CS196895B1 - Electric connection of the exciting semiconductor system with the phase compoundness of the sysnchronnous alternator - Google Patents

Description

(54) Electrical wiring of excitation semiconductor system with phase compounding of synchronous alternator

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the electrical connection of a synchronous alternator phase phase excitation semiconductor system, which compensates for the no-load voltage of the reactive current drawn by the synchronous alternator system.

It is known to electrically connect a phase compound excitation semiconductor system using a Boucherot circuit consisting of series shifting the voltage primary winding of a mixing transformer with a choke and a capacitor connected in parallel to the voltage primary winding of the mixing transformer.

From the theory of the Boucherot circuit, it is known that the alternating current flowing into the voltage primary winding of a mixing transformer is given by:

where U is the phase voltage of the synchronous alternator,

X _T is the phase reactance of the choke, j is the operator indicating that the current I ₂ is shifted by 90 ° beyond the phase voltage U.

Furthermore, it is strong that the current flowing through the choke is given by:

It = yi ² 2 + I ² c (2), where I _c is the current flowing through the capacitor of the Boucherot circuit.

Since the voltage U _{2 of the} mixing transformer, and therefore the capacitors connected in parallel, is always less than the nominal phase voltage U of the synchronous alternator, the current I _{c is} small and does not affect the current I _T against current I ₂ too much. nor its phases.

Furthermore, it is known that the equations given for the Boucherot circuit are assuming that the phase reactance X _{T of the} choke and the phase reactance X _{c of the} capacitors are the same, i.e. the choke is in series resonance with the capacitor. As a consequence, the excitation current of the synchronous alternator load dependent on the value of the ohmic resistance of the excitation circuit and is therefore the same whether it is a synchronous alternator cold or warm, as in Equation (1), the ohmic resistance does not occur, and the current I ₂ is proportional to the exciting current load.

The phase reactance X _{T of the} choke, deciding on its type size and construction, is based on the formula (1):

Xt = ............... · .....: · ^(31>

It is therefore necessary to know the current I ₂ at a known, eg rated voltage U of the synchronous alternator. The current I ₂ depends on the number, turns N _{2 of the} voltage primary winding and on the number of turns N _{3 of the} secondary winding of the mixing transformer according to the formula:

N ₂

With the known ratio given by the design of the mixing transformer, it is also necessary to know the current I ₃₀ , ie alternating current in the secondary windings N _{3 of the} mixing transformer, to calculate the current I ₂ .

The current I ₃₀ is given by:

I30 ~ Ibo · ki (5), where I _Bo is the idle current of the synchronous alternator, known from its idle characteristic at the rated voltage and given by the calculation of the synchronous alternator ak, is the current transfer of the excitation semiconductor rectifier and thus kj is a known value. Thus, it is possible to calculate the value of the current I ₂ from the equation (4J ₎ and thus from the equation (3) the reactance of the choke.

It can be seen from the equation (1j) that current I ₂ is proportional to the phase voltage U of the synchronous alternator at a constant phase reactance X _{T of the} choke. According to equation (4), current I _{2 is} proportional to current I ₃₀ . the voltage of the synchronous alternator, as well as the direct current I _B o of (5), ie.

Ibo = (6), which will also be proportional to the phase voltage of the synchronous alternator. The known excitation line X _T is thus obtained. I _B0 , i.e. the no-load excitation current dependence on voltage, or better the no-load excitation voltage dependence. The drive line then intersects characteristic load, i.e. _on the line U = f [Ibo) at the rated voltage, as was determined from the rated voltage and the current I _Bo, as known quantities.

This would only be the case if the choke current I> r was negligibly small and did not have a phase shift of almost 90 ° beyond the phase voltage of the synchronous alternator.

In reality, however, a relatively small current I _T reactor to the nominal current of the synchronous alternator causes for the fact that it is nearly purely inductive, a synchronous reactance, and the ohmic resistance of the synchronous alternator such voltage decrease, that the characteristic of the terminal voltage of U = f (I _Bo J Synchronous alternator differs considerably from the idle characteristic U _o = f (I _Bo ) Due to the steep course of the characteristic U = f (I _Bo ), its lever intersects with the excitation line X _T. I _Bo at considerably less voltage than the rated voltage The voltage given by this intersection is actually the open-circuit voltage of the self-excited synchronous alternator, which is in fact disproportionately lower than the nominal voltage required.

An attempt to increase it would lead to a larger type choke whose reactance would have to be lower than that calculated from the known values of the synchronous alternator and the mixing transformer. Even at a lower phase reactance X _{T of the} choke, ie at a more inclined excitation line X _T. I _B0 is not fully guaranteed that the nominal no-load voltage is reached because the choke of lower phase reactivity draws more current and this again reduces the terminal voltage characteristic U = f (IboJ, so that the position of the intersection line X _T. I _Bo and U = f (I _Bo J does not significantly increase even with the increased compound effect of the current primary winding N _{2 of the} mixing transformer flowing at idle current I ₂ .

This difficulty is eliminated by the electrical wiring of the phase-shift excitation semiconductor system of the synchronous alternator according to the invention, characterized in that a compensation capacitor is connected in parallel to the Boucherot circuit.

The electrical wiring of the phase compounding phase synchronous alternator alternator according to the invention is simple, therefore reliable, and provides a smaller type of Boucherot circuit choke, designed according to known data from the synchronous alternator and mixing transformer. This connection can be accomplished by simply connecting the compensating capacitors in cases where the device is already finished and other adjustments, eg reducing the phase reactance of the choke by adequately routing a suitable branch would be difficult and costly and would be associated with operational difficulties such as increased choke warming. or they would not be entirely successful.

An example of the electrical connection of a phase semiconductor excitation system of a synchronous alternator according to the invention is shown in the accompanying drawing, in which Fig. 1 shows a circuit diagram in which three-phase circuits are drawn in a single-pole for clarity. Fig. 2 shows circuit characteristics.

The stator winding 1 of the synchronous alternator is connected in series with the current primary winding N _{2 of the} mixing transformer. The voltage transformer primary winding N ₂ is connected in series with a choke 2 connected to the terminals of the synchronous alternator. A capacitor 3 is connected in parallel to the voltage primary winding N _{2 of the} mixing transformer.

The series combination of voltage primary winding N ₂ with choke 2 and capacitor 3 forms the Boucherot circuit.

A diode rectifier 4 (for example in a three-phase bridge version) is connected to the secondary winding N _{3 of the} mixing transformer, connected to the excitation winding via rings and brushes 5 of the synchronous alternator. A compensation capacitor 6 is connected in parallel to the Boucherot circuit 2, N ₂₎ 3.

In FIG. 2, the vertical axis plotting the voltage U synchronous alternator and the horizontal axis excitation current load _bo synchronous alternator. The idle characteristic of the synchronous alternator U _o = ϊ (I _Bo ) is indicated by line 20, excitation line X _T. Or, it is indicated by a line 21 resp. 21 'and the terminal voltage U of the synchronous alternator on the idle current I _Bo is indicated by line 22 (U-f (I _Bo )). The excitation line shown by line 21 intersects the no-load characteristic (line 20) at the rated voltage U _{N of the} synchronous alternator. Due to the voltage drop on the synchronous reactance and the ohmic resistance of the stator winding 1 of the synchronous alternator, the line voltage-dependence line voltage U = f (I _Bo ) gives lower voltage values than the idle characteristic U _o = f (I _Bo ). Synchronous alternator unloaded current lj network should then place the desired voltage U _N U _of the voltage only, the intersection of lines 21 and 22nd

This would occur if there was no compound effect of the current primary winding of the mixing transformer N ₂ .

Since the current I _{T of the} choke and the current I ₂ in the voltage transformer primary winding N ₂ at the low current Ic, the flowing capacitor 3 of the Boucherot circuit are almost equal to the nominal current I _{3 of the} synchronous alternator small and offset by its phase voltage almost 90 ° , the compound effect of the current primary winding Nj of the mixing transformer by the current I _{T will be} small and at its

Claims (3)

SUBJECT The electrical wiring of the synchronous alternator excitation semiconductor system, consisting of a diode excitation rectifier, a mixing transformer and a Boucherot circuit consisting of a series connection of the voltage primary respecting, will only result in a slight shift of the excitation line 21 to the new position indicated by dashed line 21 '. have a synchronous alternator the actual open circuit voltage U _by ”significantly lower than its nominal voltage U _N. By connecting a compensating capacitor 6 of the same reactance X _c as the capacitor 3 of the Boucherot circuit, the same capacitive current will flow into it at the same voltage: As the current I ₂ = -, for the Boucherot circuit X _T = X _c . The capacitive current of the compensating capacitor 6 is only negligibly smaller than the current I _{T of the} choke, loading at the current I ₂ = 0 the synchronous alternator, because I _T = FI ² 2 + I ² c and current I _c = is at A _c low voltage U ₂ small. Thus, the compensation capacitor 6 practically completely compensates the current I _{T of the} choke 2, which changed the no-load characteristic 20 to the characteristic of the terminal voltage 22 and the excitation line 21, respectively. 21 'gave no-load voltage U _o ', respectively. U ” _o <U _N. Thus, when using a compensating capacitor 6, the current 1j = I _T = I ₂ will not flow through the stator winding 1 of the synchronous alternator, ie it will be L = 0 and the synchronous alternator will actually have a no-load characteristic given by line 20 rated voltage U _N. Even the small compound effect of the current winding of the mixing transformer disappears from the current Ιτ · If the compensating capacitor 6 has less reactance than the capacitor 3 of the Boucherot circuit, the current I _{T of the} choke 2 will be overcompensated and the open circuit voltage of the synchronous alternator will rise above the rated value. OF THE INVENTION it is a mixing transformer winding with a choke and a capacitor connected in parallel to the voltage primary winding of the mixing transformer, characterized in that in parallel to the Boucherot circuit (2, N ₂ , 3) a compensation capacitor (6) is connected.