Adjustment of small internal combustion generators

The regulation of small internal combustion generators. Compared with large power plants in the power grid, the operating economy of small internal combustion generators is much worse, but they have the advantage of quick starting, so they are often used as backup generator sets to start power generation when the power grid is cut off. Usually, this type of generator is used as an isolated unit to supply power within a small range. Due to the loss of support from the large power grid, the frequency and voltage regulation tasks during operation are heavy and not easy to stabilize.

As is well known, the regulation of active power is a commodity that cannot be stored. The amount of electricity needed by the outside world (including energy loss during transmission and transformation) determines how much electricity the power plant needs to generate. The two must be balanced so that the frequency can be maintained steadily at 50Hz. If the load decreases, the speed of the generator or the frequency of the power grid will increase, and the speed of the running motor will also increase accordingly, so that the machinery it drives consumes more electricity. The supply and demand of electricity will reach a new balance at a slightly lower frequency. In order to restore the frequency to its original value, the power plant should turn down the throttle of the internal combustion engine to reduce the power generation of the generator. Generally, the prime mover used for power generation is equipped with a speed control system, which can be adjusted by the on duty personnel to make a small upward and downward movement of the speed control characteristic curve, so as to operate at the rated frequency under specific loads. Adjusting the frequency mainly involves adjusting the fuel intake of the internal combustion engine.

If the adjustment of reactive power only changes the active output of the generator without making corresponding adjustments to the excitation of the generator at the same time, it will affect the reactive power output of the generator. At this point, it will inevitably disrupt the supply-demand balance of reactive power and affect the voltage level of the power grid. When the demand for reactive power exceeds the supply in the system, the voltage will decrease. When a single-phase grounding fault occurs in a neutral ungrounded system, at least one phase of the line's ground voltage will rise. Based on this, the existence of single-phase grounding fault can be confirmed.

When determining which phase is grounded based on the indication of the three-phase line to ground voltmeter, the three voltmeters serving as insulation monitoring will have two possible demand quantities that will be appropriately reduced (such as the excitation current of transformers and motors will be reduced), so that reactive power can achieve a new balance at a slightly lower voltage level. At this point, the response of the power plant should be to increase the excitation of the generator, that is, to increase the reactive power output of the generator to restore voltage. Generally, small generators are equipped with voltage automatic adjustment systems, and their voltage adjustment characteristics must also be adjusted to slightly decrease the terminal voltage of the motor as the reactive power output increases, otherwise unstable states may occur during operation. So, just like frequency regulation, the on duty personnel need to fine tune the excitation to reduce the fluctuation range of the system voltage. If the generator does not have an automatic voltage adjustment system, the excitation of the generator can only be manually adjusted by the on duty personnel based on the current voltage value, which generally meets the requirements.

Characteristics of small generator set regulation: There are differences between voltage regulation and frequency regulation. In a system, the frequency values are consistent regardless of the region, and the balance of active power is also the power balance of the entire system. However, the voltage level is not consistent in different power consumption regions, and the reactive power balance is mainly the balance in different regions. The power plant's ability to regulate voltage can only be limited to a small area around it.

When multiple generators are running in parallel and using the above method to regulate one unit, the effect on system frequency and voltage is not significant. Its main function is to regulate the load distribution between units, especially for small units in large systems. The output size will not have a substantial impact on voltage and frequency, and the units can be adjusted as needed. So the regulation of small generators running on the grid is much simpler.

Display of capability: (1) The voltage between two phases is lower than the phase voltage value, and the voltage between one phase and the ground is lower than the phase voltage value. This situation occurs when the ground voltage is relatively high, and the phase with the lowest ground voltage may not necessarily be the ground fault phase. When the phase with a lag of 120° compared to the phase with a rise in ground voltage changes, changing the excitation can change the reactive power output and power factor of the generator; When the excitation current remains constant, increasing the active output will result in a decrease in the reactive output of the generator. To prevent this decrease, the excitation must be increased accordingly. When operating at low power factor, it will inevitably increase the burden on the excitation system. In order not to exceed the excitation current at full load rated conditions, the generator output (kilowatts and kilovolt amperes) should be limited. In order to ensure the stable operation of the generator and maintain a certain stability margin between parallel motors, the excitation of the generator should be controlled to avoid leading phase operation. The excitation current should not be reduced too small, and measures should be taken to prevent demagnetization.

It plays a very important role in operation and is also the weakest and most prone to failure part of the generator in terms of structure. Therefore, in order to ensure power generation safety, sufficient attention must be paid to the excitation system. Necessary inspections should be carried out both after shutdown and before startup, especially for the electric brush device of the coaxial excitation machine. The technical condition of the electric brush, brush holder, and commutator surface should be checked, and blowing should be carried out if necessary; Regularly check the electric brush for sparking and jumping during operation; Strengthen the inspection, maintenance, and upkeep of the excitation system. This is one of the important means to prevent generator failures.

The characteristic is 'raising troops for a thousand days, used in one day'.

Therefore, when not in use, it is likely to get damp. The most proactive preventive measure is to request the manufacturer to perform moisture-proof treatment on the winding insulation. If the internal temperature of the generator can be raised 5-10°C above the ambient temperature on site, it is an effective moisture-proof method. If it has been dampened or the insulation is not qualified, do not apply voltage to the motor and it must be dried first. In addition, implementing a regular trial operation system for generators is also a common method to ensure that the units are in good condition. One phase is the faulty phase.

The value is high, and the relative ground voltage is lower than the phase voltage value. This situation occurs at relatively young ages. At this point, the phase experiencing a ground fault is the one where the ground voltage drops.