FR2548790A1 - ELECTRICAL POWER SUPPLY SYSTEM FOR ACTIVE SECTIONS OF DIGITAL DIGITAL FLUTES - Google Patents

Abstract

ELECTRICAL POWER SUPPLY SYSTEM USED FOR ELECTRIC POWER SUPPLY ACTIVE SECTIONS OF DIGITAL SUBMERSIBLE FLUTES. THE FP POWER SUPPLY FREQUENCY IS EXACTLY EQUAL TO THE SEISMIC DATA ACQUISITION FS SAMPLING FREQUENCY, OR EQUAL TO AN EXACT MULTIPLE OF THIS FS SAMPLING FREQUENCY.

Description

The present invention relates to a power supply system

  used to electrically power the active sections of the submerged digital flutes. The power supply in connection with the seismic flats became interesting in the first place

  in the context of the introduction of digital flutes.

  This is in keeping with the fact that a large part of the electrical circuits, which were previously planned on the prospecting vessel, are now mounted in electron-active modules arranged along the flume. The distance between the electronic modules can be from 50 to 100 m, and the total length of the fl Mte can reach several kilometers The energy required to power the electronic modules can be from 500 to 1000 W. The power supply system presents difficulties in this respect. It is concerned with its practical implementation, and the difficulties are generally associated with the following conditions: (1) Weight and space problems (copper / isolation)

  because of the electrical dimensions (10-20 m 2 Cu).

  The fl ight must be neutral with respect to buoyancy in the water. 2) Electrical losses due to long distances and conditions on the reduced copper section. 3) Corrosion phenomena in the connectors, the flute being constituted by interconnected equal sections (typically 50 to 100 m). 4) Disturbances of the magnetic compasses mounted along the edge to determine its exact position. Magnetic fields from the power supply conductors, in particular some of the stationary continuous fields, being

cry, ticks.

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  ) Electrical interference between power supply conductors and sensitive (magnetic / capacitive) hydrophone conductors, if the power supply is based on AC voltages. The above-mentioned problems can be remedied by various possible solutions: 1) Weight problems are reduced by using high voltages and by returning the current to the hull of the ship by the sea (return by the water of

  sea), or by means of a conventional three-phase system.

  High voltages are, in general, undesirable for safety reasons, and they involve dimensional problems with respect to the insulation in the connectors. The return of the current by the sea is excluded, for reasons of safety, and it can not, moreover, be used in fresh water A three-phase system seems very favorable, especially given the redundancy (removal of one of the power supply conductors), but this system requires AC, this which involves significant problems

of transmodulation.

  2) Electrical losses are reduced by increasing copper cross-section and using DC or DC voltages Increased copper cross-section implies weight problems, and DC voltages would disturb, in the context

  feeding conditions in question, the reading of the compasses.

  3) Corrosion problems are reduced by using AC voltages, which, on the other hand, involves interference interference problems.

with the inputs of the hydrophones.

  4) Disturbances of magnetic compasses due to

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  the power supply are eliminated by means of an alternating voltage of a few tens

  hertz or more Interfering problems will occur with respect to hydro inputs.

  ) Interference problems of hydrophone inputs are eliminated by using a continuous power supply which, in turn, produces significant problems

for reading the compass.

  As can be seen from the foregoing, it is necessary to satisfy important and contradictory conditions for the design of electrical power installations for digital seismic feeder. Even in connection with the conventional technique in which all active electronic assemblies are on board, there is a problem with the fact that the sector frequency has an influence on the ismic signals (current approximately 200 Hz). At present, this problem is solved in a certain way by means of filters. efficient narrow bandwidths which suppress some of the seismic signals and which also produce amplitude and phase variations in the final part of the frequency band (+ / 2-5 Hz)

  away from the center frequency.

  For digital flutes, DC voltages have been used preferably up to now, and an indefinite degradation of the cowiras readings has been achieved.

  This is very unfavorable, and at the present time the processing of seismic data is improving more and more, and increasingly stringent conditions are being imposed for detecting the position of a flute.

(three-dimensional control 1.

  DE-A-3,228,526 discloses a power supply device for electrically powering receivers of two electronic sonics for acoustic waves, the receivers being arranged at equal intervals along a hydrophone cable of Very long length To avoid problems of the DC voltage, for example voltage drop, electrolytic effects, etc., it is suggested, according to this patent application, a power supply device that can power the electronic device located at an This is achieved by connecting to each apparatus 10 an intensity regulator comprising three intensity transformers. However, the publication does not say anything about how one avoids the frequency of electrical power supply has an adverse influence on the measurement signals that are collected, not to mention how to adjust the frequency power supply in relation to the sampling frequency

  used for the acquisition of seismic data.

  The present invention provides a principle for completely or partially eliminating the aforementioned problems, and is achieved in a system of the type mentioned in the preamble which, according to the invention, is characterized in that the frequency of power supply is exactly equal to the sampling frequency used to collect the seismic data

  or equal to an exact multiple of this sampling frequency.

  The invention will now be described in greater detail with reference to the accompanying drawing given solely by way of non-limiting example, of which: FIG. 1 illustrates the folding effect of the spectrum of the sampled signal; Fig. 2a illustrates a sinusoidal power supply frequency; FIG. 2b illustrates a first example of the effects of a sampling frequency according to the invention; FIG. 2c illustrates a second example of the effect of a sampling frequency according to the invention; Figure 2d illustrates sample pulses corresponding to the example of Figure 2b; FIG. 2 e schematically represents a switching circuit for a sampling circuit; FIG. 3 is a block diagram of a mode

  of the present invention.

  FIG. 1 illustrates how the problem of aliasing (usually called "aliasing") occurs in the case of signal sampling. If a periodic or sinusoidal function of equal frequency & fp , is sampled with a frequency fs, new frequency components (fs + fp) and (fs fp) appear around the sampling frequency fs in the sampled output signal. It is particularly important to note that the frequency signal fs fp will be in the seismic gaumme in question, if the frequency

  power supply fp and sampling frequency fs have approximately the same value.

  By using anti-aliasing filters, this refolding should not occur, normally. However, it is not possible to rely on this condition because the anti-aliasing filters are not necessarily good enough. In addition, it is sometimes preferred to sample the seismic signal without using anti-aliasing filters, thereby eliminating the distortion and amplitude and phase variation that these filters produce. conditions

  it is assumed that the seismic signal does not contain in itself significant frequency components above the Nyquist frequency (fs / 2).

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  FIGS. 2a to 2e illustrate the effect of sampling a periodic function (for example, the frequency of the quartz coming from the power supply conductor, f) with a period equal to (1 / fs = 1 / fp) and double (l / fs = 2 / fp) of the function. As can be seen from FIGS. 2a to 2e, the aliasing of the spectrum of the power supply frequency is eliminated by synchronizing it and giving it a value which is an integer multiple of the sampling frequency. digital flutes with selectable sampling frequencies of 1, 2 and 4 m / s (1 kHz, 500 Hz and 250 Hz), the ideal power frequency will be exactly equal

at 1 k Hz.

  As shown in FIG. 2a, which reproduces a periodic function, preferably a sinusoidal function, of a power supply frequency fp (t), sampling is carried out at each of the points pn-1, pn, pn + 1, etc., the sampling taking place at time intervals corresponding exactly to one wavelength It must be clear that the sampling can also take place at time intervals corresponding exactly to a multiple of the wavelength λ, for example 2 λ, i.e. at the points pn-1, pn + 1, pn + 3, etc. An attempt has been made to illustrate the result of this sampling in FIGS. 2b and 2c, this sampling producing a pure DC component which does not involve degradation of the seismic signals received. In FIGS. 2b and 2c, the continuous signal obtained is denoted by f (t), and the result comprising a continuous signal is the same for sampling at λ and 2 Å, respectively, which is apparent from said figures. Figure 2 d illustrates an example of a sequence

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  It is possible to use a co-routing signal which can be used, the signal of the signal SS having the form of short pulses TS Pn-1, Pn, etc., which influence a switch SW represented on FIG. 2 e itself included in an assembly. for sampling circuit. In FIG. 3, the reference numeral 1 denotes a three-phase alternating-current jenerator, which supplies, via a power supply unit (PS) 2, an alternating voltage to a cable of hyi O of: ophone 3 which may have a length of, for example,

3,000 to 6,000 m.

  In addition, the reference 4 designates a timer (MC) which, on the one hand, is connected to the hydrophone cable 3 to comrander the flow of data transmitted by the vessel towing the cable, and which is received by the various modules of the In addition, signals from the clock 4 co mlandent the frequency or the rate of acquisition of the seismic data. On the other hand, the ryctieur 4 is connected to a unit; The divisional frequency which performs an entire division of the clock frequency, and this divided frequency is sent to a phase comparator (PPL) 6 which not only receives the sampling frequency, but also detects the frequency fp supplied by the receiver. 2 of the phase comparator 6 a signal is transmitted to a frequency control oscillator (VCO) 7, which itself adjusts the frequency of the supply voltage from the unit

power supply 2.

  I 1 must be clear that the adjustment of the supply frequency fp can also be achieved by a separate oscillator, for example up quartz oscillator of the same type as that used by the timer 4, the two oscillators then operating in parallel. Ule and imposing, because of their accuracy, the same value at the sampling frequency and the power supply frequency, respectively, so that the latter is exactly equal to the sampling frequency or to an exact multiple of said sampling frequency.

Claims (3)

  1 power supply system (2) to be used for electrically powering active sections of submerged digital streamers (1), characterized in that the power supply frequency (fp) is exactly equal to the sampling frequency (fs) ) used to collect seismic data or exactly equal to a multiple of that sampling frequency. System according to Claim 1, characterized in that the power supply frequency (fp)   is set by a timer (4, MC) which also sets the seismic data acquisition frequency (fs).   3. System according to claim 1, characterized in that the power supply frequency (fp) is regulated by a separate crystal oscillator of the same type as the crystal oscillator of the timer which regulates   the frequency of acquisition of the seismic data.