METHOD OF MONITORING THE GRADING MARGIN BETWEEN TIME-CURRENT CHARACTERISTICS OF INTELLIGENT ELECTRONIC DEVICES

• US 20120212348A1
• Filed: 11/05/2009
• Published: 08/23/2012
• Est. Priority Date: 11/05/2009
• Status: Active Grant

• Current Assignee: Alstom Technology Ltd. (Alstom SA), Schneider Electric USA, Inc. (Schneider Electric SE)
• Original Assignee: Alstom Technology Ltd. (Alstom SA), Schneider Electric USA, Inc. (Schneider Electric SE)
• Inventors: Subramanian, Sankara, Richards, Simon, Wixon, Alan
• Granted Patent: US 8,981,951 B2
• Time in Patent Office: Days
• US Class Current: 340/638
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 7/30 Staggered disconnection

Abstract

A method of monitoring the grading margin between at least two time-current characteristics of Intelligent Electronic Devices (IED_A, IED_B) installed in an electrical power system, each Intelligent Electronic Device comprising a counting means, the grading margin comprising a safety margin set by a user, characterized in that it comprises, when a fault occurs which causes a fault current in the electrical power system, a step of providing a warning to the user when the safety margin is infringed upon.

Claims

1. A method of monitoring the grading margin between at least two time-current characteristics of Intelligent Electronic Devices (IED_A, IED_B) installed in an electrical power system, each Intelligent Electronic Device comprising a counting means, the grading margin comprising a safety margin set by a user, the method comprising, when a fault occurs which causes a fault current in the electrical power system, a step of providing a warning to the user when the safety margin is infringed upon, characterized in that:

when the fault persists beyond a given duration;

the Intelligent Electronic Device (IED_B) closest to the fault issues a trip command which increments the counting means it contains to a predefined target,

when the predefined target is reached, a trip is issued by the Intelligent Electronic Device (IED_B) closest to the fault so that the Intelligent Electronic Device closest to the fault outputs a command signal to be applied to a circuit breaker which interrupts the fault current, and

when the fault current is in interrupted;

the step of providing a warning to the user comprises the following elementary steps;

an upstream Intelligent Electronic Device (IED_A) calculates a level of timeout the counting means it contains has attained, memorizes the fault current just prior to the instant when the fault current has been interrupted and calculates a time remaining for the upstream Intelligent Electronic Device to trip (Δ

t) which is compared with the safety margin, and

a warning is raised if the time remaining for the upstream Intelligent Electronic Device to trip (Δ

t) is less than the safety margin.

3. Method according to claim 1, wherein the grading margin is automatically increased when a warning is provided to the user.

4. Method according to claim 3, wherein the automatic increase in the grading margin is restricted to a maximum allowed time-adder.

5. Method according to claim 1, wherein the counting means is a trip counter or a unit intended to implement a time integration algorithm.

6. Method according to claim 3, wherein the counting means is a trip counter or a unit intended to implement a time integration algorithm.

7. Method according to claim 4, wherein the counting means is a trip counter or a unit intended to implement a time integration algorithm.

2. (canceled)