NO347214B1

NO347214B1 - Electric power supply assembly

Info

Publication number: NO347214B1
Application number: NO20200584A
Authority: NO
Inventors: Ole Johan Bjerknes; Ole A Heggdal; Jan Ole Dunserud; Leif Arne Müller
Original assignee: Aker Solutions As
Priority date: 2020-05-18
Filing date: 2020-05-18
Publication date: 2023-07-10
Also published as: NO20200584A1

Description

Electric power supply assembly

Technical Field

The present invention relates to electric power supply to remote locations. In particular, the invention regards power supply of multiple multiphase power transmissions through one single cable or umbilical.

Background Art

There are known power cables and power umbilicals that are arranged for transmitting two sets of three-phase electric power. Typically, three conductors are then arranged centrally in the cable, and additional three conductors are distributed outside of the inner cables.

When transferring electric power over large distances, problems may occur due to crosstalk. Crosstalk occurs when a power-transmitting main cable is arranged alongside an adjacent cable or other metallic elongated structure. Some power will then be transferred to the adjacent cable. This may cause problems in various ways. For instance, it may increase corrosion on the adjacent cable, and it may be difficult to control the power supplied to a load connected to the adjacent cable. It may even affect the power supplied to the load that receives power from the main cable.

To avoid or reduce such problems, it is known to rotate the first and second sets of conductors with respect to each other in helical patterns. By doing so, crosstalk will still occur, but the crosstalk from each phase of a three-phase system will cancel each other out.

While being an effective solution to reduce crosstalk, the rotation results in larger power umbilicals due to the diameter needed to obtain the mutual rotation of the 3-phase conductor sets. Furthermore, this solution results in complex umbilical production that requires large, complex and heavy production facilities.

Hence, an object of the present invention may be to provide a way to avoid the need of mutual rotation of the power conductors for long power umbilicals or power cables.

Summary of invention

According to the present invention, there is provided an electric power supply assembly configured to transfer power between a respective first three-phase power supply and a second three-phase power supply at a first location, and a respective first electric consumer and a second electric consumer at a second location. At the first location, the assembly comprises a first location transformer. At the second location, the assembly comprises a second location transformer. The assembly further comprises a power umbilical extending between the first and second locations. The power umbilical comprises three primary lines and three pairs of secondary lines. The two respective secondary lines of each pair of secondary lines are connected to one respective transformer winding of the first location transformer and one respective transformer winding of the second location transformer. The assembly further has at the first location, a further first location transformer connected to the three primary lines of the umbilical. It further comprises at the second location, a further second location transformer connected to the three primary lines of the umbilical.

Since the two lines of each pair of secondary lines are connected to one common winding of the first location transformer, and one common winding of the second location transformer, they will carry the same current in opposite directions. The field induced by two oppositely directed currents can substantially cancel each other out. This can be exploited to avoid crosstalk in long power umbilicals and power cables.

With the term power umbilical is herein also meant power cable. Hence, the power umbilical may comprise primary lines and secondary lines, while further comprising additional components such as control cables, monitoring cables, or fluid pipes. Moreover, the power umbilical may be in the form of a power cable, where it comprises only the primary and secondary lines configured for transferring electric power, and naturally additional components that are necessary for a power cable, such as filler materials, possible strength materials, sheath etc.

In some embodiments, the primary lines of the power umbilical can connect between a first location transformer and a second location transformer. Such transformers will typically be a step-up transformer and a step-down transformer, respectively.

In advantageous embodiments, the power umbilical can be more than 5 km, or even more than 10 km, or 40 km long.

In some embodiments, each of the two secondary lines of the respective pairs of secondary lines have the same radial distance from one of the respective three primary lines.

Advantageously, the mutual cross-sectional position of the primary lines and the secondary lines can be constant along the longitudinal direction of the umbilical.

This means that the primary and secondary lines are not designed with a helical configuration. As a result, it is possible to obtain a more compact design (reduced diameter) compared to traditional helically designed power cables or power umbilicals.

In some embodiments the two lines of each pair of secondary lines are arranged in a respective coaxial cable. An advantage of arranging the two lines in a coaxial cable, is that since they share the same center, the overall field induced by their respective currents will be substantially zero.

In some embodiments, the primary lines and the secondary lines, respectively, are configured to transfer electric power of at least 1 MW.

Detailed description of the invention

While the present invention and some alternative embodiments thereof have been discussed in general terms above, a more detailed and non-limiting example of embodiment will be presented in the following with reference to the drawings, in which

Fig. 1 is an example of a prior art assembly, wherein two three-phase power supplies are powering two three-phase electric loads at a remote location, through a power umbilical;

Fig. 2 is a cross-section view through the umbilical shown in Fig.1;

Fig. 3a is a diagram showing electric power transfer between a three-phase power supply and a three-phase power consumer, via a step-up and a step-down transformer;

Fig. 3b is a diagram corresponding to the diagram shown in Fig.3a, however with somewhat different transformer windings;

Fig. 4 is a diagram illustrating an electric power supply system according to the invention;

Fig. 5 is a phase diagram showing the electric angles between six secondary lines;

Fig. 6 is a phase diagram showing the electric angles between three primary lines;

Fig. 7 is a cross section view through a power umbilical used in an assembly according to the invention;

Fig. 8 is a diagram illustrating an embodiment of the invention;

Fig. 9 is a cross section through an alternative power umbilical; and

Fig. 10 is a cross section through another power umbilical.

Fig. 1 and Fig.2 illustrate a typical setup according to the prior art, where an operator provides electric power to two remote electric motors from a first location, hereinafter referred to as a near location 10. At a second location, hereinafter referred to as a remote location 20, there are arranged a first electric consumer 21a and a second electric consumer 21b. The electric consumers can typically be electric motors. The electric consumers 21a, 21b connect to a respective first remote transformer 122a and a second remote transformer 122b. The remote transformers 122a, 122b will typically be step-down transformers.

At the near location 10, there are arranged a first power supply 1a and a second power supply 1b. The first and second power supplies 1a, 1b are configured to power the respective first and second electric consumers 21a, 21b. Typically, the power supplies 1a, 1b can be three-phase power supplies, as shown, configured to run the remote motors. Such power supplies can for instance comprise a variable speed drive (VSD).

The first power supply 1a and the second power supply 1b are each connected to a respective first near transformer 102a and a second near transformer 102b, which typically can be step-up transformers.

Extending between the near location 10 and the remote location 20 there is a power umbilical 103. A cross-section view through the prior art power umbilical 103 is shown in Fig.2.

In the prior art embodiment shown in Fig.1 and Fig.2, the power supplies 1a, 1b are three-phase power supplies and the electric consumers 21a, 21b are electric motors run with three phase electric power. Thus, the power umbilical 3 comprises a first set of three lines (conductors) LA1, LA2, LA3 and a second set of three lines LB1, LB2, LB3. The distribution of the first and second set of three lines in the power umbilical 3 is shown in Fig.2. The power umbilical 103 has a central portion confining the three lines LA1, LA2, LA3 of the first set. The lines LB1, LB2, LB3 of the second set are distributed radially outside the central portion.

As discussed above, when a power umbilical extends over a significant length, such as several kilometers, crosstalk may become a problem. To avoid crosstalk between the lines of the first set and the lines of the second set, the lines LB1, LB2, LB3 of the second set are rotated with respect to the lines LA1, LA2, LA3 of the first set. Thus, the outer set, i.e. the set having lines LB1, LB2, LB3 of the second set, exhibit a helical pattern about the central portion.

To accomplish this rotation or helical layout, the lines LB1, LB2, LB3 of the second set need to be outside a circle that encircles the lines LA1, LA2, LA3 of the first set in the central portion of the power umbilical 103. Such a circle is indicated with the dashed line in Fig.2.

Also shown in the cross-section view of Fig.2 are a sheath 31 and filler material 32.

As a preparation for the later discussion of the present invention, reference is now made to Fig.3a and Fig.3b. These figures show a schematic illustration of the second near transformer 2b and the second remote transformer 22b, including their windings. As appears from the drawings, the three phases from the 3-phase second power supply 1b connect to three primary windings of near second near transformer 2b.

Out from the second near transformer 2b extend six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b that connect to three pairs of output windings 2b1, 2b2, 2b3. Thus, the three phases of the second power supply 1b are distributed on three pairs of conductors, constituted by the six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b.

The six secondary lines are formed of three pairs of lines that will carry oppositely directed currents, namely a first pair with secondary lines LB1a, LB1b, a second pair with secondary lines LB2a, LB2b, and a third pair with secondary lines LB3a, LB3b. This applies to the setup shown both in Fig.3a and in Fig.3b.

The second remote transformer 22b comprises input windings 22b1, 22b2, 22b3, to which the pairs of secondary lines connect.

In the embodiment shown in Fig.3b, the output windings 2b1, 2b2, 2b3 of the second near transformer are split in two parts, wherein their middle sections are earthed. Correspondingly, the input windings 22b1, 22b2, 22b3 of the second remote transformer 22b are also split in two, with their middle sections earthed.

Summarized, each phase from the three-phase second power supply 1b is transformed into three pairs of oppositely directed phases, exiting the second near transformer 2b.

Fig. 4 is similar to the schematic illustration of prior art shown in Fig.1.

However, Fig.4 depicts an embodiment according to the present invention. As shown in Fig.4, at the near location 10, the six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b extend out from the second near transformer 2b and into the power umbilical 3. At the remote location 20, the six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b exit the power umbilical and enter the second remote transformer 22b. Furthermore, three primary lines LA1, LA2, LA3 of the first set extend through the power umbilical 3 and connect to the first near transformer 2a and the first remote transformer 22a. This corresponds to the setups shown in Fig.3a and Fig.3b.

The power from the second power supply 1b is thus distributed on the six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b, which extend through the power umbilical 3. The power from the first power supply 1a is distributed on the three primary lines LA1, LA2, LA3.

Fig. 5 is a phase diagram showing the electric angles between each of the six phases.

Fig. 6 illustrates the phase angles between the three phases from the first power supply 1a.

Fig. 7 is a cross-section view through the power umbilical 3 used in an embodiment according to the invention, such as the power umbilical 3 shown in Fig. 4. The three primary lines LA1, LA2, LA3 of the first set are centrally arranged. The six secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b are distributed further out from the center. Moreover, the two secondary lines of each pair of secondary lines are arranged in proximity to one of the respective primary lines LA1, LA2, LA3.

As will be clear from this cross-section view, the crosstalk from e.g. LA1 to LB2a will be insignificant compared to the crosstalk from LA1 to LB1b. Furthermore, crosstalk from LA1 to LB1a will be substantially equal to crosstalk from LA1 to LB1b.

Moreover, crosstalk from LB1a to LA1 will be substantially equal but opposite to crosstalk from LB1b to LA1. This is because LB1a and LB1b have the same distance from LA1 and carries the same current with opposite directions.

Regarding crosstalk from the secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b to the primary lines LA1, LA2, LA3, the following relationships can be established:

Crosstalk from LB1a and LB1b to LA1 ≈ 0

Crosstalk from LB2a and LB2b to LA3 ≈ 0

Crosstalk from LB3b and LB3a to LA2 ≈ 0

Regarding crosstalk from the primary lines LA1, LA2, LA3 of the first set to the secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b of the second set, the following relationships can be established:

Crosstalk from LA1 to LB1a ≈ crosstalk from LA1 to LB1b

Crosstalk from LA2 to LB2a ≈ crosstalk from LA2 to LB2b

Crosstalk from LA3 to LB3a ≈ crosstalk from LA3 to LB3b

Thus, crosstalk from the secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b to the primary lines LA1, LA2, LA3 will substantially cancel each other out. This is because the respective two lines of each pair of secondary lines carries the same amount of current in opposite directions and are arranged close to the respective first lines.

There will, however, be crosstalk from the respective first lines to the pairs of secondary lines, such as from LA1 to LB1a and from LA1 to LB1b. These two elements of crosstalk will have the same magnitude, as indicated above. These currents, resulting from crosstalk, will be cancelled out in the second remote transformer 22b.

As a result, the lines in the power umbilical 3 don’t need the helical layout to avoid problematic crosstalk.

Fig. 8 illustrates an embodiment of the invention and shows how power from the first and second power supplies 1a, 1b at the near location is transferred to the first and second electric power consumers 21a, 21b at the remote location 10.

Fig. 9 and Fig.10 depict two further embodiments of an umbilical 3 or power cable.

The embodiment shown in Fig.9 corresponds in many respects to the embodiment shown in Fig.7. However, the three pairs of secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b are arranged in another fashion. As indicated with the dashed circle in Fig.9, the layout shown in Fig.9 enables a smaller averall diameter of the umbilical or cable 3.

In the embodiment shown in Fig.10, the respective three pairs of secondary lines LB1a, LB1b, LB2a, LB2b, LB3a, LB3b are arranged in three coaxial cables 33. Each coaxial line 33 carries two secondary lines of the same phase.

Consequently, since each secondary line in the respective coaxial cable 33 carries current in the opposite direction, the overall crosstalk generated from each coaxial cable 33 is zero or substantially zero.

Claims

Amended claims

1. An electric power supply assembly configured to transfer power between a respective first three-phase power supply (1a) and a second three-phase power supply (1b) at a first location (10), and a respective first electric consumer (21a) and a second electric consumer (21b) at a second location (20), comprising at the first location

- a first location transformer (2b);

and comprising at the second location (20)

- a second location transformer (22b);

and further comprising a power umbilical (3) extending between the first and second locations (10, 20), wherein the power umbilical comprises

- three primary lines (LA1, LA2, LA3);

- three pairs of secondary lines (LB1a, LB1b, LB2a, LB2b, LB3a, LB3b);

wherein the two respective secondary lines of each pair of secondary lines are connected to one respective transformer winding (2b1, 2b2, 2b3) of the first location transformer (2b) and one respective transformer winding (22b1, 22b2, 22b3) of the second location transformer (22b),

the electric power supply assembly further comprising, at the first location (10), a further first location transformer (2a) connected to the three primary lines (LA1, LA2, LA3) of the umbilical (3),

and further comprising, at the second location (20), a further second location transformer (22a) connected to the three primary lines (LA1, LA2, LA3) of the umbilical (3).

2. An electric power supply assembly according to claim 1, wherein the power umbilical (3) is more than 5 km, or even more than 10 km long.

3. An electric power supply assembly according to claim 1 or claim 2, wherein each of the two secondary lines of the respective pairs of secondary lines (LB1a, LB1b, LB2a, LB2b, LB3a, LB3b) have the same radial distance from one of the respective three primary lines (LA1, LA2, LA3).

4. An electric power supply assembly according to one of the preceding claims, wherein the mutual cross-sectional position of the primary lines (LA1, LA2, LA3) and the secondary lines (LB1a, LB1b, LB2a, LB2b, LB3a, LB3b) is constant along the longitudinal direction of the umbilical (3).

5. An electric power supply assembly according to one of the preceding claims, wherein the two lines of each pair of secondary lines (LB1a, LB1b, LB2a, LB2b, LB3a, LB3b) are arranged in a respective coaxial cable (33).

6. An electric power supply assembly according to one of the preceding claims, wherein the primary lines and the secondary lines, respectively, are configured to transfer electric power of at least 1 MW.