Submarine cable system and a switching method thereof

An submarine cable system includes a first and a second submarine cable circuit branches arranged in parallel between an onshore BSP and an offshore BSP, and a first and a second bus reactor circuits arranged in parallel and connected to the onshore BSP. The first and second submarine cable circuit branches each includes a first circuit breaker, a submarine cable circuit, and a second circuit breaker connected in series, a first line reactor of which one end is grounded and another end is connected between the submarine cable circuit and the first circuit breaker, and a second line reactor of which one end is grounded and another end is connected between the submarine cable circuit and the second circuit breaker. The first and second bus reactor circuits each includes a bus reactor and a circuit breaker connected in series. An example switching method for this system is also disclosed.

BACKGROUND

Installing long high voltage (HV) submarine cables generates a high negative reactive power which need to be absorbed by shunt reactors (positive reactive power) at both sides of the submarine cables. For example, installing two 230 kV submarine cables that are 90 km long will generate a negative reactive power of about 400 MVARs. Energizing the submarine cables with full rate MVARs compensation runs the risk of a Gas Insulated Switchgear (GIS) exceeding a Transient Recovery Voltage (TRV) rating or having missing zero phenomenon during switching thereof.

SUMMARY

In one aspect of this invention, an example submarine cable system comprises: a first submarine cable circuit branch and a second submarine cable circuit branch arranged in parallel between an onshore BSP and an offshore BSP, the first and second submarine cable circuit branches each including a first circuit breaker, a submarine cable circuit, and a second circuit breaker connected in series, a first line reactor of which one end is grounded and another end is connected between the submarine cable circuit and the first circuit breaker, and a second line reactor of which one end is grounded and another end is connected between the submarine cable circuit and the second circuit breaker; and a first bus reactor circuit and a second bus reactor circuit arranged in parallel and connected to the onshore BSP, each including a bus reactor and a third circuit breaker connected in series.

In another aspect of this invention, an example switching method for this example submarine cable system comprises: determining a submarine cable circuit branch to be energized; determining a bus reactor related to the submarine cable circuit branch to be energized; adjusting tap position of the determined bus reactor to reduce a load of the determined bus reactor; adjusting tap positions of the first and second line reactors in the submarine cable circuit branch to be energized to reduce a load of each of the first and second line reactors; energizing the submarine cable circuit in the submarine cable circuit branch to be energized; and immediately after energizing the submarine cable circuit, readjusting the tap positions of the first and second line and the determined bus reactor in the energized submarine cable circuit branch such that voltage levels within the energized submarine cable circuits are acceptable.

Other aspects of the disclosure will be apparent from the following description and the appended claims.

DETAILED DESCRIPTION

Embodiments disclosed herein provide a system and method for controlling shunt reactors to regulate the voltage on both sides of radial long submarine cables or Overhead Transmission Lines in all loading scenarios. Specifically, in one or more embodiments, a power management system (PMS) controller is added to a Power System Automation (PSA) system that takes input from the PSA internet and controls the tap changers of a plurality of shunt reactors to regulate the voltage or power factor on both sides of the submarine cables dynamically, i.e., constantly for all loading conditions of the system. Further, the PMS controller is redundant, with one controller installed on one side of the submarine cables taking the load, and another controller located on the other end of the submarine cables in hot standby mode.

Advantageously, embodiments disclose herein provide a system and method that makes safe energization to the highly compensated long HV submarine cables possible without jeopardizing the Gas Insulated Switchgear (GIS) integrity due to the missing zero phenomena in the AC current wave for the first two seconds of the submarine cable energization. The GIS includes the bus and breakers on one side of the submarine cable. More specifically, the onshore circuit breaker feeding the submarine cable is known as the GIS.

Installing long HV submarine cables such as two 90 km 230 kV submarine cables generates around negative 400 MVARs which need to be absorbed by shunt reactors (positive MVArs) at both sides of the submarine cables. Also, these submarine cables cannot be energized without these shunt reactors. However, the submarine cable with full tap position shunt reactors have low impedance during energization which causes high DC components, and hence results in missing the zero crossing for approximately two seconds, jeopardizing the 230 kV GIS if tripped during these two seconds after energization. This missing zero phenomena is shown inFIG.4. To address this issue, embodiments disclosed herein utilize the PMS to perform sequential switching by: fully reducing the shunt reactors compensation before energization to reduce the MVARs compensation to acceptable limit for the GIS, energizing the submarine cable, and adjusting the shunt reactors compensation at both sides of the submarine cable to the acceptable voltage limit.

FIG.1shows a schematic diagram illustrating a submarine cable system100. As shown inFIG.1, the system100includes a first submarine cable circuit branch101and a second submarine cable circuit branch102arranged in parallel between an onshore Bulk Supply Point (BSP)180and an offshore BSP190. The onshore BSP180may be a combination of equipment configured for receiving and distributing power from a power grid for energizing the submarine cable and the offshore BSP190may be a combination of equipment configured for receiving and distributing the powers from the submarine cable.

The first and second submarine cable circuit branches each include a first circuit breaker (CB)120, a submarine cable circuit110, and a second circuit breaker130connected in series, a first line reactor140and a second line reactor150. One end of the first line reactor140is grounded and the other end of the first line reactor140is connected between the submarine cable circuit110and the first circuit breaker120. One end of the second line reactor150is grounded and the other end of the second line reactor150is connected between the submarine cable circuit110and the second circuit breaker130.

The system100further includes a first bus reactor circuit103and a second bus reactor circuit104arranged in parallel and connected to the onshore BSP180. The first bus reactor circuit103and the second bus reactor circuit104each include a grounded bus reactor160and a third circuit breaker170connected in series. In one or more embodiments, the system100also includes a Power Management System (PMS)300connected to an I/O controller200.

The circuit breakers are electrical safety devices designed to protect the submarine cable circuit from damage caused by an overcurrent or short circuit and can be reset (either manually or automatically) to resume normal operation. The reactors can be variable shunt reactors configured to adapt upon receiving immediate feedback or control instructions from the PMS. Shunt reactors (SRs) are used in high voltage energy transmission systems to control the voltage or power factor during load variations. Depending on the voltage requirement needs, shunt reactors are switched on/off or reduced/increased tap changer position to provide reactive power compensation. With increasing load variations, variable shunt reactors (VSR) are developed as a means to provide more controllability for grid operators in reactive power management by continuously adjusting the compensation according to the load variation. This technology uses a tap changer, of the same type used in power transformers, to vary the inductance by changing the number of electrical turns in the reactor windings.

In some embodiments, the reactors may be defined as a set of numerous identical capacitors which are connected either in parallel or series inside an enclosure and are utilized for the correction of power factor as well as protection of submarine cable circuit. The submarine cable circuit may be a combination of equipment configured for receiving power from the onshore BSP180and delivering processed power to the offshore BSP190. In some embodiments, the submarine cable circuit may further include or connect to one or more loads which may be electric equipment used in oil and gas applications. In some embodiments, the PMS300controls a compensating voltage of the variable reactors to meet any reactive power requirements resulting from running cables over long distances.

The I/O controller200is connected to the first and second circuit breakers120and the first line reactor140and second line reactor150of the first submarine cable circuit branch101, the bus reactor160and the third circuit breaker170of the first bus reactor circuit103, and the onshore BSP180. The I/O controller200may be an interface device that sends and receives, under the control of the PMS300, control and status signals to/from the onshore BSP, the circuit breakers and/or the reactors.

FIG.2shows a flowchart in accordance with one or more embodiments. As shown inFIG.2, according to a method performed by the PMS, initially in step S10, availability of bus shunt reactors is determined for each submarine cable that is planned to be energized. That is, it is determined how many of the bus reactors are already energized. The availability of a bus reactor is detected by detecting the status of the circuit breaker disconnection of the bus reactor by an I/O controller or the PMS. If no bus reactor is available, then the method ends.

Next, in step S20, availability of the first and second line reactors in each and every branch is determined. The availability of a line reactor is detected by detecting the status of the circuit breaker disconnection of the line reactor by the I/O controller or the PMS. If one of the line reactors is not available, energization of the submarine cable circuits whose line reactor is not available is blocked. According to one embodiment, if one of the line reactors is not available, the submarine cable circuits of the submarine cable circuit branches in which the unavailable line reactor is located is blocked. In addition, if one of the line reactors is not available, a warning procedure may be initiated by which engineers or the owner may be urged to inspect the lines. If a line reactor is available, it is ready for energization. If each and every one of the submarine cable circuit branches includes at least one unavailable line reactor, the method ends.

When all of the line reactors and bus reactors are available, or when both of the line reactors in one submarine cable circuit branch and at least one bus reactor are available, then, in step S30, energization scenarios will be determined. In one or more embodiments, there are two possible energization scenarios. The first scenario is that no submarine cable circuit (submarine cable circuit branch) is energized, in which case the first submarine cable circuit is selected to be energized. In the second scenario, one submarine cable circuit is already energized, and the other submarine cable circuit (submarine cable circuit branch) requires energization.

Then, in step S40, the bus reactors are adjusted based on the above described two scenarios. In the first scenario, both bus reactors are deemed as related to the submarine cable circuit branch to be energized and the tap positions of both bus reactors are adjusted to minimum or for minimum compensation. In the second scenario, one bus reactor will be assigned for and deemed as related to the submarine cable circuit branches to be energized. That is, the tap position of the assigned one shunt reactor will be adjusted for minimum compensation as well as the line reactors connected to the cable circuit being energized. Tap position of the bus shunt reactor is adjusted to reduce a load of the bus shunt reactors. Then, in step S50, tap positions of the first and second line reactors in each submarine cable circuit branch to be energized are adjusted at both sides of the submarine cable to reduce a load of each of the first and second line reactors. In one embodiment, the adjustment of the tap positions of the bus reactors in the first and second bus reactor circuits and the adjustment of the tap positions of the first and second line reactors are done such that the tap position of the line shunt reactors at both side of the submarine cable circuit that will be energized is reduced to minimum. For example, up to 40% of a full load of each of the bus reactors and the first and second line reactors is reduced.

In step S60, the submarine cable circuits of the first and second submarine cable circuit branches are energized, that is, the power from the onshore BSP180is provided to the first and second submarine cable circuits. In one or more embodiments, the submarine cable circuits are energized by closing the GIS breaker. Instructions to close the GIS breaker are sent to the GIS breaker via the I/O controllers.

Then in step S70, immediately after the submarine cable circuits are energized, the tap position of all energized reactors are readjusted to adjust the voltage at both sides of the submarine cable. In one or more embodiments, the tap positions of the first and second line reactors are readjusted such that voltage levels within the submarine cable circuits are acceptable. In one embodiment, the tap positions of the first and second line reactors is readjusted within 1.5 seconds after the submarine cable circuits are energized. The bus reactors would be readjusted in a similar way. By readjusting the tap positions of the first and second line and bus reactors immediately after energizing the submarine cable circuits, voltage levels on the onshore and offshore BSPs as well as within the submarine cable circuits are acceptable.

In one or more embodiments, the flowchart ofFIG.2is performed in the order shown to provide automated sequential switching to allow successful energization of the 230 kV long submarine cable while the shunt reactors are connected.

FIG.3shows a schematic diagram of a submarine cable system in accordance with one or more embodiments. As shown inFIG.3, compared to the system shown inFIG.1, the PMS300is connected to the I/O controller200via a first switch400, and the system100further comprises a second switch400″ and a standby PMS300″. The first switch400is connected to the second switch400″, for example, via a cable, and the second switch400″ is connected to a standby PMS300″. The PMS300is onshore and the standby PMS300″ is offshore. The second switch400″ is connected to a second I/O controller200″, and the second I/O controller200″ is connected to the second circuit breaker130of the first submarine cable circuit branch101. In one embodiment, the second I/O controller200″ is also connected to the second circuit breaker130of the second submarine cable circuit branch101.

In this embodiment, two PMS s are configured for automating the process of energizing the system. One PMS may be a primary PMS used for controlling the entire system, while an additional PMS may be a secondary PMS used as a redundant, hot standby for the primary PMS when, for example, the primary PMS is disconnected for maintenance or experiences a failure in operation. Further, in the event of a system disturbance, either PMS may assume control of the entirety of the system. In the example shown, the onshore PMS300is used as the primary PMS and the offshore PMS300″ is used as the secondary PMS. In another embodiment, the offshore PMS300″ may be used as the primary PMS and the onshore PMS300may be used as the secondary PMS.

In one or more embodiments, as part of the process ofFIG.2(in the background), the primary PMS and redundant PMS controllers are constantly communicating with each other to determine whether there is any failure of the primary PMS. Once the primary (main) PMS has any failure, an alarm or alert is sent to the redundant PMS controller. The primary PMS controller automatically stops controlling and the redundant PMS controller takes the lead automatically. Thus, in one or more embodiments, in case the primary PMS fails, the primary PMS300can be switched to the hot standby secondary/redundant PMS300″.

FIG.4shows a missing zero phenomena for the first one to two seconds of energization of the submarine cables when the shunt reactors are in full tap positions. The maximum length of an high voltage underground cable (HV UGC) cable is often constrained by the criterion that the cable cannot have more than 50% reactive power compensation. If this limit is exceeded the current in the circuit breaker may not have a zero crossing after energization, which is referred to as the zero missing phenomenon. This is problematic if a fault occur shortly after energization. As shown inFIG.4, when the submarine cable is energized with full tap positions of shunt reactors, the zero crossing is missing for approximate two seconds, which may jeopardize the 230 kV GIS if tripped during these two seconds after energization.

FIG.5shows schematically a technical effect of one or more embodiments. From the upper section ofFIG.5, it can be seen that the missing zero crossing has been overcome by using some embodiments of this invention. More specifically, inFIG.5, the upper graph shows the voltage. The graph shows three phases. As can be seen from the graph, a disturbance occurs at the moment of closing the breaker to energize. The lower graph shows the current after energization, again with three phases. As can be seen from the lower graph, there is zero crossing of the current value for every cycle of every phase. The Ir shown inFIG.5represents the current of onshore breaker120, while the E Grid230shown is the voltage profile for the onshore GIS. As there is a zero crossing of the current value for every cycle inFIG.5, there will be no arcing inside the circuit breaker120if it opens immediately after closing.

Embodiments disclosed herein may be implemented using virtually any type of computing system, regardless of the platform being used. In some embodiments, one or more modules of the PMS may be computer systems located at a remote location. In some embodiments, the PMS may be fully implemented in a computer system. In some embodiments, the computing system may be implemented on remote or handheld devices (e.g., laptop computer, smart phone, personal digital assistant, tablet computer, or other mobile device), desktop computers, servers, blades in a server chassis, or any other type of computing device or devices that includes at least the minimum processing power, memory, and input and output device(s) to perform one or more embodiments of the invention.

FIG.6depicts a block diagram of a computer system602used to provide computational functionalities associated with described algorithms, methods, functions, processes, flows, and procedures as described in this disclosure, according to one or more embodiments. For example, the computer system602, and the processor of the computer system, may be used to perform one or more steps of the flowchart (calculations, determinations, etc.) inFIG.2. The illustrated computer602is intended to encompass any computing device such as a server, desktop computer, laptop/notebook computer, wireless data port, smart phone, personal data assistant (PDA), tablet computing device, one or more processors within these devices, or any other suitable processing device, including both physical or virtual instances (or both) of the computing device. Additionally, the computer602may include a computer that includes an input device, such as a keypad, keyboard, touch screen, or other device that can accept user information, and an output device that conveys information associated with the operation of the computer602, including digital data, visual, or audio information (or a combination of information), or a GUI.

The computer602can receive requests over network630from a client application (for example, executing on another computer602) and responding to the received requests by processing the said requests in an appropriate software application. In addition, requests may also be sent to the computer602from internal users (for example, from a command console or by other appropriate access method), external or third-parties, other automated applications, as well as any other appropriate entities, individuals, systems, or computers.

Each of the components of the computer602can communicate using a system bus603. In some implementations, any or all of the components of the computer602, both hardware or software (or a combination of hardware and software), may interface with each other or the interface604(or a combination of both) over the system bus603using an application programming interface (API)612or a service layer613(or a combination of the API612and service layer613. The API612may include specifications for routines, data structures, and object classes. The API612may be either computer-language independent or dependent and refer to a complete interface, a single function, or even a set of APIs. The service layer613provides software services to the computer602or other components (whether or not illustrated) that are communicably coupled to the computer602. The functionality of the computer602may be accessible for all service consumers using this service layer. Software services, such as those provided by the service layer613, provide reusable, defined business functionalities through a defined interface. For example, the interface may be software written in JAVA, C++, or other suitable language providing data in extensible markup language (XML) format or another suitable format. While illustrated as an integrated component of the computer602, alternative implementations may illustrate the API612or the service layer613as stand-alone components in relation to other components of the computer602or other components (whether or not illustrated) that are communicably coupled to the computer602. Moreover, any or all parts of the API612or the service layer613may be implemented as child or sub-modules of another software module, enterprise application, or hardware module without departing from the scope of this disclosure.

The computer602includes an interface604. Although illustrated as a single interface604inFIG.6, two or more interfaces604may be used according to particular needs, desires, or particular implementations of the computer602. The interface604is used by the computer602for communicating with other systems in a distributed environment that are connected to the network630. Generally, the interface604includes logic encoded in software or hardware (or a combination of software and hardware) and operable to communicate with the network630. More specifically, the interface604may include software supporting one or more communication protocols associated with communications such that the network630or interface's hardware is operable to communicate physical signals within and outside of the illustrated computer602.

The computer602includes at least one computer processor605. Although illustrated as a single computer processor605inFIG.6, two or more processors may be used according to particular needs, desires, or particular implementations of the computer602. Generally, the computer processor605executes instructions and manipulates data to perform the operations of the computer602and any machine learning networks, algorithms, methods, functions, processes, flows, and procedures as described in the instant disclosure.

The computer602also includes a memory606that holds data for the computer602or other components (or a combination of both) that can be connected to the network630. For example, memory606can be a database storing data consistent with this disclosure. Although illustrated as a single memory606inFIG.6, two or more memories may be used according to particular needs, desires, or particular implementations of the computer602and the described functionality. While memory606is illustrated as an integral component of the computer602, in alternative implementations, memory606can be external to the computer602.

The application607is an algorithmic software engine providing functionality according to particular needs, desires, or particular implementations of the computer602, particularly with respect to functionality described in this disclosure. For example, application607can serve as one or more components, modules, applications, etc. Further, although illustrated as a single application607, the application607may be implemented as multiple applications607on the computer602. In addition, although illustrated as integral to the computer602, in alternative implementations, the application607can be external to the computer602.

There may be any number of computers602associated with, or external to, a computer system containing a computer602, wherein each computer602communicates over network630. Further, the term “client,” “user,” and other appropriate terminology may be used interchangeably as appropriate without departing from the scope of this disclosure. Moreover, this disclosure contemplates that many users may use one computer602, or that one user may use multiple computers602.

WhileFIGS.1and3show various configurations of components, other configurations may be used without departing from the scope of the disclosure. For example, various components inFIGS.1and3may be combined to create a single component. As another example, the functionality performed by a single component may be performed by two or more components.

The same principles disclosed herein may be applied to another submarine cable starting from offshore BSP (190), to another offshore BSP, and so on. In this situation, the offshore BSP (190) may be deemed as an onshore BSP.