# 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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### How do I write first order numerical method for finding power?

I'm new in this just taking the lectures on YouTube according to this, a self learner you can say I'm stuck in a problem of how to write numerical method for finding power of motor in the given set of ...
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### Is it safe to be around electric power plant? [closed]

So I work near this big electric power plant and it’s always buzzing and like a tower type thing sometimes throwing out the trash or driving by it in the entrance I just wanted to know if it’s safe to ...
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### A question regarding Reactive power

Why does the production of reactive power not require extra fuel unlike active/real power?
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### Importance of power factor [closed]

I understand the difference between reactive power, but why is power factor so important? A system with low PF draws more current; well wouldn't a larger load, be it resistive or reactive, draw a ...
1 vote
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### Armature Winding

This might seem like a silly question, buy why aren't armature windings usually done in a simple manner as shown in the image, why does it have to be more complicated such as lap winding etc?
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### Why would a motor have 100kW in 90kW out?

I might have phrased my question wrong but our lecturer asked us a question about why a motor (or generator I am not sure) would have 100kW in and 90kW out. He proceeded with saying that it had ...
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1 vote
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### What's the per phase equivalent circuit of induction motor with asymmetric windings?

We know that there's T equivalent circuit and inverse Γ-equivalent circuit for 3 phase induction motor(IM). When the IM is operating under normal situation, the windings are symmetrical, so all 3 ...
1 vote
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### Mechanic and electric power after imbalance in power system?

After a power imbalance (for example a generator disconnection) in the electric grid, generation and consumption are not equal. This causes a dynamic transient in generators described by the Swing ...
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### Which problem occurs with large synchronous motors in the event of high starting current?

So I was performing a test just recently with a synchronous motor at my school, and the teacher said that starting synchronous motors with a high starting current would cause problems to the machine. ...
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### Relative Permeability of Rotor

I am working on an example question from a electric machinery textbook. The question provides a simplified version of rotor and stator as shown in the picture below (please excuse me for the poor ...
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### 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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### 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, ...
1 vote
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### 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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### 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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### 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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### 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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### 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 ...
1 vote
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...
1 vote
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### 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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### 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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### 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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### 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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### 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 ...
1 vote
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### 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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### 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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### 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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### 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 ...
1 vote
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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 ...