Canned Motor Research Articles

Research on the flywheel clearance flow and heat transfer characteristics in a horizontal canned motor reactor coolant pump

Flywheel is an important component for the canned motor reactor coolant pump (RCP). The flywheel of horizontal canned motor reactor coolant pump (HRCP) is different from RCP’s flywheel. Its clearance width or different thermal conductivity structure would affect the flow structure of flywheel clearance flow, and then affect temperature distribution of the clearance, which would further affects the life and stability of flywheel. Therefore, it is necessary to analyze the flow and heat transfer characteristics of flywheel clearance flow in detail. This paper applies a Detached Eddy Simulation (DES) method to study the flywheel clearance flow of HRCP. The results show that the DES method can capture the small-scale vortex structure in turbulence Taylor-Couette flow and then give a more refined flow field morphology. The authors further study the regularity of flywheel clearance flow with different thermal conductivity structure, and the results indicate that optimizing thermal conductivity structure can effectively reduce flywheel’s temperature. The authors also investigate the heat dissipation mechanism of different flywheel clearance structures.

Experimental study on the internal temperature rise of a high-speed canned motor pump for liquid rocket engines

High-speed electric pumps are now gradually applied in liquid rocket engines. Compared with the pumps with dynamic seals, the canned motor pumps are more reliable, and thus suitable for delivering risky propellants. However, the partial flow diverted to the air-gap for cooling and lubrication faces the risk of overheating caused by its friction against the rotor. This paper performed an experiment on this issue with a high-speed canned motor pump for a notional rocket engine. Impellers with and without balance holes, as well as different configurations of jet holes, were adopted and their effects were analysed. Results showed that the internal temperature rise decreased by up to 78% when the balance holes were removed, and decreased by up to 40% when the jet hole configuration was modified. Both factors influenced the internal temperature rise by varying the flow rate of the cooling recirculation. The study suggested that the high-speed canned motor pump should be designed with an appropriate flow rate of the cooling recirculation, so as to control the temperature rise of the propellant and ensure safe operation of the rocket engine.

DETERMINING OPTIMAL SIMULATION SETTINGS FOR THE CENTRIFUGAL PUMP PARTS OPTIMIZATION PROCESS

This paper explores the optimal simulation settings required by the optimization process of centrifugal canned motor pump parts using the CH 6,3/32-2,2-2 pump as an example. The optimization of centrifugal pump parts is particularly important in order to increase pump characteristics: pump efficiency, net positive suction head, as well as other optimization criteria. The optimal conditions to obtain a geometric model and optimal mesh properties, initial and boundary conditions, solver settings were investigated. The mathematical models used in the simulation were also presented. In conclusion, there have been revealed optimal simulation settings.

Influence of non-uniform inflow on performance of reactor coolant pump and improved design

In Chinese Advanced Passive (CAP) series reactors, the two canned Reactor Coolant Pumps (RCP) are directly connected to the bottom of the steam generator (SG) rather than a longer pipe for the full development of inflow, which leads to a decrease in head and efficiency of RCP. However, the head of the RCP determines whether the reactor coolant system can circulate normally. The efficiency determines the power of cannedmotorstator. Overload power under limited size conditions will bring failure risk to the canned motor stator. With such a large impact, we first employed numerical simulation to investigate the influence mechanism of the non-uniform inflow and improve the RCP design, and then verified by experiment. It is found that the flow separation due to the SG asymmetrical structure and the abrupt change of cross section when linking to the inlet pipe is the main cause of non-uniform inflow. Accordingly, we proposed an improved RCP design which can effectively improve the head and efficiency of RCP by more than 1% under non-uniform inflow condition. This research reveals the formation mechanism of the non-uniform inflow of RCP and proposes the improved design scheme to improve the performance of RCP under the non-uniform inflow conditions for the first time, which provides guidance for the design of the RCP.

Volute clapboard and clearance of wear-ring effect on the operation characteristics of canned motor pump

Canned Motor Pump (CMP) is widely used in petroleum, chemical, electric power, aerospace engineering, and military manufacturing industries due to its good sealing performance. In the structure of canned motor pump, the rotor of the motor and the impeller of the pump are fixed on the same shaft. Therefore, balancing the axial force and the radical force of the rotor is a key task for its reliable operation. The numerical simulation study of CMP is carried out in this paper, aiming to improve the pump efficiency and balance the axial force and radial force. The internal flow and rotor force characteristics of CMP under different radial clearances of front or back wear-rings and different volute partitions are studied. The results show that with the increase of wear-ring gap, external performances decline, and the front wear-ring gap contributed the largest influence. Under the working conditions of 0.6QBEP and 0.8QBEP, front wear-rings contributed the largest influence to axial force, and the degree of influence decreases with the rate of flow increase. Radial clearances of front or back wear-rings have less impact on the radial force of the impeller. Adding clapboard for volute has a greater impact on the value and direction of radial force, and it can promote the balance of radial force. However, the effectiveness value will decrease. The research in this paper can provide theoretical basis and reference for performance prediction and hydraulic optimization of CMP.

Fractional Order Active Disturbance Rejection Control for Canned Motor Conical Active Magnetic Bearing-Supported Pumps

Active magnetic bearings (AMBs) are electromagnetic mechanism systems in which non-contact bearings support a rotating shaft using attractive forces generated by electromagnets through closed-loop control. For complete support of a five degree of freedom (DOF) rotor system, most AMB structures include two radial actuators and one for the axial direction. Conical active magnetic bearings (CAMBs) is one of the development directions of conventional magnetic bearings in which the requirement of the axial bearing can be eliminated. In this paper, we propose a structure with a CAMB integrated into a canned motor pump to eliminate the need for mechanical bearings and shaft seals. However, this system necessitates a more complicated control strategy due to a significant coupling effect between rotor motion and hydrodynamic disturbances. This paper presents a fractional order active disturbance rejection control (FOADRC) including a fractional order extend state observer (FOESO) and a proportional derivative controller (PD) to track and reject lumped disturbances actively. The proposed controller achieves better performance than the integer-type ADRC and traditional PID controller. The control performance of the proposed FOADRC is illustrated in terms of very good disturbance rejection capability that is demonstrated through MATLAB/Simulink simulation results.

Investigation of the self-balance impeller of a canned motor pump for axial force reduction

Canned motor pump is widely used in the transportation of chemical industry. The common failure component of the pump is the sliding bearing. The service life of the bearing will be directly reduced if it bears too much axial force. Thus, it has higher requirements on the axial force balance of the impeller. In this study, the axial force and the axial force self-balance position of the canned motor pump impeller were calculated and analyzed by numerical calculation and experimental verification. By deducing the theoretical formula of the clearance, the relationship between the total axial force of the impeller and the size of the axial clearance is obtained, which can be concluded simply to a functional equation. Based on the principle of curve fitting, an iterative asymptotic strategy is proposed to solve the self-balance position. This method successfully avoids the problem that the axial clearance falls into “solving interval traps.” The results show that the axial force is sensitive to axial clearance at a special interval. The axial clearance size decreases with the flow rate increasing. This study is of great significance for solving the axial force balance state of impeller.

Electromagnetic‐Thermal Analysis of High‐Temperature Direct Drive Electric‐Actuated Valve Canned Permanent Magnet Synchronous Motor

The high‐temperature electric‐actuated valve widely adopts the split structure, and the valve stem drives the opening and closing of the valve after passing through the high‐temperature packing and sealing structure. However, the transmission chain is too long, which cannot meet the pursuit of small volume and lightweight in the nuclear industry. In this paper, a novel integrated structure of high‐temperature direct drive electric‐actuated valve canned permanent magnet synchronous motor (DDEAV‐CPMSM) is proposed. The structure omits the dynamic sealing structure composed of stuffing box, pressure plate and pressure sleeve, as well as the transmission structure of gears and couplings, and the reliability is significantly improved. This paper focuses on the calculation of the dimension parameters, thermal load design, and electromagnetic vibration of DDEAV‐CPMSM, and compares it with the integrated structure of the induction motor to explore the optimal topology of the high‐temperature electric‐actuated valve. Aiming at the problem of serious heat generation in limited space, it is difficult to simulate the running time of high‐temperature valve. Based on the magneto‐thermal coupling method, a 3D temperature field model considering high‐temperature heat source, canned sleeve eddy current loss, and hydraulic friction loss is established. The steady‐state temperature distribution of the system at high temperature and the transient temperature change law of valve opening and closing are analyzed, and the minimum time of secondary start‐up and the maximum running time under fault conditions are further studied, to provide a theoretical basis for the application of DDEAV‐CPMSM. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Research on the inlet preswirl effect of clearance flow in canned motor reactor coolant pump

For a pressurized water reactor power plant, the reactor coolant pump (RCP) is a kernel component. And for a canned motor RCP, the rotor system's properties determines its safety. The liquid coolant inside the canned motor RCP fills clearance between the metal shields of rotor and stator, forming a lengthy clearance flow. The influence of inlet preswirl on rotordynamic coefficients of clearance flow in canned motor RCP and their effects on the rotordynamic characteristics of the pump are numerically and experimentally investigated in this work. A quasi-steady state computational fluid dynamics (CFD) method has been used to investigate the influence of inlet preswirl. A vertical experiment rig has also been established for this purpose. Rotordynamic coefficients on different inlet preswirl ratios (IR) are obtained through CFD and experiment. Results show that the cross-coupled stiffness of the clearance flow would change significantly with inlet preswirl, but other rotordynamic coefficients would not change significantly with inlet preswirl. For the case of clearance flow between the stator and rotor cans, influence of inlet preswirl is not so significant as the IR is not large enough.

The Effect of Inflow Distortion on the Rotordynamic Characteristics of a 1400-MW Reactor Coolant Pump Annular Seal

The annular seal between stator and rotor substantively acts as a bearing that affects the rotordynamic characteristic of the turbomachinery rotor system. The rotor wake turbulence in a canned motor Reactor Coolant Pump (RCP) will lead to inflow pressure distortion at the annular seal entrance, thus further affecting the seal rotordynamic characteristics and threatening the stable operation of RCP. In order to obtain the seal rotordynamic coefficients, a transient numerical method applies the mesh deformation technique to simulate the multiple-frequency elliptical rotor whirling orbit model. The transient solutions were proposed to solve the unsteady reaction forces of annular seals at five excitation frequencies for each case. The inflow pressure distortion patterns were simplified as harmonic functions, including two important influence parameters that are impeller blades number m and pressure fluctuation ratio λ. The numerical results showed that with nonuniform time-averaged pressure distribution at the entrance of the annular seal in Case 2, the inflow distortion significantly affects the seal rotordynamic coefficients, while the rotational spinning speed in Case 3 can weaken the time-averaged nonuniformity and accordingly make a dent in the influence. Increasing impeller blades number m and pressure fluctuation λ both result in a sharp diminution of the negative stiffness Keff, as well as an obvious increase in the effective damping Ceff, which will strengthen rotor misalignment and system stability. In addition, the larger impeller blades number m and higher pressure fluctuation λ will make the effective damping Ceff more independent of the whirling frequency. These results provide theoretical guidance for the operation safety of RCP.

Study on Axial Clearance Size and Leakage of Canned Motor Pump under Axial Force Self-Balance State

Canned motor pump is widely used in chemical industry. Due to the particularity of its application, it is necessary to ensure that the medium does not leak completely. If the axial force of impeller is too large, it will directly affect the performance of canned motor pump. Therefore, the floating impeller could be used in the pump to balance the axial force. In this paper, the relationship between axial clearance and leakage rate at the key part of canned motor pump is studied by means of numerical calculation and experimental verification. It is found that the fitting curve is highly consistent with the calculated value, which provided a good theoretical basis for further study of axial clearance control axial force and experimental axial force self-balance. In addition, the leakage rate increases with the increase of axial clearance. The static pressure in the axial clearance first increases and then decreases with the decrease of radius, and the maximum static pressure value is about 10.5% ∼ 15.8% near the clearance inlet. This study is of great significance to the theoretical research on the self-balance state of axial force of impeller.

Root Cause Analysis of In-Situ AP1000 Reactor Coolant Pump Lock Cup Failure

The failure of the large-scale canned motor reactor coolant pump (RCP) of Sanmen Unit 2 caused the unit to shut down in the first cycle of operation. In order to analyze the causes of the RCP fault, based on the fault characteristics and cause analysis methodology, this paper develops the RCP fault root cause analysis method. Through the RCP manufacturing record investigation, on-site operation data evaluation, disassembly and inspection forensics analysis, design analysis and test verification, root cause analysis and evaluation, the root cause of the RCP failure is confirmed that the lower thrust runner lock cup is affected by the resonance flow induced vibration. The initial flaw continues to expand under the action of the resonance and eventually separates. The lock cup fragment makes two holes on the stator can and eventually leads to the RCP failure. The root cause analysis method established in this study can be used for the analysis and treatment of similar complex problems.

Research on the clearance flow between stator and rotor cans in canned motor RCP

Canned motor reactor coolant pump (canned motor RCP) is the only long-term continuously running kernel equipment in the reactor system, the safety and stability of the canned motor RCP is the guarantee of the reactor security. In the usual working condition, the auxiliary impeller drives the primary cooling water flow upward into the clearance between the stator and rotor cans to bring the heat produced by the motor, forming a clearance flow with axial temperature gradient. A coupling analysis method is presented to study temperature field of the canned motor and the influence of viscosity temperature effect on clearance flow. The results indicate temperature at outlet of the clearance between stator and rotor cans is about 10 degrees higher than the inlet. What’s more, the differences of results with dynamic viscosity defines as quadratic fitting and results with dynamic viscosity defines at average clearance temperature are less than 1%. As to design method of the clearance, electromagnetic conversion efficiency and starting torque, motor cooling performance and stability of rotor system should be comprehensively considered in the clearance design process.

Energy balance analysis for a canned motor pump used for heat supply system

A canned motor pump is widely used for transporting the liquids without leakage. In this work, the pump is applied for heat supply system. For this application, between the rotor and stator for cooling the canned motor there is a circulating flow, which will flow back in the pump passage with higher temperature, and bring the mixing of the liquid having different temperature between the main stream and the circulating flow. The steady state internal flow has been investigated for the pump, and the pump hydraulic performance has been compared with the experimental data. With the consideration of both mechanical energy and internal energy as the effective energy increment of the working fluid, an efficiency assessment is proposed for a canned motor pump. The proposed efficiency shows the same tendency as hydraulic efficiency, and is more understandable compared with that of the conventional method. The present results indicate that the proposed method of evaluating the efficiency of the canned motor pump can reasonably depict the energy balance inside the whole canned motor pump. Further, the introduction of circulating flow is helpful to predict the internal flow and heat transfer for the canned motor pump in numerical simulation with better accuracy. The present study is helpful for both development and application of high performance canned motor pump for various industries.

Design of a 1 MWth Supercritical Carbon Dioxide Primary Heat Exchanger Test System

Abstract A new generation of concentrating solar power (CSP) technologies is under development to provide dispatchable renewable power generation and reduce the levelized cost of electricity (LCOE) to 6 cents/kWh by leveraging heat transfer fluids (HTFs) capable of operation at higher temperatures and coupling with higher efficiency power conversion cycles. The U.S. Department of Energy (DOE) has funded three pathways for Generation 3 CSP (Gen3CSP) technology development to leverage solid, liquid, and gaseous HTFs to transfer heat to a supercritical carbon dioxide (sCO2) Brayton cycle. This paper presents the design and off-design capabilities of a 1 MWth sCO2 test system that can provide sCO2 coolant to the primary heat exchangers (PHX) coupling the high-temperature HTFs to the sCO2 working fluid of the power cycle. This system will demonstrate design, performance, lifetime, and operability at a scale relevant to commercial CSP. A dense-phase high-pressure canned motor pump is used to supply up to 5.3 kg/s of sCO2 flow to the primary heat exchanger at pressures up to 250 bar and temperatures up to 715 °C with ambient air as the ultimate heat sink. Key component requirements for this system are presented in this paper.

Research on the flywheel clearance flow in canned motor RCP

Canned motor reactor coolant pump (canned motor RCP) is one of the most important parts of the reactor coolant system (RCS), the safety and stability of the canned motor RCP is the guarantee of the reactor security. Flywheels are introduced in the canned motor RCP to improve the coasting performance. When the canned motor RCP works, the reactor coolant water flows through the guard ring of the flywheel and the wall of stator, forming a clearance flow with large axial thermal gradient. The structure of the clearance flow directly affects the distribution of the temperature. So study on the flow and heat transfer characteristics of the clearance flow is necessary for the safety of the canned motor RCP. A varying clearance width transient CFD method is presented and used in the study of the clearance flow in this work. The results indicate that the friction loss induced by the clearance flow would decrease as the clearance width increases within certain limits, but the friction loss would increase with the increases of the clearance width if the clearance width exceed a certain range. As to the thermal barrier function of the clearance flow, the function would be weakened as the clearance width increases. These two effects should both be taken into consideration in the designing of flywheel clearance.

Electromagnetic Shielding Effect of a Canned Permanent Magnet Motor

Due to use of the metallic cans in the air gap, the electromagnetic shielding effect is formed, which is the prominent characteristic of the canned motor. In the flux field, eddy current induction occurs on both cans that thus affects the characteristic of the air gap flux field, and generates a loss that is the highest loss of the canned motor. In this paper, a combination method is proposed and stressed to analyze the shielding effect, based on a typical canned permanent magnet synchronous motor. First, the dq vector decomposition of the eddy current is studied. Second, the effect of the load angle on the loss distribution is studied. Finally, compared with the ordinary motor, the feature of can loss due to rotor speed and conductivity variation is shown. The three-dimensional finite element method is adopted, considering the end effect.

Electrical–thermal modeling of a double-canned induction motor for electrical performance analysis and motor lifetime determination

In nuclear and chemical fields, canned motor pumps are one of the safest ways to pump dangerous fluids. The canned motor pump is a compact unit integrating a hydraulic part and an induction motor with a common shaft. The particularity of the motor is that two non-magnetic cans are inserted in the air gap for leak tightness reasons. This study is therefore motivated by the fact that on one side classical electromagnetic and thermal models are not applicable for the canned motor, and on the other side new European standards about electrical machines require the design of motors with higher efficiency. In this work, an analytical model that combines electrical and thermal approaches has been performed to determine both electrical performances of the canned motor and the stator lifetime through the prediction of the maximum temperature of the winding for different operating conditions.

Flow Resistance Modeling for Coolant Distribution within Canned Motor Cooling Loops

Taylor–Couette–Poiseuille (TCP) flow dominates the inner water-cooling circulation of canned motor reactor coolant pumps. Current research on TCP flow focuses on torque behaviors and flow regime transitions through experiments and simulations. However, research on axial flow resistance in a large Reynolds number turbulent state is not sufficient, especially for the various flow patterns. This study is devoted to investigating the influence of annular flow on the axial flow resistance of liquid in the coaxial cylinders of the stator and rotor in canned motor reactor coolant pumps, and predicting the coolant flow distribution between the upper coil cooling loop and lower bearing lubricating loop for safe operation. The axial flow resistance, coupled with the annular rotation, is experimentally investigated at a flow rate with an axial Reynolds number, Rea, from 2.6 × 103 to 6.0 × 103 and rotational Reynolds number, Ret, from 1.6 × 104 to 4.0 × 104. It is revealed that the axial flow frictional coefficient varies against the axial flow rate in linear relation sets with logarithmic coordinates, which shift up when the flow has a higher Ret. Further examination of the axial flow resistance, with the Rea extending to 3.5 × 105 and Ret up to 1.6 × 105, by simulation shows gentle variation rates in the axial flow frictional coefficients against the Rea. The relation curves with different Ret values converge when the Rea exceeds 3.5 × 105. A prediction model for TCP flow consisting of a polygonal approximation with logarithmic coordinates is developed to estimate the axial flow resistance against different axial and rotational Reynolds numbers for the evaluation of heat and mass transfer during transition states and the engineering design of the canned motor chamber structure.

Modeling and thermal analysis of a canned permanent magnet machine with a novel network model

Due to use of cans in the airgap, the eddy current induction occurs and generates can loss. The loss on cans is considerably high and leads to excessive temperature rise of a canned motor, a fast and accurate temperature is necessary. In this paper, a compensation element assisted thermal model is proposed and stressed, due to the inaccuracy of tradition thermal network model. First, the studied canned motor is described. Second, the thermal analysis principle is studied. Then, the novel thermal network model with compensation element is studied, with thermal resistance calculation. Finally, compare motor temperature that is measured by thermal network model and finite element (FE). FE is used as reference and complement.