What is the Phase Modulation Operation of Generator

What is the Phase Modulation Operation of Generator?

Answer: The phase modulation operation of a generator refers to the operating state in which the generator does not emit active power but only transmits inductive reactive power to the power grid, thereby regulating system reactive power and maintaining system voltage level. Phase modulation operation is to make the generator work in the motor state (i.e. idle synchronous motor), and the active power consumed by the generator during phase leading operation can come from the prime mover or the system. When the generator operates with phase modulation, it can operate under excitation or under excitation. During overexcited operation, the generator emits inductive reactive power; During underexcitation operation, the generator emits capacitive reactive power. Generally, during phase modulation operation, it refers to the state in which the generator operates under overexcitation and emits inductive reactive power.

Hydrogenerators far from the load center are generally not considered for phase adjustment operation.

What is the leading phase operation of a generator? What is the impact on the generator? What inspections should be carried out on the generator for the incoming phase?

Answer: When the power system operates normally, its load is inductive. During normal operation of the generator, the phase of the voltage is the phase of the leading current, and the generator emits active power and inductive reactive power to the system. If there is a situation where the phase of the current exceeds the phase of the voltage during operation of generator, we call it in the leading phase operation state. At this time, the generator emits active power and absorbs inductive reactive power (or emits capacitive reactive power) to the system.

When the reactive power of the power system is excessive, the voltage of the system will increase. One measure to reduce the voltage is to allow the generator to absorb the excess reactive power of the system and operate it in the leading phase state. The more absorption, the deeper the phase transition. In general, the design of the generator also takes into account the unfavorable operating conditions for the generator, allowing for short-term phase leading operation.

However, different generators may exhibit significant differences when operating in the leading phase. After the generator enters the phase and operates, the magnetic leakage at the end of the generator increases compared to normal conditions, resulting in heating of the metal parts at the end, local temperature rise, and increased end vibration. The greater the depth of phase transition, the higher the end temperature rise. According to experimental measurements, the highest temperature at the end of the stator core during phase transition occurs at the top of the core teeth, followed by the pressure finger, which is consistent with theoretical analysis.

During maintenance, it is necessary to carefully inspect the upper and lower ends of the stator winding, especially the top of the iron core teeth, the slot opening of the wire rod, and the pressure finger part for any abnormalities, especially after the generator enters the phase, especially after the deep phase. If problems are found, they should be reported and dealt with in a timely manner. Generators that are not suitable for further phase operation should apply for shutdown. The adverse effects of entering the generator are quite complex and may require long-term operation to detect the problem.