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Linear load and nonlinear load, which is a basic principle of electrical. But UPS always encounter this two kinds of load, so there must be a clear understanding, to correctly understand and use the UPS.
In the national standard GB/T6270.3 of linear load and nonlinear loads are clearly explained, as follows:
1, linear load linearload
When applies variable sine voltage, the load impedance parameter ( Z ) constant is a constant that load.
2, nonlinear loads non-linearload
Load impedance parameter ( Z ) is not always constant, with time and other parameters such as voltage or changes the load.
From the above description can be seen, this is the essential difference between the two kinds of load, the sinusoidal voltage effect, its impedance value is changed. And they are capacitive load or inductive load it doesn matter. In the linear load, inductive, a capacitance, but also pure resistive. The power factor is not the same, but as long as they meet the above conditions, are the linear load. Do not think that only pure resistive load is linear, and the inductive and capacitive load is nonlinear, it is not right. Don put the linear, nonlinear problems, and the power factor of issue confused, this is two different ideas.
Linear load and nonlinear load is an essential distinction between, in sinusoidal voltage function, linear load current is sinusoidal. Nonlinear load current is sinusoidal.
In a lot of load, nonlinear load is very complex, there are many kinds of current waveform. A peak, Shuangfeng and so on. In order to explain the nonlinear and linear current differences of degree, using a parameter to express, this is the peak factor. In the GB/T7260.3 standard that is:
In 3, peak factor peakfactor
Periodic quantity peak each other are the root of value ratio.
Note: the term " peaking factor " ( crestfactor ) and the synonymous.
A generalization of the maximum peak factor of load is a desktop personal computer, crest factor is about 2.7. A computer system of the current crest factor is about 2.3. Sinusoidal current crest factor is 1.4. So UPS can with nonlinear load peak factor is set to 3, fully able to meet the need of load. Especially for large UPS peak factor is 3, no problem. Only extremely individual small UPS peak factor is set to 5.
For the peak factor of knowledge, there is an issue that needs to cause the attention of people, it is argued, peak factor refers to the load starting impact current of multiples, according to this data to UPS peak factor, this is wrong.
UPS brings the load mostly computer equipment, communications equipment, these devices is more nonlinear loads. Therefore, whether UPS with nonlinear load, can bring many nonlinear loads, with nonlinear load will cause what effect, these problems are the factory / supplier concerns, it is broad user concerns. But all kinds of nonlinear load, there must be a common accreditation standards. Therefore, IEC standard is developed a non-linear reference load ( Referencenon-linearload ), as the standard of the appendix on their standard. In this standard are given in Annex E of this benchmark nonlinear load circuit, as shown in the following picture:
GB standards are also provided for each parameter value. For example, in a load of S, adjustable resistor R1 connected in series with the resistance RS should be consumed 0.7 of S, namely, the power factor is 0.7, the load voltage ripple voltage of 5%. UC=1.22U, R1=UC2/0.66S, RS=0.04U2/S, C=0.15/R1. A single nonlinear load capacity for single-phase 33KVA.
When in use, the single-phase UPS, adjust R1 to power reaches UPS rated power output, up to a maximum of 33KVA. For three-phase UPS, available three identical single-phase benchmark nonlinear load, are respectively connected with each phase voltage, or are respectively connected with each phase voltage (depending on its design .). To form a three-phase balanced load, maximum capacity not exceeding 100KVA.
This is the GB/T7260.3-2003 standards related content. In 2000 released a standard? YD/T1095-2000 communication uninterruptible power supply - UPS " communications industry standard, although according to EN and IEC standards also use this benchmark nonlinear load, but in the instructions for use are different.
The communication industry standards in Appendix A A4 nonlinear load connection with UPS in A4.1 ( UPS33KVA single-phase following ), and A4.3 ( three-phase UPS100KVA following ) regulations. It and our national standard EN, IEC, the GB standard is exactly the same.
The problem occurs when the UPS rated capacity single-phase three-phase over 33KVA, over 100KVA connection method. In our country the communications industry standard A4.2 and A4.4 and GB standard somewhat difference.
The communication industry standards for:
A4.2 for the rated capacity of more than 33KVA single-phase output UPS, available capacity of 33KVA nonlinear load, only increase the linear resistor in parallel with the R1 to obtain the UPS meet the requirements of apparent power and active power.
The meaning is clear, is to use linear load resistor in parallel with the R1 directly, and the regulation of the nonlinear load capacity are respectively equal to the measured UPS rated output apparent power and active power value ( generally large power UPS load power factor of 0.8 ), is actually made a greater baseline nonlinear load.
But the GB standard is not this statement, the record:
A ) and our country of the communications industry standard same content ( omitted)
B ) rating of at least 33kVA single-phase UPS, using the apparent power of 33kVA benchmark nonlinear load, plus linear load, so as to achieve the UPS rated apparent power and rated active power.
The meaning is clear, is the 33KVA nonlinear load after a good tune will no longer move, as a fixed equipment. If the UPS single-phase capacity exceeding 33KVA, at baseline nonlinear load on the outside and a linear load. Of course not pure resistive load. Using the linear load plus 33KVA nonlinear load, adjust to the requirements of UPS rated apparent power and active power. Is not a linear resistance and load resistance R1 is connected in parallel. But a linear load to the last 33KVA fixed nonlinear load.
The two method is obviously different, the two action on UPS results are not the same. For example, a 100KVA single-phase output UPS, in accordance with the GB standard uses a 33KVA benchmark nonlinear load, and the last is about 67KVA linear load regulation suitable detection can be carried out. But according to our country of the communications industry standard will change the nonlinear load value of R1, so that the total capacity to meet the requirements of the 100KVA values, to detect. Of course, our country of the communication industry standards to be strict to the more.
The capacity of more than 100KVA three-phase UPS nonlinear load connected, our this communication industry standards are as follows:
A4.4 for the rated capacity of more than 100KVA three-phase UPS output, can use the third nonlinear load (i.e., 3 33KVA nonlinear loads are respectively connected with the three-phase - in this article the authors note ), then in each linear load increase linear resistance, so that the total capacity to achieve the requirement of the UPS rated capacity and active power.
The single phase UPS, in each nonlinear load resistance and shunt resistance, so that the total capacity up to UPS for numerical.
And GB standards of writing is very clear:
C ) and Chinas communication industry standard of the same content ( omitted)
D ) rating of at least 100kVA three-phase UPS, according to c), 100kVA should be used to benchmark nonlinear load, plus linear load, so as to achieve the UPS rated apparent power and rated active power.
For larger than 100KVA three-phase UPS, two kinds of standard difference and larger than 33KVA single-phase output UPS of the same. Are the linear load in where the problem of.
Our country of the communications industry standard EN chose standard the nonlinear circuit, but in the use are different. The more strict request. The two apparently is different.
The market of our country UPS is a lot of imported equipment, particularly for large capacity UPS are imported equipment. The European UPS manufacturers specify their products are in line with the EN50091 ( or IEC ) and other standards. In the marked with specific performance index, to allow non-linear load capacity dimensioning, have different processing methods. Many UPS do not indicate this, some general annotation conforms to the EN50091-1 standard does not specifically state data, and some manufacturers carefully, to larger than 100KVA three-phase UPS, is written in accordance with the EN50091-1 standard for 100KVA.
As a famous brand UPS technical performance indicators is written like this:
Outputnom.power100 - 800KVA
Permissiblenon-linearloadAccordingtoEN50091-1100KVA
If a three-phase 800KVAUPS, which is in accordance with the EN standard with 100KVA benchmark nonlinear load, coupled with the parallel linear load transferred to 800KVA ( 640KW ). Then a UPS to China inspection is qualified or unqualified?? according to the our country the communications industry standard should take 800KVA nonlinear load, can pass? If not, how to do?
In the actual operation in our country, the communication industry standards and some practical problems. For example, A4.2 more than 33KVA single-phase output UPS, only increase the linear resistor in parallel with the R1. If detected a 100KVA UPS, and the resistance is very easy, resistance value original 1/3 left and right, other devices? Capacitance constant, voltage ripple can guarantee 5%? Current to original 3 times, diode, series resistance will not be burned? According to the standard that only increases the parallel resistance can apparently cannot be applied?.
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