Common Faults Of UPS Power Supply And Content Of UPS Load Bank Detection

The purpose of UPS is to identify whether the actual technical indicators of UPS can meet the requirements of use. Testing UPS is usually divided into two aspects: dynamic testing and steady-state testing. The steady state test is to test the phase voltage, line voltage, no-load loss, power factor, efficiency, output voltage waveform, distortion and output voltage of the input and output terminals at no load, 50% rated load and 100°C. % of rated load conditions. frequency, etc. The dynamic test is generally to test the change of the UPS output voltage waveform when the load changes suddenly (generally choose the load from 0% to 100% and from 100% to 0%) to test the dynamic characteristics and the feedback path of the energy UPS.

1. Steady-state test

The so-called steady-state test refers to the test when the device enters the "system normal" state, generally measuring waveform, frequency and voltage.

1. When the waveform

is usually in no-load state and full-load state, it is necessary to pay attention to whether the waveform is abnormal, and use a distortion measuring instrument to measure the distortion of the output voltage waveform. Under normal working conditions, connect a resistive load and use a distortion measuring instrument to detect the relative capacity of the total harmonics of the output voltage waveform, which should meet the requirements of the product regulations, generally less than 5%.

2. Frequency

Generally, the frequency of the output voltage can be observed with an oscilloscope and measured with a "power disturbance analyzer". At present, the output voltage and frequency of UPS can generally meet the requirements. However, when the frequency circuit and local oscillator of the UPS are not accurate enough, it is also possible that the frequency of the UPS output voltage will change when the frequency of the mains is unstable. When synchronizing with the mains, the accuracy of the UPS output frequency can generally reach ±0.2%.

3. Output voltage

The output voltage of the UPS can be tested and judged by the following methods:

(1) When the input voltage is 90% of the rated voltage, the output load is 100% or the input voltage is 110% of the rated voltage, and the output load is When 0, the output voltage should remain within ±3% of its nominal value.

(2) When the input voltage is 90% or 110% of the rated voltage, one phase of the output voltage is no-load, the other two phases are 100% rated load or two-phase no-load, and the other phase is 100% load, the output voltage should be maintained. The phase difference should be kept within 4° within ±3% of the rated value.

In order to keep the magnitude and phase of the load voltage within the allowable range in the presence of unbalanced loads, the inverter design must be able to adjust each phase individually. In the case of separately controlling the voltage amplitude and phase of each phase, the three-phase load voltage can always be symmetrical. Some UPSs cannot regulate each phase individually, so when a single-phase load is connected, the output voltage will be significantly unbalanced. For this type of UPS, this test cannot be performed, and the three-phase load must be balanced as much as possible during use.

In addition, the above-mentioned unbalanced load is more severe if one of the phases is unloaded, leaving two-phase rated load, or two-phase no-load and another one-phase rated load. load, the other phase is 70% of the rated load or one phase is the rated load, and the other two phases are 70% of the rated load. Test the output voltage (each phase voltage, line voltage) and the voltage regulation accuracy of the three-phase output unbalance.

When the input DC voltage of the UPS inverter varies by ±15% and the output load varies from 0% to 100%, the output voltage value should be kept within the range of ±3% of the rated voltage value. This indicator ostensibly repeats the one described earlier, but in reality it is more demanding than the previous one. This is because when the input signal of the control system changes in a large range, it exhibits obvious nonlinear characteristics. To make the output voltage not exceed the allowable range, the requirements for the circuit are even higher.

4. Charger startup test. In order to protect the battery and avoid the impact on the power grid when the charger is started, the general UPS charger has a current-limiting start-up function when it is started. The transition process of the charger from startup to normal operation is generally more than 10s, and the current is generally one-tenth of the battery capacity.

5. No battery load test. When the UPS does not carry a battery, the UPS only has a voltage regulation function. The dynamic performance of the rectifier can be checked by adding a load without the battery. It is generally required to ensure that the output voltage recovers to within (100±1)% within 20ms. For this function, different UPS have different designs.

6. High-order harmonic test. Usually, when the total amount of high-order harmonic components of the UPS power supply is less than 5%, it can be tested by using a harmonic analyzer. A good UPS can filter out all harmonics below the 11th harmonic, and the waveform is very stable. When choosing a UPS, try to choose a UPS that does not contain harmonics below the 11th order.

7. Output short circuit test. This test is generally not performed to prevent damage to the UPS equipment. This is because the output short-circuit protection function of some UPS is not perfect. For a UPS with bypass supply, the output short circuit test must be performed with the bypass supply disconnected. Otherwise, when the output circuit is short-circuited, the UPS will cut off the load to the bypass power supply while limiting the current, and at the same time blow the bypass power fuse for protection. In this way, the current limit of the output short-circuit protection will not be seen, and the fuse of the bypass power supply will be burned, which should be avoided,can also listThe test contents of the UPS load bank , such as temperature rise protection performance test, working temperature test, vibration test, synchronous tracking test, withstand voltage test, battery charging test, high temperature, high humidity test and reliability test, different load properties test, etc. As a product is officially produced, especially mass production, all the above tests are required. However, as the user agrees and accepts, it is not necessary and impossible to do such a comprehensive test. Generally, there are static test, dynamic test and discharge test.