Transformer X/R - Ratio
Summary
TLDRThis educational video script guides viewers on how to model a transformer's X/R ratio when it's not explicitly provided in the data sheet. Using a 750 kVA, 50 Hz, three-phase transformer from ABB as an example, the script demonstrates how to calculate the X/R ratio using Excel, given the transformer's rating, load loss, and impedance percentage. It also highlights the importance of accurate X/R ratio input in simulation software like ETAP and Power Factory for accurate power system analysis, emphasizing the impact on real and reactive power loss, voltage drop, and peak asymmetrical current during short circuit studies. The presenter encourages power system engineers to use correct X/R ratios for precise transformer modeling in simulations.
Takeaways
- 📚 The tutorial covers how to model a transformer's X/R ratio and determine it if not provided in the data sheet.
- 🔍 The example used is a 750 kVA, 50 Hz, three-phase transformer from ABB with HV side voltage at 11 kV and LV side voltage at 433 volts.
- 🔢 The transformer's impedance is given as 5%, but the X/R ratio is not specified in the data sheet.
- 🛠️ The video demonstrates using simulation software like ETA and Power Factory to model the transformer and input parameters.
- 💡 Power Factory allows specifying parameters such as short-circuit voltage, copper loss, and X/R ratio in per unit.
- 🔧 The presenter shows how to calculate the percentage resistance (R) using the formula: full load loss divided by transformer rating, multiplied by 100.
- 📈 To find the percentage reactance (X), the presenter uses the impedance triangle formula: √(Z^2 - R^2), where Z is the total impedance.
- 📊 An Excel calculation is used to determine the X/R ratio, showing that the calculated value matches what the software provides.
- ⚠️ The importance of accurate X/R ratio in transformer modeling is emphasized for its impact on power loss, voltage drop, and short-circuit studies.
- 📈 The typical X/R ratio might be 3.5, but the actual ratio should be calculated using the transformer data for precise modeling.
- 👨🏫 The session aims to educate power system engineers on the significance of entering the correct X/R ratio in simulation software.
Q & A
What is the main topic of the video script?
-The main topic of the video script is how to model a transformer's X/R ratio, find out the transformer X/R ratio if it is not given in the transformer data sheet, and how to enter that parameter in various simulation softwares.
What is the transformer rating and voltage details provided in the example from ABB?
-The example transformer from ABB is a 750 kVA, 50 Hz, three-phase transformer with an HV side voltage of 11 kV and an LV side voltage of 433 volts.
Why is the X/R ratio important in transformer modeling?
-The X/R ratio is important in transformer modeling because it has a significant impact on real and reactive power loss, voltage drop, and peak asymmetrical current during short circuit studies.
What is the impedance given for the ABB transformer example?
-The impedance for the ABB transformer example is given as 5%.
What is the load loss of the transformer mentioned in the script?
-The load loss of the transformer mentioned in the script is 7.3 kilowatts.
How does the script suggest finding the X/R ratio if it's not specified in the data sheet?
-The script suggests using an Excel calculation where you input the transformer rating, load loss, and impedance, then use formulas to calculate the percentage resistance (R) and percentage reactance (X) to find the X/R ratio.
What are the two simulation softwares mentioned in the script?
-The two simulation softwares mentioned in the script are ETAP and PowerFactory.
What is the difference between how ETAP and PowerFactory handle impedance and X/R ratio?
-ETAP requires you to specify the impedance directly, while PowerFactory allows you to choose between specifying short-circuit voltage and copper loss or the X/R ratio, and it can calculate the missing value if one is provided.
How does the script describe the process of calculating percentage resistance (R)?
-The script describes the process as dividing the transformer load loss by the transformer rating and then multiplying by 100 to get the percentage resistance (R).
What formula is used to calculate percentage reactance (X) in the script?
-The formula used to calculate percentage reactance (X) in the script is the square root of (Z^2 - R^2), where Z is the total impedance and R is the resistance.
What impact does the X/R ratio have on power system analysis?
-The X/R ratio has a significant impact on power system analysis as it affects the calculation of real and reactive power losses, voltage regulation, and the behavior of the system during fault conditions.
Why is it crucial for power system engineers to enter the correct X/R ratio in simulation software?
-It is crucial for power system engineers to enter the correct X/R ratio in simulation software to ensure accurate modeling and analysis of the power system, which is essential for reliable operation and planning.
Outlines
🔍 Understanding Transformer X/R Ratio from Data Sheets
The first paragraph discusses the process of determining the X/R ratio of a transformer when it's not explicitly provided in the data sheet. The speaker uses a 750 kVA, 50 Hz, three-phase transformer from ABB as an example, noting its primary and secondary voltages and impedance percentage. The lack of a specified X/R ratio leads to a discussion on how to input parameters into simulation software like ETAP and PowerFactory. The speaker emphasizes the importance of accurately determining the X/R ratio, as it affects real and reactive power losses, voltage drop, and peak asymmetrical current during short-circuit studies. An Excel calculation is introduced to calculate the percentage resistance (R) using the formula: full load loss divided by transformer rating, multiplied by 100.
📊 Calculating Percentage X and its Impact on Transformer Modeling
The second paragraph delves into calculating the percentage reactance (X) using the impedance triangle formula, which is the square root of (Z^2 - R^2), where Z is the total impedance and R is the resistance percentage previously calculated. The speaker demonstrates how to find the percentage X, which is crucial for accurate transformer modeling in simulation software. The calculated X/R ratio is compared to typical values, highlighting that using the actual calculated ratio is essential for precise modeling. The speaker stresses the significance of entering the correct X/R ratio for power system engineers to ensure accurate simulation results. The paragraph concludes with an encouragement to subscribe for upcoming educational sessions on similar topics.
Mindmap
Keywords
💡Transformer
💡X/R Ratio
💡Transformer Data Sheet
💡Simulation Software
💡Impedance
💡Load Loss
💡Excel Calculations
💡Per Unit
💡Short Circuit Study
💡Power System Engineers
Highlights
Introduction to modeling a transformer's X/R ratio when not provided in the data sheet.
Example of a 750 kVA, 50 Hz, three-phase transformer from ABB with HV side voltage of 11 kV and LV side voltage of 433 volts.
Impedance given as 5% but no specific X/R ratio provided.
Using ETA simulation software to model the transformer without an X/R ratio.
Comparison with Power Factory simulation software which allows specifying short-circuit voltage and copper loss.
Four options in Power Factory for specifying transformer parameters: short-circuit voltage, copper loss, X/R ratio, and reactance in per unit.
Explanation of how to find the X/R ratio using the transformer's data sheet and simple calculations.
Calculation of percentage R (resistance) using the formula: transformer load loss divided by transformer rating.
Method to calculate percentage X (reactance) using the impedance triangle.
Demonstration of Excel calculations to determine the X/R ratio.
Importance of accurate X/R ratio for real and reactive power loss calculations.
Impact of X/R ratio on voltage drop and peak asymmetrical current in short circuit studies.
Stress on the importance of entering the correct X/R ratio in transformer modeling for accurate simulation results.
Comparison between typical X/R ratio of 3.5 and the actual calculated ratio of 5.039.
Emphasis on the practical application of correctly calculated X/R ratio for power system engineers.
Invitation to subscribe for upcoming educational sessions on similar topics.
Transcripts
uh good morning friends uh today let's
see how to model a transformer xbr ratio
or how to find out the transformer x by
ratio if it is not given in the
transformer data sheet and how to enter
that parameters in a various simulation
softwares
okay so i have taken just an example
which is directly available from a data
that's a 750 kva transformer
from abb so hope it's visible for you so
the transformer rating is 750 kva 50
hertz three phase transformer hv side
voltage is 11 kv lv side voltage is 433
volt
and the impedance is given as five
percentage
but they have not specified x by ratio
if you take uh simulation software like
eta i mean the same transformer i have
modeled it it's a 750 kva transformer
i have a model it is a three-phase
transformer
transformer hv side is 11 kv lv side is
433 volt
and
750 kv is the transformer rating
impedance
i can
give it sub 5
and what's expire ratio which i need to
do now that's that's a question so
that x by r ratio is not directly
available
here in the transformer data sheet
okay let's quickly compare another
simulation software which is uh
excellent power factory
so here also i have a model the same
thing it's 11 kv bus 415 volt plus 750
kv transformer
so 750 kva 11.433 kv transformer it's a
three-phase transformer uh it's an mva
so i have given just 0.75750 kv a
transformer
and the hv site voltage is 11 kv lv site
voltage is 0.433
here instead of
impedance they have specified as short
circuit voltage both are same either it
is percentage set or uk in percentage
so i mean so you see here the software
the excellent allows you to choose what
you want to choose
like you can specify
sound circuit voltage
and copper loss
short circuit voltage and
resistance that is
re
some circuit voltage and x by r ratio
reactants in per unit and resistance in
per unit so you have four options uh
to select
so probably means what is if you select
this this is almost equivalent to what's
what's the etab software so here now i
do not know the x buyer ratio
so how to find out this x-bar ratio is a
question so
if you're using excellent power factory
probably means instead of using this
option you may go with this option short
circuit voltage uk and copper loss
and
probably
from the data sheet
from the data sheet
you can understand what's the copper
loss which is given as load loss about 7
300 kilowatt
sorry 7300 watt that is 7.3 kilowatt so
that you can specify
so that is seven point three kilowatt
so
impedance or a short circuit voltage
five percent copper loss is seven point
three kilowatt which i can directly
specify
and if i change the option to x by ratio
the software find out the x bar ratio
but
i mean for the e tab uh doesn't have
that option you have to give percentage
exit and expire ratio or you have to
specify percentage x and or
values
right now i mean let's quickly have a
look how to find out this i am just
going for a small excel calculations
so i have made
input
transform rating is 750 kva
load loss is 7.3 kilowatt impedance is 5
percentage these are all inputs which i
have taken it from the
transformer data seat so 750 kva
and 7300
watts that is 7.3 kilowatt that's the
loss copper loss or a load loss
impedance five percentage these are all
things which i have taken as an input
and i'm making a small calculations
how to find out percentage r that is uh
resistance in percentage
so percentage in resistance can be
calculated using a formula transformer
load loss or a full load loss divided by
transformer rating that gives the r in
per unit if you multiply by 100 you will
get percentage r
so i have made a formula you can see i
mean 7.3 divided by 750 7.3 kilowatt is
the loss and
750 kv is the transformer rating so
transformer load loss divided by
transformer rating multiply by 100 i got
percentage r
then how to find percentage x
is that is known
so percentage result is known
and
probably means using an impedance
triangle you can easily find out what's
the percentage x that is uh means x is
square root of z square minus r square
so you can see i means it is root of
five square minus point nine square it
is four point nine then the exposure is
straightforward you know percentage x
you know percentage or the expiry is
5.038
so that's the same value which the
software is also giving so if you are
using eta so means you can calculate
this
x by ratio using a small simple
calculations
from an excel sheet so i mean this is a
really important
as we know this expire has an impact
in terms of real and reactive power loss
in low flow and of course to an extent
voltage drop and it has a
means huge impact with respect to the
peak asymmetrical current
in the short circuit study it means
entering this value
is really important so if you give
probably typical x by r so probably that
x by r might be different
so that's what i am trying to stress i
mean it's typically that x by r is 3.5
but actual x player ratio we have
calculated using the transformer data
set 5.039 which may give a higher peak
asymmetrical current so
it's uh just to brush up
means power strum engineers i mean
to enter the right x by r ratio
in the transformer modeling when you are
using a different simulation softwares
thank you hope the session is useful and
probably we are coming up with quite a
lot of other similar sessions uh please
subscribe our channel for uh i mean
upcoming sessions thanks
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