Troubleshooting of Air Circuit Breakers (ACB)

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Troubleshooting of Air Circuit Breakers (ACB)

There are numerous air circuit breakers in distribution amenities, which are typically employed as low-voltage main switches or branch circuit switches with big capacity, and play a crucial function in the power supply system.

Once the fault arises, it will cause widespread power outages and economic losses.

The following demonstrate air circuit breaker operating fault analysis and repair methods.

Cause

  • Under-voltage release is not coupled to the supply.
  • The under-voltage, shunt, and magneto thermal release connection links were not appropriately adjusted.
  • The magneto thermal release was removed from the ACB, but the release trip bar remained free.
  • Trip The mechanism spring latch is not in the appropriate position or has been misplaced.
  • The under-voltage release coil burned out or became open circuit. 
  • The bimetal element of the magneto thermal release bent permanently.
  • After an overload (or) short circuit fault, the breaker may not reset (ONLY FOR MANUALLY RESET TYPE ACB), and the tripping mechanism may become stuck due to excess dust.  

Solution

  • Provide rated voltage for under-voltage release.
  • Adjust the connecting connector of the releases appropriately.
  • Lock the trip bar at the provided position.
  • Fix the spring correctly.
  • Replace the under-voltage release.
  • Replace the magnetic thermal release.
  • Reset the breaker by pushing the OFF/RESET button.
  • Clean and oil the tripping mechanism with CRC 2-26 (Multipurpose lubricant prevents water, humidity, condensation, and corrosion-related electrical and electronic failure.).

Cause

  • Supply of shunt release is lacking.
  • Under-voltage release continues. 
  • Misplaced under-voltage (or) shunt release pins. 
  • Due to dust, release sticks.

Solution

  • Verify shunt release control wiring and supply.
  • Check control wiring.
  • Verify pin placement.
  • Clear the release of dust and clean it with CRC 2-26.

Cause

  • The trip push button connecting link is brief. (Not correctly adjusted)
  • The latch of mechanism is jammed due to dust.

Solution

  • Configure the push button connection properly.
  • Cleaning the latch of mechanism with CRC 2-26.

Cause

  • The connection between C.T. & magneto thermal release is either slack or open circuit.
  • Overload setting of the magneto thermal release is more than real load current.
  • Magneto thermal release connection is not correctly set.

Solution

  • Tighten the C.T. terminals in case of an open circuit.
  • Make the ACB overload setting based on the actual load current.
  • Connect the magneto thermal release linkage to the trip bar properly and confirm that it tripped.

Cause

  • Excess dust had accumulated in pole assembly.
  • The nylon rollers of pole assembly do not rotate smoothly.
  • The setup for the pole connector has been disturbed.
  • The nylon rollers of pole assembly are damaged.

Solution

  • Cleaning the pole assembly mechanism with the CRC 2-26.
  • Remove grease & dust with a brush, then apply fresh grease.
  • Use CRC 2-26 to clean and lube the nylon rollers.
  • Contact the manufacturer of the circuit breaker.

Cause

  • Arcing contact gap is not correctly controlled.
  • The thickness of the arcing contact is lowered below the defined limit (>0.5 mm).

Solution

  • Adjust the spacing between arcing contacts to 0.9 ± 0.1 mm.
  • Replace the fixed and movable arcing contacts.

Cause

  • Arc chutes have rough deion plates.
  • The breaker is activated without the arc chute in place.

Solution

  • Clean the dielectric plates & side insulating strips of arc chutes using CRC 2-26.
  • Always run the ACB with the arc chute in place and keep it clean.

Cause

  • Threads of the mechanical indicating assembly have worn out. 
  • The shutter assembly is not correctly mounted in the cradle.
  • Secondary isolating contacts are not correctly matched, and the dovel pin is damaged.
  • The telescopic rail gets jammed.

Solution

  • Replace the mechanical indication assembly.
  • Place the shutter assembly correctly in the cradle.
  • Match the fixed & moving secondary isolation contacts correctly.
  • Replace the dovetail pin.
  • Cleaning the telescopic rail using CRC 2-26. 
  • Remove dust, grease, and re-lubricate.

Cause

  • Poor termination (high millivolt drop over termination on ACB).
  • Dusty environment.
  • Use undersized cable (or) bus bars. 
  • The ambient temperature is high.
  • Busbars hardware is loose, transferring heat back to the breaker.

Solution

  • Cleaning the terminals using CRC 2-26 and properly reterminate. 
  • Ensure the millivolt drop is within the stated limits.
  • Do routine maintenance of the circuit breaker.
  • Utilize cables (or) bus bars with suitable ratings.
  • To reduce load current, select and install the suitable ACB rating.
  • Tight & loose joints in the busbar connection.

Cause

  • The motor is not getting proper supply.
  • A loose connection in the secondary isolating contacts.
  • The motor has burnt out.

Solution

  • Check limit switch on the motor.
  • Adjust secondary isolating contacts correctly. 
  • Replace the motor.

Cause

  • The breaker is not in the service position.
  • The closing coil is not getting power.
  • Closed coil burned out (or) open circuited

Solution

  • Set the breaker to the service position.
  • Check the control circuit to check that the coil is receiving power. 
  • Replace the coil that closes the circuit.