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Electrical Motors
Published in Moncef Krarti, Energy-Efficient Electrical Systems for Buildings, 2017
It should be noted from Equation 4.4 that when the slip factor approaches zero (i.e., α = 0), the motor speed approaches the synchronous speed. However, when the slip factor is close to unity (i.e., α = 1), the motor speed is close to zero (i.e., ωR = 0), indicating the rotor is stationary, often referred to as the locked-rotor condition. For low slip factors, it can be shown that the torque generated by the motor is proportional to the slip value. As the motor becomes loaded, the rotor slows down and the slip factor increases inducing higher current and torque. The rotor speed continues to decrease until the induced torque matches the load torque (i.e., full-load condition). Figure 4.6 shows typical speed–torque relationship for an induction AC motor. In particular, it can be seen at high speeds (close to the synchronous speed), that is, at low slip factors, the torque increases significantly without any loss of speed (i.e., slip). As the speed decreases (i.e., the slip factor increases), the torque reaches a maximum value, called the breakdown torque, as noted in Figure 4.6. It can be shown that the maximum torque occurs when the slip factor is such that the rotor inductive reactance becomes equal to the rotor resistance.
Electrical Systems
Published in Moncef Krarti, Energy Audit of Building Systems, 2020
One main difference between the two motor types (synchronous vs. induction) is the mechanism by which the rotor magnetic field is created. In an induction motor, the rotating stator magnetic field induces a current, and thus a magnetic field, in the rotor windings, which are typically of the squirrel-cage type. In a magnetic motor, the rotor cannot rotate at the same speed as the magnetic field (if the rotor spins with the same speed as the magnetic field, no current can be induced in the rotor because effectively the stator magnetic field remains at the same position relative to the rotor). The difference between the rotor speed and the stator magnetic field rotation is called the slip factor.
Multiple slips and double stratification in MHD flow of hybrid nanofluid past a permeable sheet: triple solutions and stability analysis
Published in Waves in Random and Complex Media, 2023
Rusya Iryanti Yahaya, Norihan Md Arifin, Najiyah Safwa Khashi'ie, Fadzilah Md Ali, Siti Suzilliana Putri Mohamed Isa
The effects of multiple slips on the flow can be analyzed by incorporating the linear velocity, thermal, and solutal slips into the boundary conditions [50]: where is the kinematic viscosity of the hybrid nanofluid, is the velocity slip factor, is the thermal slip factor, is the solutal slip factor, and the suffixes of w and ∞ refer to the condition at the surface of the sheet and ambient fluid, respectively.
A study of rotating stall in a vaneless diffuser of radial flow pump
Published in Journal of Hydraulic Research, 2018
Yaguang Heng, Antoine Dazin, Mohamed Najib Ouarzazi, Qiaorui Si
The diffuser loss coefficient in stable conditions is: which is depending only on the length of streamline L, and the streamline in the vaneless diffuser is known as a logarithmic spiral (Fig. 9) (from the continuity equation and moment of momentum equation, and assuming that the flow is 2D, axisymmetric). The length of streamline L can be estimated by Eq. (7). It depends only on the value of the absolute flow angle α at diffuser inlet and is thus increasing with the flow rate decrease, as shown in Fig. 10. The diffuser inlet flow angle was estimated from the calculation of the velocity triangle at impeller outlet, using Stodola slip factor. The evolution of the diffuser loss coefficient versus the length of streamline was drawn in Fig. 11. It can be seen that the losses increase linearly with the streamline length for small value of L, that is, for operating conditions without rotating stall (stable conditions). Moreover, it is noticeable that the experimental slope (≈ 0.32) is close to the theoretical one λ/DH (=0.28, with a value of the friction factor extracted from the Moody diagram), as it was assumed in Eq. (6). What is particularly notable in Fig. 11 is that the arising of rotating stall corresponds to a clear drop of the losses. This is confirmed again in Fig. 12, presenting the evolution of the loss coefficient as a function of the flow rate. In this figure, the loss coefficient drop at the arising of rotating stall is also obvious. After this drop, the losses increase again with decreasing flow rate, but this time with a clear, much smaller slope than the one () calculated based on the length of logarithmic spiral, which represents the conditions without rotating stall.