A METHOD FOR PHASIC SEQUENTIAL COUPLING OF THREE-PHASE SHORT-CIRCUIT GENERATORS

Abstract: Coupling of the asynchronous machine to the a.c. mains is effected in the way that the contacts arranged for the purpose are closed when the voltage across them before coupling is at a maximum. Coupling can be done by several stages, from two and upwards. The coupling device, which primarily aims at coupling of windmill generators, has the effect that because of the precise coupling relative to the maxima of the voltages, the d.c. link in the current will be negligible, with the result that the transient torques will become insignificant. In this way, it is avoided that coupling will cause the rotary system of the windmill to oscillate. The lack of d.c. will also result in small voltage drops in the mains. If the windmill has no transformer of its own, the current surges can be dampened further by effecting coupling over impedances which are cut out stepwise at voltage maxima over these.

Description: A method for phasic sequential coupling of three-phase short-circuit generators. The object of the invention is soft coupling to the a.c. mains, preferably of asynchronous windmill geηe- rators. The general coupling method used today is direct (one stage) coupling of the generators to the a.c. mains by the use of three-phase contactors at a speed equal or close to the machine's synchronous speed. Such coup- ling will set up a direct current in at least two of the phases. This direct current sets up a static magnetomotive force in the machine's air gap. At the same time, currents will be induced in the rotor, even if the machine runs synchronously. The field which is set up by the rotor currents will together with the static field create strong torque pulsations which can make the entire rotary system hunt violently, with a * harmful effect on shafts, gear unit, and mill arms. The coupling method also results in heavy voltage drops in the mains which may disturb local consumers. The invention is characteristic in that the sequential coupling of the -single phases, especially the first power-producing coupling and short-circuit of any series impedances, is made arcund the respective volt- age maxima of the contacts used for the purpose before coupling. Such phase voltage control has not been established in the known designs of sequential couplings. Compared to the known technology, the result is a considerable reduction in both coupling surges and torque changes since the direct current transients can be kept at a reasonable minimum during coupling at times of phasic voltage maxima. OMPI Fig. 1 shows a coupling made w_ith external shortable series impedances, which coupling applies to both star and delta-wound stators. Fig. 2 corresponds to Fig. 1; however, with a star- wound stator and a separate neutral point brought out. Fig. 3 shows a delta-coupled generator with shortable series impedances internally in the delta coupling. Fig. 4a shows a phase rotation module (A) for phase control of semiconductor contactors. Fig. 4b shows the diagrammatic construction of the phase rotation module (A) . Fig. 5a shows a time lag module (B) . Fig. 5b shows the diagrammatic construction of a time lag module (B) . Fig. 6 shows an activation module (C) for semiconduc¬ tor contactors. Fig. 7 shows a contact arrangement made with series impedances and based on semiconductor contactors. Fig. 8 shows a simplified diagram of the entire arrangement. Fig. 1. On a three-phase generator, whose windings (not shown) can be either star or delta-coupled, two contact connections (1) and (4), (2) and (5), and (3) and (6) respectively emanate from each of the three generator terminals; (1), (2), and (3) of these con¬ tacts being connected to the a.c. mains via impedances of a purely ohmic or ohmic/inductive nature (7), (8), and (9), while contacts (4), (5), and (6) are con¬ nected direct to the a.c. mains. Fig. 2 shows the .same contact and series impedance arrangement with the same reference designations as used in Fig. 1, but the generator, v/hich is shown in star coupling, has a neutral point brought out. Fig. 3 shows generator windings with internal contact and series impedance arrangements which on the surface are in the form of delta coupling. The reference desig- nation corresponds to those used in Figs. 1 and 2. When soft coupling is aimed at, contacts (1), (2), and (3) coupled to the series impedances are closed sequen¬ tially, whereafter contacts (4), (5), and (6) placed over series impedances (7), (8), and (9) are closed sequentially so that direct coupling to the a.c. mains is established. Fig. 4a. Via terminals Ust the module receives the phase a.c. voltage from one of the contacts (1) - (6) as long as it is open and emits a phase-controlled closing signal as logical "1" across terminal Uout when a logical "1" signal is received across terminals Ugo. Fig. 4b. The phase input Ust is fed via an isolating transformer across an R.C. phase ro-cation link to an operator amplifier whose square voltage output is sup¬ plied via a diode to two one-shoτ generators, one of which is triggered on a rise in signal voltage, while the other is triggered on a fall in signal voltage. At a phase rotation of approx. 90 C in the R.C. link, one one-shot generator will be activated at the positive maximum of the phase voltage, while the other will be triggered at the negative maximum. The Q ou puts of both one-shot generators are supplied to a two-input nand gate which will emit a positive output impulse for each Q-pulse which means that a positive pulse is emitted in both the positive and negative maxima of the phase voltages. These phase marking pulses are car¬ ried orward as one input to the next two-input nand / -- o j F gate, whose other input (Ugo) at a change to logical •100 "1" will activate it at the first coincidence with a phase marking pulse. Fig. 5a. As a time lag link across terminals Uin the module receives a control voltage in the form of logical "1" and emits, with an adjustable time lag, an 105 output voltage in the form of logical "1" across the output terminal Uout. Fig. 5b. At transition to logical "1" at Uin, a one-shot generator is triggered whose Q goes in logic¬ al "0" over a selectable interval of time. At the same 110 time an R.C. link is activated from Uin and emits a delayed logical "1" signal which together with the above-mentioned Q signal arrives at a following nand gate after the Q signal has gone in_ logical "0". At the end of the one-shot generator's impulse period 115 both input signals to the nand gate will be in logical "1" whereafter the output signal goes in "0" which is ' inverted via the following nand gate. Therefore, Uout will go in logical "1" with a time-lag relative to Uin which corresponds to the one-shot generator's adjust- 120 able pulse period. Fig. 6 shows a known building module for activation of a triac. Logical "1" across terminals Uin results in (galvanically separated herefrom) a corresponding out¬ put activation voltage for the gate circuit in a triac. 125 Fig. 7 shows contacts (1) - (6) replaced by triacs with gate inputs (la) - (6a). Fig. 8. Logical "1" on . phase-controlled blocks (A) triggers a triac activation via the associated module block (C) at the first phase amplitude peak. After 130 activation of the uppermost (A)-block the next phase- controlled (A)-block is activated via an inserted time " BU RE4 OMPI lag block (B) and at the same time controls its (O- module and transmits a control " signal to the next set of (A), (B), and (C)-modules and so on until the last 135 (A), (B) , and (C)-modules have been activated. The num¬ bers of the (A)-terminals and the numbers of the (C)-terminals correspond to the connecting points shown in Fig. 7. The coupling time of a single phase is uncritical for 1 0 the coupling shown in Fig. 1 since, thanks to the other open contacts, a closed circuit has not yet been established. So it will be possible in this case to do without the uppermost (A)-module and feed the coupling command direct to the uppermost module (C) and direct 45 to the following module (A) , whereafter the first power-supplying coupling is established at the subse¬ quent phasic voltage maxima over a coupling contact, at the same time as the following module (B) is activated. The time lag in ' this module may be of the 150 order of 100 msec before the following (A)-module is activated and phasically controls the coupling of the last phase, this coupling being less critical when the above-mentioned pause is of a reasonable duration, e.g. 40-100 msec. As regards generator coupling with- 155 out series impedances, such as may be imagined with small units, coupling has then been finally estab¬ lished, but when it is a matter of large generators, it will, as shown in the diagrams, be necessary first to establish a connection via series impedances (7), 160 (8), and (9), whereafter a sequential short-circuit of these is proceeded with via contacts (4), (5), and (6) where the time lags in the (3)-elements may be of the same size as before and where the phasic coupling time is selected by the following (A)-modules close to the 165 peak voltage time of the a.c. voltage sequence over the respective series impedances. sυ aEA OMPI With regard to the couplings shown in Figs. 2 and 3 the block diagram shown in Fig. 8 must be observed completely when series impedances are used, whereas 170 the last three module sets can be excluded if the se¬ ries impedances are excluded. To make the method cheaper, it will be possible to exclude two impedances and a coupling contact e.g. in the coupling, Fig. 1. The first power-supplying coup- 175 ling is then made via the impedance. There will then be a pause of approx. 400 msec, before the third phase is ' coupled whereby the induced voltage will become almost as large as and in phase with the mains volt¬ age. Hence coupling at voltage maximum is unnecessary. -BUREAU OMPI

Claims: C l a i m s : Claim 1. A method for phasic sequential coupling of three-phase short-circuit generators in both initially open and closed star coupling and delta coupling with and without connected neutral point and with or with¬ out shortable series impedances, where because of the mechanical transmission loads it is important that pro¬ tection should be provided against initial- directional torque changes during the coupling phase originating from transient direct currents in the stator winding, characterized in that the sequential coupling of the single phases, especially the first power-supplying coupling and short-circuit of any series impedances, is done around the respective voltage maxima of the contacts used for the purpose before coupling. Claim 2. A device for performance of a method as claimed in claim 1, characterized by means for forced sequential control of coupling relative to the first phasically controlled coupling time. Claim 3. As claimed in claim 1 for coupling initially closed delta and star couplings where onlyone series impedance is used, characterized in that the first power-supplying coupling is carried out with series impedance v/hich is shorted before coupling of the last phase. *

Inventors: DRONEN OLAV
Applicants: DRONEN OLAV
Application year: 1982
Main classification: H02J3
IPC codes: H02J3