Q: Magnetic arc extinguishing in DC applications
Some HVDC (Direct Current High Voltage) loads have permanently built-in "arc extinguishing magnets" that help to "extinguish" or cut off the arc formed when the connector is disconnected. This increases the DC rating of the connector and helps extend the electrical life at rated load. While arcing can also occur when the connector is closed, the arc generated when the connector is disconnected is much larger.
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Magnetic arc extinguishing characteristics are listed in the "Features" filter on the DigiKey website. However, the precursor is that the product's specification indicates that the product has magnetic arc extinguishing properties. However, even if a product has this feature, it will not necessarily be listed in the datasheet. If the product has a polarized output, it is likely to have this feature.
In general, electromechanical contactors with a polarized DC rated output can handle current in both directions, but only when the connector is closed and the polarity must be correct when the connector is disconnected. If the connector is disconnected with incorrect polarity, it will have the opposite effect, i.e., increase the arc, accelerate the damage to the connector surface, and may pose a hazard. AC load devices typically do not require an arc extinguishing magnet because the AC waveform crosses the zero point and extinguishes the arc on its own when the connector is disconnected.
To determine which product is right for your application, look at the connector rating life cycle or on-off chart for the test conditions specified in the datasheet.
Some datasheets also list the on/off times, including the arc duration:
Electromagnetic arc extinguishing applications:
-For speeding up high-voltage DC charging and safely shutting off and disconnecting current loads
- Solar and wind energy are used for safe switching and disconnection of DC loads during the inverter process, as well as when transferring energy storage to and from the battery
- For energy storage or backup systems, drones or fleet management, or even in forklift charging systems
Sensata's Description:
All Sensata Gigavac contactors can carry bidirectional currents on a closed connector. The term "bidirectional" refers to the ability to switch/disconnect while the current flows. Most Sensata Gigavac contactors are designed and optimized to disconnect current in the direction of current flow for maximum current disconnection capability. We also offer contactors in a bi-directional design. This type of device is typically achieved by changing the orientation of the internal arc extinguishing magnet.
Polarization:
The power terminals on the polarization contactor are marked with a positive (+) and a negative (-). This mark is used to guide the correct installation of the product. Most contactors have an internal arc extinguishing magnet (which disconnects when the current flows) for disconnecting the load. This is especially important for disconnecting loads of 48V and above. Arc extinguishing magnets are designed for the flow of current in a specific direction. Improper installation may limit or disable the effectiveness of the arc extinguishing magnet and significantly shorten the life of the contactor. In applications where the system voltage exceeds 48V, care should be taken to install the contactor in the correct direction of current flow. A properly installed contactor should allow current to flow into the positive (+) terminal and out of the negative (-) terminal.
Bidirectional:
If a bidirectional contactor is used, the main power terminals can be connected in any direction. Regardless of the direction in which the current flows, the internal arc extinguishing magnet is configured to break the arc formed.
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