Effects of Generator excitation

Effects of Generator under excitation 

If a generator is operating in an under-excited condition, it could result in increased fuel consumption for the following reasons.

Understanding under excitation: 

• Excitation refers to the supply of DC voltage to the rotor windings of a synchronous generator establish its magnetic field. 

• Under-excitation means the generator is producing less reactive power than its rated capacity, causing the generator to operate at a lower excitation voltage. 

• This leads to a decrease in the generator’s ability to produce reactive power (leading to a power factor of less than 1), affecting overall system efficiency. 

How under excitation affects fuel consumption: 

1.) Efficiency losses:

o In under-excitation, the generator becomes less efficient, as it may require additional mechanical power to maintain the same real power output. The system may need more fuel to compensate for these inefficiencies. 

2.) Increased Reactive power demand:

o Under-excitation may require the generator to absorb more reactive power from the grid, or it could be unable to supply reactive power efficiently to the load. This often requires the turbine to work harder to compensate, leading to higher fuel consumption. 

3.) Lower Power Factor: 

o Operating under-excitation can lead to a lower power factor (more reactive power consumption), causing the generator to use more fuel to maintain its real power output. A lower power factor typically means that the generator is less efficient in converting fuel into useful electrical power. 

4.) Load imbalance: 

o Under-excitation might also cause an imbalance between real and reactive power output, making the system less stable and potentially requiring more fuel to correct or stabilize the system. 

In an under-excited condition, the generator tends to consume more fuel because it operates less efficiently, requires more mechanical power to produce the same electrical power output, and could need additional fuel to compensate for lower power factor and increased losses. 

Effects of Generator Over-excitation 

Over-excitation refers to the condition where the generator is supplied with more DC voltage to its rotor windings than required for normal operation. This increases the magnetic field strength and causes the generator to produce more reactive power than needed. Here are the key effects of over-excitation on a synchronous generator: 

1.) Increased reactive power output: 

o Over-excitation leads to the generation of more reactive power (VARs), which can be useful in systems that require voltage support. In grid applications, this can help maintain voltage levels at distant loads or stabilize the system. 

o While this can be beneficial for voltage control in certain scenarios, excessive over-excitation can lead to problems, especially if reactive power exceeds the system’s needs. 

2.) Reduced efficiency:

o Increased fuel consumption: over-excitation can reduce the overall efficiency of the generator because producing excessive reactive power often requires the turbine to work harder, thus consuming more fuel to maintain the same level of active (real) power. 

o Losses in the system: Excessive excitation may cause higher losses due to the increased current in the rotor, stator, and other components of the generator. These losses reduce the generator’s overall efficiency and increase fuel consumption. 

3.) Potential for overheating: 

o Over-excitation increases the magnetic field strength, which can result in increased eddy current losses and core losses in the generator. 

o These losses can cause the generator’s core and windings to overheat, potentially damaging the equipment if sustained over time. 

4.) Voltage instability: 

o If over-excitation is too high, it can cause the generator to produce more reactive power. This could lead to voltage instability, where the system voltage becomes too high, potentially causing damage to sensitive electrical equipment or causing voltage regulation problems. 

o Over-voltage can lead to flash-over (insulation breakdown) and can damage both the generator and connected equipment. 

5.) Reduced power factor: 

o over-excitation can lead to a situation where the generator’s power factor is too high (the generator is producing too much reactive power), which may result in inefficient operation of the generator and overall system. 

o A high reactive power output can increase the load on the generator and reduce its overall real power output efficiency, leading to higher fuel consumption for the same real power. 

6.) Excitation control system stress:

o Operating in over-excitation for extended periods can stress the excitation control system. The system may work harder to regulate the voltage, and if not properly manage, this could result in control system failures or other operational problems. 

7.) Impact on system stability: 

o While over-excitation can help with voltage regulation in some cases, excessive reactive power can create instability in the grid or system. If too many generators are over-excited, it could cause excessive voltage to rise and result in voltage collapse or tripping of generators. 

Over-excitation can have both positive and negative effects: 

• Positive: it can help boost voltage support in certain applications and maintain system stability.

• Negative: it leads to inefficiency, higher fuel consumption, overheating, damage to equipment, and voltage instability if not properly controlled. 

Ideally, the excitation of a generator should be carefully controlled to ensure it operates within optimal parameters. Balancing the need for reactive power support without causing negative effects on efficiency, system stability, and fuel consumption.