設置有低頻保護環(huán)節(jié)的AVR，在發(fā)電機轉(zhuǎn)速升至頻率轉(zhuǎn)折拐點（一般為45HZ）之前， 發(fā)電機勵磁電流不允許大于銘碑規(guī)定值，否則有刷發(fā)電機轉(zhuǎn)子繞組或無刷發(fā)電機交流勵磁機定子繞組、電樞繞組將因持續(xù)的超大勵磁電流而過熱直至燒毀。在發(fā)電機升速過程，若出現(xiàn)勵磁電流超大，說明AVR低頻保護失效，應更換AVR。低頻保護特性一般在AVR生產(chǎn)廠已調(diào)試好，其電位器旋鈕已固封，發(fā)電機調(diào)試時無需調(diào)節(jié)，但有的廠家未固封，此時可用小螺絲刀調(diào)節(jié)“頻率轉(zhuǎn)折”電位器，順時針轉(zhuǎn)，低頻保護點頻率升高，若升至45Hz之前，還出現(xiàn)超大勵磁電流，說明該AVR低頻保護功能不滿足要求，應更換。

4、電壓穩(wěn)定性檢査

電壓穩(wěn)定性對發(fā)電機輸出電壓質(zhì)量的影響主要有：

（1） 發(fā)電機電壓波動率

穩(wěn)定性好電壓波動率小。穩(wěn)定性差電壓波動率大，不適用于幾乎所有用電設備。柴油發(fā)電機組標準規(guī)定：電壓波動率≦0.5%，穩(wěn)定性越好，電壓越穩(wěn)定。

（2） 穩(wěn)態(tài)電壓調(diào)整率

穩(wěn)定性好，穩(wěn)態(tài)電壓調(diào)整率小，即從空載到滿載電壓變化小。穩(wěn)定性差，則穩(wěn)態(tài)電壓調(diào)整率大，從空載到滿載電壓上升或下降大，也不適用于幾乎所有用電設備。國家標準規(guī)定：發(fā)電機穩(wěn)態(tài)電壓調(diào)整率有≦±1.0%、±2.5%、±5.0%三類指標， 依不同勵磁方式發(fā)電機而定。穩(wěn)態(tài)電壓調(diào)整率越小，電壓越穩(wěn)定。

（3） 瞬態(tài)電壓調(diào)整率

穩(wěn)定性好，瞬態(tài)電壓調(diào)整率小，從空載突加負載至滿載，或從滿載突減負載至空載瞬變的過程中，電壓變化小，電壓恢復速度快。穩(wěn)定性差，則瞬態(tài)過程電壓變化大，反應速度慢。國家標準規(guī)定：發(fā)電機瞬態(tài)電壓調(diào)整率為≦ （-15%?＋20%）、 ≦ （-20%?+ 25%）、≦ （-25%?+ 30%） 3類指標，依不同勵磁方式發(fā)電機而定。瞬態(tài)電壓調(diào)整率越小，電壓越穩(wěn)定。起動電動機能力也越強。

電壓穩(wěn)定性檢査方法：調(diào)節(jié)“電壓穩(wěn)定性”電位器，順時針轉(zhuǎn)，發(fā)電機電壓波動率好， 但穩(wěn)態(tài)、瞬態(tài)電壓調(diào)整率變差；逆時針轉(zhuǎn)調(diào)節(jié)器旋鈕，發(fā)電機電壓波動率變差，但穩(wěn)態(tài)、瞬態(tài)電壓調(diào)整率變好。發(fā)電機要求既有合格的電壓波動率，也有合格的穩(wěn)態(tài)、瞬態(tài)電壓調(diào)整率，通過調(diào)節(jié)“電壓穩(wěn)定性"電位器，上述3項性能指標中任1項不合格，說明該AVR不合格，應更換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.