Understanding Why Small Generators Shut Off Under Initial Load

Introduction

While generators are designed to provide reliable power in various scenarios, there are instances where a small generator may shut off when subjected to the initial load. This article aims to explore the reasons behind such behavior and provide relevant solutions for ensuring smoother operation.

Key Insights on Generators and Load

When a small generator is tasked with supplying power, it often faces specific challenges due to its limited capacity. Understanding these challenges can help in diagnosing and addressing potential issues promptly.

Load Characteristics and Requirements

For a small generator to function optimally, the load characteristics must be understood and appropriately considered. Initial loads can significantly impact the generator's performance. Here are some critical points:

Real Load vs. Rated Power: The initial load may equate to the real load (kW) being nearly the same as the rated power (kVA) of the generator. Even with capacitors connected to motors as loads, reactive loads (kVAr) are still required from the grid system. Reactive Power Compensation: Small generators equipped with PMG excitation typically have limitations in compensating for reactive power demands. This limitation can cause the generator to trip when a motor as a load begins to draw an initial load greater than the generator's capacity. Generator Capacity: To mitigate these issues, it's crucial to ensure the generator is appropriately sized for the anticipated load. Sizing the generator based on the locked rotor amps (LRA) and operating voltage will help prevent overload conditions.

Common Scenarios Leading to Generator Shutdown

Generator shutdowns under initial load can manifest in various ways, including the engine stopping, voltage dropping to zero, or circuit breakers tripping. Understanding these scenarios can help in pinpointing the root cause and implementing appropriate solutions.

Engine Stalling and Load Adequacy

One common issue is that the generator's prime mover (typically a gas or diesel engine) may not have sufficient power to keep the generator turning under the initial load. This can cause the generator to shut off.

Voltage Collapse

The starting current of motors can be up to five times the steady-state current. Other load types can also have starting surges, which can easily overwhelm a generator that is not appropriately designed to handle such current spikes. This phenomenon is often referred to as voltage collapse.

Recommendations for Smooth Generator Operation

To avoid generator shutdowns under initial load, the following recommendations can be implemented:

Proper Load Assessment: Carefully assess the load to be supported by the generator. Use the locked rotor amps (LRA) and operating voltage from the motor nameplate to ensure the generator is adequately sized. Surge Capacity: For applications with high starting current loads, consider upgrading to a generator with built-in surge capacity or use surge protectors to prevent overload conditions. Reactive Power Compensation: Ensure that reactive power requirements are met either by the generator itself or by additional capacitors, as needed. Regular Maintenance: Maintain the generator and its components regularly to prevent wear and tear that could lead to failure.

Conclusion

Understanding and addressing the reasons behind small generator shutdowns under initial load is crucial for maintaining reliable power supply. By considering the characteristics of the load, the appropriate sizing and maintenance of the generator, and taking preventive measures, users can ensure optimal performance and longevity of their generator systems.