Downhole DC/DC Converter with Two-Conductor Cable
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Solution Overview
Problem
Existing power transmission systems for downhole equipment, particularly for electric submersible pumps, face limitations due to the use of heavy three-conductor AC cables and uncontrolled start-up of motors, which can lead to burnout issues caused by high physical resistance in viscous oils or deposits.
Innovation Solution
A power transmission system utilizing a medium voltage DC power supply and a downhole DC/DC converter, connected by a two-conductor cable, which powers a switched reluctance motor (SRM) or induction motor, allowing for direct drive without a gearbox and incorporating modular design, cooling channels, and sensors for operational control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If three-conductor AC cable is used to provide power to downhole equipment, then the system can operate with standard AC power sources, but the cable weight becomes very high and cable length is limited to 5-7 km due to mechanical strength limitations
Solution Approach 1:
The patent changes the electrical parameters by converting from AC to DC power transmission. This allows the use of two-conductor cables instead of three-conductor AC cables, significantly reducing cable weight while enabling transmission over longer distances without exceeding mechanical strength limitations
2Ease of operation
If three-conductor AC cable is used, then standard AC power sources can be utilized, but the maximum operational voltage is limited to less than 5 kV requiring high current for high power applications
Solution Approach 1:
The system changes the voltage parameter by using DC power transmission at medium voltage levels (exceeding 5 kV), which is higher than the AC system limitation. This reduces the current required for high power applications while maintaining power transmission capability
3Device complexity
If AC power is provided with surface-based power electronics control, then the system structure is simplified, but the start-up of ESPs is uncontrolled leading to potential motor burnout due to high physical resistance in viscous oils or deposits
Solution Approach 1:
The patent introduces a downhole DC/DC converter as an intermediary device that provides controlled start-up capability. This converter acts as a mediator between the power source and the motor, enabling controlled operation even though the power electronics control remains at the surface, thus preventing motor burnout while maintaining relatively simple system structure
4Reliability
If DC power supply is used to enable controlled motor operation, then motor burnout is prevented, but the system requires downhole DC/DC converters and two-conductor cables which differ from standard AC systems
Solution Approach 1:
The system changes the fundamental power transmission parameters from AC to DC, enabling controlled motor operation. While this requires different components (DC/DC converters and two-conductor cables), it provides superior reliability and control capability for downhole motor applications
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces the weight and power losses of the cable, enables controlled motor operation, and prevents burnout by using a lighter cable and providing precise temperature management, allowing for efficient and reliable operation of downhole equipment.
Implementation Method 1
A two-conductor cable connects the power source to the downhole DC/DC converter. The cable receives the DC voltage supply as an input and provides an output DC supply at a different voltage to the DC power supply
Implementation Method 2
A suitable SRM can include a stator and a rotor, each typically having cooling channels carrying a cooling fluid
Implementation Method 3
An induction motor or switched reluctance motor (SRM) is provided for driving the downhole equipment
Data Source
AI summary
A power transmission system for use with downhole equipment in a borehole includes a power source that is positioned at the surface providing a DC power supply, a downhole DC/DC converter and a two-conductor cable connecting the power source and the downhole DC/DC converter. The power transmission system receives the DC voltage supply as an input and provides an output DC supply at a different voltage to the DC power supply for provision to the downhole equipment.