Application Technology of UPS Power Supply in Cable TV System

1. Application of UPS in Cable TV System

Since the existing electricity is prone to power outages, voltage fluctuations, surges, noise interference, frequency deviations and flash jumps, and unexpected natural disasters or man-made accidents such as earthquakes, lightning strikes, power transmission and transformation system disconnections or short circuits, these power supply failures will have many adverse effects on the cable TV system and even directly lead to interruptions of cable TV system services. Therefore, uninterruptible power supply systems are increasingly being used in CATV front-end machine rooms, thousand-line power supply systems and other places.

1. UPS is configured in the front-end computer room

The front-end machine room is the core of the cable TV system. In order to ensure its stable operation, a three-phase input and single-phase output type is generally selected. The online UPS with a rated power of generally 10kVA uses the new wing device IGBT module launched in recent years, etc. Its external battery pack can be increased or decreased as needed, laying a hardware foundation for the long delay of UPS. The display circuit of this UPS can accurately reflect the operating status and related data of the equipment. At the same time, it has a powerful self-diagnosis function and can provide uninterrupted and high-purity power for front-end equipment such as satellite receivers, modulators, optical transmitters, and network switches. Before the front-end machine room in our county was connected to the UPS, whenever the TV station tripped and the power went out, the power supply of the trunk amplifier and the front-end signal were interrupted. Even if the several sets of programs transmitted by the city and county optical cables are guaranteed by attached batteries, the program is interrupted because of the power outage of the modulators and other equipment in the machine room. CATV users in the area where the power is not cut off still cannot receive cable TV programs, and users are very dissatisfied. Since the front-end computer room was equipped with UPS, cable TV programs can still be transmitted normally even if there is a power outage at the TV station, which improves user satisfaction with the TV station.

In some cities where multifunctional interactive services are developed, the reliability of the power supply system in the front-end computer room is required to be higher. Generally, hot backup connection or UPS parallel redundant connection can be adopted. The parallel connection of UPS system not only improves reliability, but also increases load capacity.

2. Outdoor Cable TV Uninterruptible Power Supply (Cable UPS)

Many active devices in the wired network are located in the wild. The fluctuation of the grid voltage and the large temperature difference between day and night can easily damage the power supply, optical receiver, amplifier and other equipment, resulting in network interruption and increased equipment maintenance costs. According to statistics, about 45% of the causes of damage to CATV equipment are attributed to power failures. Therefore, it is particularly important to provide high-quality, uninterrupted power for these devices. In recent years, outdoor uninterruptible power supplies have gradually been widely used. The biggest feature of this type of cable TV uninterruptible power supply (Cable UPS) is that it can withstand various harsh environments such as high temperature, humidity, cold, wind and sand, so Cable UPS has become a necessary facility to ensure uninterrupted signals. The biggest difference between Cable UPS and traditional UPS is that it uses gel batteries as backup energy, and does not require regular charging and discharging maintenance.

2. Scientific use of UPS

1. Selection of UPS rated output capacity

Before determining the rated output capacity of the UPS, the total capacity of the load must be calculated first. Cable TV systems generally choose online UPS, and its optimal load capacity should be controlled between 60% and 70% of its rated capacity. For example, the equipment that requires uninterrupted power supply in the front-end computer room of our county includes satellite receivers, modulators, optical transmitters, centralized power supplies, network switches, etc. The total power is calculated to be 5500VA, so 5500VA-70%a"7857VAo. Considering network upgrades, there must be a certain amount of room for expansion, so we choose a 10kVA UPS based on the host power of 10kVA. Its optimal load capacity is 6kVA-7kVA (not suitable for full load or excessive light load). After determining the host power, it is also necessary to reasonably select input and output wiring and air switches.

2. Calculation of battery working time

The working time of the battery can be determined according to the following formula: The working time of the battery when fully loaded = (battery capacity x voltage) l (host power x 0.7), where 0.7 is the power factor. For example, the UPS system in the front-end computer room of our county: the host rated power is 10kVA, and two groups of batteries (20 cells per group, voltage is 12V/cell, capacity is 100 Ah) are used in parallel. That is, the battery voltage is 12Vx20=240 V, and the battery capacity is 100Ahx2=200 Ah. It is calculated that when the system is powered off, the working time of the battery is: (200A-1ix240V)/(lOkVAx0.7) 6.86 hours, which is calculated when the system is fully loaded. And calculated according to the actual load: (200 Ah x240V)/5500VA } 8.73 hours, that is, the UPS system can last up to 8.73 hours when the power is off.

3. Other considerations

1) Choose a UPS with strong overload capacity. The stronger the overload capacity, the less likely it is to switch to bypass when starting a nonlinear load, and the more reliable the protection of the load. That is, when there is a general overload or startup surge current impact at the output end, the inverter's own overload capacity can be relied on to bear the short-term overload current, thereby improving the reliability of the UPS.

2) In order to ensure that the battery can be efficiently and fully utilized, a charger with constant current charging characteristics should be selected.

3) As the instantaneous starting current of inductive loads (such as TV screen walls, etc.) is large, try not to connect them to the UPS. When a power outage occurs, try to keep only the necessary key equipment, because the battery power supply time is closely related to the size of the load.

In order to improve the reliability of the cable TV system, in addition to selecting the right UPS, daily maintenance should also be done carefully. The maturity of technology has made the maintenance of the UPS electrical part extremely small, mainly the maintenance of the battery. The battery is an important pillar of the UPS and also a relatively weak link in the UPS system. A large proportion of UPS failures are caused by battery problems. The quality of battery performance will directly affect the reliability of the UPS system. Although maintenance-free batteries are used, certain maintenance is quite necessary. In daily work, in addition to recording the data on the UPS and charger panels every day, you should also pay attention to the following points:

1. Float charge Voltage Setting has a considerable impact on the life of the battery.

Artificially increasing the float charge voltage is harmful to the battery. Experiments have shown that setting the float charge voltage of the battery too high or too low will significantly reduce its life. If the float charge voltage is too high, it will cause corrosion of the positive electrode of the battery, and the water in the electrolyte will be decomposed into hydrogen and oxygen to overflow, resulting in a decrease in capacity or even damage; if the float charge voltage is too low, the battery will be undercharged and the electrode will be sulfated. The float charge voltage should be set strictly according to the manufacturer's instructions. Regularly measure the voltage of each battery terminal online. When the voltage difference between each single battery is too large, equalization charging should be performed.

2. If there is no power outage for a long time, the mains power should be turned off every 3 months or so to allow the UPS battery to discharge the load once to ensure the activity of the battery.

If the battery is not discharged for a long time, not only will the capacity be reduced due to sulfation, but the UPS will not be able to output a large enough current when saving battery , causing the load to lose power. Generally, only 30%-50% of the rated capacity of the battery pack is required for artificial discharge. During the discharge process, excessive or extremely small current discharge should be avoided, and the discharge voltage should not be lower than the termination voltage of the dry battery to avoid deep discharge of the battery. Based on the actual load, the artificial discharge time should be controlled as: (30%-50%) x rated capacity of the battery pack: actual load. During the discharge period, test records should be kept for later comparison.

3. The life of the battery has a lot to do with daily maintenance and correct use. For example, our county and the neighboring county opened city and county optical cable programs at the same time, and the batteries configured were the same.

The neighboring county allowed the battery to discharge regardless of the length of the power outage, causing the battery to be completely damaged in a short time. The temperature and humidity in our county's computer room are strictly controlled, and the technicians are dedicated to maintenance. Until now, the battery is still running well. Once, due to a long power outage, a momentary negligence caused the battery to discharge excessively, resulting in the battery not being able to charge after power was restored. The technicians carefully increased the charging voltage and charged it slowly. After a period of time, the charging current finally gradually increased. At this time, the voltage was adjusted to the normal value and charging continued until it was fully charged.

3. Daily maintenance of UPS

In order to improve the reliability of the cable TV system, in addition to selecting the right UPS, daily maintenance should also be done carefully. The maturity of technology has made the maintenance of the UPS electrical part extremely small, mainly the maintenance of the battery. The battery is an important pillar of the UPS and also a relatively weak link in the UPS system. A large proportion of UPS failures are caused by battery problems. The quality of battery performance will directly affect the reliability of the UPS system. Although maintenance-free batteries are used, certain maintenance is quite necessary. In daily work, in addition to recording the data on the UPS and charger panels every day, you should also pay attention to the following points:

1. Float charge Voltage Setting has a considerable impact on the life of the battery.

Artificially increasing the float charge voltage is harmful to the battery. Experiments have shown that setting the float charge voltage of the battery too high or too low will significantly reduce its life. If the float charge voltage is too high, it will cause corrosion of the positive electrode of the battery, and the water in the electrolyte will be decomposed into hydrogen and oxygen to overflow, resulting in a decrease in capacity or even damage; if the float charge voltage is too low, the battery will be undercharged and the electrode will be sulfated. The float charge voltage should be set strictly according to the manufacturer's instructions. Regularly measure the voltage of each battery terminal online. When the voltage difference between each single battery is too large, equalization charging should be performed.

2. If there is no power outage for a long time, the mains power should be turned off every 3 months or so to allow the UPS battery to discharge the load once to ensure the activity of the battery.

If the battery is not discharged for a long time, not only will the capacity be reduced due to sulfation, but the UPS will not be able to output a large enough current when saving battery , causing the load to lose power. Generally, only 30%-50% of the rated capacity of the battery pack is required for artificial discharge. During the discharge process, excessive or extremely small current discharge should be avoided, and the discharge voltage should not be lower than the termination voltage of the dry battery to avoid deep discharge of the battery. Based on the actual load, the artificial discharge time should be controlled as: (30%-50%) x rated capacity of the battery pack: actual load. During the discharge period, test records should be kept for later comparison.

3. The life of the battery has a lot to do with daily maintenance and correct use. For example, our county and the neighboring county opened city and county optical cable programs at the same time, and the batteries configured were the same.

The neighboring county allowed the battery to discharge regardless of the length of the power outage, causing the battery to be completely damaged in a short time. The temperature and humidity in our county's computer room are strictly controlled, and the technicians are dedicated to maintenance. Until now, the battery is still running well. Once, due to a long power outage, a momentary negligence caused the battery to discharge excessively, resulting in the battery not being able to charge after power was restored. The technicians carefully increased the charging voltage and charged it slowly. After a period of time, the charging current finally gradually increased. At this time, the voltage was adjusted to the normal value and charging continued until it was fully charged.