UPS structure
The UPS system in the substation generally consists of three parts: the power UPS host, the bypass voltage stabilizer cabinet, and the output feeder cabinet (three-in-one can also be used for low power).
Rectifier:
There are two main functions:
First, change alternating current (AC) into direct current (DC) and supply it to the inverter after filtering;
Second, it provides charging voltage to the battery and acts as a charger;
Inverter:
Convert direct current (DC) into alternating current (AC) for use by the load;
Battery:
UPS is used as a device for storing electric energy, so that it can provide uninterrupted power to the load after inverting the direct current when the mains power fails. Its capacity determines the duration of its sustaining discharge (power supply);
Static switch:
Also known as a static switch, it is an AC switch composed of two SCRs in anti-parallel, and its closing and opening are controlled by a logic controller;
Isolation transformer, voltage regulator:
In the input or output part, AC and DC are isolated. In addition to isolation, the voltage stabilizer has the function of stabilizing voltage;
Four operating modes of UPS
(1) Normal operation mode:
Under normal AC power supply, the rectifier converts AC power to DC power, eliminates the "power pollution" in the mains, and charges the battery at the same time. Then supply the inverter to convert the direct current into alternating current, providing more stable power to the load.
(2) Power failure mode:
When the AC power supply is abnormal or the rectifier or reactor fails(Air Conditioning Power Inverter: AC Power Inverter), the battery pack provides DC power to the inverter, so that the AC output will not be interrupted, thereby achieving the effect of protecting the load.
(3) Standby power mode:
When the inverter has abnormal conditions such as the inverter fuse blown, short circuit, etc., the inverter will automatically cut off to prevent damage. If the bypass AC power supply is normal at this time, the static switch will switch the power supply to the bypass The backup power is output to the load.
(4) Maintenance bypass mode:
When the UPS needs to be repaired or the battery needs to be replaced and the load power supply cannot be interrupted, first cut off the inverter switch and then activate the maintenance bypass switch, and then cut off the rectifier and bypass switch. The AC power supply continues to supply AC power to the load through the maintenance bypass switch. At this time, maintenance personnel can safely maintain the UPS.
Some requirements of power system UPS
(1) The monitoring system and remote communication system are very important to the substation, so the reliability of the UPS system as the power supply also has very high requirements;
(2) Most of the loads of the integrated automation system are single-phase loads. Therefore, most of the dedicated UPS power supplies for power systems require three-phase/single-phase input and single-phase output medium and small power UPS, and the capacity is generally within the range of 60kVA;
(3) The bypass static switch should have two working modes, automatic and manual, to realize uninterrupted switching;
(4) Because the substation has a 220V or 110V DC system and a DC charging screen to charge the battery. Therefore, the power dedicated UPS does not have a battery, and directly uses the DC system as the DC input of the UPS, and does not need to have a charging function;
(5) The DC input end of the power dedicated UPS is generally required to be equipped with a back-injection noise suppressor, such as a backstop diode, so that the impact of the UPS on the DC bus is as small as possible;
(6) After the UPS power supply is full of all equipment, more than 40% of the power supply capacity should be reserved. After the UPS loses AC power, the uninterrupted power supply can be maintained for no less than 60 minutes.