The correct selection of a synchronous alternator for coupling with an internal combustion engine is a crucial phase in the design of a generator set. An engineering-optimized choice ensures operational continuity, energy efficiency, reduced mechanical wear, and precise adaptation to specific application requirements.

1. Determining the Required Power

Sizing the alternator must begin with an accurate assessment of the active power (kW) and reactive power (kVAr) demanded by the load. This analysis should take into account:

• Load regime (continuous and peak)
• Presence of non-linear and/or unbalanced loads
• Power factor of the system (cosφ)
• Any transients or temporary overloads (e.g., motor startups)

Technical note: It is generally advisable to slightly oversize the alternator compared to the engine’s rated power to optimize response to transients and ensure better voltage stability.

2. Selecting the Number of Poles

The number of poles of the alternator directly determines the rotational speed in relation to the nominal frequency:

• 2 poles (3000 rpm at 50 Hz): Compact solution, suitable for intermittent service or stable loads. Ideal for high-speed engines.
• 4 poles (1500 rpm at 50 Hz): Greater mechanical strength, lower dynamic stress. Recommended for continuous operation, harsh environments, or variable loads.

Best practice: For industrial applications or extended operation, 4-pole alternators are preferable. For portable or occasional use, 2-pole alternators are more compact and cost-effective.

3. Mechanical Compatibility with the Engine

It is essential to verify full mechanical compatibility between the alternator and engine in terms of:

• Flange and shaft in accordance with SAE standards (or other standards)
• Type of coupling (direct or via flexible joint)
• Sizing and alignment of the support frame

A properly engineered mechanical coupling prevents vibrations, misalignments, and abnormal mechanical stresses, thereby increasing system lifespan.

4. Voltage Regulation Technology

Voltage regulation technology plays a fundamental role in the alternator’s ability to respond to dynamic load variations while maintaining a stable output voltage. The main available solutions include:

a. Capacitor Regulation

• Simple and low-cost (self-regulating alternator)
• Suitable for predominantly resistive loads and portable gensets or non-critical uses
• Limited capacity to manage unbalanced or inductive loads

b. Compound Regulation

• The excitation system is proportional to the load current
• Provides more stable regulation than capacitor systems, with partial compensation for voltage drop under load
• Intermediate solution between capacitor regulation and AVR, suitable for moderately variable and inductive loads or for applications requiring mechanical robustness

c. Electronic Regulation (AVR)

• Active voltage control with regulation precision typically ±1%
• Effective handling of non-linear and unbalanced loads
• Widely used in professional and industrial applications

5. Efficiency and Sizing Considerations

In addition to nominal power, it is important to consider:

• Overall electrical efficiency
• Thermal losses and dissipation capacity
• Tolerance to variable load cycles
• Electromagnetic compatibility (EMC) in sensitive environments

A high-efficiency alternator contributes to reducing the specific fuel consumption of the genset and ensures greater operational reliability.

The selection of an alternator must be based on a thorough technical analysis of the load profile, operating conditions, and performance requirements. Every application – from a portable generator to a critical system requiring uninterrupted operation – calls for careful evaluation of the number of poles, excitation technology, and the necessary voltage stability.

In this context, the solutions offered by Linz Electric cover a wide range of needs: from the E1C series with capacitor regulation to brushless PRO models with AVR, ensuring high performance, reliability, and long operational life.

A well-informed and technically sound selection allows for the creation of generation systems that are reliable, efficient, and perfectly suited to real operating conditions.