# Questions tagged [three-phase]

AC power with three legs run 120 degrees out of phase

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### Why is the three-phase voltage 440V, if single-phase alone is 230V?

Why it is not 230V ×3, why only 440V?
100 views

### Relation between phase angle and current direction

In a triphasic system (any), is there a way to tell if the current is entering or leaving a phase/line/load just by the angle of the phasor of the source ? In the following picture we can see the ...
55 views

### Stepper motor, why so many wires (10)?

I recently bought a stepper motor secondhand and out of curiosity opened up the back cover to see how the wires were connected, currently it looks like 3 phases are connected (4 wires, 3 phase wires, ...
68 views

### Relating input torque on BLDC motor shaft with output current

I am trying to build a drone generator with a gasoline engine and a 14-pole,170KV, 2KW BLDC skateboard motor (this one). Before designing the system and running it, I wanted to clear out a fundamental ...
46 views

### How do I calculate deformant and real power of this circuit?

I have this circuit, the load is RL: I need to calculate the apparent, real, reactive and deformant power assuming L is very large. Since L is very large that means Q= 0 var and Pload=~Uav*Iav and S=...
122 views

### Which one of these is the phase 1? [closed]

Which one of these is the phase 1? And why isn't there a neutral wire at all? The cable is Chinese. The device it powers is a 3-phase motor that powers hydraulics. I am sorry for asking this question ...
501 views

### Effect of Reversed Phase Polarity on Active & Reactive Power of 3-Phase System?

I am trying to investigate the Power/Energy of 3-Phase System under Different Faults. I have a Three Phase Source and Load, Load is balanced i.e same phase angle and current (Phase-Neutral V = 230 ...
175 views

### How to calculate V/f value for an Induction motor?

I want to implement constant V/f in variable speed Inverter of a 3-phase Induction motor, 1500 rpm, 4-poles. I also know the equation: V/f = 4.44 × N x Phi Phi is maximum value of flux, f is ...
59 views

### Why would a motor manufacturer offer multiple coil winding types?

I'm currently looking through a part catalog from a motor manufacturer and notice that you can purchase this motor with different motor winding types. Specifically, you can order the motor coil wound ...
254 views

### Can a single phase SMPS be converted to run from three phase?

If you have a switch-mode power supply that runs off 240 VAC single phase, is it possible to convert it so that it runs off 3P+N (415V phase-to-phase) by only changing the bridge rectifier? I have ...
23 views

### How to change V and F in constant V/F control of an ACIM?

If I generate 3-Phase PWM outputs to drive a 3-phase ACIM and use constant V/F method for speed control then how will I change V and F of the generated PWM outputs? I will generate PWM's using LUT ...
53 views

### Converting single-phase to three-phase for City & Guilds 2391 practical

For my City and Guilds 2391 course, I will be testing a three-phase distribution board with a motor and single-phase sub-main. I am finding it hard to memorize the test procedures. So for me it's ...
79 views

### VFD as general use inverter

I'd like to have 3ph 208 in my house for general use (not a motor). If I run the output of a single phase to 3 phase VFD through inductors or a 1:1 transformer will it smooth the SPWM .output into an ...
32 views

I have been trying to determine whether or not I can run one line from 3-phase power into a power conditioner that requires single-phase input. The current draw on this line would be around 10 A. ...
142 views

### Calculating heat generated by resistance wire on 3 phase current

I am designing a heating element consisting of resistance wires coiled around a tube to heat water flowing in the tube. All three heating elements (loads) will have the same resistance and will be ...
633 views

### What is the formula for calculating the no load current of a 3-phase motor? [closed]

I am looking for the formula, not a rule of thumb. Is there a way to calculate the no-load current?
10k views

### Why don't the currents clash in a 3 phase delta connection?

Consider 3 windings, a, b and c. L1 is connected to A, L2 to B and L3 to C. The 3 windings are then connected in delta. If we could freeze frame the voltage waveform where L1 and L2 are positive ...
309 views

### Cable size for 3-Phase 800 Amp

On a 800 AMP heating unit that is fed from 480VAC, 3 phase power. Will each conductor pull 800A or 266A ?
42 views

### Which capacitor in series with resistor circuit to reduce remanence effects of transformer?

The "Comparative Analysis of Mitigation Techniques for Inrush Current of Transformer" mentions "Pre-insertions resistor with capacitor method" as an inrush mitigation technique: When circuit ...
99 views

### What is the power of a three phase circuit?

P = sqrt(3)*U * I * cos(f) is the real power for a symmetric load (U and I are RMS values of voltage and current of a single load), but what about generators?Do they have to have equal electromotive ...
50 views

### Calculations for 3-phase circuit in multisim

I have homework exercise which is looks like, and I'm trying recreate situation in multisim. Is my approach is good - are values of elements are proper? After calculations I will end with some exact ...
51 views

### What AC mains phase information can be deduced from measuring at two distinct devices, connected via ethernet?

I a have a house with 3x20A grid connection. With the usual big loads like washing machines, kitchen. For each socket in the house (many...) I want to determine the phase a wall socket is connected to ...
45 views

### How to find phase sequence in 3 phase system using micro controller without zero cross over?

I have 3 ADCs which are connected to 3 phases respectively. I have to find the phase sequence when it comes in picture... I'm getting an ADC value for particular phase, but how can I find the sequence ...
118 views

### Trouble in understanding current flow in this three phase DC-AC inverter circuit

Shown in the figure is one of the six steps of a 3-phase voltage source inverter where switches 1,5,6 are closed. The tutorial that I learnt this concept from draws the following equivalent circuit of ...
114 views

### Designing a 3-phase pure sine inverter. Where do I start? [closed]

I'm trying to design a 3-phase pure sine inverter which will be powered by a 128 cell battery bank (3.0v-4.2v/384v-537v). Since 384v is still above the 325v peak of a 250Vrms sine wave, I figured I ...
54 views

### Three phase system represented as a vector

In multiple locations I've been seeing the following: "Any three phase system can be defined by the vector As: $A_s = \frac{2}{3}[Ax(t) + (c)Ay(t) + (c^2)Az(t)]$ Where $c=e^{j\frac{2\pi}{3}}$...
38 views

### calculate phase voltages based on a PWM signal

Is there a method by which I can calculate phase voltages based on a PWM signal? I have as input PWM feedback signals and the DCLink voltage and as output there should be calculated voltages for each ...
102 views

### 3-phase rectification using individual step down transformers for each phase

I'm looking make a simple low-voltage DC power supply from a 3-phase supply. Looking into 3-phase rectifiers I came across the below articles https://www.gprectifier.com/news/rectifier-11261763.html ...
57 views

### Is there such a different phase control relay?

PROBLEM The standard phase control relay is output from any phase. However, there will be no output when that phase is gone. PROPOSAL When any phase is gone, the switch of the phase distribution ...
1k views

### Three phase systems - are there any single phase devices that are connected between two phases instead of between one phase and neutral?

In star system, single phase consumers are connected between a line and neutral but are there any single phase devices connected between two phases (would that even be considered a single phase device?...
51 views

### Generic 3 phase relay switch

I have a water fill level sensor which is capable to power a 3A single phase 230V motor. However, I have a three phase water pump. Is there a generic "switch" / relay which "operates" on single phase ...
55 views

### Protection on the AC side vs DC side

The circuit below shows a three phase rectifier with 3 filter inductors at the input side, and a capacitor, a MOV, and fuse at the output side. I wonder what the differences are in protecting the AC ...
203 views

### How to determine time needed to stay in a voltage vector state in Space Vector PWM for 3 phase inverter?

I need some clarifications on how and when to switch between voltage vector states (for the sake of discussion lets take V1 and V2 in the image below). Below is the image of 6 possible voltage vector ...
51 views

### Three phase systems - when is potential of a star node equal to zero?

I had to find total impedance of the following three phase circuit with symmetric line voltages: I've been told that nodes 1 and 2 can be connected because their potentials are equal (zero).After ...
3k views

### Why is the air gap between the stator and rotor on a motor kept as small as it is?

Between the stator windings and rotor is a small air gap. What would happen if this gap were larger than it is? Surely the magnetic field set up by energizing the stator windings would still cut the ...
61 views

### Does using only 2 phases (400V) in a 3 phase transformer affect anything?

I just witnessed a 3 phase control transformer in the mcc that steps down 400V to 230V connected only with 2 phases on the 3 400V terminals, and on the other side (secondary) are your live and neutral ...
126 views

### What is the purpose of these diodes?

What is the purpose of these didoes? I couldn't find it because I don't know it's name. Thank you. simulate this circuit – Schematic created using CircuitLab
134 views

### Correlation b/w output voltage frequency and angle theta for Conventional Space Vector PWM 3-Phase inverter drive

Im writing code for SP-PWM for a 3 phase voltage source inverter but since im a bit naive to the topic I need some clarifications regarding some questions I have. Lets cut to the point. For 3-phase ...
119 views

### Why are all my motors and transformers failing at this specific location?

At my job there is a vacuum oven. There is a 50 hp, enclosed cooling fan. that circulates N2 gas upon quench, the design of the unit runs 480 volts through a reduction transformer to 230 volts. This ...
278 views

### Understanding this power supply design

I'm doing some kind of reverse engineering to this very old power supply design. I'm having hard time trying to understand it all. I'm asking for some hints that help me read this schematic. From this ...
38 views

### How to choose high frequency inductors for high voltage line filtering?

I saw these inductors 680 uH (RL-1294-680) in each power line like shown below. The line to line voltage is 480 VAC. The inductor used has a saturation current of 280 mA. So I suppose I shouldn't ...
160 views

### RMS value of a line to neutral voltage on a three phase inverter

Basically, I feel like this is an incredibly simple thing, but my brain is stuck on it for hours now, and I can't find the answer anywhere. How do I find the RMS value of the signal shown, assuming ...
807 views

### 12VDC to 3 Phase 400V

In order top prevent my seldom used deep well pump (3 Phase, 400V) I plan to daily spin it up for a few seconds. Where the pump is located, the is no power supply (I operate the pump using a ...
341 views

### How can I find the slip speed of a slip ring induction motor without knowing the rotor speed (rated RPM)

The Rotor of a 4 pole, 50hz slip ring induction motor has a resistance of 5ohm per phase and inductance of 150mH per phase. Calculate the slip speed at which max torque occurs. I have used Ns = 120f/...
49 views

### How to estimate the power consumption of a motor when running at low load

I am trying to calculate the electrical power cost-saving of reducing the amount of time a machine runs idle (when the motor is running unloaded). From the meter data, the amps when idling is about ...
398 views

### An overseas company is making a machine for me and they need to know whether I want 1,2 or 3 phase and what voltage

I'm in Quebec and the company making the machine is in China. The machine is an industrial sized T-Shirt sublimation machine that does two sided printing. So there's a large heated plate that is ...
369 views

### Transformer Sizing with Mixed Loads (Three-Phase & Single-Phase)

I am trying to size/validate the rating on the medium voltage main transformer for an industrial plant. For some reason I can't find many resources that indicate how to properly do this when you have ...
1k views

### Identifying direction of rotation for a three phase motor, without applying three-phase power

Suppose I have a typical smallish (say, <3kW) three phase induction motor. Likely 400V star-connected, but methods that work with any motor would be preferred. I can ensure that the supply phase ...