## 3 Dry-Low Emission Gas Turbine
### Faults in DLE Gas Turbine  
The conversion of the combustion system from the non-premixed type in a conventional gas turbine to the lean premixed in DLE type results in different major faults of each combustion mode, creating challenges for the manufacturers. Various severe faults that possibly induce the gas turbine tripping problems for both conventional and DLE gas turbines are summarized in Table 3. Subsequently, the causes and prevention activities of the faults will be analyzed in detail. One of the gas turbine failures that cause the plant to shut down is the turbine blade fault. According to [70], there are various causes of blade fault, such as creep, oxidation, and fatigue due to high mechanical and thermal stresses. Statistics indicate that fatigue failure contributes to almost 50% of all component damages in gas turbines [71]. Similarly, the fatigue failure also causes problems in the compressor blade, as reported in [72]. The damage experienced in blades and nozzles (stationary blades) will be hard to cure since they have complicated configurations. Further, the root cause of this fault is distinctive depending on the material used, operation conditions, and the component's reliability, which leads to incorrect sensor readings. A faulty sensor creates an uncontrolled combustion system, leading to improper operating temperature and pressure. Hence, the system produces undesired emissions that turn the trip alarm on and contribute to the trip event [73]. Therefore, it is crucial to identify the malfunctioning part in instrumentation to ensure the precision of operational parameter readings. Another problem with the gas turbine is vibration. According to [74], this fault happens because of various sources, including misalignment, shaft unbalance, and bearing problems. In the worst case, extremely high vibrations cause catastrophic failure that is dangerous to the environment and humans. Figure 17: DLN-1 staging. Aside from it, [PERSON] in [75] mentioned an error that usually occurs during start-up called compressor surge. This fault occurs when the inside pressure is lower than the incoming air pressure. Thus, the airflow to the compressor is blocked. At the same time, there is a possibility of flow rate oscillation that might result in powerful vibrations, causing damage to the system [76]. The effective way to prevent the surge is through active surge control, expanding the operating range of the compressor using a feedback controller. The fault in the igniter also contributes to the gas turbine tripping problem, as reported in [77]. Eroded tips at the igniter produce a weak ignition during starting that interrupts the early combustion stage. It is usually caused by substance removal due to excessive discharge. This error requires expensive downtime to diagnose, resulting in component replacement. The following fault is a shaft locked in the compressor rotor [78]. This fault is caused by rotor blades rubbing against the compressor case, resulting in a coast-down below the limit. Since rubs are common due to physical contact between materials, the effective technique to eliminate this problem is by conducting shaft alignment. In DLE operation, the tight operating region is the challenge that sometimes disturbs the combustion stability and creates problems due to a lean burning operation. The combustion that significantly leans further eventually causes the flame to blow out. This phenomenon is widely known as the LBO fault, which will be thoroughly discussed in the next section. In many cases, as reported in [79; 80; 81; 82; 83; 84], LBO fault is considered the most common problem in DLE systems, which leads the gas turbine to trip. Other problems are observed before the blowout, such as auto-ignition, flashback, and combustion instability. Auto-ignition is an event in which gas ignites spontaneously without any external ignition sources.