In this video tutorial Part 1, we are going to be reviewing a book by Grainger and Stevensons,
specifically on chapter 12 on unsymmetrical fault types
and the topic of this conversation is building the symmetrical component sequence network diagrams.
So this book can be purchased on amazon and it’s a costly book but it is one of those books that can be
used throughout your career and not just student or book work,
but throughout the career and I personally use this book all the time.
I have a hard copy and I use this book all the time for all sorts of different references
in the power system industry so highly recommended purchasing this book
and having it on your shelf.
Now in chapter number 12 in this part at least,
we are going to introduce what we are going to talk about in the subsequent parts but in this chapter,
we go over a lot of different types of faults involved and will be talking about three phase faults,
single line to ground faults,
line to line faults and double line to ground faults.
These four different fault types and again,
really delving into how to construct the sequence network diagrams
based off on the type of faults and the equations that are involved,
so just to give you a reference so that we can have a good level set of mind
when thinking about these types of faults.
A three phase fault is a fault that has all three phases touching each other
and it may or may not touch the ground at the end of the day they are the same fault type,
and you have fault current that are going through each of these three phases
and typically the fault current is a perfectly balanced fault current
which means phase currents on A, B and C are the same magnitude
and 120 degrees displaced
and may have this zf which is the fault impedance
which means it is an extra impedance that may be on the line or externally contributes or reduces the fault current.
So that is what the Zf is, just the extra impedance that may be encountered
with the faults.
So a three phase fault perfectly balanced in terms of symmetrical components
we only have the positive sequence component involved
because it is a perfectly balanced fault and negative and zero sequence components do not exist in a three phase fault,
perfectly balanced three phase faults.
Now single line to ground fault is a fault in which one of the phases touch the ground
and you may or may not have fault impedance Zf involved,
and so you may have a phase A to ground fault or phase B to ground fault or phase
C to ground fault, but typically one of the phases touches the ground.
And at the type at the inception of the fault,
fault current will only exist on one of the phases,
the fault phase, right, and the other phases will simply have the load currents
but the fault current would be considerably larger than the load currents.
So that, in terms of symmetrical components,
Single Line to Ground faults will only have, single line to ground faults have positive negative and zero sequence components
and typically all three components are the same magnitude and the same angle.
For a Line to Line fault however it
does not involve a ground mode and because it doesn’t involve a ground mode
we should not see zero sequence components.
In Line to Line faults two phases are faulted together,
and in this case it is Line B and Line C are faulted together,
touching each other and you may or may not have a fault impedance in between
but you may also have A to B faulted together or A to C faulted together in this case it is B to C.
In this type of fault type again like we mentioned does not have a ground mode
but you can expect the positive sequence and negative sequence fault currents between them.
Again Line Current B for the faulted current and Line current C
for the faulted current are typically of the same current and of the same magnitude.
Typically Line Current B and Line Current C are equivalent.
And the Line Current A that is the un faulted Phase just has the load current during the inception
of the fault.
For a double line to ground fault however you do have two different faults,
two different lines are in contact with each other
but you also have a contact to ground so a double line to ground fault that kind of looks like this,
we have these two currents and they may not be as symmetrical as line to line fault right,
and they have different fault currents and different angle because you have the ground involved
and we may also have a fault impedance involved.
And so again thses two currents are similar to each other
but they may not be the same. And then Line A current
or the un-faulted phase current would just have the load current
at the inception of the fault.
In terms of symmetrical components a double Line to ground fault
will have positive negative and zero sequence components involved.
Now in the next part we will be talking about three phase faults in much more detail
and then single line to ground faults, line to line faults and double line to ground fault
and look at how the sequence network diagrams are derived.
Thank You.