1.10.3 The controlled three-phase circuit with a centre tap
Conditions:
La=0; Ld=0
Figure 1.30
It is a regime of unremitting current
Conditions:
La=0; Ld=0
Figure 1.31
It is a regime of limiting-unremitting current
Conditions:
La=0; Ld=0
-
Figure 1.32
It is a regime of intermittent current
Condition: La=0; Ld = ∞
Figure 1.33
It is a regime of unremitting current
1.10.4 The account of a stage of switching for three phase rectifier with centre tap
Conditions: La≠0, Ld=∞, α≠0
Figure 1.33
Let's assume that a control pulse is applied to the thyristor VS2 and it is turned on, the VS1 is turned off at the same time.
Let's locate a reference mark at the moment of control pulse applying to the VS2.
Then
Figure 1.34
At
From here, we should find γ
Commutating voltage drop is
1.10.5 External characteristic
In relative units
where А=0.87 for Δ/Υ and Υ/Υ;
A=0.5 for Y/Z.
1.11 Three-phase bridge rectifier
Figure 1.35
1.11.1 Conditions: α=0; La=0; ra=0.
VS1, VS3, VS5 – a cathode group; VS4, VS6, VS2 – an anode group.
At each moment of time two thyristors are on-state - one of them is from the cathode group, another - from the anode group. This of thyristors from cathode group is conducting, which have highest EMF arranged to his anode. This of thyristor from anode group is conducting, which have lowest EMF arranged to his anode.
In result the potential of the common cathodes ( “+” of the rectifier ) varies according a top envelope of phase EMF, and potential of the common anodes ( “-“ of the rectifier ) varies according a bottom envelope of phase EMF.
The rectified voltage is equal to a difference of potentials of positive and negative poles of the rectifier and it is a difference of phase EMF of conducting thyristors. Frequency rate of pulsations of the rectified voltage with reference to frequency of a power line is equal to 6.
The direct component of rectified voltage
The peak-inverse voltage of thyristor
As the current of secondary winding of the transformer i2a has not a direct component so a primary current i1A is determined as
Let's demand to the equipment for Ld =∞ :
Constant component of a thyristor current
RMS- value of a thyristor current
RMS value of a current of a secondary winding of the transformer
RMS value of a current of a primary winding of the transformer
Full power of windings S1, S2 and type power of transformer ST
Practically exceeding ST about power of rectified current Pd is only 5 %. Exceeding URM about Ud0 also is only 5 %. As frequency rate of pulsations of a curve of the rectified voltage is twice greater than for the three-phase rectifier with center tap, the level of the highest harmonics in it is less. Therefore the given circuit has the widest application. The primary winding may be connected in a triangle. Only the waveform of a linear current will be changed in this case.