The associated schematic is something out of a theoretical textbook, safety earthing does not come into it.Q1 But what if the motor builds a short circuit and someone touches it. In short, how do we ground such a load?
The transformer has a high voltage side H1, H2, H3 and a low voltage side X0, X1, X2, X3.i: What are those connections in yellow highlights?
Not sure, this is going outside my experience. It appears to be trying to represent a "neutral" connection, compare to the X connections to the right of the triangle.ii: What does that dashed line in green highlight represent?
Hi
Could you please help me with these queries? Thank you.
Regards
PG
Helpful link(s):
1: https://www.researchgate.net/post/W..._manipulate_3_phase_line_to_higher_phase_line
In a practical situation, the metal structure of the motor is connected to the local safety earth.
The high voltage can be selected connecting the various taps as defined in the table.
If our incoming high voltage is 480 volts, we connect 2 to 3 in each of the three windings.
then when there is 480v on the HV winding, there will be 120/208v on the LV winding.
Not sure, this is going outside my experience. It appears to be trying to represent a "neutral" connection, compare to the X connections to the right of the triangle.
As far as I see, it cannot.How can it be a neutral connection because there is no neutral in delta connection?
As far as I can see, a y-connected system is safer compared to delta one because it has a neutral connection which can be used for ground purposes
Thank you, JimB, MrAl.
MrAl, though that query about 48 phases was quite old, your explanation was very good. Thanks.
Why didnt you start a new thread?
Thank you, JimB, MrAl, Tony Stewart.
MrAl, I always try to combine related topics under one thread. It makes easier for me to refer back to the material.
Tony Stewart, thank you for your help with that 48 phases query. MrAl also replied to that query but at the moment I won't pursue 48 phases topic any further until I'm done with intuitive understanding of three phase systems.
Q1:
i:
Suppose, you have mains supply coming from a single phase generator. There is one live wire and one neutral. The neutral wire is grounded at the grid and also in your home. I'm sure that the neutral wire at the generator's end is also grounded. Do you agree that the neutral wire is grounded all along its path from the generator to your home?
Always at every Y or single ph. distribution transformer... Centre tap to N , Earth, not always in homes.
ii:
I assume that you agree that the neutral wire is grounded at many points along its path. Now suppose that the neutral wire isn't grounded anywhere along its path to your home. Do you think that it would help you if your electric appliances are grounded in this case?
Standards allow 20% tolerance including return ,10% for feeders and source with tap switchers and 10% in last 50m to home. Earth to home, is desire-able for neural loss unless your home is hit by lightning and causes ground shift on all faucets, so NO not safer but better regulation which ends up costing you more power in motors consumption. You can test by looking for <5% on neutral to ground at full single phase load.(not dual line loads like ovens)
Q2:
This is the main question.
This shows you a general picture of Wye three phase system and how its grounding is done. A Y-connection has a 'natural' neutral/ground point.
Could you please show/tell that how a delta system is grounded? This might be helpful here. Thank you.
It is isn't except on bleeder loads to ground for electrostatic and PD reduction on Y-Y except. maybe shunt reactors to prevent SC surge from faults or series caps which QH prefers on UHV lines ...
Or PF caps are used with 4th on N to earth... As a cap divider and PF correction. Dont quote me on that, Ive only seen rack mounted 3phase PF caps
Regards
PG
Any time a surge load or short occurs on one line to neutral or line-line , the other phase voltages have overvoltage transients from imbalanced loads. N.B. ok?Hi
The following query(ies) is a follow-on to Q2 which was discussed in posts #6 and #7 above.
The transformer is a Δ-Y one and it resides within the building; let's call it in-house transformer.. Its input is 480V and output is 208Y/120. "480V" is coming from the mains transformer which is placed on the pole; let's call it mains transformer.
i: "208Y/120" means that line-to-neutral is 120V and line-to-line voltage is 208V. Right?
Yes
ii: Do you know what such boxes are called?
Junction box?
iii: The mains transformer is supplying the building with 480V. This box is directly connected to the mains line coming to the building. As you can see it reads 277/480V. I believe that it could mean that the mains transformer has secondary in Y configuration where line-neutral voltage is 277V and line-to-line is 480. Do I have it correct?
Yes but probably Z connected phases
Thank you for helping me with the queries.
Regards
PG
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