CN113228438B

CN113228438B - Insulation bushing for subsea equipment applications

Info

Publication number: CN113228438B
Application number: CN201980072914.XA
Authority: CN
Inventors: 伊恩·沃特森
Original assignee: Huawei Marine Networks Co Ltd
Current assignee: HMN Technologies Co Ltd
Priority date: 2019-01-30
Filing date: 2019-01-30
Publication date: 2023-04-14
Anticipated expiration: 2039-01-30
Also published as: EP3834262A1; JP7230212B2; CN113228438A; WO2020156654A1; JP2022515252A

Abstract

A sleeve for providing a barrier between an internal electronics unit of a subsea installation and 5a subsea installation's outer housing, wherein the sleeve is comprised of a composite material comprising an elastomeric matrix material and a particulate filler material.

Description

Insulation bushing for subsea equipment applications

Technical Field

The present invention relates to an insulating bushing for subsea equipment, such as a subsea telecommunications amplifier, switch, multiplexer or demultiplexer.

Background

The trend towards higher capacity submarine cable systems increases the electrical power dissipation in subsea equipment, which in turn requires optimizing the heat transfer efficiency of all the components of the equipment in order to minimize the operating temperature of critical components.

It is desirable to minimize and determine the maximum long term operating temperature of critical components in equipment such as subsea repeaters, particularly components such as pump lasers, to ensure the high reliability required of subsea equipment. For internal electronic units, the temperature increase above the subsea environmental level is proportional to the dissipated electrical power.

A particularly interesting thermal flow path is the thermal flow path between the outer housing of the repeater, which is at local ground potential, and the repeater internal unit, which can operate at a different voltage of several kilovolts than the outer housing.

Current solutions use an electrically insulating sleeve between the outer housing of the repeater and the internal electronics module of the repeater. Such sleeves are typically provided as an extruded cylindrical shell of Low Density Polyethylene (LDPE). LDPE has a dielectric strength of about 20KV/mm and a thermal conductivity in the range of 0.30 to 0.33W/mK. Alternatively, high Density Polyethylene (HDPE) may be used, which provides marginal improvement, having a dielectric strength of about 70KV/mm and a thermal conductivity in the range of 0.40 to 0.45W/mK. Thus, while such a shell has good electrical insulating properties, its thermal conductivity is low, resulting in significant thermal gradients within the repeater structure.

The manufacture of the sleeve is difficult and dimensional control is critical to assembly and performance efficiency. The current method of manufacturing PE insulating sleeves is to extrude the material into a tube. This process requires the polymer to be heated until molten, then extruded through a die under vacuum to form a tube, which is then pulled through a series of water-cooled slots to produce a continuous cylinder. As the size of high capacity repeaters increases to accommodate more electronics, forming thin-walled structures of larger diameters becomes more difficult to achieve.

Furthermore, the contact area between the inner electronic module and the insulating sleeve and between the insulating sleeve and the outer pressure housing is limited due to the rigidity of the polymer material. Current PE bushings are manufactured to ensure an interference fit between it and the outer pressure sleeve once inserted into the repeater housing. The electronic module is then dynamically expanded to clamp against the inner diameter of the insulative sleeve to form a tight contact for heat transfer. Despite the radial clamping force exerted by the electronic module, the contact area percentage is determined by the dimensional accuracy of the mating parts and the compliance of the insulating sleeve material itself, and the contact efficiency does not exceed 50% at the maximum.

Because of the limitations in the thermal conductivity of the liner material, it is typically operated at 0.65A line current and 12KV Direct Current (DC) system voltage, with each amplifier producing 35W of power, in view of the conventional low electrical power output of devices such as repeaters. However, today's new higher capacity requirements place higher demands on the thermal performance of subsea equipment.

The current trend for high functionality/high fiber count systems drives the need for high power repeaters that typically operate at line currents of 0.65 to 1.5A and voltages up to 20KV DC, where each repeater produces 80W or more of power. The temperature rise within these new repeater designs needs to be reduced as much as possible to ensure performance and reliability of critical components over the life of the system.

To achieve the necessary reduction in critical component temperatures in higher capacity systems, thermal conductivities in excess of 1.5W/mK are required. This is not possible with the insulating materials currently used, such as LDPE.

It is known that higher thermal conductivity can be achieved by adding ceramic fillers such as boron nitride. Such fillers can be difficult to distribute within the polymeric matrix and can have a detrimental effect on the manufacturing process of the component. Adding fillers to insulating polymers such as polyvinyl compounds can increase manufacturing difficulties. Due to the extrusion process, the dispersion and distribution of the filler is random, and therefore the thermal and electrical properties of the material vary throughout the barrel structure.

Fillers significantly change the extrusion process parameters of the polymer due to changes in viscosity and specific heat. This can lead to poor dimensional stability of the tube, poor surface finish, excessive stress in the material and premature cooling in the mold, leading to plugging and sticking. Fillers can also be abrasive, causing excessive die and tool wear.

The use of a high percentage of filler material also reduces the flexibility of the substrate, making the sleeve too brittle to use and susceptible to damage.

It is desirable to develop a sleeve for subsea telecommunications repeater electronics that has improved heat transfer efficiency while maintaining high voltage insulation.

Disclosure of Invention

According to a first aspect, there is provided a sleeve for providing a barrier between an internal electronics unit of a subsea installation and an outer casing of the subsea installation, wherein the sleeve comprises or consists of a composite material comprising an elastomeric matrix material and a particulate filler material.

The ratio of the particulate filler material to the elastomeric matrix material may be selected such that: the thermal conductivity of the composite material is at least 1W/mK, and the dielectric strength of the composite material is at least 80KV/mm. The resulting sleeve can provide dual functions of both acting as a high voltage DC electrical insulator and reducing thermal gradients between the internal electronics and the external repeater housing over a 25 year service life.

The elastomer matrix material may be a silicon elastomer and the particulate filler material may be boron nitride. Combinations of such materials have been shown to produce composite materials with good properties for such applications. The use of such materials reduces the steady state operating temperature of critical components within the repeater for a given power dissipation, while allowing operation at increased higher system voltages with improved HV aging/lifetime characteristics and reliability.

The amount of particulate filler material may be less than or equal to 45% (%) of the weight of the composite material. Ratios of such components have been shown to produce particularly good performance.

The sleeve may be manufactured using compression molding. The use of compression molding to produce the sleeve may result in improved distribution of the filler material in the composite material.

The subsea equipment may be or comprise a subsea telecommunications amplifier, switch, multiplexer or demultiplexer. Thus, the sleeve may be compatible for use with a variety of wet equipment. Such as undersea repeaters, branching units, and reconfigurable optical add-drop multiplexers (ROADMs).

The subsea equipment may be configured to receive at least 0.5KV of system voltage. Thus, over a 25 year service life, the sleeve may provide a barrier to components that are operating at high pressure.

The thermal conductivity of the composite material may be at least 1.5W/mK.

The dielectric strength of the composite material may be at least 90KV/mm.

The sleeve may be in the form of a circumferentially continuous hollow tube. This is a convenient arrangement for the protection of the internal electronics unit of the subsea equipment.

According to a second aspect, there is provided a method of manufacturing a sleeve for a subsea installation, the sleeve comprising or consisting of a composite material, the composite material comprising an elastomeric matrix material and a particulate filler material, the method comprising: placing a preform of the composite material into a mold cavity; and applying pressure to the preform to plastically deform the preform to form the sleeve.

This method allows for an improved distribution of the filler material in the composite material compared to extruding the material. The elastomeric material behaves more uniformly since the material is neither extruded into a tube nor injected into the mold cavity. This results in less residual stress in the material and more dimensionally stable products.

The step of placing the preform of material into the mold cavity may comprise: placing a preform of the composite material into a lower portion of a mold cavity; winding the preform on a core; and applying the upper half of the mould cavity onto the wound core. This may allow the production of a hollow and continuous sleeve member.

The method may further comprise: after the step of applying pressure to the preform to plastically deform the preform to form the sleeve, removing the formed sleeve from the mold cavity; and curing the plastically deformed material. This can stabilize the molding.

The method may further comprise: heat is applied while applying pressure to plastically deform the preform to form the sleeve. This may allow for more efficient deformation of the preform.

The sleeve formed may be in the form of a circumferentially continuous hollow tube. This is a convenient arrangement for protection of the internal electronics unit of the subsea equipment.

The elastomer matrix material may be a silicon elastomer and the particulate filler material may be boron nitride. Combinations of such materials have been shown to produce composites with good properties for such applications.

Drawings

The invention will now be described by way of example with reference to the accompanying drawings. In the drawings:

fig. 1 (a) shows an example of a subsea repeater. Fig. 1 (b) shows an expanded view of the central region of the repeater with an insulating sleeve between the inner electronics module and the outer housing of the repeater.

Fig. 2 shows a logarithmic graph of the breakdown time and the breakdown voltage of an example of the 45-bn-filled silicon elastomer composite.

Fig. 3 (a) - (f) illustrate an example of a manufacturing method for forming a sleeve.

Fig. 4 (a) - (d) show schematic representations of combinations of good and poor dispersion and distribution of filler particles in a matrix material.

Fig. 5 shows an example of a method for forming a sleeve.

Detailed Description

Fig. 1 (a) shows a subsea repeater 1. Fig. 1 (b) shows an enlarged view of the central portion of the repeater 1. The outer pressure housing of the repeater is shown at 2, which is at sea-earth potential. Inside the housing is an internal electronic module, indicated with 3. The electronic module 3 operates at a high voltage of up to about 20kV DC. The sleeve 4 provides a barrier between the internal electronics unit 4 of the repeater 1 and the outer housing 2. The sleeve 4 is composed of a composite material comprising an elastomeric matrix material and a particulate filler material. The sleeve is preferably circumferentially and/or axially continuous.

In this example, the elastomer matrix material is a silicon elastomer and the particulate filler material is boron nitride. However, other elastomers and filler materials may be used. For example, the filler material may be a particulate ceramic or refractory material. The filler material is dispersed in the elastomer matrix. The base material forms the body of the sleeve element. The matrix material may be interconnected substantially continuously throughout the sleeve element. The matrix material may comprise more than 50%, more than 70% or more than 80% of the volume of the sleeve element.

The ratio of particulate filler material to elastomeric matrix material is preferably selected such that: the thermal conductivity of the composite material is at least 1W/mK and the dielectric strength of the composite material is at least 80KV/mm.

In a preferred example, the amount of boron nitride filler is equal to 45% by weight of the composite material. Using this material ratio, empirical testing has shown that the dielectric strength of the composite increases from 20kV DC/mm for LDPE to about 100kV DC/mm for 45-percent BN-filled elastomers when uniformly dispersed and distributed within the elastomer. Furthermore, the thermal conductivity increases from 0.3W/mK for LDPE to greater than 1.6W/mK and can be achieved without compromising the high voltage insulation performance of the material. Thus, filled elastomers have been shown to provide electrical insulation properties similar to polyethylene, while providing much higher thermal conductivity.

Other ratios of filler material to elastomer matrix material of less than 45% may also be used, and also show: the dielectric strength and thermal conductivity are improved compared to using LDPE as the sleeve material.

The composite material is applied as a one-piece, thin-walled sleeve over the entire electronic component to provide a dual function of operating as a high voltage DC electrical insulator exposed to a constant electric field while providing reduced thermal gradients between the internal electronic components.

The long-term release of hydrogen or any other degradation product from the composite was also quantified by accelerated testing to confirm that there was no adverse effect on any aspect of reliability during the life of the system.

An important requirement for such subsea equipment is that the voltage is applied under steady state conditions so that the service life of the equipment should reach 25 years. When considering high pressure aging of elastomers, a key factor is determining the "N" value of the material.

The empirical formula for predicting the time to failure T at DC voltage V is:

T.V ^N ＝C (1)

where C is a constant for a given material.

If the voltage varies over time, the equation is:

∫V ^N .dt＝C (2)

for stabilizing the linear ramp to the breakdown voltage V _B Lower failure and ramp to failure time T _B The above integral gives:

(V _B ^N .T _B )/(N+1)＝C (3)

taking logarithm:

N.LOG(V _B )+LOG(T _B )＝LOG(C.(N+1)) (4)

therefore, LOG (T) at different slopes _B ) For LOG (V) _B ) The graph of (a) will have a negative slope with a gradient of N.

An example of 45-percent bn-filled silicon elastomer is shown in fig. 2. Typically for LDPE materials, an "N" value of 4.75 is employed in the subsea equipment and cable industry to predict the life of the polymer molded article when exposed to any applied voltage. From empirical testing, fig. 4 shows that the "N" value for the filled elastomer is above 4.75 with a confidence of 99.7% and a predicted value of N =7.6.

A convenient method of forming the sleeve is by compression moulding. Fig. 3 shows an example of such a manufacturing method for producing the sleeve described herein.

As shown in fig. 3 (a), an uncured elastomer to be rolled into an uncured sheet 30 is placed in a cavity 31. In fig. 3 (b), a cylindrical core 32 is placed on the sheet 30, which forms the inner diameter of the insulating sleeve. In fig. 3 (c), sheet 30 is wound around core 32 and crimped to form seam 33. In fig. 3 (d), the upper half of the mold cavity 34 is then applied over the assembled material. In fig. 3 (e), pressure P and optionally heat are then applied to the mold assembly 35 to plastically deform the material to form the tube to the correct dimensions. In fig. 3 (f), the mold sleeve 36 is removed from the tool after molding and then cured to stabilize the molding.

Fig. 4 (a) - (d) show the differences between materials with good and poor dispersion and/or good and poor distribution. By using compression moulding, good dispersion and good distribution of the boron nitride filler can be ensured, as shown in figure 4 (d), since this is achieved at the sheet rolling stage. Since the tool cavity is already filled by 90% before the pressure is applied and therefore the distance traveled by the material is small, the undesired turbulent interruption of the filler distribution during the sleeve molding process is limited.

Thus, the use of compression molding to produce the sleeve may improve the distribution and dispersion of the filler material in the composite material, which is necessary to ensure uniform thermal and electrical properties, as compared to extrusion of the composite material. The elastomeric material behaves more uniformly since the material is neither extruded to form a tube nor injected into the mold cavity. This results in less residual stress in the material and more dimensionally stable products. This manufacturing method provides scalability for future products. Furthermore, it has been found that the mode of dispersion of the particulate filler in the matrix remains substantially uniform after compression molding, whereas if the particulate filler is added to an injection molding material, it is difficult to ensure uniform dispersion of the filler.

Fig. 5 summarizes one example of a method of manufacturing the sleeve. In step 501, the method includes placing a preform of a composite material into a mold cavity. The method then proceeds to step 502, where pressure is applied to the preform to plastically deform the preform to form the sleeve.

The method provides the ability to manufacture a one-piece thin-walled compliant sleeve of high dimensional adaptability using a 45% Boron Nitride (BN) filled silicon elastomer capable of covering the entire electronics module within an underwater repeater. The resulting sleeve provides dual functions of both acting as a high voltage DC electrical insulator and reducing the thermal gradient between the internal electronics and the external repeater housing over a 25 year service life.

It has been found that replacing the extruded LDPE sleeve with 45% bn-filled silicon elastomer composite increases the thermal conductivity of the sleeve from 0.3W/mK of LDPE to >1.6W/mK, and it has been found that it can be achieved without adversely affecting the high voltage insulation properties of the material. It has been found that the dielectric strength of the sleeve increases from 20kV/mm DC to 100kV/mm, and the High Voltage (HV) life index ("N" value) increases from 4.75 for LDPE to 7.6 for the composite.

The use of such materials may reduce the steady state operating temperature of critical components within the repeater for a given power dissipation, while allowing operation at increased higher system voltages with improved HV aging/lifetime characteristics and reliability.

Another potential advantage is the increased contact area provided by the sleeve. The use of a silicone elastomer may provide a compliant interface between both the outer pressure sleeve and the inner electronic module, eliminating the risk of air gaps due to material stiffness or dimensional mismatch of mating components. The compression set of the material is limited over the operating and storage temperature range of the subsea equipment, ensuring that the electronic module remains in contact with the insulator over its lifetime. Such an elastomeric interface is more resistant to radial shrinkage of the outer pressure sleeve when the outer pressure sleeve is used in deep water applications up to 8000 m.

The compliant elastomer interface also provides additional shock and vibration isolation for the electronics that protect critical components during handling, deployment and recovery of subsea equipment.

Additional benefits include a reduction in hydrogen emissions caused by aging of the sleeve material. High temperature testing has shown that filled elastomers evolve 50% less hydrogen compared to similar volumes of polyethylene.

Simulation tests have shown that the above-described materials for the sleeve can provide significant advantages in at least some applications. For example, subsea communication enclosures are typically installed and then left in place for years, possibly while operating at relatively high voltages and continuously operating. Simulation tests have shown that the above materials can provide a barrier for components operating at relatively high voltages (e.g., greater than 400V) over a 25 year service life.

Thus, in summary, the sleeves described herein may provide in certain embodiments:

dual function of high voltage insulator and low thermal gradient interface for subsea applications

Dielectric strength increase from 20 to 100KV DC/mm

Increase of thermal conductivity from 0.3 to >1.6W/Mk

-improved ageing characteristics, "N" value higher than the industry acceptance level 4.75. For 45% BN-filled silicon elastomer, the N value is generally 7.6

Reduction of hydrogen evolution by aging of the material by 50%

Compliant interface increases thermal contact area efficiency

-providing additional shock and vibration isolation for the internal electronics of the subsea equipment

Improved high pressure performance

Simplified and flexible manufacturing process adaptable to future underwater equipment requirements

Although the sleeve has been described above for the example of a subsea repeater, the sleeve may also be applied to other subsea telecommunication devices, such as amplifiers, switches, multiplexers and demultiplexers. Such as branching units and reconfigurable optical add-drop multiplexers (ROADMs).

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A sleeve for providing a barrier between an internal electronics unit of a subsea installation and an outer casing of the subsea installation, wherein the sleeve comprises or consists of a composite material comprising an elastomeric matrix material and a particulate filler material; the elastomer base material is a silicon elastomer that forms a compliant interface between the outer housing and the internal electronics unit; the particulate filler material is boron nitride, the amount of particulate filler material being less than or equal to 45% by weight of the composite material;

the sleeve is manufactured using compression molding.

2. The sleeve of claim 1, wherein the ratio of the particulate filler material to the elastomeric matrix material is selected such that: the thermal conductivity of the composite material is at least 1W/mK, and the dielectric strength of the composite material is at least 80KV/mm.

3. The cartridge of claim 1, wherein the subsea equipment comprises a subsea telecommunications amplifier, switch, multiplexer, or demultiplexer.

4. The sleeve of claim 1, wherein the subsea equipment is configured to receive at least 0.5KV of system voltage.

5. The sleeve of claim 1, wherein the thermal conductivity of the composite material is at least 1.5W/mK.

6. The sleeve of claim 1, wherein the dielectric strength of the composite material is at least 90KV/mm.

7. The sleeve of claim 1, wherein the sleeve is in the form of a circumferentially continuous hollow tube.

8. A method of manufacturing a sleeve for subsea equipment, the sleeve comprising or consisting of a composite material, the composite material comprising an elastomer matrix material and a particulate filler material, the elastomer matrix material being a silicon elastomer, the silicon elastomer forming a compliant interface between an outer housing and an internal electronics unit; the particulate filler material is boron nitride, the amount of the particulate filler material being less than or equal to 45% by weight of the composite material; the sleeve is manufactured using compression molding; the method comprises the following steps:

placing the preform of composite material into a mold cavity; and is

Applying pressure to the preform to plastically deform the preform to form the sleeve.

9. The method of claim 8, wherein the step of placing the preform of material into the mold cavity comprises:

placing the preform of the composite material into a lower portion of a mold cavity;

winding the preform on a core; and is

The upper half of the mould cavity is applied on the wound core.

10. The method of claim 8, the method further comprising: after the step of applying pressure to the preform to plastically deform the preform to form the sleeve,

removing the formed sleeve from the mold cavity; and is provided with

The plastically deformed material is cured.

11. The method of claim 8, the method further comprising: applying heat while applying the pressure to plastically deform the preform to form the sleeve.

12. The method of claim 8, wherein the sleeve is in the form of a circumferentially continuous hollow tube.

13. The method of claim 8, wherein the elastomer matrix material is a silicon elastomer and the particulate filler material is boron nitride.