Phase Loss Detection in Soft Starters via Current Phase Shift
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for detecting phase failures in three-phase electrical devices, particularly soft starters, are inadequate when one phase lacks a current transformer, as they cannot accurately determine phase failures without additional hardware and firmware, leading to potential motor operation on two phases until a protective mechanism intervenes.
Innovation Solution
A method that analyzes the phase shift between currents in two lines to detect phase failures in the third line, eliminating the need for a current transformer in the third line and reducing hardware requirements, by determining a characterizing value for phase shift within specific ranges indicative of a phase failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current transformer is installed in all three lines to detect phase failures, then phase failure detection reliability is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the phase failure detection capability from the requirement of having current transformers in all three lines. By removing the current transformer from one line (phase) and using mathematical relationships between the remaining two phases, the system achieves phase failure detection with fewer sensors, thereby reducing device complexity while maintaining detection reliability.
Solution Approach 2:
The patent introduces an intermediary approach by using the relationship between two measured phases to infer the state of the third unmeasured phase. Instead of directly measuring all three phases, the system uses the intermediary mathematical relationship (phase shift analysis) to detect failures in the third phase, reducing hardware requirements.
2Reliability
If voltage measurement hardware and firmware are added to detect phase failures, then detection capability is improved, but device complexity increases
Solution Approach 1:
The patent makes the existing current transformers multi-functional by using them not only for current measurement but also for phase failure detection through phase shift analysis. This universal approach eliminates the need for separate voltage measurement hardware and firmware, maintaining detection capability while avoiding increased device complexity.
Solution Approach 2:
The system uses its existing current measurement infrastructure to serve the additional function of phase failure detection. By analyzing the phase shift in current measurements already being taken, the system detects phase failures without requiring external voltage measurement equipment, making the system self-sufficient.
3Measurement precision
If three current transformers are used for phase failure detection, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent extracts one current transformer from the three-phase configuration, reducing the sensor count from three to two. By using phase shift analysis on the remaining two current transformers, the system maintains adequate measurement precision for phase failure detection while reducing manufacturing costs associated with purchasing and installing three sensors.
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a method for determining a phase failure in an electrical device (1) for driving or monitoring a three-phase AC motor (2), wherein the electrical device (1) comprises a first, a second and a third line (6,7,8). In order to detect a phase failure in a line (8) in the three-phase electrical device (1), in particular in a soft starter (1), the phase failure in the third line (8) is determined by analysing the first and second lines (6,7), wherein the analysis comprises the following steps: determining a value which characterizes a phase shift between a current in the first and second lines (6,7), and outputting a signal if the value which has been determined is in a range of values which characterizes a phase failure in the third line (8).