In recent years, the cable TV industry has developed rapidly in our
country, providing viewers with a variety of TV programs and enriching our
cultural life. In particular, the multi-functional value-added services and data
services recently developed by cable TV networks have added to our country’s
information The modernization construction has injected new vitality. Therefore,
it is crucial to ensure the safe operation and high-quality broadcasting of
cable TV networks. The front-end of the cable TV system is the heart of the
system. In order to ensure the stable operation of the heart of the system, the
front-end must use an UpS uninterruptible power supply. UpS power supply can
solve the hazards caused by poor quality of mains power to front-end equipment
such as power outages, voltage sags, power surges, reduced oscillations, power
interference, power surges, power fluctuations, switching transients and
harmonic distortion. This article talks about my experience and understanding on
how to design and maintain UpS power supply.
1. How to design the UpS power system
1. Working principle of UpS continuous power supply
UpS (uninterrupted power supply) power supply consists of two parts: the
host and the battery. It can be divided into backup type and online type
according to the working mode. When the mains power supply is normal, the backup
UpS power supply directly supplies power to the load through the AC bypass
channel. At this time, the inverter on the host does not work. Only when the
mains power fails, the battery supplies power through the inverter. drive load.
Therefore, it basically does not change the quality of mains electricity.
The online UpS power supply is different. When the mains power is normal,
it first converts AC into DC, then performs pulse width modulation and
filtering, and then converts DC back into AC power to supply power to the load;
once the mains power is interrupted, it immediately Instead, the battery
inverter supplies power to the load; therefore, the online UpS power supply
outputs pure sine wave power that is completely isolated from the city grid,
which greatly improves the quality of the power supply and protects the safe and
effective operation of the load.
2. Selection of UpS rated output capacity
First, calculate the load power of the front end. In order to ensure the
high efficiency of the UpS system and extend the service life of the UpS as much
as possible, the general load power should meet 60-70% of the rated power of the
UpS. For example, in our front-end, the equipment that requires uninterrupted
power supply includes satellite receivers, modulators, mixers, light-emitting
and receiving computers, network switches, etc. The total statistical power is
4500VA, so we choose 4500÷75%≈6428VA, so we chose 6500W online host.
3. Calculate the working time of the battery
Basic parameters of the battery: voltage (2V, 6V, 12V, etc.), capacity
(65AH, 100AH, etc.)
In practice, we have summarized the following formula to calculate the
working time of the battery:
Battery pack capacity × voltage/host rated power × 0.75 (power factor) =
battery working time at full load
For example, our UpS system has a host with a rated working power of 6500W
and 3 battery cabinets with a total of 30 lead-acid batteries, each with a
voltage of 12V and a capacity of 100AH.
So battery pack voltage = 12V × 10 = 120V
Battery pack capacity=100AH×3=300AH
When the system is fully loaded, the battery working time is:
300AH×120V/6500W×0.75=7.4 hours
It shows that the battery of the system can work for at least 7.4 hours
when the power is cut off.
Calculated based on actual load power:
300AH×120V/4500W=8 hours
Our front-end UpS system can last up to 8 hours when the power is off. This
result has been proved to be correct by our many discharge experiments. If the
above formula is reversed and the required working time of the battery is
determined based on the actual local conditions, then The required battery
capacity and voltage can be determined.
4. Wiring selection
Reasonable selection of wiring is very important. If the wire diameter is
too thin, the current will be too large and it will easily generate heat and
cause a fire; if the wire diameter is too thick, it will cause waste. According
to the electrical characteristics of metal wires, generally the capacity of
multi-strand copper core wire is 6A/mm and the capacity of aluminum wire is
4A/mm. After determining the power of the host, you can refer to the following
table to select wiring and air switch.
5. Choose a brand
When purchasing an UpS power supply, you should mainly consider the
following factors: input voltage range, output voltage range, output frequency
range, bypass inverter zero switching, and the ability to resist surges,
interference, and harmonic distortion. In addition, after-sales service is also
very important. . A large amount of practice has proved that if the
"interference" potential of the neutral line at the UpS output end to the ground
line is too high, it will cause the bit error rate of the data communication of
the computing network to increase. If a high-frequency model is used, due to
high-frequency radiation, it will cause harm to the computer. The network has an
impact, so these issues should be considered when selecting.
2. UpS system maintenance
1. Host maintenance and precautions
UpS hosts are generally intelligent. They do not have high requirements on
the ambient temperature, but they require indoor cleanliness. Otherwise, dust
and moisture will cause the host to work disorderly. The parameters in the host
cannot be changed at will during use; when the power is off, avoid When starting
the UpS power supply with a load, you should turn off the load first, and then
turn on the load after the UpS starts. Otherwise, the inrush current and supply
current of multiple loads will cause the UpS power supply to be instantly
overloaded, and in severe cases, the converter will be damaged; the UpS power
supply cannot be allowed to be in constant condition. Fully loaded or
overloaded.
2. Battery maintenance and precautions
Although maintenance-free batteries are used, in a broad sense certain
maintenance is still necessary. First of all, it has high environmental
temperature requirements. The working environment is generally required to be
between 20℃-25℃. When it is lower than 15℃, its discharge capacity decreases.
For every 1℃ the temperature decreases, its capacity decreases by 1%, and the
temperature is too high ( Greater than 30℃), its life will be shortened;
secondly, it is necessary to prevent the battery from short circuit or deep
discharge. Deep discharge will cause the internal resistance of the battery to
increase or the charging voltage to be too low, resulting in reduced or even
loss of charging ability. The deeper the discharge, the longer the cycle life.
Short; Third, high current charging and discharging should be avoided, otherwise
the battery plates will expand and deform, causing the plate active materials to
fall off, increase internal resistance, decrease capacity, and shorten life;
Fourth, due to the high voltage of the combined battery, there are There is a
danger of electric shock, so there should be safety guarantees when loading and
unloading conductive connecting strips and output lines; fifthly, for areas with
infrequent power outages, it is recommended that users artificially cut off the
power of the UpS every other month to allow the UpS power supply to operate in
the inverter state Work for a period of time to prevent electrolyte
precipitation, so that the battery can maintain good charge and discharge
characteristics and extend its service life; sixth, do not touch the poles and
safety exhaust valves when transporting the battery; seventh, do not use carbon
dioxide fire extinguishers, in case of fire , you can use fire extinguishers
such as carbon tetroxide; eighth, batteries of different capacities, different
manufacturers, and different performances cannot be connected together,
otherwise it will affect the performance of the entire battery set. 5. Choose a
brand
When purchasing an UpS power supply, you should mainly consider the
following factors: input voltage range, output voltage range, output frequency
range, bypass inverter zero switching, and the ability to resist surges,
interference, and harmonic distortion. In addition, after-sales service is also
very important. . A large amount of practice has proved that if the
"interference" potential of the neutral line at the UpS output end to the ground
line is too high, it will cause the bit error rate of the data communication of
the computing network to increase. If a high-frequency model is used, due to
high-frequency radiation, it will cause harm to the computer. The network has an
impact, so these issues should be considered when selecting.
2. UpS system maintenance
1. Host maintenance and precautions
UpS hosts are generally intelligent. They do not have high requirements on
the ambient temperature, but they require indoor cleanliness. Otherwise, dust
and moisture will cause the host to work disorderly. The parameters in the host
cannot be changed at will during use; when the power is off, avoid When starting
the UpS power supply with a load, you should turn off the load first, and then
turn on the load after the UpS starts. Otherwise, the inrush current and supply
current of multiple loads will cause the UpS power supply to be instantly
overloaded, and in severe cases, the converter will be damaged; the UpS power
supply cannot be allowed to be in constant condition. Fully loaded or
overloaded.
2. Battery maintenance and precautions
Although maintenance-free batteries are used, in a broad sense certain
maintenance is still necessary. First of all, it has high environmental
temperature requirements. The working environment is generally required to be
between 20℃-25℃. When it is lower than 15℃, its discharge capacity decreases.
For every 1℃ the temperature decreases, its capacity decreases by 1%, and the
temperature is too high ( Greater than 30℃), its life will be shortened;
secondly, it is necessary to prevent the battery from short circuit or deep
discharge. Deep discharge will cause the internal resistance of the battery to
increase or the charging voltage to be too low, resulting in reduced or even
loss of charging ability. The deeper the discharge, the longer the cycle life.
Short; Third, high current charging and discharging should be avoided, otherwise
the battery plates will expand and deform, causing the plate active materials to
fall off, increase internal resistance, decrease capacity, and shorten life;
Fourth, due to the high voltage of the combined battery, there are There is a
danger of electric shock, so there should be safety guarantees when loading and
unloading conductive connecting strips and output lines; fifthly, for areas with
infrequent power outages, it is recommended that users artificially cut off the
power of the UpS every other month to allow the UpS power supply to operate in
the inverter state Work for a period of time to prevent electrolyte
precipitation, so that the battery can maintain good charge and discharge
characteristics and extend its service life; sixth, do not touch the poles and
safety exhaust valves when transporting the battery; seventh, do not use carbon
dioxide fire extinguishers, in case of fire , you can use fire extinguishers
such as carbon tetroxide; eighth, batteries of different capacities, different
manufacturers, and different performances cannot be connected together,
otherwise it will affect the performance of the entire battery set.
At the same time, the battery must be inspected, measured regularly, and
recorded. Inspection items include: float charge voltage of the entire battery
pack, float charge voltage of a single battery. When measuring the voltage of a
single battery, it should be carried out in the battery discharge state,
otherwise the measured result will be a false voltage. The rule of thumb is to ,
connect a 1-3 ohm resistance wire in parallel to both ends of the multimeter;
check whether the battery is damaged, whether there is leakage between the shell
and cover, whether there is dust and other debris on the surface, whether the
battery holder, connecting wires, and terminals are loose or corroded, etc. The
voltage of a single battery cannot be lower than 70% of the nominal value. The
sign of whether it is leakage or acid mist is to observe whether there are
crystals pouring out of the pole. If there are crystals pouring out, it is a
liquid leakage. Otherwise, it is acid mist or liquid leakage. It is mainly
concentrated at the positive and negative terminals of the battery, and the acid
mist overflows mainly near the exhaust valve. Once abnormal battery voltage,
physical damage, electrolyte leakage, abnormal temperature, etc. are discovered,
the cause should be found and the faulty battery should be replaced in time.
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