• Proceedings of the KIEE Conference
• /
• 2001.05a
• /
• pp.7-9
• /
• 2001

Many developing countries has been voltage unstable and the inter- change capability in Korea is limited by voltage instability. In analyzing voltage stability, load model has been considered as constant power, but actual loads vary as voltage changes. In order to incorporating voltage-dependent load model. we need the low-side of P-V curve that can not be obtained by general load flow algorithm. This paper proposes a modified GCF algorithm to obtain a full low-side of P-V curve and a accurate voltage assessment index considering load model. 5-bus sample system and 19-bus real power system are applied to simulate the proposed GCF. Also. the effect of reactive power compensation is illustrated in same systems.

• Proceedings of the KIEE Conference
• /
• 1995.11a
• /
• pp.89-91
• /
• 1995

This paper describes an extension or a pair or multiple load flow solutions and nose curve method developed for voltage stability analysis or AC power systems to AC/DC systems. In this approach the converters are regarded as voltage dependent loads. Assuming that the converters at the unstable (-mode) solution consume the same power equal to the power at the stable (+mode) solution, the unstable solutions or the nose curves arc determined. This method is very efficient since estimating voltage collapse point and voltage stability margin arc determined by a few iterations of multiple load flow solutions. Also the method has the advantages that since the structure or Jacobian matrix is same with that of AC load flow, modal analysis or voltage stability is readily applicable if desired.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.48 no.8
• /
• pp.958-964
• /
• 1999

The distance in load parameter space to the closest saddle node bifurcation (CSNB) point provides the worst case power margin to voltage instability and the left eigenvector at CSNB identifies the most effective direction to steer the system to maximize voltage stability under contingency. This paper presents an improved direct method for computing CSNB: the order of nonlinear systems equations is reduced to about twice of the size of load flow equations in contrast to about three-times in Dobson's direct method; the initial guess for the direct method is computed efficiently and robustly by combined use of continuation power flow, a pair of multiple load flow solution with Lagrange interpolation. It is also shown that voltage stability may be enhanced significantly with shift of generations in the direction of the left eigenvector at CSNB.

• Proceedings of the KIEE Conference
• /
• 2002.07a
• /
• pp.105-107
• /
• 2002

This paper presents a algorithm for contingency ranking using the real power ratio. The fundamemtal cause of voltage collapse is considered due to excessive power trnsfer through the line. To obtain contingency ranking, maximum real power tansferred to the load is obtained when load impedance $Z_r$ equal to line impedance $Z_s$. This algorithm is verified by simulation on a 6-bus test system.

• Proceedings of the KIEE Conference
• /
• 2002.06a
• /
• pp.146-148
• /
• 2002

This paper presents a algorithm for contingency ranking using the real power ratio, The fundamemtal cause of voltage collapse is considered due to excessive power trnsfer through the line To obtain contingency ranking, maximum real power tansferred to the load is obtained when load $impedance^{Z_r}$ equal to line $impedance^{Z_s}$, This algorithm is verified by simulation on a 6-bus test system.

• Proceedings of the KIEE Conference
• /
• 2006.11a
• /
• pp.279-281
• /
• 2006

A Voltage Instability Predictor(VIP) estimates the proximity of a power system to voltage collapse in real time. Voltage Instability Index(Z-index) from VIP algorithm is estimated using LS(Least Square) method. But this method has oscillations and noise of result due to the system's changing conditions. To suppress oscillations, a larger data window needs to be used. In this paper. I propose the new other method which improves that weakness. It uses RLS(Recursive Least Square) to estimate voltage instability index without a large moving data window so this method is suitable for on-line monitor and control in real time. In order to verify effectiveness of the algorithm using RLS method, the method is tested on HydroQuebec system in real time digital simulator(HYPERSIM).

• Proceedings of the KIEE Conference
• /
• 1997.11a
• /
• pp.235-237
• /
• 1997

The distance in load parameter space to the closest voltage collapse point (CSNB) provides the worst case power margin and the left eigenvector identifies the most effective direction to steer the system to maximize voltage stability under contingency. This paper proposes a new generation redispatch algorithm, which uses left eigenvector at CSNB to enhance the voltage stability. A Newton method is used to detect CSNB point. Proposed method is applicable to the selection of appropriate reactive power compensation and load shedding point detection. But this paper make a point of voltage stability enhancement only with generation redispatch. The proposed method has been tested for Klos Kerner 11-bus system.

• Proceedings of the KIEE Conference
• /
• 2001.11b
• /
• pp.323-326
• /
• 2001

This paper describes the algorithm which can not only take account of voltage suability but also consider small signal stability. As for voltage stability both CPF and PoC methods are utilized to pinpoint the exact voltage collapse point. Then, using the converged load flow results full system matrix is configured and its eigenvalues are computed. The suggested algorithm is applied to the Two-area system, and verified its usefulness. In addition this paper also deals with the results of analyzing the two-area system in terms of voltage stability and small signal stability.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.49 no.2
• /
• pp.56-61
• /
• 2000

In the paper, the system loss sensitivity index that implies the incremental system loss with respect to the change of bus power is derived using optimization technique. The index λ reaches $\infty$ at critical loading point and can be applied to actual power systems for following purposes. 1) Evaluation of system voltage stability 2)Optimal investment of reactive power focused on minimizing system loss and maximizing system voltage stability 3)Optimal re-location of reactive power focused on minimizing system loss and maximizing system voltage stability 4)Optimal load shedding in case of severe system contingency focused on minimizing system loss and maximizing system voltage stability. Case studies for each application have proved their effectiveness.

• KIEE International Transactions on Power Engineering
• /
• v.4A no.2
• /
• pp.58-68
• /
• 2004

This paper presents an optimal routing algorithm (ORA) for maximizing voltage stability as well as for minimizing power loss in radial power systems. In the proposed ORA, a novel voltage stability index (VSI) for real-time assessment is newly introduced based on the conventional critical transmission path framework. In addition, the suggested algorithm can automatically detect the critical transmission paths resulting in voltage collapse when additional real or reactive loads are added. To implement an effective ORA, we have developed an improved branch exchange (IBE) method based on a loss calculation index and tie-branch power flow equations, which are suggested for real-time applications. The proposed algorithm has been tested with IEEE test systems as well as a large-scale power system in Korea to demonstrate its effectiveness and efficiency.