Electric Meter Voltage Sag Detection With Switch-Based Fault Isolation
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Solution Overview
Problem
Existing methods for detecting voltage sags in electrical networks struggle to differentiate between network-induced voltage drops and local malfunctions at electric meters, particularly due to issues like contact arcing in meter cut-off devices causing carbon deposits and increased resistance.
Innovation Solution
Implementing a method in electric meters with a cut-off member, voltage, and current sensors to measure phase voltage and current, opening the cut-off device when voltage drops below a threshold, and generating alarms or alerts to distinguish between meter malfunctions and network sags, while automatically learning reference voltage intervals based on current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage detection is implemented at the electricity meter level, then voltage drop detection capability is improved, but false detection due to meter-induced local voltage drop occurs
Solution Approach 1:
The patent segments the voltage detection function into two independent parts: upstream voltage detection (before the disconnect switch) and downstream voltage detection (after the disconnect switch). By comparing voltages at these two points, the system can distinguish between network-induced voltage drops and meter-induced voltage drops, eliminating false detections while maintaining detection capability.
Solution Approach 2:
The patent introduces an intermediary measurement point (upstream voltage measurement) that acts as a reference to distinguish the source of voltage drops. This intermediary measurement allows the system to determine whether a voltage drop originates from the network or the meter itself, resolving the reliability issue.
2Measurement precision
If disconnect switch resistance increases due to carbonization, then local voltage drop at the meter increases, but this causes false voltage sag detection
Solution Approach 1:
The patent divides the voltage measurement into upstream and downstream segments relative to the disconnect switch. By measuring voltage upstream of the switch, the system captures the true network voltage before it is affected by switch resistance, thereby eliminating the harmful local voltage drop from the measurement.
Solution Approach 2:
The patent extracts the voltage measurement point from the downstream side (affected by switch resistance) and places it on the upstream side (unaffected by switch resistance). This extraction removes the harmful influence of carbonization-induced resistance increase from the voltage measurement.
3Reliability
If the switching device is opened to test for meter malfunction, then false detection due to meter faults is prevented, but service interruption occurs
Solution Approach 1:
The patent performs preliminary voltage measurement upstream of the disconnect switch before opening the switch. This preliminary action captures the true network voltage state, allowing the system to distinguish between network voltage drops and meter-induced drops without actually opening the switch during normal operation.
Solution Approach 2:
The patent implements partial testing by measuring voltage at strategic points (upstream of the disconnect switch) during normal operation, rather than requiring complete switch opening. This partial measurement approach provides sufficient information to detect meter malfunctions while maintaining service continuity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Effectively detects voltage sags in electrical networks while ensuring they are not caused by meter malfunctions, preventing potential cascading failures and allowing for timely corrective actions.
Implementation Method 1
to measure, upstream of the switching device and at regular intervals, the phase voltage and a phase current flowing on the phase conductor
Implementation Method 2
to measure, upstream of the switching device and at regular intervals, the phase voltage and a phase current flowing on the phase conductor
Implementation Method 3
when the phase voltage becomes less than a predetermined voltage threshold, to open the switching device
Data Source
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AI summary
Method for detecting a sag in a phase voltage (Vp) comprising the steps of: - measuring, upstream of a switching member and at regular intervals, the phase voltage (Vp) and a phase current (Ip) flowing through a phase conductor (13); - when the phase voltage falls below a predetermined voltage threshold, opening the switching member; - subsequent to opening the switching member, if the phase voltage returns to a normal voltage value defined according to the phase current (Ip), detecting a malfunction of the electricity meter, generating a warning message, and keeping the switching member open; - subsequent to opening the switching member, if the phase voltage remains below the predetermined voltage threshold, detecting a sag in the phase voltage (Vp), generating an alert message, and closing the switching member (12).