What are the common faults of indoor AC high-voltage vacuum circuit breakers?

The ZN63A indoor AC high-voltage vacuum circuit breaker is a three-phase AC 50 Hz, 12 kV indoor device, used for starting, stopping, controlling, and protecting high-voltage motors of 10,000-ton free forging presses. AC high-voltage vacuum circuit breakers play a critical role in enterprise production. Timely and accurate resolution of their faults to quickly restore production is essential for enterprise development. During the start/stop of high-voltage motors, frequent operations of the vacuum circuit breaker can cause damage to electrical components and wear of mechanical parts, which are major reasons for the failure of the circuit breaker to close normally. Analyzing and solving such faults is of great significance for ensuring enterprise production.

1 Working Principle of AC High-Voltage Vacuum Circuit Breaker
1.1 Arc Extinguishing Chamber

The ZN63A indoor high-voltage vacuum circuit breaker used in the 10,000-ton forging press is equipped with a ceramic vacuum arc extinguishing chamber. Its moving contact features a cup-shaped structure made of copper-chromium material, which has low electrical wear rate, long electrical life, and high withstand voltage level. When the internal gas pressure of the arc extinguishing chamber is lower than 1.33×10⁻³ Pa, it can meet the basic requirement of normal storage for no less than 20 years, and the action life of the arc extinguishing chamber is not lower than the mechanical life of the circuit breaker.

1.2 Arc Extinguishing Principle

When the ZN63A indoor high-voltage vacuum circuit breaker used in the 10,000-ton forging press completes the opening operation, the moving and static contacts are charged and opened under the action of the operating mechanism, and a vacuum arc will be generated between the contacts. Due to the cup-shaped structure of the moving contact, a longitudinal magnetic field is generated in the gap of the moving contact. The longitudinal magnetic field keeps the vacuum arc in a diffused state, distributes the arc temperature evenly on the contact surface, and maintains a low arc voltage. The vacuum arc is controlled by the longitudinal magnetic field of the circuit breaker, so the ability to interrupt current is strong and stable.

1.3 Action Principle
1.3.1 Energy Storage Action

When the knob on the high-voltage switchgear is turned to the "Energy Storage" position, the energy storage motor starts operating. The spring-hanging crank arm on the energy storage shaft rotates clockwise to stretch the closing spring. Energy storage is completed once the closing spring is pulled to its limit position. Simultaneously, the shift plate connected to the energy storage shaft drives the energy storage indicator to show that energy storage is ready. This energy storage process prepares the circuit breaker for the closing action (see Figure 1).

1.4 Circuit Breaker Inspection and Maintenance
1.4.1 Daily Inspection

(1) Check whether the operating mechanism of the high-voltage vacuum circuit breaker is normal and if the closing indication is correct.
(2) Verify that all interlock protections and signal relays are functioning normally.
(3) Ensure ammeters, voltmeters, integrated protections, and all indicator lights are in normal condition.

1.4.2 Routine Checks

(1) After the circuit breaker is put into operation, conduct routine checks in accordance with relevant operation specifications.
(2) On the weekly maintenance day, with the main machine shut down, turn the high-voltage cabinet knob to "Local", withdraw the circuit breaker trolley from the "Working Position" to the "Test Position", and inspect the electrical and mechanical components of the circuit breaker trolley for integrity.
(3) Check the tightness of bolts on all components and tighten loose bolts promptly. Regularly inspect the operating conditions of the energy storage motor, closing coil, and opening coil.

1.4.3 Cleaning and Lubrication

(1) During maintenance of the main equipment, withdraw the circuit breaker trolley from the "Working Position" to the "Test Position", then pull it out to a dedicated transfer cart, and clean the circuit breaker to keep the surfaces of insulating parts and conductive parts clean.
(2) Apply imported German lubricating grease to the transmission parts of the circuit breaker.
(3) Apply new conductive paste to the contact parts of the circuit breaker.

2 Common Faults of AC High-Voltage Vacuum Circuit Breakers

(1) Inability to store energy normally.
Cause Analysis:

Faulty microswitch S1 for energy storage, preventing the energy storage motor from running normally.
Malfunctioning limit contacts for the test/working position of the high-voltage vacuum circuit breaker, disabling the energy storage motor.
Broken spring-hanging crank arm on the drive energy storage shaft, where the energy storage motor runs but the closing spring does not stretch.

(2) Normal energy storage but failure to close.
Cause Analysis:

Defective microswitch S1: after normal energy storage, the S1 contact fails to close.
Faulty working position limit contacts of the high-voltage vacuum circuit breaker, which do not close properly.
Malfunctioning auxiliary switch QF linked to the circuit breaker main shaft.
Broken mechanical cam connecting rod, hindering normal closing operation of the mechanical mechanism.

(3) Inability to open normally.
Cause Analysis:

Burned opening coil, disabling electric opening.
Faulty auxiliary switch QF linked to the circuit breaker main shaft, preventing normal electric opening.

(4) Inability to push in or withdraw the circuit breaker trolley.

Cause Analysis:

Circuit breaker is in the closed state.
Pushing handle is not fully inserted into the pushing hole.
Pushing mechanism not fully in the test position, causing the tongue plate to fail to unlock with the cabinet.
Cabinet grounding knife is not disconnected.

3 Common Faults and Maintenance Cases of High-Voltage Vacuum Circuit Breakers

The 450 kW 6 kV high-voltage motor of the WEG 400C/D/E-06 10,000-ton forging press failed to start normally. This high-voltage motor is started by a high-voltage soft starter. Before starting, the knob of the main motor high-voltage cabinet is turned from the "Local" to "Remote" position. The starting principle is shown in Figure 2.

Diagnosis and Troubleshooting Process

After diagnosis, during the startup process, the PLC sent the motor start command to the soft starter. The soft starter received the closing command, and the relay control board, after calculation, output the closing command to the high-voltage cabinet. However, the high-voltage cabinet did not execute the closing command. The inspection process was as follows:

The energy storage indicator light of the high-voltage cabinet was on, indicating that the high-voltage vacuum circuit breaker had stored energy.
A multimeter was used to measure the voltage between terminals ln4X1 and ln4x6 of the NARI integrated protection device. It should be DC 220 V. After measurement, the voltage was normal.
The indicator light for the trolley operation position was checked. It was on, indicating that the high-voltage vacuum circuit breaker was in the working position.
The knob was in the "Remote" position, and the indication was correct.
When attempting remote closing again, the high-voltage vacuum circuit breaker still did not act.
The knob was rotated to "Local", and the trolley was shaken from the working position to the test position. The plug was removed, and terminals 10# and 20# of the plug were measured. It was found that the resistance of these two terminals was very small. Under normal circumstances, it should be 12,000 Ω, indicating that the locking electromagnet coil was burned out.
In the test position, energy storage was carried out first, and the S1 microswitch was measured, which worked normally.
In the test position, energy storage was carried out first, and the locking contact was manually closed. The resistance of terminals 4# and 14# of the plug was measured to be 198 Ω, indicating that the closing coil was normal.

From the above diagnosis, it can be seen that due to the failure of the locking electromagnet coil, the closing circuit was open, and the normal closing conditions could not be met. After replacing the locking coil, the trolley was pushed into the "Working Position", the knob was rotated to the "Remote" position, closing was normal, and the motor started normally.

Fault Cases and Solutions

(1) The 450 kW 6 kV high-voltage motor of the 10,000-ton forging press failed to start normally. Inspection found that the energy storage indicator light of the high-voltage cabinet was off. The energy storage motor drove the spring to repeatedly store energy, but it could not store energy normally. The energy storage knob was turned to "Off", and the working mode was rotated from "Remote" to "Local". The circuit breaker trolley was withdrawn from the "Working Position" to the "Test Position" for inspection.

It was found that the spring-hanging crank arm on the drive energy storage shaft was broken. The energy storage motor rotated, but the closing spring was not stretched, so energy could not be stored normally. After replacing the energy storage shaft and the spring-hanging crank arm, energy storage was normal, and the motor started normally.

(2) The 450 kW 6 kV high-voltage motor of the 10,000-ton forging press failed to start normally. Entering the high-voltage distribution room and inspecting the high-voltage cabinet, it was found that the energy storage indication was normal. In the 10,000-ton operation room, the closing button was pressed, but the high-voltage vacuum circuit breaker still could not close normally. Through the indication of the high-voltage cabinet LED light, the high-voltage vacuum circuit breaker was in the "Working Position", and the limit indication was normal.

The knob of the high-voltage cabinet was switched from "Remote" to "Local", and the circuit breaker was withdrawn from the "Working Position" to the "Test Position". When the high-voltage cabinet LED indicator showed "Test Position", the door of the circuit breaker chamber of the high-voltage cabinet was opened, the plug was pulled out, and the resistance between pins 4# and 14# was measured. The resistance could not be measured, and the circuit was open. The microswitch S1 was measured, and it was found that the contact of the microswitch S1 was faulty. After replacement, the circuit breaker closed normally, and the high-voltage motor started normally.

(3) The high-voltage vacuum circuit breaker tripped again after closing. The 450 kW 6 kV high-voltage motor of the 10,000-ton forging press is output by two output points of the PLC. When both output points are at high level, the motor starts; when one or both of the output points are at low level, it stops. After diagnosis, the two high-level output signals of the PLC were normal. The two high-level signals were sent to the relay module of the VFS soft starter.

The relay module, after calculation, sent the closing command of the incoming line circuit breaker to the circuit breaker through the input-output module, and the high-voltage vacuum circuit breaker closed. During the secondary frequency conversion startup process of the VFS, the startup current was 1.5Ie, and the output startup torque was 90%Te. However, due to a load fault during the startup process, the startup process exceeded the startup time, and the VFS soft starter sent a trip signal. The high-voltage vacuum circuit breaker received the trip signal and tripped immediately. Entering the 10,000-ton pump station, the motor was manually rotated, and the motor drove the oil pump to jam. The motor and the oil pump were completely disconnected.

The output shaft of the motor could be easily rotated by hand, while the input shaft of the oil pump was completely stuck. The oil pump was disassembled and repaired, and the connection between the output shaft of the high-voltage motor and the locking device of the input shaft of the oil pump was restored. After inspection, it was restarted. The startup signal of the high-voltage motor was normal, the high-voltage vacuum circuit breaker closed normally, and the motor operated normally. This fault was caused by an external load fault, which caused the high-voltage vacuum circuit breaker to trip again after closing, resulting in the failure of the high-voltage vacuum circuit breaker to work normally.

(4) The high-voltage vacuum circuit breaker could not trip normally after closing. When such a fault occurs, generally, the electric tripping fails, and only manual tripping can be performed. This fault is caused by a burned-out tripping coil or a fault of the rotary auxiliary switch QF. This auxiliary switch QF has 8 pairs of normally open contacts and 8 pairs of normally closed contacts. There are 16 units of the 450 kW 6 kV high-voltage motor of the 10,000-ton forging press, and 16 indoor AC high-voltage vacuum circuit breakers corresponding to them.

During use, due to frequent startup and shutdown, various faults occur during the operation of the high-voltage vacuum circuit breakers. For the fault phenomena, specific analysis is carried out, targeted maintenance strategies are proposed and repaired in a timely manner, and the equipment utilization rate is improved.

The operation status of the AC high-voltage vacuum circuit breaker directly affects the production progress of the 10,000-ton forging press. By strengthening the daily maintenance and fault handling of the equipment, classifying, analyzing, sorting out, and summarizing the faults, the scope of the fault point can be narrowed during fault judgment, the accuracy of fault judgment can be increased, and the maintenance efficiency can be improved; during maintenance, precise maintenance can be achieved, the labor intensity of maintenance personnel can be reduced, the maintenance time can be shortened, and the equipment can operate more safely and economically.

4. Conclusion

When a fault occurs in the AC high-voltage vacuum circuit breaker, troubleshooting is carried out following the principle of from simple to difficult and from the electrical part to the mechanical part. As long as the working principle of the AC high-voltage vacuum circuit breaker and the mechanical structure of the equipment are mastered, its operation method and action sequence are understood, and sufficient investigation and analysis of the fault phenomenon are carried out, the cause of the fault can surely be found. Inspection, repair, and troubleshooting can be carried out to restore the normal use of the high-voltage vacuum circuit breaker and ensure the normal production of the enterprise.