Centrifugal Pump Motor Torque Control for Turbine Mode
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Solution Overview
Problem
Centrifugal pumps switching on in a turbine case can cause damage to frequency converters and other electrical components due to uncontrolled kinetic energy dissipation, as the intermediate circuit of the frequency converter may not absorb the energy, leading to voltage rises that can destroy it.
Innovation Solution
The electric motor is operated with a negative torque to match or exceed the negative speed caused by the turbine case, preventing kinetic energy dissipation and allowing safe operation until normal conditions are restored, and then switched to positive torque to reverse flow direction and reduce kinetic energy for safe shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the centrifugal pump is switched on in turbine mode with the impeller already rotating in reverse direction, then the pump can be restarted without manual intervention, but the kinetic energy dissipation causes voltage rises in the frequency converter's intermediate circuit that can destroy it
Solution Approach 1:
The control system performs preliminary detection of turbine mode operation before the pump is switched on. When turbine mode is detected, the system pre-adjusts the motor torque to match the reverse rotation speed, preventing uncontrolled kinetic energy dissipation and voltage rises in the intermediate circuit during startup.
Solution Approach 2:
The control system continuously monitors the impeller rotation direction and speed during startup. Based on this feedback, the system dynamically adjusts the motor torque to match the turbine-induced rotation, ensuring smooth transition from turbine mode to normal motor operation without damaging voltage spikes.
2Device complexity
If the motor torque is not adjusted during turbine mode startup, then the system remains simple, but the uncontrolled kinetic energy dissipation destroys the frequency converter's intermediate circuit
Solution Approach 1:
The control system performs preliminary detection of turbine mode operation before the pump is switched on. When turbine mode is detected, the system pre-adjusts the motor torque to match the reverse rotation speed, preventing uncontrolled kinetic energy dissipation and voltage rises in the intermediate circuit during startup.
Solution Approach 2:
The control system dynamically changes the motor torque parameter during startup based on detected turbine mode conditions. By adjusting the torque magnitude and direction to match the reverse rotation, the system protects the intermediate circuit while maintaining relatively simple control logic.
3Adaptability or versatility
If the pump operates in turbine mode with reverse rotation, then the impeller rotates in the opposite direction to normal operation, but the kinetic energy must be dissipated causing damage to electrical components
Solution Approach 1:
The control system performs preliminary detection of turbine mode operation before the pump is switched on. When turbine mode is detected, the system pre-adjusts the motor torque to match the reverse rotation speed, preventing uncontrolled kinetic energy dissipation and voltage rises in the intermediate circuit during startup.
Solution Approach 2:
The control system converts the harmful reverse rotation caused by turbine mode into a beneficial controlled operation. By applying motor torque in the same direction as the reverse rotation, the system uses the existing kinetic energy to achieve smooth startup in the correct direction, transforming the harmful effect into a useful feature.
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 method minimizes the risk of damage to frequency converters and other electrical components by managing turbine-induced speed reversals, allowing safe operation and efficient transition to normal operation without overloading the frequency converter's intermediate circuit.
Implementation Method 1
the electric motor operates in motor mode. This means that the power flow is directed from the electrical side of the electric motor to the hydraulic side of the pump
Implementation Method 2
a centrifugal pump with at least one impeller which can be driven by the electric motor in normal operation for the intended conveying of a liquid medium from a suction side to a pressure side
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for operating an electric motor of a centrifugal pump (2), powered by a frequency converter, in turbine operation, wherein the centrifugal pump (2) has at least one impeller (12) which, in normal operation, is driven by the electric motor in a forward direction at a positive speed to pump a liquid medium from a suction side (9) to a discharge side (10) of the centrifugal pump (2), and wherein, in turbine operation, the medium flows through the centrifugal pump (2) in a reverse direction at a negative speed (n1), driving the impeller (12) from the discharge side (10) to the suction side (9). After the centrifugal pump (2) is switched on in turbine operation, the electric motor is driven with a negative torque such that the rotational speed of the impeller is equal to or greater than the negative rotational speed (n1) resulting from the turbine operation. The invention further relates to a centrifugal pump assembly with a control unit (6) for carrying out the method.