Mechanical Contactor Control to Prevent Contact Welding
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Solution Overview
Problem
Mechanical contactors face issues with contacts welding together due to unintentional separation during short circuit faults, rendering them unusable.
Innovation Solution
A method and controller for controlling a mechanical contactor that includes detecting unintentional contact separation using SCPD indications, opening the contactor, and maintaining it in an open position to prevent reclosing, utilizing an electromagnet with a demagnetization circuit to ensure contacts cool down.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the contactor allows contacts to be pressed together after short circuit clearance, then the contactor can be reset and reused, but the contacts may weld together due to melted material
Solution Approach 1:
The control system detects short circuit conditions and preemptively prevents contact reclosing by maintaining the electromagnet in an energized state or by blocking the control circuit, thereby preventing the contacts from being pressed together while melted material is still present on the contact surfaces
Solution Approach 2:
The control system monitors the status of the contactor and the SCPD, and based on this feedback, determines whether to allow reclosing. The system only permits reclosing after confirming that the short circuit has been cleared and the contacts are in a safe state, preventing welding while enabling reuse
2Object-affected harmful factors
If the contacts are pressed apart during short circuit, then the arc is created and melted material is formed, but the contacts may weld together when pressed together again
Solution Approach 1:
The system applies a counter-action by preventing the contacts from being pressed together while melted material is present. The control system blocks the reclosing command or maintains the electromagnet energized to keep contacts separated until the melted material cools and solidifies, preventing welding
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
Prevents welding of contacts by ensuring they remain separated and cool down after unintentional separation, allowing the contactor to be safely reset and reused.
Implementation Method 1
an electromagnet arranged to close the contactor, and maintain the contactor in the closed position, by forcing the pair of contacts towards each other when a control current runs through a coil of the electromagnet
Implementation Method 2
the electromagnet comprises a demagnetization circuit connected across the coil
Implementation Method 3
the obtaining an indication comprises detecting an increased mains current by means of a short circuit protection device, SCPD
Implementation Method 4
The melted material on the surfaces may then weld together when the contacts cool down
Data Source
Figure 1~2
Figure 3~4
Figure 5a~6
AI summary
The present disclosure relates to a method of controlling a mechanical contactor (1) comprising at least one pair of contacts (2) for conducting a mains current (Im) when the contactor is in a closed position, and an electromagnet (4) arranged to close the contactor, and maintain the contactor in the closed position, by forcing the pair of contacts towards each other when a control current (Ic) runs through a coil (5) of the electromagnet. The method comprises, while the contactor is in the closed position, obtaining an indication of unintentional separation of the contacts, and in response to the obtained indication, opening the contactor and maintaining the contactor in an open position by turning off the control current.