Gyugyi, “Understanding
FACTS”: concepts and technology of flexible AC
transmission systems, New York: IEEE Press, 2000.
[2] K.R. Padiyar, “Power System Dynamics Stability and
Control”, Indian Institute of Science, Bangalore, 1996.
[3] P.M. Anderson, B.L. Agrawal, J.E. Van
Ness,“Subsynchronous Resonance in Power
Systems”, IEEE Press, New York, 1990.
[4] IEEE SSR Working Group, “First Benchmark Model
for Computer Simulation of Subsynchronous
Resonance”, IEEE Transactions on Power Apparatus
and Systems, Vol. PAS-96, no. 5, September/October
1977.
[5] IEEE Committee Report, “Rearer’s Guide To
Subsynchronous Resonance”, Subsynchronous
Resonance Working Group of the System Dynamic
Performance Subcommittee, IEEE Transactions on
Power Systems. Vol. 7, No. 1, February 1992
[6] MATLAB and SIMULINK Demos and Documentation.
[Online]. Available: http:// www.mathworks.com/
access/ helpdesk/ help/techdoc/

Simulation of IEEE FIRST BANCHMARK Model for SSR Studies

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