Stamford vs Leroy Somer Alternator: Which Is Better for Your Generator Set?

When selecting a diesel generator set, the alternator is just as important as the engine. It converts mechanical energy into electrical power and directly affects voltage regulation, motor starting performance, efficiency, and the generator's ability to support different electrical loads.

Two established names in the generator alternator market are STAMFORD and Leroy-Somer. Both offer alternators for commercial, industrial, standby, and continuous power applications, but their product ranges, excitation systems, and available configurations differ.

So, which is better: a Stamford or Leroy Somer alternator?

The answer depends on your generator capacity, electrical load, starting requirements, excitation system, installation conditions, and local technical support.

In this guide, DIYPOWER compares Stamford and Leroy Somer alternators to help you make an informed selection for your diesel generator project.

Stamford vs Leroy Somer Alternator: Quick Comparison

Both manufacturers offer reliable alternator technologies for diesel generator applications. However, comparing specific models is more useful than choosing based solely on brand reputation.

Quick answer: Neither brand is universally better. A properly sized Stamford alternator may perform better than an unsuitable Leroy-Somer model, and vice versa. The correct comparison must be based on models operating under the same electrical and environmental conditions.

What Is a Stamford Alternator?

STAMFORD alternators are manufactured by Cummins Generator Technologies under the STAMFORD | AvK brand portfolio.

They are widely used in generator sets supplying standby, prime and continuous power in commercial, industrial and infrastructure applications.

The product portfolio includes alternators across a broad range of capacities, with different frame sizes, excitation systems, automatic voltage regulators (AVRs) and optional features.

Depending on the model, important characteristics may include:

• Brushless synchronous alternator construction

• Automatic voltage regulation

• Optional or integrated excitation arrangements

• Multiple voltage and frequency configurations

• Different insulation and enclosure options

• Support for a range of diesel and gas engine applications

For current model information and technical specifications, see the official STAMFORD Alternator Product Range.

Stamford Excitation Systems

The excitation system supplies the electrical energy needed to establish and regulate the alternator's magnetic field.

STAMFORD alternators can use different excitation arrangements, depending on the model.

Self-excited systems derive excitation power from the main alternator output. These can be appropriate for many conventional loads, but their performance during severe voltage dips must be evaluated carefully.

PMG-excited systems use a separate permanent magnet generator to supply the AVR, helping reduce the dependence of excitation power on main terminal voltage.

Other configurations, such as auxiliary-winding arrangements, may also be available on selected models.

The most suitable excitation system depends on load characteristics, motor starting requirements and protection coordination.

What Is a Leroy Somer Alternator?

Leroy-Somer alternators are part of the Nidec Power portfolio and are used in a wide range of industrial power generation applications.

The product range includes TAL and LSA alternators, along with other configurations designed for specialized applications.

Different models are available for diesel and gas generator sets, industrial power systems and other generation equipment.

Key considerations may include:

• Brushless synchronous alternator designs

• Different AVR and excitation configurations

• Industrial and standby operating ratings

• Multiple voltage and frequency options

• Application-specific winding and enclosure configurations

• Model-dependent thermal and transient performance

According to the official Nidec Power product overview, the TAL range serves standard applications, while the LSA range covers standard and critical applications across multiple power ratings.

For more details, refer to the Leroy-Somer / Nidec Power Product Overview.

Leroy Somer AREP Excitation Technology

One recognized Leroy-Somer excitation technology is AREP, which uses auxiliary windings to provide excitation power to the automatic voltage regulator.

This arrangement can help maintain excitation performance when the main output voltage changes under demanding load conditions.

AREP configurations may be useful in applications involving:

• Motor starting

• Sudden load changes

• Certain nonlinear loads

• Generator applications requiring appropriate short-circuit performance

However, AREP is not the only excitation system offered within the Leroy-Somer product portfolio.

The actual capability depends on the alternator model, winding configuration, AVR and published performance data.

Stamford PMG vs Leroy Somer AREP: What's the Difference?

Excitation technology is one of the most important technical considerations when comparing specific Stamford and Leroy-Somer alternators.

Two commonly discussed configurations are Stamford alternators equipped with PMG excitation and Leroy-Somer alternators equipped with AREP excitation.

How Does PMG Excitation Work?

A Permanent Magnet Generator (PMG) supplies power to the AVR independently of the main alternator output terminals.

During a sudden load increase, the main alternator voltage may temporarily decrease.

Because the PMG provides a separate excitation source, it can help maintain the AVR's ability to control excitation under these conditions.

Potential benefits include:

• Reduced dependence on main output voltage for AVR supply

• Support for demanding transient loads

• Excitation performance suitable for selected nonlinear loads

• Short-circuit current support where specified by the manufacturer

The actual performance depends on the specific PMG, AVR, alternator and operating conditions.

How Does AREP Excitation Work?

AREP excitation uses auxiliary windings within the alternator to supply the voltage regulator.

These windings provide excitation power based on electrical conditions in the alternator.

This arrangement can improve excitation support during load disturbances compared with certain basic self-excited configurations.

Potential benefits include:

• Excitation support during voltage disturbances

• Suitability for selected demanding electrical loads

• No separate PMG assembly in conventional AREP configurations

• Model-dependent motor starting and fault current performance

PMG vs AREP Comparison

Which is better?

PMG and AREP can both provide suitable excitation performance for demanding generator applications.

It would be inaccurate to conclude that AREP always provides better motor starting or that PMG always delivers better voltage regulation.

For a meaningful comparison, request the manufacturer's published transient voltage dip, voltage recovery and motor starting data for the specific models being considered.

Which Alternator Has Better Motor Starting Performance?

Motor starting is particularly important for diesel generator sets operating pumps, compressors, industrial machinery and HVAC systems.

When an electric motor starts, it may draw substantially more current than during normal operation.

The resulting current demand can cause a temporary voltage dip at the generator terminals.

If the dip is excessive, other connected equipment may malfunction or disconnect.

Factors That Affect Motor Starting Capability

Motor starting performance depends on:

1. Alternator rated capacity and frame size

2. Excitation system and AVR

3. Motor starting method

4. Motor starting kVA

5. Existing electrical load

6. Generator engine transient response

7. Acceptable voltage and frequency deviations

Both Stamford and Leroy-Somer offer alternator configurations suitable for motor starting applications.

However, the brand name alone does not determine starting performance.

Example: Industrial Pump Starting

Consider a diesel generator supplying a manufacturing facility with multiple running loads and a large water pump.

When the pump starts, its temporary current demand may cause a voltage dip.

Before selecting the alternator, the engineer should determine:

• Pump motor rating

• Starting current or locked-rotor kVA

• Starting method

• Existing generator running load

• Maximum acceptable voltage dip

• Required voltage recovery performance

Using these values, the generator supplier can compare suitable Stamford and Leroy-Somer model data.

For broader generator capacity planning, see our Generator Set Selection Guide.

Voltage Regulation and Nonlinear Load Performance

Modern generator sets frequently supply equipment containing power electronics.

Typical nonlinear loads include:

• Variable Frequency Drives (VFDs)

• Uninterruptible Power Supplies (UPS)

• Industrial rectifiers

• Switching power supplies

• Certain electronic lighting systems

These loads can introduce harmonic currents and affect voltage waveform quality.

How Does Winding Pitch Affect Harmonics?

Alternator winding design can influence the voltage waveform and harmonic behavior.

For example, a 2/3-pitch winding is commonly used in generator applications to reduce certain triplen harmonic components in generated voltage.

However, this design does not eliminate all harmonic distortion caused by nonlinear loads.

The overall harmonic performance depends on the complete electrical system.

Important factors include:

• Alternator winding configuration

• Load harmonic spectrum

• AVR and excitation performance

• Alternator reactance

• Connected UPS and VFD characteristics

• Generator loading and system impedance

Which Brand Is Better for UPS and Data Center Loads?

Both manufacturers offer alternators that may be suitable for UPS and data center applications.

The decision should be based on actual electrical requirements rather than brand preference.

For sensitive loads, request information about voltage regulation, transient recovery, harmonic performance, alternator sizing and compatibility with the connected power electronics.

A correctly engineered generator system may also require additional consideration of UPS input characteristics, load steps and redundancy.

Efficiency, Temperature Rise and Continuous Operation

Alternator efficiency affects the mechanical power required from the engine and contributes to the overall efficiency of the generator set.

However, efficiency varies by model, rating, operating temperature, voltage, frequency and load percentage.

Alternator Efficiency

Two alternators with the same nominal kVA rating may have different efficiency curves.

For example, their losses may differ due to winding design, core materials, cooling arrangements and operating conditions.

A valid comparison should use manufacturer data measured or calculated under equivalent conditions.

Temperature Rise and Insulation

Alternator insulation systems are designed for specified thermal conditions.

Many industrial alternators use insulation systems classified according to relevant international standards.

However, insulation class alone does not establish the permitted continuous output.

Engineers must also consider:

• Rated temperature rise

• Ambient temperature

• Cooling performance

• Duty classification

• Installation altitude

• Manufacturer derating instructions

Which Alternator Is Better for Prime Power?

Both Stamford and Leroy-Somer offer products for extended operating applications.

The correct selection depends on the required prime or continuous rating, expected load profile, operating temperature and maintenance arrangements.

Neither brand should automatically be considered superior for continuous operation without comparing the relevant models.

Stamford vs Leroy Somer: Engine Compatibility

Alternators must be mechanically and electrically compatible with the diesel engine.

Both brands offer configurations that can be integrated with major industrial engine platforms.

However, compatibility should be confirmed for each engine-alternator combination.

1. Rated Power and Speed

The alternator must support the required electrical output at the intended operating speed.

Typical four-pole generator configurations operate at:

• 1500 rpm for 50 Hz applications

• 1800 rpm for 60 Hz applications

Other speeds and pole configurations are available for specialized systems.

2. SAE Housing and Coupling

Engine and alternator coupling arrangements must match the required mechanical interface.

Important considerations include:

• SAE housing size

• Flywheel interface

• Coupling arrangement

• Single-bearing or double-bearing construction

• Shaft alignment and mounting requirements

An SAE-compatible interface alone does not guarantee complete compatibility.

3. Torsional Vibration

The rotating engine and alternator assembly must be evaluated for torsional compatibility.

For applicable projects, the engine and generator manufacturers or qualified system integrator should review torsional vibration characteristics.

This helps reduce the risk of mechanical resonance and coupling damage.

4. Physical Dimensions

Alternator length, weight, mounting configuration and cooling clearance can affect generator enclosure design.

A PMG-equipped alternator may require a different overall mechanical arrangement from a corresponding AREP-equipped model.

However, dimensions must be compared using actual model drawings rather than assuming that one brand always occupies less space.

DIYPOWER provides Alternators and Parts for generator applications, allowing customers to evaluate component requirements alongside complete generator set specifications.

Spare Parts, Maintenance and Long-Term Reliability

For B2B generator buyers, the cost of ownership extends beyond the initial equipment purchase.

Maintenance support and parts availability can significantly affect downtime.

Stamford Maintenance Considerations

STAMFORD provides technical documentation and replacement part support through its service and distribution arrangements.

Before purchasing, buyers should confirm the availability of the specific AVR, bearings, rotating rectifier components and other maintenance parts required for their alternator model.

Leroy Somer Maintenance Considerations

Leroy-Somer also provides technical support and replacement components through its service channels.

Buyers should verify the availability of model-specific AVRs, excitation components, bearings and technical documentation in their region.

How to Compare Long-Term Service Support

Rather than assuming that one manufacturer has better global support, evaluate:

• Authorized service availability in the project country

• Genuine spare parts availability

• Local technician capability

• Expected replacement component delivery time

• Warranty terms

• Maintenance documentation

• Repair or replacement costs

Procurement tip: Request the complete alternator model designation, serial number, technical datasheet and applicable warranty information when buying a generator set.

How to Choose Between Stamford and Leroy Somer

The following checklist can help B2B purchasers compare suitable alternators.

Choose a Stamford Alternator When...

A particular Stamford model meets your electrical specifications, required excitation configuration, physical installation constraints and maintenance requirements.

Stamford may be a suitable option when the project requires a specific PMG-equipped configuration or when locally available support meets the customer's operating needs.

Choose a Leroy Somer Alternator When...

A particular Leroy-Somer model meets the required capacity, load characteristics, mechanical dimensions and service requirements.

Leroy-Somer may be a suitable option where an AREP-equipped configuration matches the project's technical requirements or the customer prefers an available TAL or LSA model.

Compare the Complete Generator Set

For many customers, the alternator is selected as part of a complete diesel generator set.

A technically suitable alternator must be coordinated with the engine, controller, electrical protection, enclosure and operating conditions.

At DIYPOWER, we help customers evaluate generator set configurations for different commercial and industrial applications.

FAQs About Stamford and Leroy Somer Alternators

Is Stamford better than Leroy Somer?

Neither brand is universally superior. Both manufacture alternators for industrial and commercial generator applications. The better choice depends on the specific model, required output, electrical load, excitation system and local maintenance support.

What is the main difference between Stamford PMG and Leroy Somer AREP?

PMG uses a separate permanent magnet generator to supply excitation power to the AVR. AREP uses auxiliary stator windings for excitation supply. Both approaches can support demanding applications, but their performance must be evaluated using model-specific data.

Which alternator is better for motor starting?

Motor starting performance depends on the alternator's starting kVA capability, excitation system, AVR, load characteristics and permitted voltage dip. Both manufacturers offer configurations suitable for motor starting applications.

Are Stamford and Leroy Somer alternators compatible with Cummins and Perkins engines?

Both brands offer alternator configurations that can be integrated with different diesel engines. However, the specific engine-alternator pairing must be verified for rated power, speed, SAE interface, coupling and torsional compatibility.

Which alternator is better for data center applications?

Both manufacturers offer alternators that may be suitable for data centers. Engineers should compare transient voltage performance, nonlinear load compatibility, required rating and the complete generator system design.

Are Stamford and Leroy Somer spare parts interchangeable?

Replacement components should not be assumed to be interchangeable between brands or models. Genuine or manufacturer-approved parts should be selected using the exact alternator and component specifications.

Does a PMG alternator always provide better voltage regulation?

No. The excitation arrangement is only one factor. Voltage regulation also depends on the AVR, alternator design, load conditions and manufacturer specifications.

Does higher alternator kVA mean better performance?

Not necessarily. Higher kVA provides additional nominal capacity, but motor starting, thermal performance, efficiency and voltage response must also be considered.

Conclusion: Which Alternator Should You Choose?

Choosing between a Stamford and Leroy Somer alternator requires more than comparing brand reputation or nominal kVA ratings.

Both offer alternator technologies suitable for commercial, industrial, standby and extended-operation generator applications.

The most important factors include excitation design, voltage regulation, motor starting capability, thermal rating, mechanical compatibility and regional service support.

For many diesel generator projects, the best approach is to compare complete engine-alternator configurations under the actual application requirements.

At DIYPOWER, we help customers evaluate diesel generator set solutions based on electrical capacity, application conditions and equipment specifications.

Explore our Generator Set Range and Alternators & Parts, or contact DIYPOWER to discuss your generator configuration and alternator requirements.