设置有低频保护环节的AVR，在发电机转速升至频率转折拐点（一般为45HZ）之前， 发电机励磁电流不允许大于铭碑规定值，否则有刷发电机转子绕组或无刷发电机交流励磁机定子绕组、电枢绕组将因持续的超大励磁电流而过热直至烧毁。在发电机升速过程，若出现励磁电流超大，说明AVR低频保护失效，应更换AVR。低频保护特性一般在AVR生产厂已调试好，其电位器旋钮已固封，发电机调试时无需调节，但有的厂家未固封，此时可用小螺丝刀调节“频率转折”电位器，顺时针转，低频保护点频率升高，若升至45Hz之前，还出现超大励磁电流，说明该AVR低频保护功能不满足要求，应更换。
4、电压稳定性检査
电压稳定性对发电机输出电压质量的影响主要有：
（1） 发电机电压波动率
稳定性好电压波动率小。稳定性差电压波动率大，不适用于几乎所有用电设备。柴油发电机组标准规定：电压波动率≦0.5%，稳定性越好，电压越稳定。
（2） 稳态电压调整率
稳定性好，稳态电压调整率小，即从空载到满载电压变化小。稳定性差，则稳态电压调整率大，从空载到满载电压上升或下降大，也不适用于几乎所有用电设备。国家标准规定：发电机稳态电压调整率有≦±1.0%、±2.5%、±5.0%三类指标， 依不同励磁方式发电机而定。稳态电压调整率越小，电压越稳定。
（3） 瞬态电压调整率
稳定性好，瞬态电压调整率小，从空载突加负载至满载，或从满载突减负载至空载瞬变的过程中，电压变化小，电压恢复速度快。稳定性差，则瞬态过程电压变化大，反应速度慢。国家标准规定：发电机瞬态电压调整率为≦ （-15%〜＋20%）、 ≦ （-20%〜+ 25%）、≦ （-25%〜+ 30%） 3类指标，依不同励磁方式发电机而定。瞬态电压调整率越小，电压越稳定。起动电动机能力也越强。
电压稳定性检査方法：调节“电压稳定性”电位器，顺时针转，发电机电压波动率好， 但稳态、瞬态电压调整率变差；逆时针转调节器旋钮，发电机电压波动率变差，但稳态、瞬态电压调整率变好。发电机要求既有合格的电压波动率，也有合格的稳态、瞬态电压调整率，通过调节“电压稳定性"电位器，上述3项性能指标中任1项不合格，说明该AVR不合格，应更换AVR。
1、 What is AVR pressure regulator
AVR voltage regulator, also known as automatic voltage regulator, is designed specifically for AC brushless generators equipped with fundamental and harmonic compound excitation or permanent magnet generator excitation (PGM system). Due to the fixed transmission ratio between the generator and the diesel engine, the speed of the generator will change with the variation of the engine speed. The diesel generator has a large range of speed changes during operation, and the terminal voltage of the generator will also vary within a large range with the change of engine speed. The generator requires stable voltage to supply power to electrical equipment and charge the battery. Therefore, in order to maintain a constant voltage at a certain value, it is necessary to adjust the output voltage of the generator.
2、 The function of AVR pressure regulator
1. Self excitation establishes voltage reliability check
Start the diesel generator to the rated speed, and the generator that has been put into operation should be able to automatically establish voltage when the speed approaches the rated speed. The voltage indicated by the AC voltmeter should be close to the rated voltage. If there is no voltage indication, adjust the "voltage regulation" potentiometer and turn it clockwise to increase the voltage. If the potentiometer has been adjusted to the maximum position but there is still no voltage, use a multimeter to detect the excitation output F+and F - in DC mode, and use a multimeter to detect the power supply voltage input terminal and the detection voltage input terminal in AC mode. If there is voltage at the input terminal but there is still no voltage at the excitation output terminal, it indicates that the AVR is damaged and should be replaced with a new AVR of the same model and specification.
2. Voltage setting range inspection
The national standard stipulates that the voltage setting range of the generator should be ≥ 1.05 times the rated voltage and ≤ 0.95 times the rated voltage. During the inspection, the generator was already at no-load speed (with a frequency of 52.5Hz). Turn the "Voltage Adjustment" potentiometer knob clockwise. If the potentiometer has been adjusted to the maximum position, the generator voltage should be greater than 1.05 times the rated voltage. If it is less than this value, use a multimeter to test the excitation output F+and F - terminals in DC mode. If the measured excitation voltage does not exceed the specified value on the nameplate, it indicates that the upper limit of the AVR voltage setting range is not high enough. Turn the "Voltage Adjustment" potentiometer knob counterclockwise again. The generator voltage should be less than 0.95 times the rated voltage. If the potentiometer has been adjusted to the minimum position and the generator voltage does not fall below this value, it indicates that the lower limit of the AVR voltage setting range is not low enough and the AVR should be replaced.
3. Low frequency protection inspection
AVR with low-frequency protection is installed. Before the generator speed reaches the frequency inflection point (usually 45HZ), the excitation current of the generator is not allowed to exceed the value specified in the monument. Otherwise, the rotor winding of the brushed generator or the stator winding and armature winding of the brushless generator AC excitation machine will overheat and burn out due to continuous excessive excitation current. During the acceleration process of the generator, if there is an excessive excitation current, it indicates that the AVR low-frequency protection has failed and the AVR should be replaced. The low-frequency protection feature is generally calibrated in the AVR production plant, and the potentiometer knob has been sealed, so there is no need to adjust it during generator debugging. However, some manufacturers have not sealed it. At this time, a small screwdriver can be used to adjust the "frequency turning" potentiometer. Turning it clockwise will increase the frequency of the low-frequency protection point. If there is still a large excitation current before reaching 45Hz, it indicates that the low-frequency protection function of the AVR does not meet the requirements and should be replaced.
4. Voltage stability inspection
The impact of voltage stability on the quality of generator output voltage mainly includes:
(1) Generator voltage fluctuation rate
Good stability and low voltage fluctuation. Poor stability and high voltage fluctuation, not suitable for almost all electrical equipment. The standard for diesel generator sets stipulates that the voltage fluctuation rate should be ≤ 0.5%, and the better the stability, the more stable the voltage.
(2) Steady-state voltage regulation rate
Good stability, small steady-state voltage adjustment rate, i.e. small voltage variation from no-load to full load. If the stability is poor, the steady-state voltage adjustment rate will be large, and the voltage will rise or fall greatly from no-load to full load, which is not suitable for almost all electrical equipment. According to national standards, the steady-state voltage regulation rate of generators has three types of indicators: ≤± 1.0%, ± 2.5%, and ± 5.0%, depending on the excitation mode of the generator. The smaller the steady-state voltage regulation rate, the more stable the voltage.
(3) Transient voltage regulation rate
Good stability, small transient voltage adjustment rate, small voltage change and fast voltage recovery during the process of sudden load increase from no-load to full load, or sudden load decrease from full load to no-load transient. If the stability is poor, the transient process voltage changes greatly and the response speed is slow. According to national standards, the transient voltage regulation rate of generators is classified into three indicators: ≤ (-15%~+20%), ≤ (-20%~+25%), and ≤ (-25%~+30%), depending on the excitation method of the generator. The smaller the transient voltage regulation rate, the more stable the voltage. The stronger the ability to start the electric motor.
Voltage stability inspection method: Adjust the "voltage stability" potentiometer clockwise. The generator voltage fluctuation rate is good, but the steady-state and transient voltage adjustment rates deteriorate; Turning the regulator knob counterclockwise reduces the voltage fluctuation rate of the generator, but improves the steady-state and transient voltage adjustment rates. The generator requires both qualified voltage fluctuation rate and qualified steady-state and transient voltage adjustment rate. By adjusting the "voltage stability" potentiometer, if any one of the above three performance indicators is not qualified, it indicates that the AVR is unqualified and should be replaced.
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