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The influence of UPS power supply on the power grid and its elimination 【Analysis】

Mar 08, 2021

The influence of UPS power supply on the power grid and its elimination 【Analysis】

The ideal UPS should be purely resistive to the grid, that is, the power factor of the UPS is preferably 1, so that it does not pollute the grid. But the reality is that most UPSs generally use 50Hz low-frequency silicon controlled rectifiers, which causes a large number of harmonic feedback pollution to the mains. The problem facing all users is to control harmonic pollution, just like we control the sewage discharged from chemical plants. The harm caused by harmonic waves is great.

  The harm of harmonics mainly lies in:

   1. Make the motor generate additional loss and heat, generate pulsating torque and noise. Transform the electric power, make the motor generate additional loss and heat, and generate pulsating torque and noise. Make the power transformer coil heat, accelerate the insulation aging, shorten the life, cause additional loss and noise.

  2. Interference to protection and automatic control devices such as circuit breakers, leakage protectors, relays, etc., causing malfunctions.

   3. Shorten the life of lighting facilities.

  4. Cause measurement errors of ammeter, voltmeter, power meter, and electric energy meter.

  5. Electrostatic interference and electromagnetic interference are caused to adjacent communication lines.

  6. Cause series/parallel resonance of the electrostatic compensation capacitor of the power distribution system.

  7. Increase the loss of distribution lines, heat, shorten the insulation life, and even cause short circuits and fires.

   8. Due to harmonics, sudden voltage changes cause damage to electronic equipment and malfunctions, which affect the normal operation of computer programs. Cause data loss, or even damage the hardware, cause building automation, fire alarm system, safety protection system to malfunction, or even fail to work.

   At present, the main ways to control UPS harmonic pollution on the market are: 6-pulse rectifier + input filter; 12-pulse rectifier; 12-pulse rectifier + input filter; active filter. These methods all have a common shortcoming, that is, first pollution and then treatment. Because UPS adopts the structure of silicon controlled rectifier, it will inevitably cause harmonic pollution, and then users are forced to spend a lot of money to control harmonic pollution. If UPS does not produce or rarely produces harmonic pollution, then users do not need to spend money to deal with it.

   If you want to achieve the same index, you need to add a lot of options such as input filter, 12-pulse rectifier, etc., each additional option will further reduce the overall efficiency of the UPS. Therefore, the 12-pulse rectifier will reduce the efficiency by 2%, and the active filter will reduce the system efficiency by 4%. Therefore, in actual measurement, the overall efficiency of many 12-pulse UPSs is still less than 88%. Many people only pay attention to UPS price comparison when purchasing UPS, but they do not know how to measure the operating cost of UPS. For example, the efficiency of a HP9330C series 80KVA (64KW) UPS is 95%, while the efficiency of a 12-pulse rectifier is only about 88%.

In the 10-year UPS life cycle, the electricity cost saved by HP9330C series UPS is 64 (KW) × (95%-88%) × 24 (hours) × 365 (days) × 10 (years) × 1 (yuan/kWh) =392,448 yuan. The power consumption will be dissipated in the form of heat, so that users have to pay a lot of electricity bills for users to cool the air conditioner, and UPS unknowingly saves users nearly 400,000 yuan in electricity bills.

In recent years, energy and environmental protection issues have attracted people’s attention. Energy and the environment have also become popular topics. UPS reduces harmonic pollution and improves machine efficiency not only for protecting the environment and saving energy, but also for users. It saves a lot of electricity bills and improves economic efficiency, which further shows that UPS "green and low carbon" is the demand of the times.