Functionally Grounded DC Insulation Monitoring for Stray Current Control
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Solution Overview
Problem
Existing methods for insulation monitoring in electric installations with functional grounding are imprecise and cannot reliably detect low-level DC stray currents, leading to potential electric corrosion and operational risks, particularly in hydrogen electrolysis installations.
Innovation Solution
A method involving a DC measuring device to measure ground current and supply direct voltage, computing the first insulation resistance, and using an antiparallel diode circuit with a bypass switch to monitor the second insulation resistance, ensuring it is at least 100 times greater than the ground resistance, combined with a DC residual-current measuring device for fault protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If functional grounding is implemented to limit DC stray currents, then electric corrosion is prevented, but insulation monitoring precision deteriorates
Solution Approach 1:
The bypass switch periodically alternates between open and closed states, enabling the system to perform insulation monitoring during the open phase when the ground resistance is disconnected. This periodic switching allows precise measurement of insulation resistance without the interference of functional grounding, while maintaining corrosion protection during the closed phase.
Solution Approach 2:
The system performs insulation monitoring during brief intervals before the bypass switch closes and connects the ground resistance. By conducting measurements in advance during the open state, the system obtains accurate insulation data before the functional grounding is activated, thus preventing corrosion while maintaining measurement precision.
2Object-affected harmful factors
If ground resistance is kept low to prevent corrosion, then DC stray current is limited, but insulation resistance measurement accuracy deteriorates
Solution Approach 1:
The bypass switch extracts the ground resistance from the measurement circuit during insulation monitoring by opening the switch. This separation allows the measurement system to detect insulation resistance without the parallel path created by low-impedance ground resistance, thereby maintaining measurement accuracy while the ground resistance remains low for corrosion protection.
Solution Approach 2:
The bypass switch dynamically changes the impedance state of the ground resistance connection, alternating between low-impedance (closed) and high-impedance (open) states. During measurement, the dynamic switching to open state temporarily increases the impedance, enabling accurate insulation monitoring while maintaining the ability to quickly return to low-impedance state for corrosion protection.
3Reliability
If DC measuring device is used to measure ground current, then stray current monitoring is enabled, but component sizing increases
Solution Approach 1:
The periodic switching of the bypass switch creates time-varying current conditions that allow the DC measuring device to operate at lower current levels during the open phase. This reduces the required measurement range and precision of the DC measuring device, enabling the use of smaller, less expensive components while maintaining reliable stray current monitoring capability.
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
Enables precise insulation monitoring, preventing electric corrosion and ensuring quick shutdown in case of faults, while allowing smaller and less expensive component sizing.
Implementation Method 1
a diode voltage being measured by means of another voltage measuring device (via the antiparallel diode circuit), the second insulation resistance being computed by dividing a diode voltage change between the two states and a ground current change between the two states
Implementation Method 2
measuring a ground current, which flows in the path of the functional grounding, by means of a DC measuring device
Implementation Method 3
the first insulation resistance being computed from the supply direct voltage divided by the ground current
Data Source
AI summary
A method and insulation monitoring arrangement for insulation monitoring of an electric installation operated using a supply direct voltage and has a first insulation resistance between the positive active conductor and ground and a second insulation resistance between the negative active conductor and ground as well as a functional grounding between the negative active conductor and ground by a ground resistance. The method involves measuring a ground current, which flows in the path of the functional grounding, by means of a DC measuring device; measuring the supply direct voltage by means of a voltage measuring device; computing the first insulation resistance from the supply direct voltage divided by the ground current by means of a computing unit; the condition is valid during operation of the electric installation that the second insulation resistance being at least 100 times greater than the ground resistance.