Instruction Manual for Motor Star-Delta (Y-Δ) Reduced-Voltage Starting Control  

Applicable Object: Three-phase asynchronous motor (power ≥11kW, voltage 380V/50Hz)  

### I. Starting Principle and Purpose  
1. Necessity of Reduced-Voltage Starting  
When the motor power is large (usually ≥11kW), direct starting will generate an impact of **6-8 times the rated current**, leading to:  
- A sudden drop in grid voltage (affecting other equipment)  
- Mechanical impact (damaging couplings/belts)  
- Misoperation of protection devices  

2. Star-Delta Conversion Principle  

| **Starting Stage** | **Winding Connection** | **Phase Voltage** | **Starting Current** | **Starting Torque** |  
|--------------------|-------------------------|-------------------|----------------------|---------------------|  
| **Star (Y)**       | Winding ends shorted    | **220V**          | **1/3** of direct starting current | **1/3** of direct starting torque |  
| **Delta (Δ)**      | Head-to-tail sequential connection | **380V**      | Full-voltage rated current | 100% rated torque |  

> ⏱️ **Conversion Time**: Usually set to **4-15 seconds** (adjusted according to load inertia), ensuring the speed reaches 75%-85% of the rated speed before switching to Δ operation.  

### II. System Composition and Component Selection  
1. List of Core Components  

| **Component**      | **Model Example**       | **Specification Requirements**       | **Quantity** |  
|---------------------|-------------------------|---------------------------------------|--------------|  
| Main circuit breaker | NM1-225S/3300           | Rated current ≥1.5×I_N (motor) | 1            |  
| AC contactor        | CJX2-6511 (Δ operation) | AC-3 type, current ≥I_N     | 3            |  
| Thermal relay       | JR36-160                | Setting current ≈I_N (prevent false trip during Y starting) | 1 |  
| Time relay          | ST3PF (digital)         | Range 0.1-999s, accuracy ±1%          | 1            |  
| Buttons             | LA38-11                 | Green (start)/Red (stop)              | 2            |  

2. Protection Function Configuration  
- **Short-circuit protection**: Main circuit breaker (instantaneous trip)  
- **Overload protection**: Thermal relay (only connected to the Δ circuit to avoid misoperation in the Y stage)  
- **Voltage loss protection**: Contactor self-locking circuit  
- **Mechanical interlock**: Normally closed contacts of KM_Y and KM_Δ are connected in series (prevent simultaneous suction)  

### III. Electrical Wiring Diagram and Action Logic  
1. Main Circuit Wiring (see attached drawing)  

```mermaid
graph LR
    L1/L2/L3 --> QF[Main Circuit Breaker] --> KM1[Main Contactor]
    KM1 --> |U1/V1/W1| KM<sub>Y</sub>[Star Contactor] --> Short W2/U2/V2
    KM1 --> |U1/V1/W1| KM<sub>Δ</sub>[Delta Contactor] --> |U1-W2, V1-U2, W1-V2| Motor
```

2. Control Circuit Action Flow  

```mermaid
sequenceDiagram
    participant SB1 as Stop Button
    participant SB2 as Start Button
    participant KT as Time Relay
    participant KMY as Star Contactor
    participant KMΔ as Delta Contactor
    participant KM1 as Main Contactor
    
    SB2->>+KT: Press start → KT is energized and starts timing
    KT-->>KMY: Immediately pull in (star starting)
    KMY-->>KM1: Auxiliary contact pulls in (main circuit energized)
    KT->>-KMΔ: Timing ends → Disconnect KMY
    KT-->>+KMΔ: Simultaneously pull in KMΔ (switch to delta)
    KMΔ-->>KM1: Maintain self-locking
```

Key Wiring Notes:  
> - The 6 motor terminals (U1/U2, V1/V2, W1/W2) must be correctly marked;  
> - **KM_Δ output wires** must be strictly crossed according to phase sequence (U1-W2, V1-U2, W1-V2).  

### IV. Debugging Steps and Parameter Settings  
1. No-Load Debugging Process  

| **Step** | **Operation**                          | **Expected Phenomenon**              |  
|----------|-----------------------------------------|---------------------------------------|  
| 1        | Disconnect the main circuit, test only the control circuit | KM_Y pulls in, KT times      |  
| 2        | Simulate KT timing completion           | KM_Y releases, KM_Δ pulls in |  
| 3        | Connect the main circuit (motor unloaded) | Y starting current ≤1.5I_N, no impact during switching |  

2. Time Relay Setting Principles  
- **Light load** (fans/water pumps): 4-8 seconds  
- **Heavy load** (crushers/compressors): 10-15 seconds  
- **Formula reference**: `t = (√J × N<sub>rated</sub>)/(9.55 × T<sub>Y starting</sub>)`  
  (J-rotational inertia kg·m²; T_{Y starting}-star starting torque N·m)  

### V. Common Faults and Troubleshooting  

| **Fault Phenomenon**    | **Possible Cause**               | **Troubleshooting Method**          |  
|-------------------------|-----------------------------------|--------------------------------------|  
| Tripping during starting | KM_Y/KM_Δ pull in simultaneously | Check mechanical interlock and wiring |  
| Severe vibration during switching | Conversion time too short        | Extend KT setting time (in 2-second steps) |  
| Thermal relay misoperation | Overload protection activated in Y stage | Move the thermal relay to the KM_Δ output end |  
| Incorrect motor rotation direction | Main circuit phase sequence reversed | Swap any two incoming phases          |  

### VI. Safety Warnings  
1. **Live work is strictly prohibited**: Disconnect the main circuit breaker and verify no voltage before switching contactors;  
2. **Modification of interlock is forbidden**: Removing KM_Y-KM_Δ interlock may cause short-circuit explosion;  
3. **Grounding is mandatory**: Motor housing and cabinet PE busbar must be reliably grounded (grounding resistance ≤4Ω).  

> 📜 **Compliance Standards**:  
> - GB/T 14048.4 *Low-Voltage Switchgear and Controlgear*  
> - IEC 60947-4-1 Contactors and Motor Starters  

**Attachment**: [Star-Delta Reduced-Voltage Starting Wiring Diagram (CAD Drawing No.: YDQ-2023-STD)](example link)  
**Note**: Before actual application, verify component selection according to motor nameplate parameters (power, current, connection method) and calculate protection settings.