Добавил:
ivanov666
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:The Electromagnetic Interference in the Electrical Power Supply System. The long-term variance of the voltage specifications. Study guide
.pdf
From this it follows that the high-voltage voltages in the Power Supply
System Department at this moment partially exceed the allowable levels of
harmonic voltage components established in accordance with 32144-2013
Standard. In order to reduce the amplitudes of odd harmonics multiple of
three, and generally reduce the non-sinusoidality of the mains voltage, installation of special filter-compensating devices is required [11].
Computer load
As an example of a nonlinear load in a computer network, we consider
the operation of a personal computer and also examine the non-sinusoidal
nature of a PC current.
Fig. 3.10. The oscillogram of the current consumed by a PC without UPS
Fig. 3.11. The oscillogram of the current consumed by a PC with UPS
31
The design feature of the UPS is an uncontrolled rectifier mounted on
the input and working on the battery, not on the capacity. As a result, different non-sinusoidal coefficients were obtained for a PC without a UPS
(KNS = 1.44) and a PC with a UPS (KNS = 0.77).
We will calculate the high harmonics from a PC without a UPS and with
a UPS with active number of computers (600 units) We add the calculation
results in Tables 3.5 and 3.6, respectively:
Тable 3.5
Calculation of high harmonics from PC without UPS
Amplitude
n
1 4,96 -42,3 1,00 600,00
3 4,62 -21,6 0,93 558,87
5 4,03 16,9 0,81 487,50
7 2,83 55,8 0,57 342,34
9 1,46 86,4 0,29 176,61
11 0,3 77,3 0,06 36,29
13 0,85 27,1 0,17 102,82
15 0,98 51,3 0,20 118,55
17 1,04 84,5 0,21 125,81
19 0,58 120,2 0,12 70,16
Amplitude,
А
Phase
(in fractions
of n = 1),
о. e.
The into account
the number
of computers
(600 units.)
32
Calculation of high harmonics from PC with UPS
Тable 3.6
Amplitude
n
1 6,49 –37,6 1,00 600,00
3 4,26 0,6 0,66 393,84
5 1,94 44,4 0,30 179,35
7 0,93 10,3 0,14 85,98
9 1,25 43,1 0,19 115,56
11 0,66 94,6 0,10 61,02
13 0,44 16,7 0,07 40,68
15 0,42 85,2 0,06 38,83
17 0,27 39,7 0,04 24,96
19 0,48 44,3 0,07 44,38
Amplitude,
А
Phase
(in fractions
of n = 1),
о. е.
The into account
the number
of computers
(600 units.)
In the calculation of the high harmonics from PC without UPS, according to the data obtained, we see that the third harmonic of the current is almost equal to the first harmonic and is 93% of the amplitude of the first one.
The amplitude of the fifth harmonic is 83% of the level of the first current
harmonic, the seventh harmonic is 57% of the first one.
In the calculation of the high harmonics from a PC with UPS we see that
in comparison with the first one the third current harmonic decreased up to
66%, the fifth current harmonic – up to 30%, and the seventh decreased only up to 14%.
Analyzing the results of the experiment conducted, we clearly see that
the operation of the uninterruptible power supply (UPS) reduces the ampli-
33
tude of the harmonics and reduces the non-sinusoidal current in the network
of NSTU teaching block two. Nevertheless, the third current harmonic still
has a large amplitude in comparison with the first harmonic. This is explained by the fact that the building is heavily equipped with computer
equipment. Therefore, the value 66% obtained for this type of design can be
considered as the maximum computer load for NSTU teaching block two.
However, the prevailing third harmonic should be compensated by filters to
improve the quality of electricity in the facility.
1) Power load
As an example of a power load, let us consider the work of a variable
frequency drive on the basis of a training stand in laboratory II-340, the design of which is shown in Figure 3.12.
Fig. 3.12. Stand construction
The stand has three parts: the first is the control cabinet, in which all the
necessary components and protective switching equipment are located; the
second is an asynchronous motor located on the same frame as the direct current motor (DC motor) and the third is a workplace of a PC.
Figure 3.13 shows the control cabinet which contains: two ACS150 and
ACS550 frequency-controlled drives, a frequency starting converter for performing non-peak triggering of the asynchronous motor, a DC-DC drive
DCS800, the PM581-ETH controller, as well as the necessary switching
protection equipment [12, 20].
34
AFDACS150
DCS800
motor
AFDACS550
Fig. 3.13. Internal arrangement of the drive control cabinet
Currently, there is an increase in the electricity of consumers that need alternating current of adjustable frequency. To provide such consumers with
power supply various frequency converters are used. These devices are designed to convert a three-phase voltage with 50 Hz constant frequency into a
three-phase voltage with a variable frequency in the range from 0.2 to 400 Hz
35
and are used to smoothly control the speed of asynchronous or synchronous
C
motors by changing the frequency of the supply voltage. This feature of frequency converters makes their practical application to control various electric
drives advantage.
ACS150 and ACS550 converters consist of two power elements – an
uncontrolled rectifier and a stand-alone voltage inverter (Figure 3.14).
Commun ication
Inputs/outputs
Setpoints
Control electronic
control / monitor
UGRD008.DRW
A
1
B6
2
3
PE
Rectifier DC bus Inverter Induction
A
V
V
phase
B
1,35 * V
BC
4
5
6
motor
C
Mains
V
DC
+V
D
Fig. 3.14. Block diagram of a frequency converter
An unregulated AC voltage of industrial frequency is supplied to the input of the rectifier, which is rectified and fed to the inverter, which converts
the constant voltage into the alternating one with variable amplitude and
frequency. In addition, this type of frequency converters is characterized by
high efficiency (about 0.96), significant speed, small dimensions, relatively
high reliability and silent operation [13, 14].
The use of a frequency-controlled electric drive provides energy saving,
which is achieved by regulating some technological parameters. If it is a pump
or a fan, you can maintain the pressure or control the performance. If it is a machine, you can smoothly adjust the feed rate or its movement.
At the same time, in many electrical networks and systems high harmonics are non-linear load and a source of interference. They change the
nature of power consumption in power supply networks: the reactive power
modes change, current and voltage high harmonics appear in power net-
36
works, which leads to disturbances in the distribution network and power
quality deterioration.
We will analyze the behavior of high harmonics using ACS150 and
ACS550 frequency-controlled drives when changing the speed of the induction
motor and the moment of resistance developed by the DC motor.
To carry out the necessary measurements, a UMG103 device based on
the GridVis program that was previously mentioned was used. For the
ACS550, measurements were taken at BP speeds of 400 rpm and 695 rpm.
For each speed, 5 measurements were made, differing from each other by
the moment on the motor shaft, which was 2, 6, 10, 15, and 20 N × m. The
connection diagram of the UMG 103 device to the network is shown in Figure 3.15.
FCD
Fig. 3.15. UMG 103 device connection diagram
The results of measurements of the controlled parameters at a speed of
400 rpm and 695 rpm are shown in table 3.7 and 3.8, respectively. In Table 3.9 and 3.10, the share of each harmonic with respect to the power supply current at the measured rotational speed was calculated.
Тable 3.7
Values of controlled parameters at n = 400 rpm
Points of meas-
urements
Power supply
inputs 380 В
Parameters 1 2 3 4 5
Iс, А 0,58 0,9 1,41 2,11 2,62
cos φ 0,996 0,995 0,993 0,993 0,991
37
End of table 3.7
Points of meas-
urements
Current harmonics, consumed
by adjustable
frequency from
the networks
Parameters 1 2 3 4 5
I1, А 0,33 0,59 0,91 1,44 1,9
I3, А 0,01 0,01 0,01 0,13 0,14
I5, А 0,28 0,48 0,71 1,09 1,35
I7, А 0,25 0,4 0,56 0,76 0,9
I9, А 0,01 0,02 0,03 0,05 0,06
I11, А 0,14 0,2 0,23 0,23 0,25
I13, А 0,11 0,12 0,14 0,14 0,15
I15, А 0,01 0,02 0,02 0,02 0,03
I17, А 0,04 0,05 0,07 0,08 0,11
I19, А 0,04 0,05 0,07 0,07 0,07
Тable 3.8
The share of each harmonic in the total
current Is, %
Harmonic number, n In / Ic
1 56,9
3 1,72
5 48,28
7 43,1
9 1,72
11 24,14
13 18,97
38
End of table 3.8
Harmonic number, n In / Ic
15 1,72
17 6,9
19 6,9
Тable 3.9
Values of controlled parameters at n = 695 rpm
Points of meas-
urements
Power supply
inputs 380 В
Current harmonics, consumed
by adjustable
frequency from
the networks
Parameters 1 2 3 4 5
Iс,А 0,68 1,36 2,1 2,71 3,46
cos φ 0,997 0,995 0,994 0,993 0,991
I1,А 0,43 0,87 1,49 2,08 2,81
I3,А 0,03 0,05 0,03 0,11 0,21
I5,А 0,35 0,67 1,1 1,36 1,62
I7,А 0,31 0,55 0,83 1,01 1,13
I9,А 0,02 0,04 0,03 0,06 0,08
I11,А 0,16 0,22 0,29 0,23 0,25
I13,А 0,13 0,14 0,16 0,16 0,21
I15,А 0,02 0,02 0 0,03 0,04
I17,А 0,04 0,06 0,1 0,1 0,15
I19,А 0,04 0,07 0,09 0,09 0,14
39
Тable 3.10
The share of each harmonic in the total
current Is, %
Harmonic number, n In / Ic
1 63,24
3 4,41
5 51,47
7 45,59
9 2,94
11 23,53
13 19,12
15 2,94
17 5,88
19 5,88
where Ic, cosφ are the parameters of the mode at the input of the inverter
(measured using the UMG103 device);
Theoretically, we calculate the high harmonics (HH) current values for an
ideal converter, which has zero AC network resistance and infinite smoothing
inductance, and compare these values with those obtained experimentally on
the spectral diagram (Figure 3.16).
2
1,8
1,6
1,4
1,2
1
0,8
0,6
Current, А
0,4
0,2
0
1 3 5 7 9 111315171921
Number of high harmonic
theory
Fig. 3.16. The spectral composition of the mains current for an ideal
rectifier and for the ACS550 at 400 rpm and M = 20 N × m
experienc
40
Соседние файлы в предмете [НЕСОРТИРОВАННОЕ]