Neutral-to-Ground Voltage Measurement Using Selective Impedance Coupling
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Solution Overview
Problem
Measuring neutral-to-ground voltages in electrical systems often results in objectionable current flow, which can lead to safety hazards and equipment reliability issues due to the additional impedance introduced by multiple metering devices or intelligent electronic devices (IEDs).
Innovation Solution
A system and method for controlling IEDs to selectively couple and decouple their impedance with the neutral-to-ground voltage, ensuring that only one IED measures the voltage at a time to minimize objectionable current flow by using a switch that can be operated to change states between coupled and decoupled positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple IEDs are used to measure neutral-to-ground voltage simultaneously, then measurement coverage is improved, but objectionable current flow increases
Solution Approach 1:
The patent implements periodic action by controlling multiple IEDs to measure N-G voltage at different time intervals rather than simultaneously. The controller schedules each IED to couple its impedance to the N-G voltage sequentially, with measurement windows staggered in time. This approach maintains comprehensive measurement coverage across multiple devices while ensuring that at any given moment, only one IED is actively measuring, thereby preventing the accumulation of objectionable currents that would occur with simultaneous measurements.
2Measurement precision
If IED impedance is coupled to N-G voltage continuously, then measurement accuracy is maintained, but steady-state current flows on ground path
Solution Approach 1:
The system applies periodic action by enabling the IED impedance to couple to the N-G voltage only during brief measurement windows rather than continuously. The controller activates each IED's impedance coupling for a short duration sufficient to capture voltage data, then decouples it. This periodic coupling maintains measurement accuracy during the active windows while preventing the establishment of steady-state current paths that would occur with continuous coupling, thereby resolving the safety concern.
Solution Approach 2:
The patent employs preliminary action by having the controller pre-schedule and coordinate the measurement timing of multiple IEDs before measurements begin. The controller establishes a measurement schedule that assigns specific time windows to each IED, ensuring that impedance coupling occurs only when needed and never overlaps with other IEDs. This preliminary coordination enables accurate measurements to be taken at predetermined intervals while preventing harmful steady-state currents from developing on the ground path.
Data Source
Figure 1
Figure 2A~2B
Figure 2C
AI summary
A method and program for minimizing objectionable currents while still providing neutral-to-ground voltage measurements by controlling a switch to determine when the neutral-to-ground impedance is placed in an electrical circuit.