# 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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### Calculating omega (ω) in a separately excited DC motor

I'm currently struggling here so perhaps you can help out. I'm given "three basic equations": Magnetic flux of the field winding is given by: ...
5k views

### Why are there no “even” harmonics in AC machines?

Why are there no "even" harmonics in AC machines? In Chapman's book, he says it's because of symmetry of the flux density wave but I don't get it...
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### What is actually meant by “parallel paths” in a simplex progressive lap winding of a DC Generator?

Many of my textbooks mention "parallel path" term, but I am unable to actually understand it. Also along with this it would be quite helpful to know, how the polarity of brushes is determined?
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### Is this a universal motor? How does it work?

I want to know what type of motor this is. It has brushes, 2 coils, 1 electromagnet, and 1 commutator of copper in the middle. I have a lot of doubts because I'm learning. Is this a universal motor ...
28k views

### What is the difference between 50/51N relay and 50/51G relay [closed]

On electrical engineering field of power distribution. When it comes to ground fault detection on solidly grounded or low resistance grounded transformers. When do we use 50/51N relay and 50/51G, do ...
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### Why is the air gap in synchronous machines larger than in asynchronous machines?

The length of air gap is inversely proportional to power factor and hence result in poor operating power factor of an electrical machine. Larger air gap length means higher resistance to magnetic flux ...
2k views

### Why do we use derating factors when sizing conductors?

What is the main reason behind using derating factors in case of determining the cross sectional area of a conductor and what happens if we don't take these factors into account ?
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### Why do we want higher power factor in ac motors?

Here is a simplified 3P electric motor below: This motor is simply combined of three coils facing toward to the rotator (in the center) 120 degree apart to each other. The user wants his rotator to ...
1k views

### Which informations do I need to calculate the efficiency and horsepower of a 3 phase induction motor?

As far as I know the magnetic force is responsible for the motor rotation. So, horsepower of the motor is mostly related to magnetic flux on the coils (windings). Also magnetic flux is directly ...
273 views

### why are pm (permanent magnet) machines synchronous? and how do I start them?

Let's consider just one pole pair. I know from reading my book that a pm machine will have the angular speed of its rotor equal to the speed of the rotating magnet field that the three phase winding ...
588 views

### Simulation of OCC, for a 3 phase Alternator using MATLAB/Simulink

I was wondering if there was a way simulate a 3 phase alternator on MATLAB/Simulink and obtain its Open Circuit Characteristics by conducting an Open Circuit test. Also is there any other possible ...
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### Which is the physical insight behind the widely approved 'space vector' notation used in the analysis of the dynamic model of electric machines?

When approaching the study of electric machines in transient condition, it is customary to discard the real physical vector quantities like magnetic field and magnetic induction and to define fake ...
100 views

### What cause extreme heat when electricity connect to it? [closed]

I want to know is there a item/chemical etc, that cause extreme heat if it comes into contact with even a small bit of electric currents? I ask cause I am doing a school project and I need something ...
184 views

### How to build an Electric Vehicle (explain like I'm five) [closed]

I'm a business major investing time to learn more about Electric Vehicles. For starters, I wanted to understand the elements that come together to make a simple Electric Vehicle, maybe a scooter. I ...
161 views

### Why is -48V used? [duplicate]

Why does telecommunications equipment in the field (e.g. a BTS site) run on -48V? What is the advantage of running it at a voltage lower than ground rather than using a positive voltage?
183 views

### “Phantom” touches on appliance's capacitive buttons. A serious problem? [closed]

We have two electronic devices that operate well by themselves. Device 1 has touch (I assume capacitive) buttons. If device 1 and 2 are turned on they are fine. But if device 2's motor is engaged, ...
178 views

### eddy current brakes

I am trying to make an eddy brake prototype It works perfectly using a permanent magnet, but I have to make it using an electromagnet which is not working. I am using a solenoid purchased from Amazon ...
115 views

### Transformer leakage reactance

For a 4:1 transformer,the leakage reactance referred to secondary side is 0.05 pu. Then what will be the leakage reactance referred to primary? and how?
865 views

### Speed of Synchronous motor determined by frequency, but how about current?

The speed of a permanent magnet synchronous motor is determined by n = 120f/p where f is frequency, n is speed in rpm and p is number of poles. p is fixed in a motor so changing the frequency ...
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### What is meant by front and back pitch of an armature winding?

I searched the internet for these definitions and found a common definition in all websites: Back Pitch- A coil advances on the back of the armature. This advancement is measured in terms of ...
914 views

### What happens if the primary and secondary side of a transformer are short circuited mistakenly?

I have described the condition in the transformer picture I have attached. Will the transformer still function in this condition?
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### Why starting current in star-delta starter becomes 1/√3 times that of DOL starter?

I have seen this statement in a question paper. I was asked to prove it but I can not find the logic.
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### Salient pole vs cylindrical rotor

Why is the salient pole rotor in a synchronous machine made of laminated steel whereas a cylindrical rotor does not have any lamination?
512 views

### Does “crawling” absent incase of slip-ring induction motor?

In case of wound rotor induction motor no. of stator & rotor pole must be same otherwise the motor will not operate. Please can anybody explain the physical reason behind it. As the no. of stator ...
888 views

### How to filter the stepped wave from inverter?

I have a 1KVA inverter/ups setup at my home, did the installation very recently. Everything works perfectly CFLs,Ceiling fans and stuff. It has stepped sine wave output (when on battery) at a max ...
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### How can cities save electricity? [closed]

So I read about exercise equipment that produces electricity but very little, is anyone working to improve on it? I feel like this has a lot of potential to fight obesity and save on electricity no ...
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### 3-Phase Generator Frame Ground

I have a couple of basic questions on three phase generator connections. I am trying to connect a three phase machine (datasheet) as a generator to a three phase load on a breadboard, as shown: ...
557 views

### Electric shock from laptop due to capacitive coupling?

If a person touches an exposed wire (the wire has a ground-prong) on the 20V side of a power cable while barefoot, I heard that it is possible to receive a shock of higher than 20V due to capacitive ...
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### Why sinusoidally varying torque in induction machine not visible

We know that torque in an induction machine varies as $k\times[\cos(2wt)+\cos(\beta)]$ but we don't feel it. Why it's so?
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### power factor of a dc machine

To some this might be a weird question, But I am really confused about the definition of reactive power(of what I know, I think it is used to create magnetic flux).. If am correct, then how is the ...
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### Identifying position transfer function for a DC motor

I am trying to identify a simple position/speed system based on the inputs and outputs using a DC motor equipped with a qudrature encoder.For the soft i am using xcorr and arduino blocks to apply a ...
1k views

### Electrical Machines based on Electric Fields

Our teacher asked us this question during the lecture for Power Electromagnetics. We know that Electric Fields and Magnetic Fields are easily transformable into one another. And they are used greatly ...
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### Is it possible to connect a UPS in parallel with the mains?

Short version: When a UPS is plugged in to the mains, is it possible to plug the UPS output back to the same mains? Will that work as an emergency power backup for the mains circuit? Longer version: ...
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### Electrical generator vs torque

I know that the electrical generators have mechanical and electrical power losses. But does electrical or magnetic phenomena in a generator produce a counter torque? Or all the electrical power losses ...
3k views

### Why do AC motors have various back EMF shapes?

I just saw in one of the threads that apparently, a permanent magnet synchronous motor and a brushless DC motor have different back EMF shapes. But why? I thought those two were exactly the same in ...
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### Operation of a Growler to test armature shorts

Can someone explain to me how a Growler for testing electric motor armatures works please? I have obviously read the Wikipedia Growler page but it is still foggy. So the growler unit acts as the ...
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### Vehicle-to-grid technology

As I understand, vehicle-to-grid technology is about using the battery of your electric car to give electricity for the microgrid. How would this be useful as we are just moving electricity from place ...
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### Could a significant amount of electricity be generated from public hand-operated generators?

So imagine you're at a bus stop at a train station. You're bored and have got nothing to do. So you see a big crank-handle sitting there doing nothing, and because you're bored, you decide to spin it ...
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### Regarding a statement given in my 'Electrical Machines' textbook about synchronous machines?

I was reading the introductory chapter of my textbook on machines and when the author comes to a little introduction on synchronous machines, I was stuck on a statement midway. It goes: "When ...
710 views

### What kind of sensor is this?

I've got a m1000 automated tape dispenser and I've just recently found this sensor at the cutting blades. As far as I know the wire from the cutting blades to the main board was only for ...
4k views

### why dc machines have double layer winding?

why do dc machines always have double layer winding?is it possible to create a single layered winding dc machine? More generic Question: Can anyone explain the logical evolution of dc machine from ...
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### What sort of electric “motor” would I need to launch a puck?

As the title suggests I am looking at making a hockey puck launcher so I can do some off ice technique training as a goal tender. I have no one to train with so I wanted to create a puck launcher ...
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### Find the peak load of a power plant for the given load equation

The daily load demand of a grid is given by $$P=P_{max} \cdot cos(\pi t/24)$$ Here $-12hrs ≤ t ≤ 12hrs$. Maximum power occurs at ($t=0$) and minimum occurs at ($t= ±12$). A $10 GW$ hydro ...
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### High voltages Transmission lines?

I am having a doubt in why are the transmission lines are sent at a very high voltages? I also went through quite a few sources which said that it is to decrease the losses in the lines. BUt I am not ...
4k views

### what happens in a seperately excited DC generator when load increased

A book about electrical machines states as below ...
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### Can I use a 220v engine to build up a RC car?

sorry for the noob question, but I'd like to build myself a small RC car. I've found this motor in a blender, which runs at 220v. Can I power it with a lower voltage? What should I use? Thanks a ...
1k views

### Isn't current flow a wrong term?

In most text books and other electronics material it's said current is flowing through the circuit. Isn't this wrong? As current is flow of charge. Is there anything such as flow of flow of charge?
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### Electricity consumption of electrical machines - why do they consume electricity when they are not turned on?

The question is, why do electrical machines consume power when they are not turned on (they are plugged into an outlet)? Also, suppose there is a seven-port USB hub with AC power. Is the power ...
14k views

### Will a gas generator survive an EMP?

Not really sure where to ask this question. I was watching an episode of a TV show involving a gas generator and it got me wondering whether electricity could still be generated by a gas generator ...
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### Programmable power supply

I have been assigned to design a kind of programmable power supply. Can't decide on a way to make it. Need help with this. This is a high level block diagram of the required system: ...