Question
1. A 25 kW , two speed induction motor is to be used for driving a knife of paper cutting machine at Business times newspaper factory. The motor is to meet the following requirements; a. For knife setting and adjustment, the motor requires to be operated in low and high speed. b. For paper cutting operation, up and down movement is required. Propose the right type of motor starter to be used and hence draw the main circuit and control circuit diagrams coupled with proper switching sequence to fulfil the above requirements.
Ask by Medina Stewart. in Tanzania
Mar 11,2025
Upstudy AI Solution
Tutor-Verified Answer
Answer
**Motor Starter Proposal and Circuit Diagrams**
To meet the requirements for the 25 kW two-speed induction motor used in a paper cutting machine, a **two-speed motor starter** with reversing capabilities is recommended. This setup allows the motor to operate at low and high speeds for knife setting and adjustment, and to perform up and down movements during the cutting operation.
### Main Circuit Diagram
1. **Power Supply**: Connect the motor to the power source.
2. **Two-Speed Motor Starter**: Utilize a starter that can switch between low and high speeds.
3. **Contactor for Low Speed (C1)**: Controls the low-speed operation.
4. **Contactor for High Speed (C2)**: Controls the high-speed operation.
5. **Overload Relay (OL)**: Protects the motor from excessive current.
6. **Reversing Contactors (C3 and C4)**: Allow the motor to move up and down.
### Control Circuit Diagram
1. **Start Button**: Initiates the motor operation.
2. **Stop Button**: Halts the motor.
3. **Selector Switch**: Allows selection between low and high speeds.
4. **Reversing Switch**: Controls the up and down movement of the knife.
### Switching Sequence
1. **Initialization**:
- Ensure the motor is de-energized.
- Set the selector switch to low speed.
- Set the reversing switch to the desired direction (up or down).
2. **Operation**:
- Press the start button to energize the motor.
- The motor operates at low speed for knife setting and adjustment.
- To switch to high speed, use the selector switch.
- For up and down movement, use the reversing switch accordingly.
3. **Shutdown**:
- Press the stop button to de-energize the motor.
- Ensure the motor has come to a complete stop before performing any maintenance or adjustments.
### Diagrams
**Main Circuit Diagram**:
```
Power Supply → [Overload Relay (OL)] → [Two-Speed Motor Starter] → Motor
```
**Control Circuit Diagram**:
```
Start Button → [Contactor C1/C2] → Motor
Stop Button → [Contactor C1/C2] → Motor
Selector Switch → [Contactor C1/C2] → Motor
Reversing Switch → [Contactor C3/C4] → Motor
```
**Switching Sequence Summary**:
- **Start**: Press Start → Motor runs at selected speed.
- **Stop**: Press Stop → Motor stops.
- **Change Speed**: Use Selector Switch → Switch between low and high speeds.
- **Change Direction**: Use Reversing Switch → Move knife up or down.
This configuration ensures that the motor operates efficiently for both setting and cutting operations, while the reversing mechanism allows for precise control over the knife's movement.
Solution
To address the requirements for the 25 kW two-speed induction motor used in a paper cutting machine, we need to propose a suitable motor starter and provide the necessary circuit diagrams.
### Step 1: Identify the Motor Starter Type
Given that the motor operates at two speeds and requires up and down movement for the cutting operation, a **star-delta starter** or a **direct-on-line (DOL) starter** with a reversing contactor setup would be appropriate. However, for two-speed operation, a **two-speed motor starter** with reversing capabilities is ideal. This allows for:
- Low-speed operation for knife setting and adjustment.
- High-speed operation for cutting.
- Reversing capability for up and down movement.
### Step 2: Main Circuit Diagram
The main circuit will include:
- A power supply.
- A two-speed motor starter.
- Contactor for low speed (C1).
- Contactor for high speed (C2).
- Overload relay (OL).
- Reversing contactors (C3 for up and C4 for down).
#### Main Circuit Diagram
```
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Answered by UpStudy AI and reviewed by a Professional Tutor
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Simplify this solution The Deep Dive
For a 25 kW, two-speed induction motor used in a paper cutting machine, a suitable motor starter would be a combination starter that accommodates both star-delta starting for the high power requirements and a reversing motor starter configuration to support the up and down movement needed for the knife cutting operations. This setup allows for smooth transitions between high and low speed operations, maintaining efficiency and reducing the mechanical stress on the motor and machine components. In the main circuit, you would typically include a circuit breaker for overload protection, contractor relays for controlling the motor, and a star-delta starter to manage the current during startup. The control circuit would consist of push buttons for speed selection and direction change, limit switches to prevent over-travel of the knife mechanism, and indicators for the motor's operational state. Proper labeling will enhance user understanding, ensuring safe operation while minimizing electrical hazards.
