The Bypass Type Intelligent Soft Start Cabinet engineered by China · Yongfan Electric Co., Ltd. (YOF®) is an industrial-grade motor control and protection center designed for three-phase squirrel-cage AC asynchronous induction motors across a broad power rating of 5.5 kW to 630 kW. Utilizing a dedicated microprocessor-controlled intelligent bypass soft starter as its central control unit, the cabinet integrates high-breaking-capacity Molded Case Circuit Breakers (MCCB), an engineered AC bypass contactor, precision low-voltage fuses, digital voltmeters, ammeters, rugged control pushbuttons, and clear operational LED indicator lamps into a unified, heavy-duty electrical enclosure.
During starting, antiparallel thyristors (SCRs) perform precise phase-angle voltage ramp control, progressively raising motor terminal voltage to deliver ultra-smooth torque acceleration and limit inrush current to only 2 to 4 times rated current. Once the motor reaches nominal operating speed, the internal control logic automatically engages the dedicated AC bypass contactor. Under steady-state continuous operation, motor running current flows entirely through the bypass contactor, de-energizing the thyristor power block. This operating topology achieves minimal thermal power consumption, eliminates thyristor harmonic generation during normal duty, drastically lowers internal heat buildup, and ensures long-term operational stability.
Manufactured in full compliance with GB14048.6-2008 and IEC 60947-4-2 low-voltage switchgear standards under strict ISO9001 quality assurance and national CCC compulsory safety certification, this cabinet delivers unmatched reliability for global industrial infrastructure and processing plants.
Specifically engineered to mitigate mechanical stress and electrical grid surges across heavy starting inertia and variable industrial load profiles:
Equipped with 12 distinct digital protective functions constantly escorting motor and driven equipment during starting, running, and stopping cycles.
Features an innovative "Delay Bypass Switch" timing algorithm that prevents large-current switching arcs from pitting contactor contacts, significantly extending electrical life.
Clear industrial LCD panel with structured menus provides real-time voltage/current monitoring, intuitive parameter configuration, fault history, and rapid troubleshooting.
Built-in RS485 communication port running standard Modbus-RTU protocol, paired with PC supervisory software for remote monitoring, start/stop automation, and SCADA integration.
| No. | Protection Function | Technical Operational Description & Trigger Threshold |
|---|---|---|
| 1 | Start-up Timeout Protection | Shuts down immediately if motor fails to reach full rated speed within the preset acceleration ramp window. |
| 2 | Input Phase Loss Protection | Trips within < 3 seconds upon detection of missing incoming power phase on line terminals. |
| 3 | Output Phase Loss Protection | Instantaneous trip (< 3 seconds) if motor cable or output connection becomes open-circuited. |
| 4 | Three-Phase Current Unbalance | Protects motor against severe winding heating when current deviation across phases exceeds 50% (< 3s lag). |
| 5 | Starting Overload Protection | Fast thermal trip protection activated when acceleration current exceeds 5 times motor rated current (Ie). |
| 6 | Running Overload Protection | Inverse-time electronic thermal overload modeling tailored to motor continuous duty class. |
| 7 | Power Supply Over-Voltage | Inhibits start and triggers fault alarm when incoming line voltage exceeds 130% of nominal rating. |
| 8 | Power Supply Under-Voltage | Prevents motor stall and high-slip burnouts during severe grid voltage brownout conditions. |
| 9 | Load Short-Circuit Protection | Instantaneous microsecond-level gate pulse blocking coordinated with upstream molded case breaker. |
| 10 | Thyristor Over-Temperature | Internal heat-sink thermistor sensor locks out starting if junction temperature exceeds safe thermal limits. |
| 11 | Phase Sequence Detection | Verifies correct positive sequence rotation to protect machinery from unexpected reverse rotation. |
| 12 | Instantaneous Over-Current | Fast hardware comparator detection trips instantly upon locked-rotor or abnormal mechanical jamming. |
Figure 1: Schematic Diagram of Main Circuit Interconnection
As illustrated in the schematic, the power transmission path flows systematically through four core stages to provide total control and maximum equipment safety:
| Component | Standard Function in Cabinet |
|---|---|
| MCCB | Short-circuit breaking & manual power isolation |
| Soft Starter | Smooth voltage/torque acceleration & deceleration control |
| Bypass Contactor | Zero-loss continuous running & thermal reduction |
| Induction Motor | Heavy-duty 3-phase squirrel cage driven machinery |
Figure 2: Outline & Mounting Size Dimensional Drawing (A × B × C)
The cabinet is fabricated from premium cold-rolled electro-galvanized sheet steel with electrostatic thermosetting powder coating, offering exceptional mechanical rigidity, anti-corrosion resilience, and IP30/IP40 ingress protection.
| Specification (Power Rating) | Overall Dimensions (mm) | Mounting Configuration | ||
|---|---|---|---|---|
| A (Width) | B (Height) | C (Depth) | ||
| 5.5 - 75 kW | 420 mm | 1000 mm | 380 mm | Compact Floor Standing / Wall Mountable |
| 90 - 220 kW | 550 mm | 1250 mm | 550 mm | Standard Heavy-Duty Floor Standing |
| 250 - 400 kW | 650 mm | 1500 mm | 650 mm | Heavy-Duty Industrial Floor Standing |
| 450 - 630 kW | 700 mm | 1750 mm | 650 mm | High-Capacity Free-Standing Cubicle |
As an established Chinese electrical equipment manufacturer and verified global exporter, China · Yongfan Electric Co., Ltd. (YOF®) provides full-service OEM and ODM contract manufacturing for engineering contractors, system integrators, and industrial machinery distributors worldwide:
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