Power system UPS power supply selection principle - Database & Sql Blog Articles

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1. The importance of load

Whether there is a potential abnormality in the power supply. In principle, there is no power abnormality and there is no need to set up the UPS. Whether the load is important is determined by the partial damage of the load caused by the abnormal power supply. Damage includes direct losses and indirect losses. Direct losses include defective products on the production line, and important data for technology research and development are lost. Indirect losses include the time required to restore power and social credibility. According to the size of the damage, measure the total investment of the UPS system. In order to improve the reliability, whether to use the UPS, whether the UPS is set up for backup and bypass, determine the operation mode.

2. The impact of power quality on the load

The impact of power quality on the load includes: the voltage drop range and duration of the power supply voltage; the daily voltage distortion range and frequency accuracy. The load has a strong bearing on the power quality, which can simplify the system and improve the reliability and reduce the cost. For example, when the bypass is added, the 0.02~0.2S instantaneous power failure conversion mode is generally adopted. Daily voltage distortion, frequency accuracy is generally not a special load, enough power supply under the mains power supply, generally do not need to consider the impact of the power supply on the load. Computers that are sensitive to power supply voltage transients and power outages have an effect even if the supply voltage is reduced by 10% and a half cycle. You need to provide quality power.

3. UPS capacity selection

The UPS capacity is selected according to the following factors, characteristics, calculation load, surge current, peak current, overload capability, and load abrupt condition.

The payload capacity is compensated by the following values.

(1) About the inrush current

UPS calculation capacity capable of withstanding peak current = payload capacity X surge current (maximum value) / UPS rated current, the value is generally 5 to 10 times the effective capacity.

The load is put into the power supply, generating considerable inrush current, especially for computers and peripherals. When the UPS is powered, in order to reduce the UPS capacity, the load is input or selected to operate the UPS mains in sequence; when the current returns below the rated current, the power is not converted to the rectifier and the inverter is powered.

(2) About peak current

a UPS capable of withstanding peak currents;

Capacity = payload capacity X peak current (maximum value) / UPS rated current;

The peak capacity is generally 2 times the effective capacity;

A UPS with a peak factor of 2.5 or higher, with a peak current withstand capability of 250% PA, generally does not exceed the rated capacity of the UPS. It can be used directly without compensation.

(3) About overload

The UPS overload capacity is generally 1.1 times of the effective load, and the load overload is more than 1.1 times to protect the UPS.

(4) Load mutation

Most of the UPS load changes within 0"100% range, the output voltage fluctuation can be controlled within _10%l~A. Therefore, the payload capacity can be compensated.

(5) Generator-UPS cooperation

In some locations, the UPS is switched to the self-supplied generator after the mains power failure. When supplying power to the generator, it should be able to provide large inrush current when the UPS starts, without affecting the operation of the generator.

a. Select the rectifier device lower starting current UPS. For example, a 12-pulse rectifier, the self-supplied generator capacity should be twice that of the rectifier.

b. Select several groups of UPSs in parallel, and the group delay starts. It can be combined with a ramp start function to prevent all UPS starting at the same time to generate excessive surge current.

c. Select the UPS with the rectifier charger input power controllable, so that the rectifier charger inputs part of the power, and the insufficient power is provided by the battery.

d. Select a UPS with a limited charge current function. When the generator is started, limit charging and set the charging current to 0 amps. That is, the charging can be stopped while the generator is running, thereby reducing the power absorbed by the UPS from the generator.