Method and apparatus for measuring prospective short circuit current
AssigneeEaton Intelligent Power Limited
InventorsCharles J. Luebke, Amjad Hussain
Life of this patent
Estimating the term…
Abstract
A method of determining a prospective short circuit current for an electrical system including a source includes connecting a test load between either: (i) a first phase line and a second phase line of the electrical system or (ii) the first phase line and the neutral line of the electrical system, employing a sensor coupled to the electrical system to measure a voltage drop across the test load, determining a voltage value based on at least the measured voltage drop across the test load, determining a total effective impedance for the first phase line to the source, and determining the prospective short circuit current based on the voltage value and the total effective impedance.
Claims16
A method of determining a prospective short circuit current for an electrical system including a source and based on a power factor of either 0.7 or 0.9, comprising
- connecting a test load between either:
- (i) a first phase line and a second phase line of the electrical system or (ii) the first phase line and a neutral line of the electrical system;
- employing a sensor coupled to the electrical system to measure a voltage drop across the test load;
- determining a voltage value based on at least the measured voltage drop across the test load;
- determining a total effective impedance (Zs) for the first phase line to the source, wherein Zs is equal to ZS=RS±jXS, wherein Rs is a total resistance for the first phase line to the source and Xs is a total reactance for the first phase line to the source, wherein Zs is calculated from a positive value for Rs that is determined by solving a quadratic equation for Rs, and wherein the quadratic equation is selected from the following quadratic equations:
- 8Rs2+4RLRs+(RL2−Zeq2)=0,
- 4.92Rs2+4RLRs+(RL2−Zeq2)=0,
- 2Rs2+2RLRs+(RL2−Zeq2)=0, and
- 1.23Rs2+2RLRs+(RL2−Zeq2)=0,
- wherein RL is a resistance of the test load and wherein Zeq is an equivalent impedance value that is calculated based on either (i) a nominal line-to-line voltage for the electrical system and a current flowing through the test load, or (ii) a nominal phase voltage for the electrical system and the current flowing through the test load;
- and
- determining the prospective short circuit current based on the voltage value and the total effective impedance.
An electrical device structured to be coupled to an electrical system between a source and a load and structured and configured to determine a prospective short circuit current for the electrical system based on a power factor of either 0.7 or 0.9, comprising:
- a test load;
- a switch structured to selectively connect the test load between either:
- (i) a first phase line and a second phase line of the electrical system or (ii) the first phase line and the neutral line of the electrical system;
- a sensor structured to generate a signal indicative of a voltage drop across the test load;
- and
- a controller structured and configured to:
- determine a voltage value based on at least the signal indicative of a voltage drop across the test load,
- determine a total effective impedance (Zs) for the first phase line, wherein Zs is equal to ZS=RS+jXS, wherein Rs is a total resistance for the first phase line to the source and Xs is a total reactance for the first phase line to the source, wherein Zs is calculated from a positive value for Rs that is determined by solving a quadratic equation for Rs, and wherein the quadratic equation is selected from the following quadratic equations:
- 8Rs2+4RLRs+(RL2−Zeq2)=0,
- 4.92Rs2+4RLRs+(RL2−Zeq2)=0,
- 2Rs2+2RLRs+(RL2−Zeq2)=0, and
- 1.23Rs2+2RLRs+(RL2−Zeq2)=0,
- wherein RL is a resistance of the test load and wherein Zeq is an equivalent impedance value that is calculated based on either (i) a nominal line-to-line voltage for the electrical system and a current flowing through the test load, or (ii) a nominal phase voltage for the electrical system and the current flowing through the test load
- determine the prospective short circuit current for the electrical system based on the voltage value and the total effective impedance.
Dependencies are inferred from the claim text.