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C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 4, July-August 2012, pp.1254-1260
      Calculation of Available Transmission Capability Based on
                       Monte Carlo Simulation
        C.Prasanna Kumari*                              A. Hema Sekhar** M.Tech (Ph.D)
                          PG Student                               Associate Professor
                                               Department of EEE


Abstract -- With the further development of                 creation     and      formation   of     Regional
power markets, large amount of electric power               Transmission Organizations (RTO), initially called
wheeling and frequent transmission transaction              for by Federal Energy Regulatory Commission
is emerging, accurately determining Available               (FERC) order No.2000 and further enhanced by its
Transmission        Capability     (ATC)      and           2003 White Paper Wholesale Power Market
broadcasting the ATC information in time are                Platform”, are expected to bring increased
very important to prevent and relieve                       efficiency of power market through improved grid
transmission congestion effectively. In practical           management and increased customer access to
power markets, there are large amount of                    competitive power supplies. The ATC value is
uncertainties     involved     in   Transmission            required to be posted on Open Access Same-time
Reliability Margin (TRM) and Capacity Benefit               Information System (OASIS) by FERC’s order
Margin (CBM) of ATC. Considering calculation                889, 2000 and White Paper to make competition
accuracy and time, a novel approach is                      reasonable and effective. The ATC value between
proposed to calculate ATC based on Monte                    two points is given as
Carlo simulation and sensitivity analysis                               ATC=TTC−TRM−CBM−ETC (1)
considering large amount of uncertainties
impacting the value of ATC. The steady state                where TTC is Total Transfer Capability, TRM is
constraints and voltage stability and transient             Transmission Reliability Margin, CBM is Capacity
stability constraints are taken into account. The           Benefit Margin, and ETC is Existing Transmission
iterative solution based on PSASP by China                  Commitment including retail customer services
EPRI is developed. IEEE 14-bus test system is               between the same two points.
used to verify the presented approach. The
results show that the model and algorithm is                ATC computations should consider limits imposed
correct and effective. The research achievements            on the system components such as thermal, voltage,
are undergoing to transfer to the application in            and stability limits. In addition, uncertainties in
certain provincial power system in China, and               load forecasts and simultaneous transfers should be
some new problems are suggested in the end of               taken into account. For these reasons, uncertainties
paper.                                                      should be quantified properly to increase the
                                                            efficient use and the security of the system and to
  Index Terms -- Available Transmission                     provide necessary information for system operation
Capability (ATC), Transmission Reliability                  and planning. Uncertainties are expressed by two
Margin (TRM), Capacity Benefit Margin                       margins, TRM and CBM, during ATC calculations.
(CBM), Monte Carlo Simulation, Sensitivity                  Factors such as transmission line and generating
Analysis                                                    unit outages may dramatically affect ATC if they
                                                            are not taken into consideration.
I. INTRODUCTION                                             NERC defines TRM as “the amount of transfer
         NORTH       America Electric Reliability           capability necessary to provide a reasonable level
Council (NERC) defines Available Transmission               of assurance that the interconnected transmission
Capability (ATC) as a measure of the transfer               network will be secure.” TRM accounts for the
capability remaining in the physical transmission           inherent uncertainty in system conditions, its
network for further commercial activity over and            associated effects on ATC calculation, and the need
above already committed uses. ATC is an                     for operating flexibility to ensure reliable system
indication of the expected transfer capability              operation as system conditions change.
remaining on the transmission network. It is
available transfer capability that could be scheduled       There are several calculating TRM approaches:
to the designated path under the conditions
considered in calculating ATC values. ATC is a              Take a fixed percentage of TTC (say 4%) as TRM.
market signal that refers to the capability of a            This approach is relative conservative and not
system to transport or deliver energy above that of         accurate.
already subscribed transmission uses. The



                                                                                               1254 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 4, July-August 2012, pp.1254-1260
Monte Carlo statistical approach, which is based on     reflects the recent market activities, while it is hard
the repeated computation of TTC using variations        to deal with uncertainties. Monte Carlo simulation
in the base data, gives the difference between the      in [11] can process uncertainties of power systems
maximum and the minimum. This kind of                   within a shorter computation time.
computation is very time consuming with the
system expansion.                                          Considering calculation accuracy and time, a
                                                        novel method is proposed in this paper to calculate
Sensitivity analysis approach is realized by            ATC based on Monte Carlo simulation and
calculating several gradient values to take             sensitivity analysis considering large amount of
uncertainties into consideration.                       uncertainties, which have large impacts on the
NERC defines CBM as “the amount of firm                 value of ATC. The steady state constraints and
transfer capability preserved for Load Service          voltage stability and transient stability constraints
Entities (LSEs) on the host transmission system         are taken into account. The iterative solution based
where their load is located, to enable the access to    on PSASP by China EPRI is developed. IEEE 14-
generation from interconnected systems to meet          bus test system is used to verify the presented
generation reliability requirements.” Preservation      approach. The results show that both model and
of CBM for a LSE allows that entity to reduce its       algorithm are correct and effective.
installed generating capacity below what may
otherwise     have     been    necessary    without        The paper is organized as follows. In Section II
interconnections to meet its generation reliability     the Monte Carlo based probabilistic approach
requirements. The transmission capacity preserved       dealing uncertainties in ATC calculation is
as CBM is intended to be used by LSE only in            introduced. The mathematical model of ATC
times of emergency generation deficiencies. A LSE       computation and Sensitivity analysis approach are
would get the benefit from CBM by sharing               described in
installed capacity reserves with other parties
elsewhere in the interconnected network.                   Section III. The numerical examples are given
                                                        and discussed in Section IV. Last are conclusions
   ATC is calculated hourly, daily or monthly           in Section V.
based on market requirements. Certain factors
should be taken into account in ATC calculations          II .   MONTE CARLO BASED
such as the list of contingencies that would              PROBABILISTIC APPROACH FOR
represent most sever disturbances, accuracy of load
forecast and distribution, unit commitment, system      ATC CALCULATION
topology and configuration, and maintenance                       Using Monte Carlo simulation and
scheduling. System control devices such as voltage      sensitivity analysis to calculate ATC has three
regulators and reactive power control devices also      parts: i) construct the operation states of power
have a direct impact on ATC values.                     systems using Monte Carlo simulation; ii) assess
                                                        the states by power flow calculation; iii) calculate
   The literature of ATC calculation can be divided     the value of ATC by repetitive linear iteration
into two categories: deterministic methods and          based on sensitivity analysis.
probabilistic methods. Repeated power flow (REP)
in [2], continuation power flow (CPF) in [3], and                Monte Carlo simulation is a computer
optimal power flow (OPF) in [4] and [5] are based       simulation method based on the probabilistic
on power flow computation. For these methods, the       theory and the statistic technique. It can easily deal
steady state constraints can be easily considered but   with the uncertainties. Its computation time nearly
dynamic stability constraints are difficult to be       does not increase with power systems’ scale and
taken into account, and the computation time is         complexity. It is very suitable for sampling for the
longer. Sensitivity analysis in [6] can provide         system with large scale. In this paper we sample
results with shorter computation time. References       the operation states according to the system
[7] and [8] adopt AI methods to deal with               element’s probabilistic distribution using Monte
uncertainties of power systems with a shorter           Carlo simulation as follows:
computer time, but with the system expansion, the
validity and effect of the algorithm is still to be               For generators and transmission lines,
verified. These methods all belong to deterministic     two operation states: operation or fault, are
methods. The probabilistic methods include:             supposed while the corresponding probability
stochastic programming in [9] and enumeration           distribution is two-point distribution.
method in [10] which consider uncertainties, but
the computation time will increase rapidly when                  For transformers, besides two states of
the size of system increases. Bootstrap procedure in    operation and fault, there exist other states, such as
[12] computes the distribution of ATC value that        transformer tapping in different positions. When
                                                                                             1255 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 4, July-August 2012, pp.1254-1260
sampling the states of transformers, two steps are       constraints are taken into account. It is desired that
needed, firstly according to two-point distribution      the method calculating ATC should be easy, fast
to randomly create a state, and then select a            and efficient. The security margin concept, instead
tapping position. The corresponding probability          of direct stability analysis, is adopted in this paper.
distribution of transformer tapping can be given         Stability constrains here are divided into voltage
based on actual operation data.                          stability and transient stability. Checking these
                                                         margins after completing power flow calculation is
         For loads, we think that every bus load is      as an alternative of complicated stability
a random variable fluctuating around the forecast        computation. The mathematical model and detailed
value, and can be modeled by normal distribution         ATC calculation processes are described in Section
N(µ, σ2), where µ is the vector of the forecasted
load, and σ, which is estimated by the system                III. ATC COMPUTATION MODEL
running experiment, is variance vector.
                                                         ATC Computation Model
         After getting the current operation state,               The objective of ATC calculation is point
the repeated linear iteration based on sensitivity       by certain percentage (say 1%) step by step to
analysis is used to calculate ATC, which utilizes a      repeat computing power flow until 15% increase of
tangent vector at an initial solution of power flow      load, and making sure it is convergence of every
equations to predict the next operating point that is    power flow and satisfied all constraints, which
closer to the right solution, then improve the           indicates the present operation state at least with
precision by the repeat linear iteration. In this        15% voltage stability margin.
paper, the derived sensitivity formula describes the
relation between the injection power, the line           B. Computation Processes
power flow and bus voltage by the first partial                    The ATC computation processes based on
derivative matrix.                                       Monte Carlo and sensitivity analysis are listed as
                                                         follows.
          A load factor λ is added to represent the      Construct the initial state by sampling in terms of
increase of generator output and load demand.            the probabilistic distribution of each equipment.
That can be presented as                                 Compute power flow of the initial state, and
follows:       PLi=PLi0+λKpli,        QLi=QLi0+λKqli,    evaluate the corresponding operation state. If all
        0
PGi=PGi +λKpgi, where K is the multiplier to             constraints are satisfied, then go on to Step 3, or
designate the rate of load or power                      return to Step 1.
change. If the node is fixed, then K is constant.        Repeatedly increase load power in the sink and
Then the power flow equation is changed from             generators’ output in the source, and compute
F(δ, V)=0 to F(δ, V, λ)=0, and the changes of λ          relevant sensitivity factors as following:
correspond to the change of the operating pattern        a. Compute the sensitivities of the constraints with
of power systems.                                        respect
Using the first-order sensitivity of bus voltage, line   to the load factor λ, including ∂V/∂λ, ∂Sij/∂λ,
power and generator active power with respect to λ       ∂PG/∂λ, expressed by (4) to (8).
to describe the interaction of the system
parameters. That is to say: Using ∂V/∂λ the                  Max J  ∑PLd                      (2)     a) Solving ∂V∂λ

sensitivity of bus voltage to λ, ∂Sij/∂λ the                            d R
sensitivity of line power to λ and ∂PG/∂λ the
sensitivity of generator active power to λ to               The constraints include:
describe the interaction of the system parameters.                          N
When the system parameters changed, the load
factor λ can be decided by the first order                                          V (G cosδ  B sinδ )  0
                                                                 Pi −Vi j∑1         j  ij   ij  ij   ij
sensitivity. Then the updating ATC value can be                                 N
obtained.
                                                                                    V (G sinδ − B cosδ )  0
                                                                 Qi −Vi j∑1 j    ij     ij      ij   ij
         The sensitivity analysis can calculate ATC
                                                                    min         max
sententiously, quickly and exactly, and enhance                  Vi     ≤Vi ≤Vi      i N
precision by the repeated linear iteration.
                                                                      min               max
                                                                 Sl         ≤ Sl ≤ Sl         l NL                       (3)
                                                                       min                    max
         In ATC calculation, the thermal                         PGk            ≤ PGk ≤ PGk         k NG
constraints, voltage constraints, generator capacity
                                                                       min                    max
constraints, load demand, and power flow balance                 QGk            ≤ QGk ≤ QGk          k NG



                                                                                                       1256 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                   Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                          Vol. 2, Issue 4, July-August 2012, pp.1254-1260
       −45 ≤δi ≤ 45 i N
                                                                                                         ~                              *        Bc                *              *        *
                                                                                                                           &                             *
Where R is the set of load in sink, PLd refers to the
                                                                                                         Sij Vi [V i ( j                         2     ) (V i −V j ) y ij ] ,
load linked
                                                                                          we can get
to bus d; N is the number of nodes, and NL the number
                                                 min
of branches, NG the number of generators; Vi         and                                                        2
Vi
   max
        are the                                                                                          Pij Vi gij −ViV j (gij cosδij bij sin δij )
Lower and upper voltage limits of bus i, respectively;
   min                                                                                                            2 B c
Sl
   max
       and                                                                                               Qij  −Vi ( 2 bij ) −ViV j (gij sin δij −bij cos δij )
Sl     are the thermal stability constraints of branch l;
     min      max          min       max
PGk , PGk , and QGk , QGk                 are the output                                                          2     2
limits of generator k.                                                                                   Sij  Pij Qij                                                                                                    (6)
    Δi is the phase angle of voltage of bus i. This
paper adopts the lemma “the absolute values of                                              Then
phase angles of all buses voltages are less than 45”                                                        ∂Sij                  ∂Sij ∂V               ∂Sij          ∂V j                ∂Sij ∂δ           ∂Sij ∂δ j
as the simplified criterion to verify transient                                                                                                   i                                                  i
stability in [6]. After every power flow calculation,                                                         ∂λ                ∂Vi              ∂λ          ∂V j       ∂λ                   ∂δi   ∂λ        ∂δ j    ∂λ    (7)
checking the absolute value of phase angle of each                                          where
bus voltage to see whether within 45, if it is, then                                                           ∂Sij                                   ∂Pij                           ∂Qij
the system is regarded as transient stability.                                                                                      1 (P                       Q                             )
                                                                                                                                        S
For voltage stability assessment, an experiential                                                               ∂Vi                         ij    ij         ∂Vi        ij              ∂Vi
criterion: more than 15 percentage margin far from                                                              ∂Sij                                    ∂Pij                          ∂Qij
voltage collapse, is taken instead of computing the                                                                                 1 (P                          Q                          )
                                                                                                                                       S          ij
voltage collapse point under each state, which is                                                               ∂Vj                         ij           ∂V    j        ij             ∂V j
realized by increasing load in the sink From power                                                              ∂Sij                                   ∂Pij                           ∂Qij
flow equations F (δ, v, λ)  0 , we can get                                                                                         1 (P                      Q                              )
                                                                                                                                        S
                                                                                                                ∂δi                         ij    ij          ∂δi            ij            ∂δi
                          ∂P                                                                                    ∂Sij                                   ∂Pij                           ∂Qij
             ∂P    ∂P               dδ                                                                                              1 (P                       Q                             )
                                                                                                                                     S
             ∂δ    ∂V     ∂λ                                                                                    ∂δ j                        ij              ∂δ j                        ∂δ j
                                        dV   0.                                                                                                  ij                         ij
             ∂Q     ∂Q        ∂Q                                                        (4)
                                        dλ
                                                                                          where Pij and Qij are real power and reactive power
             ∂δ    ∂V         ∂λ
                                                                                          flowed in branch ij; yij, g ij and bij are parameters
Then
                                                                                          of line ij; Bc is susceptance of line-to-ground.
             ∂δ         ∂P         ∂P −1 ∂P
                                                                                                        ∂                          PG
                    ∂λ     − ∂δ ∂V           ∂λ                                         (5) c) Solving
             ∂V          ∂Q      ∂Q          ∂Q                                                                                     ∂λ
                                                                                                                       ∂P
              ∂λ         ∂δ        ∂V        ∂λ
                                                                                                                                   G
             ∂P    ∂P                                             ∂P                                                       ∂λ            K Pg                                                                  (8)
        ∂δ         ∂V
where                                              is the Jaccobian matrix;   ∂∂Qλ is a column
             ∂Q    ∂Q                                                                     where KPg is the change factor of generator’s real
             ∂δ    ∂V                                                                     power. b. Compute ∆λ by (9), (10) and (11).
                                                                     ∂λ



                                                                                                                               0
Vector. Amongst all elements, except those KPi or                                                V              −V
                                                                                                     lim,i                 i

KQi related to the sink and the source are not zero                                   ∆λVi                                                                                                                     (9)
                                                                                                   ∂Vi ∂λ
elements, the remainder is zero.                                                                          0
               Sij                                                                               P     −P
   b) Solving ∂                                                                                      G,lim                     G


                ∂λ
                                                                                      ∆λ G           ∂PG ∂λ                                                                                                  (10)
From the branch power flow equation                                                                                                 0
                                                                                                                       − Sij
                                                                                                     S
                                                                                                                                                               ∂Sij                   ∂λ  0
                                                                                                         lim,i , j


                                                                                                         ∂Sij              ∂λ                                                                                 (11)
                                                                                      ∆λ S                                             0
                                                                                                     −S lim,i                  −Sij
                                                                                                                                                                ∂Sij                  ∂λ  0
                                                                                                                     , j



                                                                                                             ∂Sij ∂λ


                                                                                                                                                                                        1257 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 4, July-August 2012, pp.1254-1260
Where when ∂Vi/∂λ>0, Vlim,i is the upper limit; when
                                         0
∂Vi/∂λ<0, Vlim,i is the lower limit; Vi is the initial
magnitude of Vi; ∂Vi/∂λ is the sensitivity of Vi with
respect to λ; Slim,i j is the thermal limit of branch ij;
∂Sij/∂λ is the sensitivity of power in                                                 76
branch ij with respect to λ; PG,lim is the maximum
                                                                                                                                     Gen. 3
                                                                                                                                     Gen. 8
                                                0                                      74                                            Gen. 6
output of generators in the source point; PG is the
initial output of all generators in the source point;                                  72




                                                                          ATC ( MW )
∂PG/∂λ is the sensitivity of PG with respect to λ.                                     70
c. Find the minimum increment of ∆λ.
                                                                                       68




     ∆λ  min{∆λV , ∆λS , ∆λG }                             (12)                            66


d. Modify λ.                                                                                64

         (n1)         (n)
     λ           λ         ∆λ                           (13)                            62
                                                                                             0   10   20       30    40      50      60       70   80
                                                                                                           Generator’s output (MW)
                                                                        Fig. 1. The effect of the generation on ATC


After n times of iteration, if ∆λ is less than the              by China EPRI is developed. IEEE 14-bus test
                                                                system is used to verify the presented approach.
preset error ε, then to stop iterative computation,             The single line diagram and parameters of the test
and the last λ is the                                           system can be found in [15]. Bus 2 is supposed as
                                                                the source bus, bus 12, 13 and 14 are selected as
                                                                the sink buses, then ATC is defined as:
                                                                ATC=P12+P13+P14. This paper will verify the
 Maximum value under the specified condition.                   approach from the flowing three aspects:
  e. Update load and power generation by (14).                  (1) The influence of active power change of one
                                                                generator on ATC value. In the test system, there
                                  0                             are 5 generators: bus 1 is set as the slack bus; bus 2
                 PLi  PLi             λK pli
                                                                is the source bus, so consider the influences of bus
                              0                                 3, 6, 8 separately. The constraints of the generator’s
                 QLi  QLi         λKqli                     (14)
                                                                active power are: G3 (15MW, 80MW), G6
                          0                                     (10MW, 45MW) and G8 (10MW, 40MW). Select
                 PGi  PGi  λKPgi
                                                                5MW as the incremental active power, then active
                                                                power change of each generator is used to study the
                                                                influences on the value of ATC with the results
where PLi and QLi are real and reactive load power              shown in Fig.1. Analyzing Fig.1 we can
of bus i, Kpli and Kqli are the multipliers to
designate the rate of load change, KPgi is the                     conclude: the active power increase of non-source
multiplier to designate the rate of power change,                  generator has the influence on the value of ATC;
PGi is active power generation, and superscript 0 is               and different electrical distance of non-source
the initial state.                                                 generator has different influence. In the tests
   (4) Compute power flow of the updated state, if                 generators 6 and 8 are near the source, their
power flow is convergent normally, then evaluate                   influences to ATC are more evident than generator
the corresponding operation state. If all constraints              3 that is far from the source bus. It also suggests
are satisfied, then return to Step 3, or go to Step 5.             active power generation and unit commitment have
   (5) The ATC computation is terminated if any                    obvious influences on the value of ATC.
of the constraints is not satisfied. The value of ATC
can be calculated by the recent power flow results                (2) The influence of load change on ATC. Select
as follows.                                                    0.02 per unit as the step, increase the load of each
          ATC= ∑PLd                                            node from 80% to 120% of the forecast value, then
                                                             (15)
                       d R                                     we can get the relation curve of load change with
                                                               ATC shown in Fig.2. From Fig.2 we can conclude:
IV. NUMERICAL TESTS                                            when the load increases, the value of ATC will
                                                     [14]      decrease. It refers to the accuracy of load forecast is
   The iterative solution based on PSASP/UPI
                                                                                                                          1258 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
                Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                      Vol. 2, Issue 4, July-August 2012, pp.1254-1260
important in ATC calculation.                                                            calculation should consider not only the influences
                                                                                         of single uncertainty, but also the ones of these
                     70
                                                                                         uncertainties’ combination. For example, multi-
                     68
                                                                                         fault and multi-uncertainty impact the value of
                                                                                         ATC at the same time. After sampling and
          ATC (MW)




                     66
                                                                                         calculation, we can get a series of results
                                                                                         representing different states, selecting the
                     64                                                                  minimum one as the finial ATC value. Compare to
                                                                                         deterministic methods, the presented approach in
                     62                                                                  this paper can give the value of ATC more
                                                                                         accurate. For this test, we select the result of Case 5
                     60                                                                  as the finial result. If we take out CBM (5%), the
                     58
                                                                                         finial ATC is 57.20495%=47.3438MW.
                      -0.2    -0.15   -0.1    -0.05     0      0.05   0.1   0.15   0.2
                                             Load variation (p.u.)
                                                                                         We are undergoing to transfer the research
Fig. 2. The influence of load changing on ATC                                            achievements to the application in certain
                                                                                         provincial power system in China.
   (3) The influence of different uncertainties on
ATC. Suppose the actual load value changes within                                        V. CONCLUSIONS AND NEXT WORK
2% of forecasting value, the fault probability of                                                 According to the ATC definition of North
the generators is supposed at 0.02, the fault rate of                                    America Electric Reliability Council (NERC), this
the lines is 0.01, and the fault rate of the                                             paper mainly studies two margins of ATC: TRM
transformers is 0.02. Assume transformers’ tapping                                       and CBM. Considering calculation accuracy and
have 5 levels, the probability distribution of each                                      time, a novel method is proposed to calculate ATC
level is: 100% 0.5, 102.5% 0.15, 97.5% 0.15, 105%                                        based on Monte Carlo simulation and sensitivity
0.10, and 95% 0.10, respectively. Using Monte                                            analysis considering large amount of uncertainties
Carlo sampling in terms of the probabilistic                                             involved in TRM and CBM, which have large
distribution of each equipment to construct a series                                     impacts on the value of ATC. The steady state
of system states, and then use sensitivity analysis to                                   constraints and voltage stability and transient
get corresponding ATC values, and select the                                             stability constraints are taken into account. The
                                                                                         iterative solution based on PSASP by China EPRI
minimum as the final result. The examples are
                                                                                         is developed. IEEE 14-bus test system is used to
shown in Table I.
                                                                                         verify the presented approach. The results show
In Table I, Case 1 is the IEEE standard state, there                                     that the model and algorithm is correct and
is no load change no fault; Case 2 only has load                                         effective. Compare to the deterministic methods,
change; Case 3 have load and transformers’ tapping                                       the proposed approach gives the value of ATC
adjustment simultaneously; Case 4 have load                                              more accurate. When we transfer the theoretical
change and one line fault; Case 5 has load change                                        achievements to practical applications, we found
and one non-source generator fault.                                                      some work needed further study.
                      TABLE I
       ATC CALCULATION RESULTS
                                                                                         1.       The proposed approach in this paper, like
                                                                                         most of other methods, is mainly suitable for
                     Case                    ATC/MW                                      theoretically calculating ATC at a time point. But
                          1                   63.662                                     in practical power markets, load and trading
                          2                   61.357
                                                                                         scheme are continuously change, so it is necessary
                          3                   65.373
                                                                                         for ATC computation approach to consider load
                                                                                         demand and relevant bidding strategies continuous
                          4                   58.937
                                                                                         variation. The states, stochastically produced in
                          5                   57.204
                                                                                         terms of probability distribution introduced above,
                                                                                         should be related to current system operation, and
                                                                                         when simulating continuous ATC calculation, it
Analyzing Table I, we can conclude that
                                                                                         should be additionally considered the transfer
uncertainties play an important role in ATC
                                                                                         probability from the current state to next one. Unit
calculation. For example, load change and
                                                                                         commitment and maintenance scheduling even
transformer tapping adjustment make the value of
                                                                                         bidding strategies should be taken into account.
ATC great change; the fault of line, transformer
and generator will decrease the value of ATC. Load
                                                                                         2.      Existing Transmission    Commitment
change randomly all the time, the fault of
                                                                                         (ETC) should be considered more detailed in
components and transformer tapping can be viewed
                                                                                         continuous ATC calculation. Because in power
as specific probability distribution. The ATC
                                                                                                                              1259 | P a g e
C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and
               Applications (IJERA) ISSN: 2248-9622 www.ijera.com
                     Vol. 2, Issue 4, July-August 2012, pp.1254-1260
markets, ATC is an important signal to all              [9] C. Y. Tsai, C. N. Lu. "Bootstrap application in
participants, and the decision and evaluation about          ATC estimation," IEEE Power Engineering
the risk of different trading is also worth of               Review, vol. 21, pp. 40-42, Feb. 2001.
consideration.                                          [10] S. X. Zhou, L. Z. Zhu, X. J. Guo, Power
                                                             system voltage stability and control. Beijing:
How to improve ATC is an attractive issue. FACTS             China Electric Power Press, 2004.
device is a good choice, and it can not only            [11] Power system analysis software package
improve the value of ATC, but also improve the               PSASP 6.1 User’s Manual. Beijing: Electric
stability of the system. But how to decide the               Power Research Institute, 2001
optimal installation position of the FACTS device       [12] F. Wang, G. B. Shrestha, "Allocation of TCSC
and how to coordinate multiple FACTS devices are             devices to optimize total transfer capability in
still need further research.                                 a competitive power market," in Proc 2001
                                                             IEEE PES Winter Meeting, vol. 1, pp.
VI. REFERENCES                                               587~593.
[1] Transmission Transfer Capability Task Force.
    Available transfer capability definitions and
    determination. North American Electric              VII. BIOGRAPHIES
    Reliability Council, Princeton, NJ, June 1996.          Yajing Gao was born in Hebei Province,
[2] C. S. Wang, G. Q. Li, Y. X. Yu, W. Jiang,               China, on Dec 31, 1980. She received the B.S.
    "Study on transmission transfer capability of           degree in Electrical Engineering, from North
    interconnected electric power system (I),"              China Electric Power University (NCEPU) in
    Automation of Electric Power Systems, vol. 23,          2002. Now she is pursuing the Ph. D. degree at
    no. 3, pp. 23-26, Mar. 1999.                            NCEPU. Her research interest is electricity
[3] Y. J. Dai, J. D. McCalley, V. Vittal,                   markets.
    "Simplification expansion and enhancement of
    direct interior point algorithm for power
    system maximum load ability," IEEE Trans.               Ming Zhou received the B.S. and M.S.
    on Power Systems, vol. 15, no. 3,                       degrees in Electrical Engineering from North
    pp. 1014-1021, Aug. 2000.                               China Electric Power University (NCEPU) in
[4] Q. H. Diao, S. Mohamed, Y. X. Ni, "Inter-area           1989 and 1992, respectively. Now she is
    total transfer capability calculation using             pursuing Ph. D. degree at NCEPU. Since 1992,
    sequential quadratic programming method in              Ms. Zhou has been with the Department of
    power market." Automation of Electric Power             Electrical Engineering at NCEPU, where she is
    Systems, vol. 24, no. 24, pp. 5-8, Dec. 2000.           currently an associate professor. Her areas of
[5] A. Kulyos, Y. Akihiko, "Consideration of an             interest include AI applications to power
    appropriate TTC by probabilistic approach,"             systems, electricity markets, and power system
    IEEE Trans. on Power Systems, vol. 19, no. 1,           operation and management.
    pp. 375-383, Feb. 2004.
[6] X. Luo, A. D. Patton, C. Singh, "Real power             Gengyin Li (M’03) was born in Hebei
    transfer capability calculations using multi-           Province, China, on May 18, 1964. He
    layer feed-forward neural networks," IEEE               received the B.S., M.S. and Ph.D. degrees, all
    Trans. on Power Systems, vol. 15, no. 2, pp.            in Electrical Engineering, from North China
    903-908, May 2000.                                      Electric Power University (NCEPU) in 1984,
[7] A. B. Khairuddin, S. S. Ahmed, M. W.                    1987 and 1996, respectively. Since 1987, Dr.
    Mustafa, A. A. M. Zin, H. Ahmad, "A novel               Li has been with the Department of Electrical
    method for ATC computations in a large-scale            Engineering at NCEPU, where he is currently
    power system," IEEE Trans. on Power                     a professor and deputy head of the
    Systems, vol. 19, no.2, pp. 1150-1158, May              Department. His research interests include
    2004. Armando, S. Leiteda, G. C. C. João,               electricity markets, power quality, analysis and
    "Transmission capacity: availability, maximum           control of power systems, and new
    transfer and reliability," IEEE Trans. on Power         transmission and distribution technologies.
    Systems, vol. 17, no. 3, pp. 843-849, Aug.
    2002.                                                   Yuekui Huang was born in                  Hunan
[8] F. Xia, A. P. S. Meliopoulos, "A methodology            Province, China, on Oct 20, 1980.
    for probabilistic simultaneous           transfer
    capability analysis," IEEE Trans. on Power
    Systems, vol. 11, no. 3, pp. 1269-1278, Aug.
    1996.

                                                                                            1260 | P a g e

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  • 1. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 Calculation of Available Transmission Capability Based on Monte Carlo Simulation C.Prasanna Kumari* A. Hema Sekhar** M.Tech (Ph.D) PG Student Associate Professor Department of EEE Abstract -- With the further development of creation and formation of Regional power markets, large amount of electric power Transmission Organizations (RTO), initially called wheeling and frequent transmission transaction for by Federal Energy Regulatory Commission is emerging, accurately determining Available (FERC) order No.2000 and further enhanced by its Transmission Capability (ATC) and 2003 White Paper Wholesale Power Market broadcasting the ATC information in time are Platform”, are expected to bring increased very important to prevent and relieve efficiency of power market through improved grid transmission congestion effectively. In practical management and increased customer access to power markets, there are large amount of competitive power supplies. The ATC value is uncertainties involved in Transmission required to be posted on Open Access Same-time Reliability Margin (TRM) and Capacity Benefit Information System (OASIS) by FERC’s order Margin (CBM) of ATC. Considering calculation 889, 2000 and White Paper to make competition accuracy and time, a novel approach is reasonable and effective. The ATC value between proposed to calculate ATC based on Monte two points is given as Carlo simulation and sensitivity analysis ATC=TTC−TRM−CBM−ETC (1) considering large amount of uncertainties impacting the value of ATC. The steady state where TTC is Total Transfer Capability, TRM is constraints and voltage stability and transient Transmission Reliability Margin, CBM is Capacity stability constraints are taken into account. The Benefit Margin, and ETC is Existing Transmission iterative solution based on PSASP by China Commitment including retail customer services EPRI is developed. IEEE 14-bus test system is between the same two points. used to verify the presented approach. The results show that the model and algorithm is ATC computations should consider limits imposed correct and effective. The research achievements on the system components such as thermal, voltage, are undergoing to transfer to the application in and stability limits. In addition, uncertainties in certain provincial power system in China, and load forecasts and simultaneous transfers should be some new problems are suggested in the end of taken into account. For these reasons, uncertainties paper. should be quantified properly to increase the efficient use and the security of the system and to Index Terms -- Available Transmission provide necessary information for system operation Capability (ATC), Transmission Reliability and planning. Uncertainties are expressed by two Margin (TRM), Capacity Benefit Margin margins, TRM and CBM, during ATC calculations. (CBM), Monte Carlo Simulation, Sensitivity Factors such as transmission line and generating Analysis unit outages may dramatically affect ATC if they are not taken into consideration. I. INTRODUCTION NERC defines TRM as “the amount of transfer NORTH America Electric Reliability capability necessary to provide a reasonable level Council (NERC) defines Available Transmission of assurance that the interconnected transmission Capability (ATC) as a measure of the transfer network will be secure.” TRM accounts for the capability remaining in the physical transmission inherent uncertainty in system conditions, its network for further commercial activity over and associated effects on ATC calculation, and the need above already committed uses. ATC is an for operating flexibility to ensure reliable system indication of the expected transfer capability operation as system conditions change. remaining on the transmission network. It is available transfer capability that could be scheduled There are several calculating TRM approaches: to the designated path under the conditions considered in calculating ATC values. ATC is a Take a fixed percentage of TTC (say 4%) as TRM. market signal that refers to the capability of a This approach is relative conservative and not system to transport or deliver energy above that of accurate. already subscribed transmission uses. The 1254 | P a g e
  • 2. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 Monte Carlo statistical approach, which is based on reflects the recent market activities, while it is hard the repeated computation of TTC using variations to deal with uncertainties. Monte Carlo simulation in the base data, gives the difference between the in [11] can process uncertainties of power systems maximum and the minimum. This kind of within a shorter computation time. computation is very time consuming with the system expansion. Considering calculation accuracy and time, a novel method is proposed in this paper to calculate Sensitivity analysis approach is realized by ATC based on Monte Carlo simulation and calculating several gradient values to take sensitivity analysis considering large amount of uncertainties into consideration. uncertainties, which have large impacts on the NERC defines CBM as “the amount of firm value of ATC. The steady state constraints and transfer capability preserved for Load Service voltage stability and transient stability constraints Entities (LSEs) on the host transmission system are taken into account. The iterative solution based where their load is located, to enable the access to on PSASP by China EPRI is developed. IEEE 14- generation from interconnected systems to meet bus test system is used to verify the presented generation reliability requirements.” Preservation approach. The results show that both model and of CBM for a LSE allows that entity to reduce its algorithm are correct and effective. installed generating capacity below what may otherwise have been necessary without The paper is organized as follows. In Section II interconnections to meet its generation reliability the Monte Carlo based probabilistic approach requirements. The transmission capacity preserved dealing uncertainties in ATC calculation is as CBM is intended to be used by LSE only in introduced. The mathematical model of ATC times of emergency generation deficiencies. A LSE computation and Sensitivity analysis approach are would get the benefit from CBM by sharing described in installed capacity reserves with other parties elsewhere in the interconnected network. Section III. The numerical examples are given and discussed in Section IV. Last are conclusions ATC is calculated hourly, daily or monthly in Section V. based on market requirements. Certain factors should be taken into account in ATC calculations II . MONTE CARLO BASED such as the list of contingencies that would PROBABILISTIC APPROACH FOR represent most sever disturbances, accuracy of load forecast and distribution, unit commitment, system ATC CALCULATION topology and configuration, and maintenance Using Monte Carlo simulation and scheduling. System control devices such as voltage sensitivity analysis to calculate ATC has three regulators and reactive power control devices also parts: i) construct the operation states of power have a direct impact on ATC values. systems using Monte Carlo simulation; ii) assess the states by power flow calculation; iii) calculate The literature of ATC calculation can be divided the value of ATC by repetitive linear iteration into two categories: deterministic methods and based on sensitivity analysis. probabilistic methods. Repeated power flow (REP) in [2], continuation power flow (CPF) in [3], and Monte Carlo simulation is a computer optimal power flow (OPF) in [4] and [5] are based simulation method based on the probabilistic on power flow computation. For these methods, the theory and the statistic technique. It can easily deal steady state constraints can be easily considered but with the uncertainties. Its computation time nearly dynamic stability constraints are difficult to be does not increase with power systems’ scale and taken into account, and the computation time is complexity. It is very suitable for sampling for the longer. Sensitivity analysis in [6] can provide system with large scale. In this paper we sample results with shorter computation time. References the operation states according to the system [7] and [8] adopt AI methods to deal with element’s probabilistic distribution using Monte uncertainties of power systems with a shorter Carlo simulation as follows: computer time, but with the system expansion, the validity and effect of the algorithm is still to be For generators and transmission lines, verified. These methods all belong to deterministic two operation states: operation or fault, are methods. The probabilistic methods include: supposed while the corresponding probability stochastic programming in [9] and enumeration distribution is two-point distribution. method in [10] which consider uncertainties, but the computation time will increase rapidly when For transformers, besides two states of the size of system increases. Bootstrap procedure in operation and fault, there exist other states, such as [12] computes the distribution of ATC value that transformer tapping in different positions. When 1255 | P a g e
  • 3. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 sampling the states of transformers, two steps are constraints are taken into account. It is desired that needed, firstly according to two-point distribution the method calculating ATC should be easy, fast to randomly create a state, and then select a and efficient. The security margin concept, instead tapping position. The corresponding probability of direct stability analysis, is adopted in this paper. distribution of transformer tapping can be given Stability constrains here are divided into voltage based on actual operation data. stability and transient stability. Checking these margins after completing power flow calculation is For loads, we think that every bus load is as an alternative of complicated stability a random variable fluctuating around the forecast computation. The mathematical model and detailed value, and can be modeled by normal distribution ATC calculation processes are described in Section N(µ, σ2), where µ is the vector of the forecasted load, and σ, which is estimated by the system III. ATC COMPUTATION MODEL running experiment, is variance vector. ATC Computation Model After getting the current operation state, The objective of ATC calculation is point the repeated linear iteration based on sensitivity by certain percentage (say 1%) step by step to analysis is used to calculate ATC, which utilizes a repeat computing power flow until 15% increase of tangent vector at an initial solution of power flow load, and making sure it is convergence of every equations to predict the next operating point that is power flow and satisfied all constraints, which closer to the right solution, then improve the indicates the present operation state at least with precision by the repeat linear iteration. In this 15% voltage stability margin. paper, the derived sensitivity formula describes the relation between the injection power, the line B. Computation Processes power flow and bus voltage by the first partial The ATC computation processes based on derivative matrix. Monte Carlo and sensitivity analysis are listed as follows. A load factor λ is added to represent the Construct the initial state by sampling in terms of increase of generator output and load demand. the probabilistic distribution of each equipment. That can be presented as Compute power flow of the initial state, and follows: PLi=PLi0+λKpli, QLi=QLi0+λKqli, evaluate the corresponding operation state. If all 0 PGi=PGi +λKpgi, where K is the multiplier to constraints are satisfied, then go on to Step 3, or designate the rate of load or power return to Step 1. change. If the node is fixed, then K is constant. Repeatedly increase load power in the sink and Then the power flow equation is changed from generators’ output in the source, and compute F(δ, V)=0 to F(δ, V, λ)=0, and the changes of λ relevant sensitivity factors as following: correspond to the change of the operating pattern a. Compute the sensitivities of the constraints with of power systems. respect Using the first-order sensitivity of bus voltage, line to the load factor λ, including ∂V/∂λ, ∂Sij/∂λ, power and generator active power with respect to λ ∂PG/∂λ, expressed by (4) to (8). to describe the interaction of the system parameters. That is to say: Using ∂V/∂λ the Max J  ∑PLd (2) a) Solving ∂V∂λ sensitivity of bus voltage to λ, ∂Sij/∂λ the d R sensitivity of line power to λ and ∂PG/∂λ the sensitivity of generator active power to λ to The constraints include: describe the interaction of the system parameters. N When the system parameters changed, the load factor λ can be decided by the first order V (G cosδ  B sinδ )  0 Pi −Vi j∑1 j ij ij ij ij sensitivity. Then the updating ATC value can be N obtained. V (G sinδ − B cosδ )  0 Qi −Vi j∑1 j ij ij ij ij The sensitivity analysis can calculate ATC min max sententiously, quickly and exactly, and enhance Vi ≤Vi ≤Vi i N precision by the repeated linear iteration. min max Sl ≤ Sl ≤ Sl l NL (3) min max In ATC calculation, the thermal PGk ≤ PGk ≤ PGk k NG constraints, voltage constraints, generator capacity min max constraints, load demand, and power flow balance QGk ≤ QGk ≤ QGk k NG 1256 | P a g e
  • 4. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 −45 ≤δi ≤ 45 i N ~ * Bc * * * & * Where R is the set of load in sink, PLd refers to the Sij Vi [V i ( j 2 ) (V i −V j ) y ij ] , load linked we can get to bus d; N is the number of nodes, and NL the number min of branches, NG the number of generators; Vi and 2 Vi max are the Pij Vi gij −ViV j (gij cosδij bij sin δij ) Lower and upper voltage limits of bus i, respectively; min 2 B c Sl max and Qij  −Vi ( 2 bij ) −ViV j (gij sin δij −bij cos δij ) Sl are the thermal stability constraints of branch l; min max min max PGk , PGk , and QGk , QGk are the output 2 2 limits of generator k. Sij  Pij Qij (6) Δi is the phase angle of voltage of bus i. This paper adopts the lemma “the absolute values of Then phase angles of all buses voltages are less than 45” ∂Sij ∂Sij ∂V ∂Sij ∂V j ∂Sij ∂δ ∂Sij ∂δ j as the simplified criterion to verify transient  i   i stability in [6]. After every power flow calculation, ∂λ ∂Vi ∂λ ∂V j ∂λ ∂δi ∂λ  ∂δ j ∂λ (7) checking the absolute value of phase angle of each where bus voltage to see whether within 45, if it is, then ∂Sij ∂Pij ∂Qij the system is regarded as transient stability.  1 (P Q ) S For voltage stability assessment, an experiential ∂Vi ij ij ∂Vi ij ∂Vi criterion: more than 15 percentage margin far from ∂Sij ∂Pij ∂Qij voltage collapse, is taken instead of computing the  1 (P Q ) S ij voltage collapse point under each state, which is ∂Vj ij ∂V j ij ∂V j realized by increasing load in the sink From power ∂Sij ∂Pij ∂Qij flow equations F (δ, v, λ)  0 , we can get  1 (P Q ) S ∂δi ij ij ∂δi ij ∂δi ∂P ∂Sij ∂Pij ∂Qij ∂P ∂P dδ  1 (P Q ) S ∂δ ∂V ∂λ ∂δ j ij ∂δ j ∂δ j dV 0. ij ij ∂Q ∂Q ∂Q (4) dλ where Pij and Qij are real power and reactive power ∂δ ∂V ∂λ flowed in branch ij; yij, g ij and bij are parameters Then of line ij; Bc is susceptance of line-to-ground. ∂δ ∂P ∂P −1 ∂P ∂ PG ∂λ  − ∂δ ∂V ∂λ (5) c) Solving ∂V ∂Q ∂Q ∂Q ∂λ ∂P ∂λ ∂δ ∂V ∂λ G ∂P ∂P ∂P ∂λ  K Pg (8) ∂δ ∂V where is the Jaccobian matrix; ∂∂Qλ is a column ∂Q ∂Q where KPg is the change factor of generator’s real ∂δ ∂V power. b. Compute ∆λ by (9), (10) and (11). ∂λ 0 Vector. Amongst all elements, except those KPi or V −V lim,i i KQi related to the sink and the source are not zero ∆λVi  (9) ∂Vi ∂λ elements, the remainder is zero. 0 Sij P −P b) Solving ∂ G,lim G ∂λ ∆λ G  ∂PG ∂λ (10) From the branch power flow equation 0 − Sij S ∂Sij ∂λ  0 lim,i , j ∂Sij ∂λ (11) ∆λ S  0 −S lim,i −Sij ∂Sij ∂λ  0 , j ∂Sij ∂λ 1257 | P a g e
  • 5. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 Where when ∂Vi/∂λ>0, Vlim,i is the upper limit; when 0 ∂Vi/∂λ<0, Vlim,i is the lower limit; Vi is the initial magnitude of Vi; ∂Vi/∂λ is the sensitivity of Vi with respect to λ; Slim,i j is the thermal limit of branch ij; ∂Sij/∂λ is the sensitivity of power in 76 branch ij with respect to λ; PG,lim is the maximum Gen. 3 Gen. 8 0 74 Gen. 6 output of generators in the source point; PG is the initial output of all generators in the source point; 72 ATC ( MW ) ∂PG/∂λ is the sensitivity of PG with respect to λ. 70 c. Find the minimum increment of ∆λ. 68 ∆λ  min{∆λV , ∆λS , ∆λG } (12) 66 d. Modify λ. 64 (n1) (n) λ λ ∆λ (13) 62 0 10 20 30 40 50 60 70 80 Generator’s output (MW) Fig. 1. The effect of the generation on ATC After n times of iteration, if ∆λ is less than the by China EPRI is developed. IEEE 14-bus test system is used to verify the presented approach. preset error ε, then to stop iterative computation, The single line diagram and parameters of the test and the last λ is the system can be found in [15]. Bus 2 is supposed as the source bus, bus 12, 13 and 14 are selected as the sink buses, then ATC is defined as: ATC=P12+P13+P14. This paper will verify the Maximum value under the specified condition. approach from the flowing three aspects: e. Update load and power generation by (14). (1) The influence of active power change of one generator on ATC value. In the test system, there 0 are 5 generators: bus 1 is set as the slack bus; bus 2 PLi  PLi  λK pli is the source bus, so consider the influences of bus 0 3, 6, 8 separately. The constraints of the generator’s QLi  QLi  λKqli (14) active power are: G3 (15MW, 80MW), G6 0 (10MW, 45MW) and G8 (10MW, 40MW). Select PGi  PGi  λKPgi 5MW as the incremental active power, then active power change of each generator is used to study the influences on the value of ATC with the results where PLi and QLi are real and reactive load power shown in Fig.1. Analyzing Fig.1 we can of bus i, Kpli and Kqli are the multipliers to designate the rate of load change, KPgi is the conclude: the active power increase of non-source multiplier to designate the rate of power change, generator has the influence on the value of ATC; PGi is active power generation, and superscript 0 is and different electrical distance of non-source the initial state. generator has different influence. In the tests (4) Compute power flow of the updated state, if generators 6 and 8 are near the source, their power flow is convergent normally, then evaluate influences to ATC are more evident than generator the corresponding operation state. If all constraints 3 that is far from the source bus. It also suggests are satisfied, then return to Step 3, or go to Step 5. active power generation and unit commitment have (5) The ATC computation is terminated if any obvious influences on the value of ATC. of the constraints is not satisfied. The value of ATC can be calculated by the recent power flow results (2) The influence of load change on ATC. Select as follows. 0.02 per unit as the step, increase the load of each ATC= ∑PLd node from 80% to 120% of the forecast value, then (15) d R we can get the relation curve of load change with ATC shown in Fig.2. From Fig.2 we can conclude: IV. NUMERICAL TESTS when the load increases, the value of ATC will [14] decrease. It refers to the accuracy of load forecast is The iterative solution based on PSASP/UPI 1258 | P a g e
  • 6. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 important in ATC calculation. calculation should consider not only the influences of single uncertainty, but also the ones of these 70 uncertainties’ combination. For example, multi- 68 fault and multi-uncertainty impact the value of ATC at the same time. After sampling and ATC (MW) 66 calculation, we can get a series of results representing different states, selecting the 64 minimum one as the finial ATC value. Compare to deterministic methods, the presented approach in 62 this paper can give the value of ATC more accurate. For this test, we select the result of Case 5 60 as the finial result. If we take out CBM (5%), the 58 finial ATC is 57.20495%=47.3438MW. -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 Load variation (p.u.) We are undergoing to transfer the research Fig. 2. The influence of load changing on ATC achievements to the application in certain provincial power system in China. (3) The influence of different uncertainties on ATC. Suppose the actual load value changes within V. CONCLUSIONS AND NEXT WORK 2% of forecasting value, the fault probability of According to the ATC definition of North the generators is supposed at 0.02, the fault rate of America Electric Reliability Council (NERC), this the lines is 0.01, and the fault rate of the paper mainly studies two margins of ATC: TRM transformers is 0.02. Assume transformers’ tapping and CBM. Considering calculation accuracy and have 5 levels, the probability distribution of each time, a novel method is proposed to calculate ATC level is: 100% 0.5, 102.5% 0.15, 97.5% 0.15, 105% based on Monte Carlo simulation and sensitivity 0.10, and 95% 0.10, respectively. Using Monte analysis considering large amount of uncertainties Carlo sampling in terms of the probabilistic involved in TRM and CBM, which have large distribution of each equipment to construct a series impacts on the value of ATC. The steady state of system states, and then use sensitivity analysis to constraints and voltage stability and transient get corresponding ATC values, and select the stability constraints are taken into account. The iterative solution based on PSASP by China EPRI minimum as the final result. The examples are is developed. IEEE 14-bus test system is used to shown in Table I. verify the presented approach. The results show In Table I, Case 1 is the IEEE standard state, there that the model and algorithm is correct and is no load change no fault; Case 2 only has load effective. Compare to the deterministic methods, change; Case 3 have load and transformers’ tapping the proposed approach gives the value of ATC adjustment simultaneously; Case 4 have load more accurate. When we transfer the theoretical change and one line fault; Case 5 has load change achievements to practical applications, we found and one non-source generator fault. some work needed further study. TABLE I ATC CALCULATION RESULTS 1. The proposed approach in this paper, like most of other methods, is mainly suitable for Case ATC/MW theoretically calculating ATC at a time point. But 1 63.662 in practical power markets, load and trading 2 61.357 scheme are continuously change, so it is necessary 3 65.373 for ATC computation approach to consider load demand and relevant bidding strategies continuous 4 58.937 variation. The states, stochastically produced in 5 57.204 terms of probability distribution introduced above, should be related to current system operation, and when simulating continuous ATC calculation, it Analyzing Table I, we can conclude that should be additionally considered the transfer uncertainties play an important role in ATC probability from the current state to next one. Unit calculation. For example, load change and commitment and maintenance scheduling even transformer tapping adjustment make the value of bidding strategies should be taken into account. ATC great change; the fault of line, transformer and generator will decrease the value of ATC. Load 2. Existing Transmission Commitment change randomly all the time, the fault of (ETC) should be considered more detailed in components and transformer tapping can be viewed continuous ATC calculation. Because in power as specific probability distribution. The ATC 1259 | P a g e
  • 7. C.Prasanna Kumari, A. Hema Sekhar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 4, July-August 2012, pp.1254-1260 markets, ATC is an important signal to all [9] C. Y. Tsai, C. N. Lu. "Bootstrap application in participants, and the decision and evaluation about ATC estimation," IEEE Power Engineering the risk of different trading is also worth of Review, vol. 21, pp. 40-42, Feb. 2001. consideration. [10] S. X. Zhou, L. Z. Zhu, X. J. Guo, Power system voltage stability and control. Beijing: How to improve ATC is an attractive issue. FACTS China Electric Power Press, 2004. device is a good choice, and it can not only [11] Power system analysis software package improve the value of ATC, but also improve the PSASP 6.1 User’s Manual. Beijing: Electric stability of the system. But how to decide the Power Research Institute, 2001 optimal installation position of the FACTS device [12] F. Wang, G. B. Shrestha, "Allocation of TCSC and how to coordinate multiple FACTS devices are devices to optimize total transfer capability in still need further research. a competitive power market," in Proc 2001 IEEE PES Winter Meeting, vol. 1, pp. VI. REFERENCES 587~593. [1] Transmission Transfer Capability Task Force. Available transfer capability definitions and determination. North American Electric VII. BIOGRAPHIES Reliability Council, Princeton, NJ, June 1996. Yajing Gao was born in Hebei Province, [2] C. S. Wang, G. Q. Li, Y. X. Yu, W. Jiang, China, on Dec 31, 1980. She received the B.S. "Study on transmission transfer capability of degree in Electrical Engineering, from North interconnected electric power system (I)," China Electric Power University (NCEPU) in Automation of Electric Power Systems, vol. 23, 2002. Now she is pursuing the Ph. D. degree at no. 3, pp. 23-26, Mar. 1999. NCEPU. Her research interest is electricity [3] Y. J. Dai, J. D. McCalley, V. Vittal, markets. "Simplification expansion and enhancement of direct interior point algorithm for power system maximum load ability," IEEE Trans. Ming Zhou received the B.S. and M.S. on Power Systems, vol. 15, no. 3, degrees in Electrical Engineering from North pp. 1014-1021, Aug. 2000. China Electric Power University (NCEPU) in [4] Q. H. Diao, S. Mohamed, Y. X. Ni, "Inter-area 1989 and 1992, respectively. Now she is total transfer capability calculation using pursuing Ph. D. degree at NCEPU. Since 1992, sequential quadratic programming method in Ms. Zhou has been with the Department of power market." Automation of Electric Power Electrical Engineering at NCEPU, where she is Systems, vol. 24, no. 24, pp. 5-8, Dec. 2000. currently an associate professor. Her areas of [5] A. Kulyos, Y. Akihiko, "Consideration of an interest include AI applications to power appropriate TTC by probabilistic approach," systems, electricity markets, and power system IEEE Trans. on Power Systems, vol. 19, no. 1, operation and management. pp. 375-383, Feb. 2004. [6] X. Luo, A. D. Patton, C. Singh, "Real power Gengyin Li (M’03) was born in Hebei transfer capability calculations using multi- Province, China, on May 18, 1964. He layer feed-forward neural networks," IEEE received the B.S., M.S. and Ph.D. degrees, all Trans. on Power Systems, vol. 15, no. 2, pp. in Electrical Engineering, from North China 903-908, May 2000. Electric Power University (NCEPU) in 1984, [7] A. B. Khairuddin, S. S. Ahmed, M. W. 1987 and 1996, respectively. Since 1987, Dr. Mustafa, A. A. M. Zin, H. Ahmad, "A novel Li has been with the Department of Electrical method for ATC computations in a large-scale Engineering at NCEPU, where he is currently power system," IEEE Trans. on Power a professor and deputy head of the Systems, vol. 19, no.2, pp. 1150-1158, May Department. His research interests include 2004. Armando, S. Leiteda, G. C. C. João, electricity markets, power quality, analysis and "Transmission capacity: availability, maximum control of power systems, and new transfer and reliability," IEEE Trans. on Power transmission and distribution technologies. Systems, vol. 17, no. 3, pp. 843-849, Aug. 2002. Yuekui Huang was born in Hunan [8] F. Xia, A. P. S. Meliopoulos, "A methodology Province, China, on Oct 20, 1980. for probabilistic simultaneous transfer capability analysis," IEEE Trans. on Power Systems, vol. 11, no. 3, pp. 1269-1278, Aug. 1996. 1260 | P a g e