Solusyon para sa Medium-Voltage Motor Control and Protection Gamit ang Vacuum Contactor-Fuse (VCF) sa isang Coal Conveying System

1. Proyekto Background

Ang sistema sa pagpadala og coal adunay 15 ka belt conveyors nga gipatuman pinaagi sa medium-voltage motors. Ang sistema molihok sa komplikado nga kondisyon, ang motors kasagaran nagpatuman sa dako nga carga ug madalas nga pagpangita. Aron mapahimulos kini nga mga suliran ug makamit ang epektibong kontrol ug reliable nga proteksyon sa panahon sa pagpangita sa motor, ang proyekto komprehensibong naggamit og Vacuum Contactor-Fuse (VCF) combination devices alang sa 6kV medium-voltage motor power distribution. Kini nga solusyon detalyado ang teknikal nga features, advantages, ug application sa VCF, naghatag og reliable nga reference para sa katul-anang working conditions.

2. Core Advantages ug Technical Features sa VCF

2.1 Advanced Equipment Structure ug Insulation Technology

• ​Equipment Type: Kini nga solusyon gigamit og withdrawable VCF structure aron mas sayon ang pag-install, maintenance, ug replacement.
• ​Core Technology: Gigamit ang epoxy resin composite insulation ug Automatic Pressure Gelation (APG) technology, ang vacuum interrupter direkta nga gi-encapsulate sa epoxy resin, siguraduhon ang dako nga improbiso sa insulation performance, mechanical strength, ug environmental stability.
• ​Operating Mechanism: Ang operating mechanism gidesinyo ngadto sa precision ug may low power consumption.

2.2 Comprehensive Composition ug Wide Applicability

• ​Equipment Composition: Ang VCF gisusunod sa optimized combination sa high-voltage current-limiting fuses (capable of interrupting a wide range of short-circuit currents) ug frequently operable VCX vacuum contactors, forming a classic F-C circuit solution.
• ​Core Advantages: Ito naghatag og long operational life, stable performance, ug low noise.
• ​Application Scope: Wastong gamiton sa high-voltage auxiliary power systems sa thermal power plants, ug sa metallurgical, petrochemical, ug mining industries. Ito ang suitable para sa controlling ug protecting loads sama sa high-voltage motors, transformers, ug induction furnaces.

2.3 High Adaptability ug Safety Features

• ​Cabinet Compatibility: Ang VCF withdrawable unit compatible sa dimensions ug five-prevention interlocking positions sa circuit breaker withdrawable units sa 800mm-width middle-mounted switchgear, enabling seamless replacement without any modifications to existing switchgear.
• ​Maintenance Convenience: Ang withdrawable design allows safe ug convenient replacement sa high-voltage fuses outside the cabinet.
• ​Holding Method: Ang vacuum contactor mahimo mog configure sa electrical o mechanical holding based on customer requirements.
• ​Phase-Loss Protection: Equipped with comprehensive phase-loss protection. Sa event sa phase loss, ang fuse operates ug mechanically interlocks aron masiguro nga ang VCF disconnects the motor circuit, effectively preventing motor damage due to single-phasing.

3. Key Technical Parameters (7.2kV Rating)

4. Protection Control Principle

Ang VCF protection gisubdivided batasan sa magnitude sa current para sa optimal performance:

• ​Low Current Range (< 4kA)​: Handled by the vacuum contactor for normal breaking and overload protection.
• ​High Current Range (> 4kA)​: Rapidly interrupted by the high-voltage fuse to address short-circuit faults.
• ​Curve Coordination: The contactor’s protection curve is set below the circuit breaker’s curve to ensure the contactor acts first during overloads. Simultaneously, a properly matched fuse with protection settings lower than the upstream circuit breaker is selected to completely avoid unintended tripping.

5. Advantages of VCF vs. Vacuum Circuit Breaker

For frequently started and stopped motor loads, VCF offers significant advantages over vacuum circuit breakers:

6. Core of VCF Selection: Fuse Selection Guide

The performance of VCF hinges on correct fuse selection, considering the following factors:
Working voltage, working current, motor starting time, starts per hour, motor full-load current, and short-circuit current at the installation point.

6.1 Selection Rules and Steps

1. ​Rated Voltage: The fuse’s rated voltage must not be lower than the system working voltage (7.2kV in this case).
2. ​Rated Current Calculation:
• Use the formula: Iy=N×In×δI_y = N \times I_n \times \deltaIy​=N×In​×δ
• IyI_yIy​: Equivalent current during starting (A)
• NNN: Starting current to full-load current ratio (typically 6)
• InI_nIn​: Motor rated full-load current (A)
• δ\deltaδ: Comprehensive coefficient (based on starts per hour, n, from the table below)

1. ​Curve Matching: Plot the calculated IyI_yIy​ value and the motor’s starting time on the fuse manufacturer’s time-current characteristic curve. Select the fuse rated current corresponding to the curve immediately to the right of this point.
2. ​Additional Check: The selected fuse’s rated current must be ​**> 1.7 times the motor’s full-load current**.

6.2 Selection Example

For a 7.2kV system with a directly started 250kW high-voltage motor:
In=30AI_n = 30AIn​=30A, 16 starts per hour, starting time of 6s.

• Calculation: Iy=6×30A×2.1=378AI_y = 6 \times 30A \times 2.1 = 378AIy​=6×30A×2.1=378A
• Selection: On the fuse time-current curve, locate the curve to the right of the point (378A, 6s), corresponding to a fuse rated current of 100A.
• Verification: 100A > 1.7 × 30A (51A), meeting the requirement. Thus, a 100A or higher-rated high-voltage motor protection fuse can be selected.

7. Conclusion

From a comprehensive cost-performance analysis:

• While vacuum circuit breakers have lower procurement costs, their shorter operational life makes them unsuitable for frequent starts/stops, leading to higher long-term maintenance costs and failure risks.
• The VCF solution combines the advantages of vacuum contactors (long life, low overvoltage, suitability for frequent operation) and fuses (ultra-fast interruption of short-circuit currents), all at an economical overall cost.
• For the coal conveying system and other applications with frequent operation and heavy-load starting characteristics, VCF is an ideal solution offering high performance, reliability, and cost-effectiveness.