Adjustment of small internal combustion generators Cui Lunyuan's small internal combustion generators are much less economical to operate than large power plants in the grid, but they have the advantage of rapid start-up, so they are often used as backup generator sets to start when the grid is powered off. Power generation. Usually, this kind of generator is used as an isolated unit to supply power in a small range. Due to the loss of support from the large power grid, the frequency and voltage adjustment tasks in operation are heavier and less stable.

The regulation of active power is well known, and electricity is a commodity that is basically unstorable. How much electricity is needed by the outside world (including the loss of power during power transmission and transformation), how much electricity is to be sent by the power plant, and the two must be balanced, and the frequency can be maintained at 50 Hz smoothly. If the load is reduced, the speed of the generator or the grid The frequency of the motor will increase, and the speed of the running motor will be correspondingly accelerated, so that the machinery it drives will use more electricity, and the supply and demand of the electric energy will reach a new balance at a slightly lower frequency. In order to restore the frequency to the original value, the power plant should shut down the throttle of the small internal combustion engine to reduce the power generation of the generator. The prime movers for general power generation are equipped with a speed control system, which is fine-tuned by the duty personnel to make the position of the speed regulation characteristic curve. A small amount moves up and down so that it runs at the rated frequency under a specific load. Adjusting the frequency is mainly to adjust the oil intake of the internal combustion engine.

The regulation of reactive power, such as changing only the active output of the generator, without corresponding adjustment of the excitation of the generator, will affect the reactive output of the generator. At this time, it will destroy the balance of supply and demand of the original reactive power and affect the voltage level of the power grid. When the reactive power in the system is over-supplied, the voltage will decrease, and the reactive power will be analyzed. When the neutral-phase ungrounded system has a single-phase ground fault, at least one phase of the line rises to ground. Based on this, the presence of a single-phase ground fault can be confirmed.

According to the indication of the three-phase line to the ground voltmeter to determine which phase is grounded, the three voltmeters used for insulation monitoring can be appropriately reduced in two kinds of demand (for example, the excitation current of the transformer and the motor is reduced). Reactive power achieves a new balance at a slightly lower voltage level. At this time, the response of the power plant should be to increase the excitation of the generator, that is, increase the reactive output of the generator to restore the voltage. Generally, small generators are equipped with an automatic voltage adjustment system, and the voltage adjustment characteristics must also be adjusted to a slight decrease in the terminal voltage of the motor as the reactive output increases, otherwise an unstable state may occur during operation. Therefore, as with the frequency adjustment, the on-duty personnel are required to fine-tune the excitation to reduce the fluctuation range of the system voltage. If the generator does not have a voltage automatic adjustment system, the on-duty personnel can only manually adjust the excitation of the generator according to the current voltage value, and generally can also meet the requirements.

3. Small generator set adjustment features U) Voltage regulation and frequency adjustment are different. In a system, the frequency values ​​are consistent regardless of the region. The balance of active power is also the power balance of the whole system, and the voltage level is inconsistent in different power areas. The reactive power balance is mainly in the balance of different areas. The ability of the power plant to regulate the voltage can only be within a small area around it.

When multiple generators are operated in parallel, the effect on the system frequency and voltage is not significant when adjusting one unit by the above method. The main reason is to adjust the load distribution between the units, especially in small units in large systems. There is no substantial impact on voltage and frequency, and the unit can be adjusted as needed. Therefore, the adjustment of small generators connected to the grid is much simpler.

The energy display shows that: (1) the two relative ground voltages are lower than the phase voltage value, and the relative ground voltage is lower than the phase voltage value. This situation occurs when the situation is relatively large. At this time, the phase with the lowest ground voltage is not necessarily the ground fault phase, and when the phase lag of the voltage rise of 120 is changed, the excitation can be changed to change the power generation. The reactive output and power factor of the machine; when the excitation current remains unchanged, the active output is increased, and the reactive output of the generator is reduced. If it is not to be reduced, the excitation must be increased accordingly. When operating at low power factor, the load on the excitation system must be increased. In order not to exceed the excitation current at full load rated conditions, the generator output (kW and kVA) should be limited. In order to ensure the stable operation of the generator, maintain a certain stability margin between the parallel motors, control the excitation of the generator, avoid the phase-in operation, and not reduce the excitation current too small, and take measures to prevent the loss of magnetism.

It has a very important role in operation, and it is also the weakest part of the generator and the most faulty part. Therefore, in order to ensure the safety of power generation, the excitation system must be given sufficient attention. After the shutdown and before starting the machine, it is necessary to carry out the necessary inspection, especially the brush device of the coaxial exciter. The technical condition of the brush, the brush holder and the surface of the commutator should be checked, and if necessary, the cleaning should be carried out; During operation, always check the brush for fire and beating; strengthen the inspection, repair and maintenance of the excitation system. This is one of the important means to prevent generator failure.

The characteristic is "to raise a soldier for a thousand days, use it in one direction."

Therefore, when it is not in use, it is likely to be wet. The most active precaution is to ask the manufacturer to protect the winding insulation from moisture. If the internal temperature of the generator is higher than the environment 5~10 at the scene, it is an effective method for moisture prevention. If it is wet and the insulation is unqualified, it must not be applied to the motor and must be dried first. In addition, the implementation of the regular test run system of the generator is also a common method to ensure that the unit is in good condition. (Editing the phantom) One phase is the fault phase.

The value is high, and the relative ground voltage is lower than the phase voltage value. This situation occurs when it is relatively small. The ground fault that occurs at this time is the phase where the ground voltage drops.

(Editor Xu Lin)

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August 28, 2019