Key Considerations for Purchasing a Mobile Trailer-Mounted Diesel Generator Set

Mobile trailer-mounted diesel generator sets are specialized power solutions designed for challenging environments, such as remote locations with long power supply lines or limited infrastructure. Due to these unique operational demands, their performance and reliability requirements exceed those of conventional stationary generators. To ensure a wise investment and optimal performance, users must carefully evaluate several critical factors during the purchasing process. Below are the key considerations, elaborated with professional detail and clarity.

1. Characteristics of Electrical Equipment

The selection of a diesel generator set begins with a thorough understanding of the electrical equipment it will power.

• Equipment Type and Power Requirements: Identify the categories of electrical loads (e.g., motors, lighting, or sensitive electronics), their rated power (in kW or kVA), and peak demand.
• Motor Specifications: Mobile trailers often rely on single, high-capacity motors. These motors typically exhibit:
  • High Starting Load: Large inrush currents during startup (often 6-8 times the running current).
  • Low Running Load: Reduced power demand once operational.
• Starting Performance: The generator must have robust starting capabilities to handle the inrush current without stalling or requiring excessive oversizing. Failure to account for this may lead to underperformance or wasted investment.

Recommendation: Compile a detailed load profile, including starting and running power demands, to ensure the generator matches the equipment’s needs.

2. Selection of Starting Method

The starting method for large motors significantly influences generator sizing and cost. Mobile trailer applications typically involve high-capacity motors, necessitating careful selection from the following options:

• Available Starting Methods:
  • Direct On-Line (DOL) Start: High inrush current; generally impractical for large motors on mobile generators due to excessive load.
  • Y-Δ (Star-Delta) Start: Reduces starting current but still may overload smaller generators; often unsuitable.
  • Autotransformer Start: Provides adjustable voltage reduction, lowering inrush current; a viable option for mobile units.
  • Soft Start: Gradually ramps up voltage, minimizing starting load; suitable for sensitive applications.
  • Variable Frequency Drive (VFD) Start: Offers precise control over starting and running, ideal for high-efficiency setups but increases cost.
• Selection Criteria:
  • Evaluate the motor’s starting torque requirements.
  • Balance investment budget with long-term operational efficiency.
  • Consult equipment and generator manufacturers to align the starting method with system capabilities.

Recommendation: For mobile trailers, prioritize autotransformer, soft start, or VFD methods, as DOL and Y-Δ starts are rarely feasible for large motors in such applications.

3. Current and Power Calculation

Accurate sizing of the generator depends on precise electrical calculations.

• Starting Current: Calculate the peak inrush current under worst-case conditions (e.g., cold starts, maximum load). This varies by starting method.
• Running Current: Determine the steady-state current during normal operation.
• Power Sizing:
  • Use the formula:
    P (kW) = V × I × PF × √3 / 1000 (for three-phase systems), where:
    • V = Voltage (V),
    • I = Current (A),
    • PF = Power Factor.
  • Add a safety margin (typically 20-30%) to account for transients and future expansion.
• Generator Capacity: Select a unit with sufficient kVA rating to handle both starting and running loads without derating.

Recommendation: Perform detailed load calculations and verify results with the generator supplier to avoid undersizing or oversizing.

4. Environmental Considerations

Mobile trailer-mounted generators often operate in harsh or remote conditions, requiring environmental adjustments.

• Altitude Effects:
  • Diesel engine power output decreases by approximately 1% per 100 meters above sea level due to reduced air density.
  • Example: At 2000 m, expect a ~20% power reduction unless the unit is altitude-compensated.
• Temperature and Humidity: Extreme heat, cold, or moisture can affect engine efficiency and electrical components.
• Dust and Debris: Ensure the generator has adequate filtration and enclosure (e.g., IP54 or higher) for dusty environments.

Recommendation: Specify the intended operating altitude and conditions to the supplier to select a generator with appropriate derating or enhancements (e.g., turbocharging for high altitudes).

5. Additional Practical Considerations

Beyond technical specifications, practical factors influence long-term performance and cost-effectiveness.

• Mobility and Portability:
  • Verify the trailer’s design suits the terrain (e.g., rugged off-road capability).
  • Check weight, dimensions, and towing compatibility with available vehicles.
• Fuel Efficiency: Opt for models with high fuel economy to minimize operational costs, especially in remote areas with limited fuel access.
• Maintenance and Serviceability:
  • Choose a unit with accessible components and minimal downtime for routine maintenance.
  • Confirm availability of spare parts and technical support in operational regions.
• Brand Reliability: Select manufacturers with a proven track record, robust warranties, and comprehensive after-sales service.

Recommendation: Request detailed specifications, fuel consumption data, and service plans from suppliers to evaluate total cost of ownership.

Conclusion

Purchasing a mobile trailer-mounted diesel generator set requires a systematic approach to ensure compatibility with electrical loads, operational reliability, and environmental adaptability. Key steps include:

1. Analyzing equipment characteristics and starting demands.
2. Selecting an appropriate motor starting method.
3. Calculating currents and sizing the generator accurately.
4. Accounting for environmental factors like altitude and climate.
5. Evaluating mobility, efficiency, and support services.

By addressing these factors and collaborating closely with equipment and generator manufacturers, users can procure a high-performance, cost-effective solution tailored to the unique challenges of mobile trailer applications. This diligence ensures efficient, stable power delivery in even the most demanding scenarios.