Weidi UPS power supply/01K00TS1101C00/1K standard machine

Weidi UPS power supply/01K00TS1101C00/1K standard machine

1000VA/800W, Built in battery 3/12V7AH

The Weidi UPS power supply supplies power to important loads such as billing systems, IDC equipment, critical financial user devices, and network management terminals. In the event of an accident, the impact can be significant. In recent years, various operators have experienced system crashes caused by UPS. After years of work practice, several issues that need to be paid attention to in reducing UPS accidents in core computer rooms have been summarized.

1. Short circuit problem in the output load of Weidi UPS power supply

Short circuits of more than 90% of the UPS output load can cause power outages or flash faults in the UPS system, resulting in the paralysis of important connected equipment. When the UPS output load is short circuited, whether it is a single machine, master-slave, parallel machine, or dual bus system, it cannot guarantee that the load will not be powered off.

2. Zero wire issue with Weidi UPS power supply

The zero line issue is an easily overlooked problem in maintenance, which may lead to serious accidents. Let's illustrate this issue with a case study.

An unmanned gateway office is located on the eighth floor of an office building. The first floor business hall is powered by the AC distribution cabinet of the gateway office on the eighth floor, and the UPS is also powered by the AC distribution cabinet. The UPS output is sent to a UPS distribution box to supply power to some billing, network management and other equipment. The fault phenomenon is that the UPS loses power for several consecutive days around midnight in winter, and the UPS displays "output short circuit", causing the load to lose power. After restarting the UPS on site, it returns to normal. Later, it was discovered that there were two reasons: firstly, the security guard at the first floor business hall used several single-phase electric heaters at night and connected them to the same alternating current, resulting in three-phase imbalance. Since the zero line current is the vector sum of the three-phase currents, the imbalance caused the zero line current to be too large.

Measure the zero line current from the main AC distribution cabinet, which is normal during the day and approximately 20A when using the electric heater at night. The second issue is that the zero wire screws of several devices on the neutral wire busbar of the UPS distribution box are loose. The false connection of the neutral wire and the excessive current of the neutral wire caused ignition, and the UPS judged it as an "output short circuit" and shut down. Tighten the neutral wire and remove the electric heater to troubleshoot. So special attention should be paid to the inspection of the neutral wire during maintenance, and the neutral wire on the entire power supply path from UPS output to the electrical load should be checked and tightened regularly.

Grounding problem of 3D UPS power supply

The grounding of UPS is also a relatively easily overlooked issue.

When the load of the UPS is asymmetric or the UPS has non-linear loads, current will flow through the neutral line, causing a voltage drop on the neutral line and resulting in a voltage difference between the neutral and ground lines, which is commonly referred to as "zero ground voltage". The larger the neutral wire current, the farther the load distance, and the smaller the cross-section of the neutral wire conductor, the greater the 'zero ground voltage'. Some sensitive loads have high requirements for "zero ground voltage", for example, if the "zero ground voltage" is greater than 1V, some servers cannot work properly.

This is because the grounding system of the core computer room is generally fixed with the UPS output neutral line and load neutral line connected to the neutral line of the mains power supply. The neutral line of the mains power supply is connected to the grounding electrode in the low-voltage incoming cabinet, and there is no isolation between the UPS output and load neutral lines and the neutral line of the mains power supply. There are many AC cables in the core computer room, and each cable contains a large amount of electromagnetic interference. All of these cables are tied together and run long lines, causing these high-frequency interferences to interfere with each other. The high-frequency interference current flows through the neutral and ground wires, causing a voltage drop between them.

Weidi UPS power supply/01K00TS1101C00/1K standard machine

The first solution is to separate the live, neutral, and ground wires of the UPS, ensuring a distance of at least 20cm between them. Other power cables should also be kept away from the UPS neutral wire. If the construction site conditions do not allow, armored shielded cables should be used for neutral and ground wires. But this method only treats the symptoms and not the root cause. When the equipment in the computer room changes, the electromagnetic interference environment also changes, and the zero ground voltage will also change, which cannot solve the problem. Secondly, adding an isolation transformer at the UPS load end and grounding the isolated neutral line can ensure that the zero ground voltage of the load approaches zero, effectively solving the problem of "zero ground voltage".

4-dimensional UPS power battery issue

UPS batteries are a vulnerable link, and accidents caused by UPS batteries account for a significant proportion of UPS total accidents. This is because UPS batteries are usually 12V batteries, which are actually composed of 6 2V batteries connected in series and welded together, making them difficult to manufacture. In addition, the grid and connecting strips are relatively thin. If one grid has a problem, the entire UPS battery will have a problem, and the failure rate is much higher than that of 2V batteries. Therefore, the following issues should be noted during installation and maintenance.

(1) Install UPS batteries using battery racks, do not use battery cabinets. One is to facilitate ventilation and heat dissipation. UPS batteries are very sensitive to temperature, with an ambient temperature of 20-25 ℃. For every 10 ℃ increase in temperature, the lifespan of the battery doubles. During the charging and discharging process of UPS batteries, a large amount of heat energy is released, which cannot be dissipated and directly affects the battery capacity and lifespan. The second is to facilitate maintenance and measurement. If installed in a battery cabinet, if the space is too small, the operator may cause short circuits in the operating tools or overlook potential faults that should have been discovered due to inconvenient operation or visual issues during inspection. There is a case study of a master-slave hot backup UPS system with a sealed battery cabinet (with ventilation holes). The panel fixed with screws is difficult to remove and can only be opened with a screwdriver. During an inspection, it was found that two battery connection wires in the bottom corner of the backup UPS battery pack were loose and leaking. UPS batteries discharge with high current. In this case, if the main UPS fails and the backup UPS battery discharges to supply the load, the consequences can be serious, and there is a possibility of fire or even explosion.

(2) Do not use an open copper nose for UPS battery connection lines, instead use a hole shaped copper nose. An open copper nose is not as secure as a hole shaped crimping and is prone to detachment; Soft copper wire should be used for connecting wires, not hard copper wire. Hard copper wire may become loose over time due to its strong grip, causing poor connection at the terminals. Under certain conditions, it may cause arcing or heat at the terminals, ultimately leading to fire; The connecting wires should be of the same length and specification, otherwise the resistance will be inconsistent. Long term use may cause some UPS batteries to be fully charged while others are not, resulting in overcharging of the fully charged UPS batteries. Moisture will overflow from the safety valve, increase the concentration of electrolyte, and corrode the plates over time, leading to poor battery consistency.

(3) Due to the heavy weight of the battery, it is necessary to handle and lift the battery correctly during installation. Do not use hooks or screwdrivers to directly hook the exposed terminals of the battery to remove it. The poles and plates are welded together, which can strain the battery terminals and, in severe cases, may cause a fire. In addition, the cables output from the battery pack should not be directly pulled from the battery terminals to the main equipment. There should be a junction box or adapter terminal in between, otherwise the battery terminals may be subjected to tension for a long time, which may damage the internal connections of the battery.