The frame-type circuit breaker, also known as the universal circuit breaker, is a mechanical switchgear that can make, carry, and interrupt current under normal circuit conditions. It can also make and carry current for a certain period of time and interrupt current under specified abnormal circuit conditions. So how to solve the problem that the universal circuit breaker cannot be closed?

First, determine whether the circuit breaker has tripped due to a non-accident reason

Non-accident tripping refers to tripping that occurs without short circuit or overload faults. There are various reasons why a circuit breaker cannot be closed. Firstly, it is necessary to determine whether the tripping is caused by short circuit or overload in the circuit, or if there is a fault in the circuit breaker itself or its control circuit. After confirming that the fault lies with the circuit breaker, it should be withdrawn (referring to drawer-type circuit breakers) for inspection.

Reasons for tripping of universal circuit breaker

1. Due to the loss of power to the undervoltage release, the universal circuit breaker cannot be closed. If the voltage is too low or the coil of the undervoltage release loses power, it will cause the universal circuit breaker to trip and prevent it from being re-closed. The following four situations can cause the coil of the undervoltage release to lose power.

a. Poor contact of components such as the closing button, relay contacts, and auxiliary contacts of the universal circuit breaker, as well as damaged components, may all lead to circuit blockage and loss of power to the trip coil;

b. Disconnection of connecting wires or loosening or detachment of crimping screws in the circuit can also lead to circuit disconnection and loss of power to the trip coil;

c. Due to the coil of the undervoltage release being in an energized working state for a long time, environmental pollution, inflexible armature actuation, or an excessively large air gap between the iron core and the armature, all can easily cause excessive current, leading to heating and burnout of the release coil, thus losing its function.

d. The protective circuit breaker is fused, causing the circuit to be blocked, and the trip coil of the undervoltage release loses power.

2. Mechanical system failure, causing the universal circuit breaker to fail to close; after multiple trips and closings, the operating mechanism of the universal circuit breaker may suffer severe wear, potentially leading to the following malfunctions:

a. If the motor drive mechanism is worn, such as damage to the worm gear and worm of the ME switch, it will not be able to drive the operating mechanism of the universal circuit breaker to perform tripping and closing operations. Replacing the worm gear and worm is relatively complex.

b. The operating mechanism is not flexible and exhibits a clamping phenomenon. Since this type of universal circuit breaker is not fully enclosed, if foreign objects such as screws and nuts are accidentally left inside the operating mechanism, it can cause a clamping phenomenon during operation, affecting the closing of the circuit breaker. Additionally, if the rotating and sliding parts lack lubricating grease, and the opening and closing energy storage spring of the operating mechanism is slightly deformed, the universal circuit breaker may also fail to close. Therefore, when encountering the above-mentioned faults, in addition to checking for foreign objects inside the operating mechanism, it is also necessary to inject lubricating grease into the rotating and sliding parts.

c. Fault in the energy storage spring of the operating mechanism. The opening and closing energy storage spring of the operating mechanism becomes slack or loses its elasticity after multiple stretches, resulting in a reduced closing force. When closing, the four-bar linkage mechanism of the universal circuit breaker cannot be pushed to the dead center position, and the mechanism cannot maintain itself in the closed position. Therefore, the universal circuit breaker cannot close normally. The energy storage spring must be replaced.

d. Wear and tear on the free-trip mechanism makes it difficult for the universal circuit breaker to re-engage, and it trips easily. Sometimes, it barely engages, and upon vibration, it trips automatically; sometimes, after re-engagement, it slips out as soon as the switch is closed. In this case, rotate the adjusting screw to adjust the relative position of the trip half-shaft and the trip latch, so that their contact area is around 2.5mm. Replace the corresponding parts if necessary.

Fault inspection and solutions for universal circuit breakers

1. Check whether the operating mechanism panel is sinking. If it is, it will affect the travel of the transmission mechanism, ultimately affecting the contact travel and causing the closing to fail. To adjust, loosen the panel fixing screws, lift the panel up, and then tighten the fixing screws.

2. Check whether the position of the stopper is correct and whether the circuit breaker is in the working position

The guide rail of the drawer-type circuit breaker features a stopper. When the circuit breaker is not in its working position or the position of the stopper is incorrect, the stopper will press against the plastic piece on the outside of the half-shaft, preventing the half-shaft from engaging with the trip latch, resulting in a fault where the circuit breaker trips immediately upon closing.

3. Voltage loss release

When the no-voltage release is not in the engaged position, the metal plate pressing the moving iron core of the no-voltage release will actuate the release mechanism under the action of spring force. For DC-operated circuit breakers, the first step should be to check the filter capacitor, followed by checking whether the coil of the no-voltage release is open-circuited, whether the metal plate on the top of the no-voltage release is deformed, and whether the gap between the metal plate and the top rod is between 0.5 and 1 mm. If the filter capacitor is damaged, it should be replaced; if the coil of the no-voltage release is open-circuited, it should be repaired or replaced; if the spring plate is deformed, it should be corrected; if the gap is improper, it should be adjusted.

4. Shunt release

If the shunt release is in the engaged position, it may also exhibit a phenomenon where it trips immediately after closing. For the shunt release, the main inspection is to check whether the normally open contacts of the control circuit’s opening button are fused together. Additionally, if the metal plate on the top of the shunt release is deformed, causing the gap between the metal plate and the top rod to be too small, such faults may also occur. If the opening button is damaged, it should be replaced. If the metal plate is deformed, it should be corrected, and the gap between the metal plate and the top rod should be adjusted to be between 0.5 and 1mm.

5. The position of the jump buckle and the half shaft is incorrect

When the circuit breaker is in the disconnected position, the distance between the trip latch and the half-shaft should be within the range of 0.8~1.0mm. If this range is exceeded, reliable locking between the half-shaft and the trip latch cannot be guaranteed, resulting in the circuit breaker tripping immediately upon closing. To adjust, loosen the cap nut (lock nut) of the adjusting screw, and turn the adjusting screw in or out until the distance between the trip latch and the half-shaft is within 0.8~1mm.

6. Overcurrent release

Check whether the drive rod of the overcurrent release can be reset and whether the energy storage rod can be re-engaged. If the drive rod cannot be reset, adjust the iron core of the overcurrent release; if the energy storage rod cannot be re-engaged, adjust the opening piece behind the energy storage rod. The distance between the head of the energy storage rod and the engaging piece should be controlled within the range of 0.5~2mm.

7. Free trip device

First, check whether the cover plate of the free-trip device is deformed. A deformed cover plate will cause the shaft sleeves on both ends of the installed half-shaft to be non-concentric, preventing the half-shaft from rotating freely. Next, check whether the effective size of the live bolt in the free-trip mechanism is appropriate. If the cover plate is deformed, it can be removed and corrected. If the effective size is not appropriate, adjustments are necessary. When making adjustments, first remove the cover plate, then remove the split pin on the connecting shaft above the live bolt, press out the connecting shaft, rotate the live bolt, and adjust it until the centers of the three connecting shafts are exactly at the center of the three round holes on the cover plate of the free-trip mechanism when the switch is closed.