The UVL series might not have a return spring, as its mechanism is similar to that of an ACB. However, UVH and UVM models do have a return spring, which can be seen after removing the front cover.
Auto-discharge / Trip-free Operation
In the previous generation springs (1st, 2nd, and 3rd), there was a hook-shaped plate designed to make it easier to hook the link mechanism. However, this design sometimes caused the spring to move abnormally, such as buckling, rather than compressing and extending in a straight direction.
As a result, this abnormal movement of the spring could reduce its strength, preventing the breaker from properly locating the correct position of the link mechanism for closing (“ON”). The VCB would trip almost immediately after it is closed remotely (electrically). This occurs because, as mentioned earlier, the link mechanism is not positioned correctly, so the breaker cannot maintain the closed (“ON”) position. This behavior is called Trip-free operation (Auto-discharge).
The 4th-generation return spring does not have the plate pieces. It is a single-piece spring design. Please refer to the reference photos below to see the difference between the previous (3rd generation) spring and the new (4th generation) return spring.
Return Spring Replacement Guide
Required tools
1. Hook/Pick Tool
2. Magnetic Pick-up Tool
3. Impact driver or Wrench
4. 10mm Wrench Socket
1. Remove the front cover
In most cases, you need to unscrew four M10 hex bolts to detach the front cover. (UVH 38 kV models use seven M10 hex bolts.)
Remove the front cover. If you are only replacing the return spring, the spring must be charged. When the breaker is OFF and the spring is charged, it is easier to replace the return spring.
Note: Normally, breaker OFF with spring discharged is required before performing work.
2. Use a hook/pick tool to hook and remove the old spring. If the spring drops into the link mechanism, use a magnetic pickup tool to retrieve it.
Warning: Do not place your hands near the mechanism. Keep in mind that the spring is charged, and it may cause serious injury if it is suddenly released.
3. Install the New Spring
Hook the bottom end first and stretch the spring. Slowly release the tension and secure the top hook in place.
Note: Make sure the top hook is properly seated and secured in the link shaft. Perform at least five manual close and open cycles to confirm that the return spring is functioning properly and to ensure that the spring does not jump out.
4. Reinstall the Front Cover
Install the front cover back onto the breaker and tighten the bolts.