Designed for Frequent Operation: A New Generation Intelligent Protection and Control Solution for High-Voltage FC Circuits

I. Solution Overview​

This solution aims to provide a comprehensive protection solution for FC circuits based on "High-Voltage Vacuum Contactors + High-Voltage Current-Limiting Fuses". It is specifically designed for the protection and control of high-voltage motors, distribution transformers, and capacitor banks within the 3kV to 12kV voltage range, particularly suited for industrial applications requiring frequent operation and high reliability (such as power plants, large factories, and mines). Its core advantage lies in the precise coordination between the vacuum contactor and the current-limiting fuse, achieving graded protection against overload and short-circuit faults, while offering economic efficiency, safety, and intelligence.

​II. Core Component Technical Characteristics​

​1. High-Voltage Vacuum Contactor (FC Circuit Operation and Overload Interruption Component)​​
The high-voltage vacuum contactor is the actuator for frequent circuit operation and interruption of overload currents. Its technical characteristics are as follows:

• ​Core Structure:​​
• ​Vacuum Interrupter Chamber:​​ Utilizes a ceramic enclosure with an internal vacuum degree as high as 1.33×10⁻⁴ Pa, ensuring the arc is successfully extinguished at the first current zero-crossing, achieving oil-free and maintenance-free operation.
• ​Insulation Mounting Bracket and Interlocking Mechanism:​​ Integrates fuse mounts and is equipped with a crucial interlocking trip mechanism. This mechanism ensures: ① If a fuse in any phase blows, it immediately triggers the three-phase simultaneous trip of the contactor, preventing single-phasing operation; ② If a fuse in any phase is not installed, it mechanically locks the contactor from closing, ensuring operational safety.
• ​Operating Mechanism:​​ Employs an electromagnetic mechanism, supporting frequent opening and closing operations up to 2000 times/hour, far exceeding the capability of circuit breakers.
• ​Operation and Interruption Principle:​​
• ​Interruption Principle:​​ Utilizes the high insulation and strong arc-extinguishing capability of the vacuum medium. The metal vapor arc generated during opening is extinguished instantly at the current zero-crossing point, with rapid dielectric strength recovery. Its chopping current is below 0.5A, effectively suppressing switching overvoltages, which is extremely friendly to motor insulation.
• ​Holding Method:​​ Supports both electrical self-hold (energy-saving, low noise) and mechanical self-hold (high reliability, anti-interference) methods. Users can choose based on operational requirements (e.g., the LHJCZR series uses mechanical self-hold).
• ​Key Rated Parameters:​​

​2. High-Voltage Current-Limiting Fuse (FC Circuit Short-Circuit Protection Component)​​
The high-voltage current-limiting fuse serves as the ultimate protection component for short-circuit faults. Its characteristics are as follows:

• ​Core Function:​​ Provides instantaneous (quick-break) protection. When a severe short-circuit fault occurs (current exceeding the contactor's breaking capacity), its fusible element rapidly melts and interrupts the circuit before the current reaches its prospective peak. The interruption time is extremely short (millisecond level), maximizing the limitation of fault current energy and protecting downstream equipment from damage.
• ​Basic Selection Principles:​​
• ​Rated Voltage:​​ Must not be lower than the system's rated voltage to prevent the overvoltage generated during fuse operation from exceeding the equipment's insulation withstand level (typically limited to below 2.5 times the phase voltage).
• ​Rated Current:​​ Requires comprehensive consideration of normal/overload currents, equipment starting inrush characteristics (e.g., motor starting current, transformer magnetizing inrush), and ensuring selective coordination with upstream protective devices (e.g., relays).
• ​Role Positioning:​​ Serves as backup protection within the FC circuit. Normal overloads and smaller short-circuit currents are cleared by the comprehensive protection device signaling the vacuum contactor to open. The fuse operates only when the fault current exceeds the contactor's breaking capacity or if the contactor fails to operate.

​III. Selection Guidance Based on Protected Object​

​1. Motor Protection Fuse Selection​
Motor starting currents are high and durations long, requiring extra caution in selection to prevent nuisance operation.

• ​Protection Coordination Logic:​​
• ​Overload Protection (e.g., stall, repeated starting):​​ Implemented by inverse-time relays, driving the contactor to open.
• ​Short-Circuit Protection:​​ Implemented by the fuse.
• ​Coordination Requirement:​​ The fuse's rated current must be greater than the motor's starting current, and its time-current characteristic curve must intersect the relay's curve at one point to achieve perfect coordination.
• ​Selection Reference (Excerpt):​​

• ​Key Point:​​ The longer the starting time and the higher the starting frequency, the larger the required fuse link rated current.

​2. Transformer Protection Fuse Selection​
Selection must ensure the fuse can withstand the transformer's closing magnetizing inrush current while providing effective protection against internal faults.

• ​Selection Reference (Excerpt):​​

​3. Capacitor Bank Protection Fuse Selection​
Capacitor bank switching generates high-frequency, high-amplitude closing inrush currents, posing special requirements for fuse selection.

• ​Special Consideration:​​ Must verify that the fuse can withstand the let-through energy (I²t) of the closing inrush current. Requirement: Inrush let-through energy < 0.7 times the fuse's minimum pre-arcing energy.
• ​Selection Requirements:​​
• Rated current is typically 1.5~2.0 times the capacitor's rated current.
• If the inrush current is too large, consider: ① Selecting dedicated capacitor fuses (e.g., WFN series); ② Adding a series current-limiting reactor with the capacitor; ③ Adding a series damping resistor in the branch.
• ​Recommendation:​​ A current-limiting reactor must be used when (Inrush Peak Current * Inrush Frequency) > 20000 or during extremely frequent operations.

​IV. Application Scope and Typical Cases​

​1. Application Scope​
The FC circuit solution is not universal. Its applicable boundaries are as follows:

• ​High-Voltage Motors:​​ ≤ 1200 kW
• ​Distribution Transformers:​​ ≤ 1600 kVA
• ​Capacitor Banks:​​ ≤ 1200 kvar
  Beyond these capacity ranges, a vacuum circuit breaker solution with higher breaking capacity and dynamic/thermal stability must be selected to ensure safety.

​2. Typical Case Validation​
This solution has been successfully applied in multiple projects, operating stably and reliably:

• ​Case 1: Chemical Plant, Texas, USA (Frequent Operation and Explosion-Proof Environment)​​
• ​Project Overview:​​ This large chemical base required frequent start-stop control for high-voltage pumps and compressor motors across multiple production lines, with environmental requirements for explosion-proofing and high reliability.
• ​Advantages Demonstrated:​​ The contactor's 2000 operations/hour frequency perfectly met process adjustment needs; precise coordination between the fuse and relay ensured accurate short-circuit protection for motors under frequent starting without nuisance operation; the low chopping current (<0.5A) provided by the vacuum interrupter effectively suppressed switching overvoltages, protecting the insulation of older motors. The overall solution saved significant investment compared to vacuum circuit breaker switchgear.
• ​Case 2: Automotive Manufacturing Plant, Bavaria, Germany (Transformer and Capacitor Compensation Protection)​​
• ​Project Overview:​​ A new smart manufacturing factory required stable, high-quality power supply for numerous robotic servo systems on automated production lines, accompanied by multiple dry-type distribution transformers and capacitor compensation banks.
• ​Advantages Demonstrated:​​ Fuse rated current selection fully considered transformer magnetizing inrush characteristics, avoiding nuisance operation during closing. For the capacitor banks, dedicated fuses successfully withstood the closing inrush impact (I²t verification passed). The contactor's low bounce ensured capacitor switching without re-ignition, safeguarding power quality on the grid.

​V. Solution Advantage Summary​

1. ​High Reliability:​​ Vacuum interrupter chamber is maintenance-free with a mechanical life of up to millions of operations; fuses provide millisecond-level quick-break protection.
2. ​Strong Safety:​​ Mechanical interlocking mechanism prevents single-phasing operation and closing with potential hazards; low chopping current protects equipment insulation.
3. ​Good Economy:​​ Compared to vacuum circuit breaker switchgear, FC switchgear offers lower cost, smaller size, and extremely high cost-effectiveness.
4. ​Intelligence:​​ Contactors can be seamlessly integrated with microprocessor-based protection devices, enabling remote monitoring, intelligent control, and data upload.
5. ​Easy Maintenance:​​ Core components are designed for maintenance-free operation; after fuse operation, only replacement with a same-specification fuse link is required, making operation simple.