Why Does a Diesel Generator Trip While Working at Infinite Bus?

Understanding why diesel generators¹ trip while synchronized with the grid can help prevent unplanned downtime and improve reliability.

Diesel generators can trip when operating at an infinite bus² due to synchronization issues³, grid disturbances, or system faults.

Let’s explore how these factors contribute to generator trips and how to mitigate them.

What Is an Infinite Bus in Power Systems?

An infinite bus is a stable electrical grid with an unlimited capacity to absorb or supply power.

In simple terms, the infinite bus refers to a power grid that is so large and stable that it can maintain voltage and frequency without being affected by any connected generators.

Characteristics of an Infinite Bus

1. Voltage and Frequency Stability

   • The voltage and frequency of the infinite bus remain constant, unaffected by small fluctuations from connected generators.
   • Generators synchronized to this bus must match its voltage and frequency precisely to avoid instability.

2. Absorbs or Supplies Power

   • The infinite bus can either absorb excess power or supply additional power depending on the demand from the system.
   • It maintains a constant power flow without being influenced by individual generators.

Role of Diesel Generators in Parallel with an Infinite Bus

Diesel generators are often synchronized with the grid to provide backup or supplemental power. When synchronized with an infinite bus, the generator must continuously match the grid’s frequency and voltage to avoid trips.

The infinite bus essentially sets the operational conditions that all generators must adhere to, making synchronization critical for smooth operation.

What Causes a Diesel Generator to Trip When Synchronized with the Grid?

There are several reasons why a diesel generator might trip when synchronized with an infinite bus.

Synchronization errors, frequency deviations, or load imbalances can cause a diesel generator to trip from the grid.

Common Causes of Diesel Generator Trips

1. Synchronization Failures

   • If the generator’s voltage, frequency, or phase angle does not match the grid’s infinite bus, the generator will be disconnected to prevent damage.
   • A mismatch during synchronization can cause large circulating currents and voltage spikes.

2. Overload Conditions⁴

   • If the generator is supplying more power than it is rated for, it can trip due to overload protection.
   • This often happens when the generator is required to carry sudden or excessive load increases beyond its capacity.

3. Frequency and Voltage Deviations

   • Diesel generators must operate within a narrow frequency and voltage range. If the grid frequency or voltage drifts beyond the generator's tolerance, it may trip automatically to protect itself from damage.

4. Reverse Power

   • If the grid's power flow starts to exceed the power output from the diesel generator (due to grid instability or issues in power supply), reverse power can occur.
   • This is detected by protection circuits, which will trip the generator to prevent it from absorbing power, which could damage the generator.

5. Protection System Settings⁵

   • The generator’s protective relays may be too sensitive or incorrectly set, leading to unnecessary trips during minor disturbances.

Key Trip Causes in a Diesel Generator

Cause	Description	Mitigation
Synchronization Failures	Voltage, frequency, or phase mismatch	Ensure precise synchronization
Overload	Generator exceeds its rated power	Use load-sharing techniques
Frequency Deviations	Grid frequency deviates outside acceptable range	Use frequency stabilizers
Reverse Power	Power flow from the grid exceeds generator output	Install reverse power relays
Protection Settings	Incorrect relay settings causing unnecessary trips	Adjust relay settings

Addressing these issues can significantly reduce generator trips while synchronized with the grid.

How Do Diesel Generators Respond to Grid Disturbances or Faults When Operating in Parallel?

When operating in parallel with the infinite bus, diesel generators must respond effectively to grid disturbances⁶ or faults.

Generators will either disconnect from the grid or adjust their operation to protect themselves from damage during disturbances.

Common Grid Disturbances and Generator Responses

1. Short Circuit Faults

   • When a short circuit occurs, the generator will detect the abnormal condition and may trip to protect its internal components from damage.
   • The generator may automatically disconnect from the grid during a fault and attempt to restart once the fault is cleared.

2. Underfrequency or Overfrequency

   • If the grid’s frequency drops (underfrequency) or rises (overfrequency) beyond acceptable limits, the diesel generator will typically trip.
   • Some generators have a frequency protection feature to prevent operating under unsafe conditions.

3. Voltage Fluctuations

   • Large voltage variations in the grid can cause the generator to trip if it is outside the generator’s operating voltage range.
   • In this case, voltage protection relays will detect the issue and disconnect the generator from the grid.

4. Grid Synchronization Faults

   • A sudden change in grid frequency or voltage can cause synchronization faults⁷, prompting the generator to trip to prevent further damage.
   • Some generators have advanced synchronization technology to prevent trips caused by minor fluctuations.

Response to Disturbances in Parallel Operation

Disturbance Type	Generator Response	Protection Mechanism
Short Circuit	Trips and disconnects from the grid	Overcurrent protection
Under/Overfrequency	Trips if frequency is out of range	Frequency protection relay
Voltage Fluctuations	Trips if voltage deviates beyond limits	Voltage protection relay
Synchronization Fault	Disconnects from grid if synchronization fails	Synchronization protection

Diesel generators equipped with advanced protection systems can minimize damage and restore operation faster after grid disturbances.

Conclusion

Diesel generators trip when synchronized with an infinite bus due to synchronization errors, overloads, frequency deviations, or grid faults. Proper synchronization, protection settings, and regular monitoring can prevent unexpected trips and ensure reliable power supply.

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