Method of the identification of weak and/or strong nodes of an electric power system

• US 6,904,372 B2
• Filed: 12/19/2002
• Issued: 06/07/2005
• Est. Priority Date: 12/20/2001
• Status: Expired due to Fees

• Current Assignee: ABB Technology AG (ABB Limited)
• Original Assignee: ABB Technology AG (ABB Limited)
• Inventors: Fulczyk, Marek, Sobierajski, Marian, Bertsch, Joachim
• Primary Examiner(s): WACHSMAN, HAL D
• Application Number:
  US10/322,585
• Publication Number:
  US 20030139887A1
• Time in Patent Office: 901 Days
• Field of Search: 702 57- 62, 702/64, 702/65, 702/124, 702/126, 702/183, 702/185, 702/188, 702/189, 702/193, 702/198, 700/22, 700/26, 700/27, 700/286, 700/291, 700/293, 307/125, 307/126, 307/130, 307/29, 307/31, 307/38, 307/39, 307/102, 324/600, 324/602, 324/605, 324/103.R, 324/141, 324/142, 340/870.01, 340/870.02
• US Class Current: 702/58
• CPC Class Codes: H02J 3/24 Arrangements for preventing or reducing oscillations of power in networks by control effected upon a single generator H02P9/00

Abstract

A method is disclosed for the identification of weak and/or strong nodes of an electric power transmission system. Electric parameters characterizing nodes and branches of an electric power transmission system are subject to computational treatment to obtain equations of power flow in all nodes of the system at assumed 100 percent system load value. Using earth as the reference point, nodal impedance values are computed for all nodes, and used to construct a P-Q curve which presents the functional relation between the system'"'"'s reactive and active load. The nodal coefficient of voltage stability is determined as the relative distance between the base load point of that node and the critical point on the P-Q curve situated most closely to the base point. The coefficient is compared with a threshold value considered to be a safe margin to maintain voltage stability for a given node.

Claims

1. A method for the identification of weak and/or strong nodes of an electric power transmission system, which analyzes functional relations between an active and a reactive load for the system, comprising:

subjecting electric parameters characterizing the nodes and branches of the system to computational treatment in order to obtain power flow equations in all nodes of the system at assumed 100 percent system load,

using the treatment to calculate complex voltage values in the nodes,

using earth as a reference node, calculating node impedance values for all the system'"'"'s nodes,

using the node impedance values to construct a curve /P-Q/ showing a functional relation between reactive load /Q/ and active load /P/ of the system, and

for a given each node, individually determining a nodal coefficient of voltage stability as a relative distance between a base load point of the given node and a critical point on the curve /P-Q/ which is situated most closely to the base load point, whereupon a numerical value of the nodal coefficient is compared with a threshold value considered to be a safe margin to maintain voltage stability for the given node, and based on that comparison, the given node is identified as weak or strong.

2. The method according to claim 1, wherein the nodal coefficient of voltage stability /k_cr/ is calculated from this relation:

$\begin{array}{cc}{k}_{\mathrm{cr}}=\frac{\sqrt{{\left(p_{\mathrm{cr}}-p_b\right)}^2+{\left(q_{\mathrm{cr}}-q_b\right)}^2}}{\sqrt{{\left(q_{\mathrm{cr}}\right)}^2+{\left(q_{\mathrm{cr}}\right)}^2}},& \text{\hspace{1em}<br><br>}\end{array}$

where;

p_cr—

represents values of active load coordinates in a node during critical operating conditions at voltage stability limits,

q_cr—

represents values of reactive load coordinates in a node during critical operating conditions at voltage stability limits,

P_b—

represents values of the coordinates of the base load point of active load in a node,

and q_b—

represents values of the coordinates of the base load point of reactive load in a node.

3. The method according to claim 1, wherein the given node is considered weak where the value of the nodal coefficient /k_cr/ is less than or equal to 0.8 or it is considered strong when the value of the nodal coefficient /k_cr/ is more than 0.8.