Hyundai HAT Series Air Circuit Breaker (ACB) troubleshooting

Many of you might have worked on vessel equipped with Hyundai HAT series Air Circuit Breakers which proves to be very reliable and efficient but…like any other machineries it requires periodical checks and maintenance. If this is not properly done the result it might be a failing UVT coil or breaker fail to close when required.

In this post will discuss about ACB troubleshooting in case that will fail to close.

Here below there are some instructions on how to troubleshoot a Hyundai HAT Series Air Circuit Breaker (ACB).

The method of periodic inspection for ACB operation is as follow:

    • The breaker is trip-free when the UVT is de-energized. Because of this, when the PUSH TO CLOSE button is depressed, the closing springs are discharged, but if the breaker is not closed, the result is acceptable.
    • If the breaker can be closed at more than 85% of the rated voltage, the result is acceptable.
    • If the breaker can be tripped at the 70% to 35% of the rated voltage after closing the breaker, the result is acceptable.

The method of periodic inspection for UVT coil operation is as follow:

    • Measure the coil resistance with an ohmmeter . If the measured resistance is much lower than the value specified below or there is no continuity, replace the UVT.
        • At rated voltage 100 – 470 V AC – coil resistance must be 160 ± 16 Ohms.
        • At rated voltage 100 – 200 V DC – coil resistance must be 160 ± 16 Ohms

As periodic inspection for terminals and mounting screw, these must be checked for loosening and must be retightened if loose.

If the ACB doesn’t close the troubleshooting comprises, generally as follow:

  • If ACB is drawn out from switchgear, it can not be closed and open owing to UVT.

When ACB has been operated for long time, it should be checked and following  procedure should apply:

    • Remove load by opening the ACB
    • Rack out ACB to test position. The control jack is connected in test position and it is disconnected in isolation position
    • Open Front Cover

    • Check UVT coil and controller as per above mentioned instructions.


UVT control device

    • If UVT coil is burnt, lock UVT Coil to energized position by rotating Lock Lever
      clockwise after lift up the Actuator Pin in order to check ACB mechanically.

    • Push “Close button” and “Open button” of ACB.
    • Check whether Closing Latch could be moved well when Close Button is pushed. If not, check whether hardened grease prevent this or not. When the motor is charged completely, the closing latch go inside fully under LRC Coil.
    • Check whether the relevant connected levers could be moved well when Open
      Button is pushed.
    • If the Closing Latch and relevant closing parts are not moved after 5-6 tryouts, clean the hardened grease by spraying a lubricant such as WD-40. This will remove the hardened grease and make all moving parts to smoothly move.

First point to be sprayed with WD 40

Second point to be sprayed with WD 40

Third point to be sprayed with WD 40

If the Closing button lever is in wrong position, ACB cannot be closing although the Closing button be pushed. In order to move it to the good position, first spray WD-40 to the Closing button lever, and then check whether is moved smoothly with flat screwdriver .

    • Unlock UVT coil and reversely assemble the breaker.

If you have any questions regarding above, please feel free to use our existing forum Seafarer’s World and will try to answer to all your queries. You can use the feedback button as well!

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