DC Insulation Monitoring With Functional Earthing Fault Isolation
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Solution Overview
Problem
Existing methods for insulation monitoring in ungrounded DC power supply systems, particularly in hydrogen electrolysis plants, fail to accurately detect insulation faults due to high load currents, leading to potential electrocorrosion from DC stray currents, and require complex and costly solutions like GFDI or NGR systems.
Innovation Solution
Implement a DC current measuring device to detect earthing current, measure supply DC voltage, and calculate insulation resistance using a computing unit, optionally with an antiparallel diode circuit and bypass switch, ensuring the second insulation resistance is at least 100 times greater than the earthing resistance, and include a DC fault current measuring device for rapid shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If functional earthing is implemented via a low-resistance earthing resistor to prevent electrocorrosion, then corrosion protection is improved, but insulation monitoring accuracy deteriorates due to the low-resistance path masking insulation faults
Solution Approach 1:
The patent introduces an antiparallel diode circuit as an intermediary component in the earthing path. This diode circuit acts as a mediator that blocks the low-resistance earthing path during insulation monitoring measurements, allowing accurate measurement of insulation resistance, while permitting normal earthing current flow during operation to prevent electrocorrosion.
Solution Approach 2:
The patent employs periodic switching of the bypass switch to alternately connect and disconnect the antiparallel diode circuit from the earthing path. During monitoring periods, the diode circuit is activated to block the earthing path for accurate measurement. During normal operation periods, the bypass switch disconnects the diode circuit, allowing the low-resistance earthing path to function for corrosion protection.
2Reliability
If DC current measuring devices are used to detect insulation faults, then fault detection capability is improved, but the system becomes unable to distinguish between load currents and fault currents due to high load current magnitude
Solution Approach 1:
The antiparallel diode circuit serves as an intermediary that isolates the measurement system from the high load currents. By blocking the earthing path during measurement, it ensures that only insulation fault currents are detected, eliminating the interference from high load currents and enabling accurate fault detection.
Solution Approach 2:
The patent converts the potentially harmful effect of high load currents into a benefit by using the antiparallel diode circuit to block them during measurement periods. This transforms the problem of high load current interference into an opportunity for clean, accurate fault current measurement by temporarily eliminating the load current path.
3Object-affected harmful factors
If GFDI or NGR systems are implemented for insulation monitoring, then corrosion protection is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the existing earthing resistor serve multiple functions: it provides corrosion protection during normal operation and becomes part of the insulation monitoring system when the antiparallel diode circuit is activated. This eliminates the need for separate GFDI or NGR systems, reducing overall system complexity and cost.
Solution Approach 2:
The patent merges the corrosion protection function and insulation monitoring function into a single integrated system using the earthing resistor combined with the antiparallel diode circuit and bypass switch. This combination replaces the need for separate complex monitoring systems like GFDI or NGR, simplifying the overall system architecture.
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
Accurately monitors insulation resistance, prevents electrocorrosion, and enables rapid system shutdown with smaller, cost-effective components by ensuring the second insulation resistance is sufficiently high relative to the earthing resistance, and provides reliable fault protection.
Implementation Method 1
an antiparallel diode circuit (16) with a bypass switch (18) connected in parallel to the antiparallel diode circuit (16), wherein a diode voltage (UD) across the antiparallel diode circuit (16) is measured
Data Source
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AI summary
The invention relates to a method and an insulation monitoring arrangement (10) for insulation monitoring of an electrical system (2) operated with a direct supply voltage (UDC), which has a first insulation resistance (Riso1) between the positive active conductor and earth and a second insulation resistance (Riso2) between the negative active conductor and earth, as well as a functional earthing between the negative active conductor and earth by means of an earthing resistance (path of the functional earthing).To carry out the method, the following steps are carried out: measuring an earth current (IE) flowing in the functional earth path by means of a DC current measuring device (14), measuring the DC supply voltage (UDC) by means of a voltage measuring device (12), calculating the first insulation resistance (Riso1) from the DC supply voltage (UDC) divided by the earth current (IE) by means of a computing unit (20), wherein during operation of the electrical system (2) the condition applies that the second insulation resistance (Riso2) is at least one hundred times greater than the earth resistance (RE).