Leakage Current Measurement in Ungrounded AC Systems
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Solution Overview
Problem
Existing methods for determining leakage current in ungrounded AC power supply systems are hazardous and complex, especially when dealing with extensive systems, as they require ground faults and can lead to arcs and electrical system damage.
Innovation Solution
A method involving a variable test resistor set to infinity, allowing for safe measurement of leakage current without ground faults, using an equivalent circuit diagram and numerical approximation to determine leakage capacitances, and calculating the leakage current without risking electrical shock or system damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ground fault measurement methods are used to determine leakage current, then measurement can be performed according to standard methods, but personnel safety is endangered and electrical system damage risk increases
Solution Approach 1:
The patent introduces a variable test resistor as an intermediary component connected between the phase conductor and earth. This resistor serves as a mediator that allows measurement of leakage current through voltage measurements across the resistor, avoiding direct ground fault conditions while still enabling calculation of the leakage current through Ohm's law (I = U/R). The intermediary resistor transforms a dangerous direct fault measurement into a safe indirect measurement.
Solution Approach 2:
The patent replaces the mechanical/electrical action of creating a direct ground fault with a computational approach. Instead of physically establishing a fault condition and measuring current directly, the system measures voltages and uses numerical approximation methods to calculate the leakage current. This substitution of direct electrical measurement with computational analysis eliminates the hazardous fault condition while maintaining measurement capability.
2Measurement precision
If intentional ground fault is created using current measuring device, then leakage current can be measured directly, but high capacitive charging currents flow and arcing can occur
Solution Approach 1:
The patent applies preliminary action by first connecting the variable test resistor with a high resistance value (initially infinity) before any measurement takes place. This preliminary high-resistance connection prevents the immediate flow of high capacitive charging currents that would occur with direct ground fault. The system then gradually adjusts the resistance down to measurement values, allowing controlled charging currents while avoiding the hazardous conditions of direct fault.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the resistance value of the test resistor during the measurement process. The resistance is changed from an initial infinite value through intermediate values to final measurement values. This continuous parameter adjustment allows the system to control the magnitude of charging currents and avoid arcing conditions that would occur with fixed low-resistance ground fault connections.
3Measurement precision
If more support test resistance values are used for numerical approximation, then measurement accuracy improves, but test duration increases
Solution Approach 1:
The patent applies partial action by using a limited set of discrete support test resistance values rather than continuously varying the resistance or using an excessively large number of measurement points. The method selects specific resistance values (e.g., 5 kΩ, 10 kΩ, 15 kΩ, 20 kΩ, 25 kΩ) that provide sufficient accuracy for numerical approximation while minimizing the total number of measurement steps. This partial sampling approach balances accuracy requirements with time efficiency.
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 accurate and safe measurement of leakage current and capacitances, reducing the risk of electrical hazards and system damage, while providing precise information on the electrical condition of the power supply system.
Implementation Method 1
a variable test resistor (20) is connected between one of the outer conductors (L1, L2) and earth (PE), wherein a test resistance value (Rvar) is to be set to infinity
Implementation Method 2
A mains voltage measuring device (24) is used to measure the operating voltage of the AC power supply system between the outer conductors
Data Source
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AI summary
The invention relates to a method and a measuring device for determining a leakage current in an ungrounded, single-phase AC power supply system. A variable test resistor is connected between one of the phase conductors and ground. Starting from a minimum permissible test resistor value, at least three support test resistor values are determined as reference points, thereby describing a functional metrological relationship between the set support test resistor values and the resulting measured test current. In an equivalent circuit diagram of the modeled AC power supply system, a system of equations is established using node and mesh equations. This system describes the relationship between currents and voltages, in particular the test current flowing through the test resistor, and the operating voltage.Extrapolating to a test resistance of zero results in a calculated test current that corresponds to the leakage current to be determined. This simulates a ground fault situation without actually creating a dangerous ground fault. This also offers the advantage that electrical systems no longer need to be switched off for leakage current measurement, and the person performing the test is not exposed to the risks associated with creating a ground fault, such as electric shock or arcing.