Configuration, installation and maintenance of UPS power supply system

　　UPS is not only an uninterruptible power supply device, but also has the function of power purification. This article will focus on the selection and configuration of UPS, the selection and configuration of battery pack capacity, and the installation and maintenance of UPS power supply .

　　UPS stands for uninterruptible power supply. With the popularization of various electronic devices, UPS power supply has been more and more widely used.

　　UPS selection and configuration

　　1. Understand the performance indicators of UPS power supply:

　　①Input voltage: 220V or 380V (three-phase four-wire), -15% to +10%.

　　②Output current: Select the wire cross-section and input fuse according to this value.

　　③ Output voltage: One is the output voltage stability, which is generally ±5%. Some are around ±3%. The other is the voltage regulation accuracy: steady state ≤ ±1%, transient ≤ ±5%.

　　④Transient voltage recovery time: ≤±50ms.

　　⑤Output capacity: Apparent power S, S = UI

　　⑥ Backup time: refers to the time the UPS can continue to work after input interruption, which is a key indicator of UPS.

　　⑦Power factor: 0.8 (lagging)

　　⑧Efficiency: ≥90% (at full load)

　　⑨Overload function: 10min (125% rated current); 10S (150% rated current).

　　⑩Current limiting: 100%~110% rated current adjustable.

　　2UPS selection:

　　UPS Model

　　① Online sine wave UPS power supply. Regardless of whether the mains power is normal or not, the power supply to the load is provided by the UPS power inverter. As long as the internal battery can provide energy to the UPS power inverter, when the mains power is interrupted, the online UPS power supply can achieve true uninterrupted power supply to the load. Its sine wave waveform distortion coefficient is the smallest, the load power supply conversion time is zero, the reliability is high, the failure rate is low, but the price is relatively high.

　　②Backup sine wave UPS power supply. Anti-interference graded voltage regulation and stabilization technology is adopted. Only when powered by batteries can high-quality sine waves be provided to the load. When switching from mains power supply to inverter power supply, there is about 4ms of power interruption for the load (mainly due to the switching time of the relay). When the backup sine wave UPS power supply is powered by mains power, the noise is small because the mains power is directly supplied to the load through the anti-interference filter. However, when the UPS power supply is in inverter operation, the noise is large because the PWM pulse width modulation frequency is generally around 8KHZ.

　　③ Backup square wave output UPS power supply. The AC power provided to the load is a square wave instead of a sine wave. This type of UPS power supply can only be connected to micro-capacitive or pure group devices. The heavier the load, the wider the square wave pulse width, and the smaller the peak value of the square wave pulse. The conversion time of this type of UPS power supply is not fixed. Its range is 4 to 9ms and cannot be controlled by the user. This type of UPS cannot be shut down and started at a certain frequency, but the cost is relatively low.

　　Load capacity, load power factor and UPS crest factor

　　When purchasing a UPS, you must first know the total capacity of the load, and also consider the power factor of the load to determine the standard power capacity of the UPS. Since the load power factor is difficult to calculate, the UPS technical specification provides the crest factor as an indicator. The higher the crest factor, the stronger the UPS's ability to withstand nonlinearity. Generally, the crest factor ratio should be greater than 3:1.

　　Battery backup time In general, when selecting the backup time, it is usually sufficient to select a full load working time of 10 minutes, 15 minutes or 30 minutes. Since batteries are expensive, long-delay UPS is generally only used in situations where the power outage lasts for a long time. In this case, it is best to choose a UPS with an external large-capacity battery function to ensure that it can provide power for a long time after the city power outage.

　　UPS neutral line cross section Since UPS loads are mostly non-linear loads, the current flowing through the neutral line is not zero. Even when the three-phase load is completely balanced, the neutral line current can reach 1.8 times the three-phase current. The smaller the load power factor, the greater the multiple. Therefore, in the UPS power supply, the neutral line cross section must not be smaller than the phase line cross section. Otherwise, it is easy to cause the neutral line to heat up, and even burn the cable to cause a fire, resulting in serious consequences.

　　Battery selection and configuration

　　Basic technical indicators of batteries:

　　① Valve-regulated sealed lead-acid batteries: one set is connected to each UPS.

　　②Float charge voltage tolerance: 1%.

　　③Float charge voltage: 2.23～2.27V/cell.

　　④Equalizing charging voltage: 2.3~2.4V/cell.

　　⑤Discharge end voltage: 1.67～1.70V/cell.

　　⑥The impact of temperature on battery life: Under floating charge operation at 25℃, the theoretical life is not less than 10 years.

　　Calculation of UPS battery capacity

　　1 Maximum battery discharge current I

　　I＝S×COSφ/η×Ei

　　Where: S is the nominal output power of the UPS power supply ;

　　COSφ is the load power factor, generally 0.8;

　　η is the efficiency of the inverter, which is generally taken as 0.8;

　　Ei is the battery discharge end voltage.

　　Battery backup time tBattery backup time t is determined according to user needs. Small and medium-sized UPS mostly use valve-controlled lead-acid batteries. The price is relatively expensive, and the full-load working time is generally selected as 10min, 15min or 30min.

　　After calculating the maximum discharge current of the battery capacity C, the standard battery capacity is calculated based on the load properties and the UPS backup time required by the user: (C=It).

　　UPS Installation

　　UPS installation location requirements

　　1 To extend the battery life, the battery should be installed in an ambient temperature range of 15℃ ~ 25℃, and the indoor temperature should not be too high.

　　2. Leave 50mm of space on the left and right sides of the UPS, 100mm at the back, and enough operating space at the front.

　　3 The external battery cabinet should be placed together with the UPS.

　　Connection between UPS, AC power and load

　　The connection between UPS and AC power and load is simple, but you should check before connection:

　　①Whether the UPS input parameters are consistent with the voltage and frequency of the AC power.

　　② Check whether the live wire and neutral wire connected to the UPS are consistent with the manufacturer's regulations.

　　③ Check whether the load power is less than the UPS output power.

　　④Be sure to distinguish the positive and negative poles when connecting the UPS to the battery.

　　When selecting the conductor cross section, the following should be considered:

　　1. Comply with cable safety standards.

　　2. Meet the cable temperature rise requirements.

　　3Meet the voltage drop requirements.

　　① AC input current I phase. Because P = 3 × U phase × I phase × COSφ (for single-phase output: P = UICOSφ). Therefore, I phase = P/(3 × U phase × COSφ) = S/(3 × U phase).

　　② DC output current I = P/U (U should take the minimum value). After finding the AC input I phase and DC output current I, look up the table to determine the cross-sectional area of ​​the wire.

　　UPS Maintenance

　　Based on years of work experience, I recommend the following aspects for maintaining the UPS power system:

　　1. Master the basic knowledge of UPS, read the equipment manual carefully, understand the meaning of various warning information, warning codes, indicator lights, as well as the causes and countermeasures. Be familiar with the functions of various switches and buttons on the equipment. Be familiar with various UPS operations, understand the connection relationship, and understand the method of substitution.

　　2 Strengthen daily inspections and maintenance, check whether the equipment has any alarms, odors, or abnormal noises, check whether the joints are loose or hot, whether the cooling fan is operating normally, whether the various indications of the equipment are normal, and solve problems in a timely manner when they are discovered.

　　3. Develop a regular maintenance plan: Measure the output voltage, current, power, battery internal resistance and terminal voltage of the equipment regularly every month. Perform a verification discharge test on the battery every quarter or half a year, and generally discharge 30% to 40% of the rated capacity. Clean the inside of the UPS once a year and check whether all connectors are in good contact.

　　4 Battery discharge: In the battery discharge operation, if the battery is discharged offline using a dummy load, it is not only cumbersome to disassemble, but also unsafe. It needs to be disassembled and installed for recharging afterwards. In order to ensure the safety and effectiveness of the battery discharge test, it is necessary to find problems (lag battery, reverse polarity battery, etc.) and ensure safe and reliable power supply (no over-discharge, short circuit, power supply interruption, etc.). Here is a method of directly using the load to discharge the battery: that is, turn off the UPS AC input switch to discharge the battery. Since the UPS power supply is mostly used in important network communication systems, the load does not change much, so the discharge current is basically unchanged when the load is directly discharged. In this way, the discharge termination voltage can be determined according to the battery voltage and discharge conditions, and the discharge time can be calculated. The discharge in each quarter will be compared with this record, and problems can be found and eliminated in time.