Questions tagged [electric-machine]

Electrical Machines are Electro-Mechanical energy converters. They maybe classified into motors (electrical -> mechanical) and generators (mechanical -> electrical).

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43 views

Need some help with design for reduced friction acceleration of a ferromagnetic mass through a barrel

I would like to levitate (by that I mean just enough to not make contact with the surface of the barrel) and accelerate a ferromagnetic mass along a barrel of a certain length. I have a few questions ...
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33 views

Identifying the components of an electric motor

I need to calculate the magnetic field in the airgap of this electrical motor (also other things such as torque) but I'm having difficulty identifying its components (airgap, rotor and its nucleus, ...
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52 views

Force of attraction on the actuator arm

An actuator system is shown below. All dimensions are in centimeters. The magnetic material is cast steel, whose magnetization characteristic is shown in Fig. 1.7. The magnetic core and air gap have a ...
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70 views

Is there any way to estimate transformer's estimated remaining lifetime without testing the oil (or degree of polymerization)?

The common parameter for transformer health monitoring is testing the oil and sediments (N.B., there might be others I don't know). The insulating strength of oil is decreased due to faults, overload, ...
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56 views

Standard equation for delivered power from synchronous generator wrong for fractional kW machines?

When synchronous machines get to a certain size (in the \$MW\hspace{-0.8mm}s\$) the armature resistance is a lot smaller than the synchronous reactance, \$R_A << X_s\$, because of this \$R_A\$ ...
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72 views

Three phase induction motor connected in single phase power system

I'm trying to figure out an experiment in a lab that we did with a three phase motor connected in a single phase power supply. The schematic is as below: I measured all currents in the motor windings,...
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75 views

Can someone verify my understanding of induction motors?

Here's my understanding of the induction motor, it would be really helpful if someone can verify it. 3 phase AC supply given to stator, sets up an rotating magnetic field (RMF,) \$ B \$ (discussing ...
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43 views

Oversized electrical motor, synchronous, vs asynchronous

I know that a oversized motor would consume more energy than a well sized one, and in a low load scenario it will present a lower power factor than a well-sized one too. My question is, what is the ...
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32 views

Exciting the rotor and stator of a slip ring induction motor at different frequencies, will it develope torque?

I came across this question as I was preparing for an exam, I am unable to understand the theory behind it. The textbook says the motor can run a 600 and 2400 rpm but gives no explanation. Could ...
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51 views

Is it viable to short pitch different windings by different degrees of short pitching in the same synchronous generator?

In the design of a synchronous generator one can chose to eliminate or reduce harmonics at the expense of emf. The pitch factor \$K_p = \cos(\alpha/2)\$, which is always less than or equal to 1, ...
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127 views

What is the difference between applied voltage and induced voltage at primary side of transformer specifically?

I am not able to understand difference between applied voltage and induced voltage. Whenever voltage is applied at primary side of transformer there will be primary current producing flux using ...
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227 views

Is there non conductive solder?

I am making a project in my university and I really need to find a way to glue back together two blocks of the stator (part of an electric motor). As you probably know the sator is composed of sheets ...
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41 views

Why can't we increase diameter of induction motors as we can do in axial flux motors?

Axial flux motors have high torque to weight ratio. One of the reason is that it has larger diameter. which means since T=F*r . if r-->radius increases torque increases. More specifically I read it ...
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How does mutual flux in a synchronous generator remain constant like in a transformer?

Given is the flux per pole of of a synchronous generator 1)Is it field/rotor flux per pole ? 2)The generated emf per phase is given by E=4.44Nfφ where φ is the flux per pole But from transformers, we ...
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60 views

Effects of decreasing the field voltage of a synchronous machine

I am running a simulation of a synchronous machine in matlab and I have some behaviour I cant quite grasp my head around. The machine is running as a motor with only about 20% of its maximum load, ...
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36 views

Why does the armature voltage of a synchronous machine (generator) decreases with a increase of active power

I am running a simulated synchronous machine in matlab and strugling to understand its behaviour. The machine is running as a generator, keeping everything else at nominal value if I increase the load ...
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69 views

Why is a beep sound produced when turning on a brushless DC (BLDC) motor?

Today, out of my 50 electric motors I noticed a beep sound is being produced whenever I turn a BLDC motor on. What actually vibrates in the motor and what actually vibrates it?
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Waveform of induced EMF in a basic AC generator

Consider the following simple generator. A bar permanent magnet is rotating at a constant angular speed by some external means. Two coils of wire are placed in the same plane as the axis of the bar ...
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69 views

Grounding concept for an electrical machine test rig

I'm tasked wich building a test rig for electrical machines which consists of Machines mounted on top of a large ground plate which is connected to PE through a thick cable A torque transducer: The ...
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119 views

Why does the rotor magnetic field lag the rotor current by 90° in a 3 phase induction motor?

I was trying to understand load angle in electrical machines, generally denoted by delta, and I found out that while delta needs to be less than 90° in synchronous machine for steady state stability, ...
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114 views

Difference between unbalance load connected to grid vs isolated generator

Given two cases as following- CASE 1 An isolated 3-phase synchronous generator in star connected to a star-star 3-phase transformer and then secondary of transformer is connected to a highly unbalance ...
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62 views

Maximum torque condition of pmsm motor

In FOC, maximum torque is achieved by keeping rotor and stator flux at 90 degree electrical angle. Why does electrical 90 degree separation produce maximum torque? [edit: removed the linked video] It ...
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84 views

What is the difference between a droop and slip?

I see several synchronous machines have an actual rotation speed at less than synchronous speed e.g. synchronous speed is 1800 rpm and the actual rotation is 1780 rpm. However, we don't call it slip ...
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FOC VFD for PMSM drive

I have a question related to field-oriented control FOC. Why is FOC (Vector Control) also called variable frequency drive (VFD) even though frequency variation is not spoken about during the analysis?
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How can i choose the right VFD for an electric motor?

I have a 1.5kW three phase electric motor that is in a delta configuration. This motor has a motor voltage of 230/400V and a rated current of 5.9/3.4A. What sort of VFD should i be looking for that ...
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156 views

Why is the magnitude of mutual flux in a transformer independent of the current in primary?

Consider a transformer with no load, Given \$\phi= \phi_m \sin (\omega t)\$ \$e_1 = N_1 \dfrac{d \phi}{dt} = N_1\omega \phi_m \cos (\omega t)\$ \$E_1 = e_{1rms} = N_1\omega \phi_m \ \frac{1}{\sqrt{2}}...
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What other ways besides using magnetic fields can we use to convert mechanical energy to electrical energy and vice versa?

I have just started to read Electric machinery fundamentals by Stephen Chapman and there is one question in my mind after reading the first paragraph. What are the other mechanisms, besides using ...
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49 views

In a delta generator, will each phase voltage always be shifted 120°?

I'm confused by all the different phases and angles. Where I live we have a delta generator (3P3W) 230 V system. I was told that the three voltage phases will always be shifted 120° from each other... ...
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27 views

SPIM Rated Torque

What determines the rated torque of an induction motor? Is it purely limited to max continuous current adherent to heat dissipation requirements, or is there more to it? From what I understand, motors ...
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96 views

Why does peak torque increase on increasing air gap in induction motor?

I have been trying for a while to summarize the effects of increasing air gap in an induction motor with constant load. I understand that increasing air gap with constant supply voltage demands high ...
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33 views

Winding Factor in Single Phase Induction Motors

How does one compute the winding factor in a Single Phase Induction Motor? I have checked Wikipedia, but it only states the relevant formulae for three-phase machines with no explanation of the theory....
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99 views

What is a good circuit model for an AC generator?

A very simple electrical AC generator can be made by spinning magnets around a fixed stator coil. The changing magnetic field induces current in the stator winding. It would seem that at a fixed ...
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304 views

How can we neglect copper losses in open circuit test then neglect core losses in short circuit test of transformer?

When we perform open circuit test, we measure the core losses and we neglect the copper loss resistance (and also the leakage flux inductance?). But when we perform the short circuit test we measure ...
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91 views

Question about outdated "amplidyne" technology

Can someone please help me understand something better about "amplidyne" technology that was used back in the day. What I know It appears to be a dc motor generator that acts like an ...
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62 views

what is the relationship between rated voltage and angular speed frequency in an AC generator?

in Ac generator, the internal voltage is directly proportional to the mechanical speed by the equation: E = K * magnetic flux * mechanical speed but does this hold also for the terminal voltage? I ...
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101 views

Does an electric motor benefit by being given a rest?

Will the following two scenarios give different results on the wear/safety of a consumer-grade electric motor: A: Run motor for 12 hours/day for 20 days B: Run motor for 24 hours/day for 10 days (In ...
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40 views

Is the orthogonal spacing of dq axis of AC motor with respect to electrical or mechanical angle?

In FOC of AC machines, we try to align the stator flux to Q axis and maximize the value. The idea behind this logic is when rotor flux and stator flux are orthogonal, we generate max flux. But is the ...
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48 views

picture of dq axis in multi pole motor

How does the dq axis of multi pole motor look like? Typically online images search show dq axis for motor with one pole. Consider a 4 pole stator PMSM motor. Will there be multiple dq axis for each ...
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80 views

Symmetrical Components - Three-phase D-Y transformer with unbalanced voltage and loads

I have a Delta-Wye transformer, N1/N2 = 4, and am trying to solve the circuit below, with 120VAC applied to terminals VAB only. On the secondary I have 1 ohms connected between a-n and 5 ohms between ...
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783 views

How can the armature current of a DC shunt motor be zero at no-load?

I have seen the mathematical explanation of this explained using back EMF, where the back EMF would equal the input voltage and hence the armature current would be zero. But I'm unable to understand ...
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Confusion - ideal transformer on load

When there is no load connected to the secondary, E is equal to U, and no current flows in an ideal transformer. Now if we connect a load on the secondary of a transformer, the primary will draw a ...
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117 views

How does the shunt mmf in a long-shunt compound DC motor remain the same?

In a circuit model like this, the textbook says that the shunt mmf is the same for no-load and fully loaded conditions of the motor. How is this possible when the armature current (Ia) changes?
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56 views

DC Motor power diminishes quickly

I have an n20 DC motor which has a gearbox with a 55mm m4 threaded shaft (see image below for visualization of the motor). I'm compressing a spring with this motor, so the motor needs to work ...
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34 views

Is the zero sequence component considered balanced?

how is the zero sequence component is balanced while the three vectors are inphase and not displaced from each other by 120°? Isn't the definition of a balanced system is one in which the magnitudes ...
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36 views

Zero sequence component in unbalanced faults rotation

I am trying to understand the physical/practical meaning of the zero sequence component, I referred to some books. however, I am not sure is me or are there different interpretation of the zero ...
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1answer
165 views

Diagram of electrostatic precipitator

I was reading an article about working of ESP at this website: https://www.electrical4u.com/electrostatic-precipitator/ Though the explanation was nice, I couldn't understand what the diagram conveys....
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185 views

Armature and terminal voltages in DC machines

In the below page I am trying to grasp the way the terminal voltage and armature voltage are related to each other. Below is my attempt to understand their relation: Do you agree with my ...
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Motor vector control and parameters estimation

Vector control methods require good estimation of magnetic flux. In Direct Torque Control it would vector of stator flux. In order to estimate it properly one has to know motor parameters such as ...
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42 views

Steady State speed of rotor in following doubly excited system

I'm trying to analyse following system - A three phase armature winding on stator and on rotor field winding and both stator and rotor are cylindrical . And armature winding is connected to a three ...
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68 views

Induced voltage in the rotor of the induction motor

Given that the resultant mmf wave in the air gap of the three phase two pole induction motor is $$F(\theta , t) = \frac{3}{2}NI_m \cos(\omega t - \theta) \tag{1}$$ what's the value of the induced ...

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