Why should one test power generators with a load bank?

What is a Load Bank and How Does it Work?

An electrical load bank (referred to by us as a load bank or dummy load) is a technical device used to simulate an electrical load for the purpose of testing power sources such as generator sets. There are four basic types of load banks:

• Resistive: The most commonly used, typical for general generator set testing. They usually have a built-in cooling system, although some models utilize external airflow.
• Inductive (Reactive): Less common than resistive, but most effective for testing emergency generators in business-critical operations, such as in data centers and hospitals.
• Resistive-Inductive (Combined): Combine resistive and inductive testing methods when both are necessary for a given application.
• Capacitive: Use electromagnetic fields to test power supply devices. They are typically used for testing rotating devices, such as motors.

Why Should Generator Sets Be Tested Under Load?

In the event of a power supply disruption, the emergency power system, based on a standby generator, is automatically activated to ensure the uninterrupted operation of critical infrastructure. Therefore, the main goal of testing a standby generator under load is to confirm the generator’s readiness to accept a full load for an extended period.

Load testing allows verification of whether the generator maintains stable electrical parameters, which is crucial for the safety of connected equipment. Additionally, when operating at full load, the generator generates more heat. These tests allow checks to ensure the cooling and ventilation systems are working correctly and that overheating does not occur. The elevated operating temperature during the test also effectively burns off excess accumulated fuel and deposits, thereby protecting the unit from the phenomenon known as “wet stacking.”

Simultaneously, the tests enable the assessment of combustion efficiency and actual fuel consumption, which is important for inventory planning. Operating under load can reveal problems that do not appear at idle—for example, vibrations, overloads, or control system errors. The tests also allow verification of whether the generator starts correctly, transfers power, and synchronizes with the grid (if that function is present).

Load tests are of key importance for units with high operational priority, for which this is a component of the technical and operational safety procedure and a requirement for compliance with standards (according to National Fire Protection Association (NFPA) standards for emergency power systems that must operate in life-threatening situations, load tests should be performed monthly) and certification. Additionally, load testing is a part of routine preventive maintenance, especially when it is not possible to use the actual building load.

Load Bank Testing Procedure

The basic activities performed by Eneria’s service team (with electrical qualifications) during a load bank test include:

Test Preparation:

• Checking the generator’s technical documentation.
• Verifying the technical condition: oil, fuel, and coolant levels, and filter condition.
• Ensuring the appropriate load: e.g., resistive, inductive.
• Selecting and connecting cables of the correct cross-section and length, corresponding to the test power rating.
• HSE (Health, Safety, and Environment) safeguards: isolating the test area, grounding both the load bank and the generator, presence of fire extinguishers, and personal protective equipment.

Generator Start-up:

• Manual or automatic start.
• Monitoring initial parameters: voltage, frequency, oil pressure, temperature, etc.

Gradual Loading:

• Adding load in increments (e.g., 25%, 50%, 75%, 100%).
• Monitoring operational stability at each level.
• Recording parameters: voltage, frequency, temperature, fuel consumption, etc.

Full-Load Test:

• Operation for a specified duration (e.g., 1–2 hours) at maximum load.
• Observing generator behavior: checking if it maintains parameters, and if any alarms or errors occur.

Ancillary System Test:

• Checking the operation of the cooling, ventilation, and lubrication systems.

Test Completion:

• Gradually removing the load.
• Shutting down and cooling the generator.
• Checking the technical condition after the test.

Documentation and Report:

• Recording the test results.
• Conclusions and potential service recommendations.
• Confirmation of the generator’s operational readiness.

Eneria Service Offer

In response to the growing demands for power system reliability in Data Center infrastructure, we are pleased to announce that Bergerat Monnoyeur has enhanced its service offering with a comprehensive load testing service for standby diesel generator sets with power ratings up to 5 MW.

As one of the few companies in Poland, we have two modern reactive load banks with a unit power of 2 MW, and one resistive load bank with a power of 1 MW. This allows us to independently conduct high-power tests. This translates into full control over the process, greater scheduling flexibility, and a higher level of safety during execution.

Thanks to the experience of our team and advanced technical facilities, we offer full flexibility in terms of the test schedule and scope—both during the commissioning of new infrastructure and during planned service inspections. If you are interested, we would be happy to present a detailed offer tailored to your requirements. Please contact us to discuss the details and arrange a convenient date for the service.

We look forward to your reply.

Author: Zofia Rzeźniczak
EPG Expert and Data Center
Zofia.Rzezniczak@eneria.pl
Mob.: +48 667 546 630