Secondary VFD for ESP Motor Stalling Prevention
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Solution Overview
Problem
In oil and gas drilling applications, electric submersible pumps (ESPs) often experience motor stalling due to magnetic saturation of transformers, which prevents adequate voltage from reaching the motor during startup or transient load conditions, limiting the system's ability to operate effectively at low frequencies with high torques.
Innovation Solution
A secondary variable frequency drive (VFD) is coupled to the high voltage side of a transformer to provide supplemental voltage and magnetic flux when the operational values of the electric motor exceed the capabilities of the primary VFD and transformer, ensuring the motor receives sufficient power to prevent stalling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a transformer is used to step up voltage for the electric motor, then voltage transformation is achieved, but magnetic saturation prevents adequate voltage from reaching the motor during high torque conditions
Solution Approach 1:
The system divides the voltage supply function into two separate VFDs: a primary VFD that operates normally, and a secondary VFD that activates only when additional voltage capability is needed. This segmentation allows each VFD to operate within its capabilities while collectively providing the full range of required voltage and torque support.
Solution Approach 2:
The secondary VFD is designed to provide both supplemental voltage during high torque conditions and to share the load during normal operation. This multi-functionality allows the system to handle both transient high-power demands and sustained operating conditions with a single added component.
2Adaptability or versatility
If the motor operates at low frequencies with high torques, then startup and transient load conditions are improved, but magnetic saturation of the transformer prevents adequate voltage delivery
Solution Approach 1:
The control system dynamically switches between primary VFD-only operation and combined primary-secondary VFD operation based on real-time monitoring of voltage and torque requirements. This dynamic adaptation allows the system to optimize performance across the full operational range, activating the secondary VFD only when low-frequency high-torque conditions are detected.
3Device complexity
If a single VFD and transformer system is used, then device complexity is minimized, but the system cannot provide sufficient voltage during transient high torque conditions
Solution Approach 1:
The secondary VFD acts as an intermediary component that bridges the gap between the transformer's limited voltage output capability and the motor's high torque requirements. By inserting this intermediate voltage supply source, the system achieves extended operational capability without requiring a complete redesign of the existing transformer and primary VFD infrastructure.
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
The secondary VFD effectively supplements the primary VFD and transformer, enabling the electric motor to operate at low frequencies with high torques by providing full-rated current for short periods, thereby preventing motor stalling and ensuring reliable pump operation.
Implementation Method 1
The transformer is configured to receive the AC voltage from the primary VFD and output a stepped up AC voltage
Implementation Method 2
the secondary VFD is configured to provide a supplemental voltage in addition to the stepped up AC voltage when the operational values of an electric motor exceed a threshold value
Implementation Method 3
The stepped up AC voltage and the supplemental voltage combine to form the output voltage... enabling the electric motor to operate at low frequencies with high torques
Data Source
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AI summary
An electric submersible pump (ESP, 22) control system (36) includes a primary variable frequency drive (VFD, 38), a transformer (42), and a secondary VFD (44). The primary variable frequency drive (VFD) is configured to receive power from a power source (34) and output a variable voltage and variable amplitude AC voltage. The transformer has a low voltage side and a high voltage side of the transformer. The primary VFD is coupled to the low voltage side. The transformer is configured to receive the AC voltage from the primary VFD and output a stepped up AC voltage. The secondary VFD is coupled to the high voltage side of the transformer, wherein the secondary VFD is configured to provide a supplemental voltage in addition to the stepped up AC voltage when the operational values of an electric motor (30) exceed a threshold value.