Power System Transformer Substation Voltage Stability of Line Assessment

Liang Wang School of Electrical Engineering

Shenyang University of Technology Shenyang, China

wl1983620@163.com

Jianyuan Xu School of Electrical Engineering

Shenyang University of Technology Shenyang, China

tengyun.sut@163.com

Abstract—By use of power system analysis software the operation to voltage collapse was simulated. Variance of voltage amplitude , phase angle, active power ,reactive powerwere figure out in each node. Simulation data were used to simulate PMU practice measure data . According to P and Q decoupling relationship of power flow equation , in jacobian matrix were solved. As voltage stability indexes were used in voltage stability assessment.

Keywords-phasor measurement unit; power flow equatio; decoupling; jacobian matrix ; voltage stability;

I. INTRODUCTION

In this paper, the structure of a real network objects, but application the power system analysis software simulate the running of it[1-5]. Using PMU measured data, according to P θ and QV decoupling relationship of power system flow equation, using the jacobian matrix elements and the node voltage stability of relations , determine voltage stability index is obtained, and through the actual simulation and operation to verify the feasibility and practicality of the method[6-9].

II. NETWORK VOLTAGE VULNERABLE NODE OF STABILITY ANALYSIS

In this paper, for power flow analysis , by the largest power law index and the sensitivity identify the vulnerability nodes of the network. The system simulation diagram show in Figure 1.

Fig. 1 Artificial chart of power system

SCADA system is supplied modern power system control center in the support.By means of solving the nonlinear equations obtained by iteration voltage amplitude and phase. The method solved a complicated process with a long time. But voltage stability can not be applied to real-time monitoring process. Power system node voltage phasor is described because the system state is an important parameter. Voltage amplitude measurement is easier, and voltage phase angle measurement is very difficult. Global Positioning System (GPS) was a high-precision synchronous clock for basing on the phase angle measurement provides a solution. Recent advances in the GPS-synchronized phasor measurement unit (PMU) of the research has made progress in, and began to equipment in the power system. If all nodes are equipped with PMU, the system bus voltage magnitude and phase angle can be measured directly. Obviously, at this time power flow equations can be solved directly without iteration, making up the real-time voltage stability analysis and accuracy requirements.

TAB.1 THE CAPACITY OF TRANSFORMERS IN SUBSTATIONS OF DACHENGHUSHITAI QIJIA

By dacheng, hushitai and qijia substation as the Accord to proportional growth, but generator active power output and reactive power generation also by the proportional growth. Substation transformer capacity, taking into account the constraints shown in Table 1, 3 substations out of PV curve, shown in Figure 2.

When the three substations of active power increase capacity to 325MW,dacheng substation total power are 660MVA, beyond the power substation capacity. According to

978-1-4244-7161-4/10/$26.00 ©2010 IEEE

the simulation results can obtain between the voltage sensitivity of each node and the total active power load of growth relationship. The voltage sensitivity is going to be close to the critical state ,in accordance with the order from big to small, and three substation voltage sensitivity are shown in Figure 3.

Fig.2 The relation between node voltages and real power increase

Fig. 3 Sensitivity curve of substations corresponding with real power increase

III. DETERMINE VOLTAGE STABILITY INDEXBy Fig.2 and Fig.3 can be concluded , in accordance with

the specific power growth of way was simulated, in the change process, dacheng substation PV curve and the sensitivity value changes the most, followed by hushitai, Qijia substation. We can identify the dacheng substation voltage stability of the worst, followed hushitai and Qijia.

Usually, non-linear flow equations can be written as flowing:

( , ) 0{( , ) 0

P UQ U

θθ

==

(1)

1 2[ , ,..., ]nP p p p= each node active

power 1 2[ , ,..., ]mQ q q q= each node reactive power; θvoltage phase angle;U: voltage amplitude. perturbation analysis is used for the type (1) deviation equation.

P PU

Q QU

J JPJ JQ V

θ

θ

θΔ Δ=

Δ Δ (2)

PΔ : node active micro-incremental change; QΔ : node reactive micro-incremental changes; θΔ : node voltage phase

angle micro-increments changes; VΔ : node voltage amplitude micro-increments changes.

The type (2) P-Q relationship was decoupled:

1 11 12 1 1

2 21 22 2 2

1 2

...

...... ... ... ... ... ...

...

n

n

n n n nn n

P B B BP B B B

P B B B

θθ

θ

Δ ΔΔ Δ

=

Δ Δ

1 11 12 1 1

2 21 22 2 2

1 2

...

...... ... ... ... ... ...

...

n

n

n n n nn n

Q C C C VQ C C C V

Q C C C V

Δ ΔΔ Δ

=

Δ Δ

11 12 1

21 22 2

1 2

...

...... ... ... ...

...

n

nP

n n nn

B B BB B B

J

B B B

θ =

11 12 1

21 22 2

1 2

...

...... ... ... ...

...

n

nQU

n n nn

C C CC C C

J

C C C

=

iij

i

PBθ

∂=∂

iij

i

QCV

∂=∂

This paper proposes from no load to a specific load, ii

QV

∂∂

and ii

Pθ

∂∂ of the offset of node i of the load as the voltage

stability index. According to this criterion can be inferenced two voltage stability indicators:

0

0

i

ipi

P

I Pθ

θ

∂∂= ∂∂

0

0

i

iQi

QVI QV

∂∂= ∂∂

i

i

QV

∂∂ and i

i

Pθ

∂∂ are any specific load of the value.

0

0

Pθ

∂∂

0

0

QV

∂∂ are initial case of the value.Node

voltage collapse, the power flow Jacobian matrix is of singular,and reflecting the voltage stability of the indicators in this paper is PiI QiI After a wide range of operating conditions of simulation, the voltage collapses near

the stability index value of PiI generally around 0.3, voltage

stability index value QiI generally around 0.1. To facilitate

control, the paper is given PiI and QiI =0.1 to determine the node point of stability and voltage stability threshold.

IV. DETERMINED TARGET TO STRIKE AND RESSULTOF ANALYSIS

Figure 4 reflects the nodes angle stability relationship. the Hushitai and the Qijia nodes during operation point of failure does not appear. From figure 5, the three substation voltage indicators of initial stages are slow decline, and dacheng node appears significant decline first, following by hushitai and Qijia.

From the three curves can be seen, Dacheng node's index value is less than Hushitai and Qijia substation, causing the first arrival threshold voltage collapse. Three substations index value reflects the worst Dacheng substation voltage stability of the all. This curves reaction the sensitivity of the results are consistent for descripting of the method to monitor the accuracy of the voltage stability.

Processing in accordance with the above analysis, lthough the maximum power method and sensitivityIndex method can reflect the trend of the node voltage, to identify the vulnerability of the system nodes. But the node voltage stability is not given. Second, the node voltage sensitivity of the operation process index values changed very little. When the node voltage is about to crash out.Mutation is skipping.It is not easy to control.It is difficult to determine the index directly to use in-line voltage stability assessment. With the emergence of PMU and widely used, for synchronized phasor data determination of voltage stabilityIndicators will be the most important issue for future research.Maintaining the Integrity of the Specifications

Fig.4 Operation index PiI corresponding with load variation

Fig.5 Operation index QiI corresponding with load variation

Considered the optimum arrangement scheme of PMU in a region of electric network this paper primary introduced the definition of voltage stability’s weak nodes and their region through a tidal current emulation and calculation method. The optimum arrangement scheme of PMU in electric network was also given. The Least-square procedure method was used in solving the equivalent resistance which completed the weak node’s dynamic voltage stability evaluation. The estimative accuracy of the scheme has been indicated according to the result of simulating test which presents a theory method lying the foundation for the dynamic voltage stability evaluation of wide region electric power network.

V. CONCLUSION

According to P- and Q-V decoupling, by simulation data solve the Jacobian matrix diagonal element values, and based on the Jacobian matrix and the voltage stability of the relationship proposed an index to evaluate the voltage stability.

Fig.6 PMU device is given the specific wiring principle and determination to obtain real-time synchronous data compared with simulation results.

Fig.6 Wiring terminal diagram of PMU

ACKNOWLEDGMENT

This thesis has been the guiding teacher seriously and laboratory to help me students, very grateful to those who helped me.

REFERENCES

[1] Xu Zhiyou and Luan Zhaowen, Measure the node voltage stability of the singular value method and the stability index[J]. Power Systems Automation, 1997, 21(8),42-44.

[2] Zhou Shuangxi,Jiang Yong and Zhu Lingzhi, Power System Voltage Stability Indicator Review . Power System Technology, 2001 , 17(6),1-7.

[3] Zhou Niancheng, Xu Guoyu. Based on the voltage phase power system of voltage stability index[J]. Chinese Motor Engineering Journal, 1997,17 (6), 425-428.

[4] Li Xingyuan,Wang Xiuying. Based on Static Equivalence and Singular Value Decomposition of the Fast Voltage Stability Analysis. Chinese Motor Engineering Journal, 2003,23(4),1-4.

[5] Xiao Jinyu,Xie Xiaorong,Li Jian. Wide Area Network Security Monitoring System and Dynamic Simulation Experiments[J]. Chinese Motor Engineering Journal, 2004,28(6),1-4.

[6] Wang Keying,Mu Gang,Han Xueshan.Power Flow Equation Solvable PMU Configuration[J]. Chinese Motor Engineering Journal, 1999,19(10),14-16.

[7] Guo Ruipeng,Han Zhenxiang. Voltage Stability Analysis of Advanced Continuation Method. Power System Automation 1999, 23(16), 13-16.

[8] Xie Xiaorong , Li Hongjun , Wu Jingtao .Phasor Technology Used in Power System Transient Stability Control of the Feasibility Analysis. Power System Technology, 2004, 28(1):10-14.

[9] Liu Daowei, Xie Xiaorong, Mu Gang. Synchronized Phasor Measurement Based Power System Line Voltage Stability Iindex. Chinese Motor Engineering Journal , 2005 , 25(1) 13-17.