Transformer X/R - Ratio

Summary

This 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

00:00

🔍 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.

05:03

📊 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.

Keywords

💡Transformer

A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. In the video, the focus is on modeling a specific type of transformer, a 750 kVA three-phase transformer from ABB, to understand its characteristics and how to represent it accurately in simulation software.

💡X/R Ratio

The X/R ratio, also known as the reactance-to-resistance ratio, is a parameter that characterizes the impedance properties of a transformer. It is crucial for determining the transformer's performance in terms of power loss and voltage regulation. The script discusses how to calculate this ratio when it's not explicitly provided in the transformer's data sheet.

💡Transformer Data Sheet

A transformer data sheet is a document that provides detailed specifications and performance data of a transformer. It typically includes information such as the transformer's rating, voltage levels, and impedance. In the video, the data sheet for a 750 kVA ABB transformer is referenced to illustrate how to find the missing X/R ratio.

💡Simulation Software

Simulation software is a type of computer program used to create models of real-world systems and analyze their behavior under various conditions. In the context of the video, software like ETAP and Power Factory are used to model the transformer and calculate its parameters, such as the X/R ratio.

💡Impedance

Impedance is a measure of the opposition that a system presents to the flow of electrical current. In transformers, impedance is often expressed as a percentage of the transformer's rated current. The script explains that while the impedance is given, the X/R ratio must be calculated.

💡Load Loss

Load loss, also known as copper loss, is the energy lost in a transformer due to the resistance of its windings when current flows through them. The video script mentions a load loss of 7.3 kilowatts for the transformer being discussed, which is a key parameter in calculating the X/R ratio.

💡Excel Calculations

Excel is a widely used spreadsheet program that can perform various mathematical calculations. In the video, the presenter uses Excel to calculate the percentage resistance (R) and reactance (X) based on the given load loss and transformer rating, which helps in determining the X/R ratio.

💡Per Unit

Per unit is a system of units used in power systems engineering to express quantities as a fraction of a base value, which simplifies calculations and comparisons. In the context of the video, the X/R ratio and other parameters are discussed in per unit terms for ease of use in simulation software.

💡Short Circuit Study

A short circuit study is an analysis performed to determine the behavior of an electrical system during a short circuit fault. The X/R ratio has a significant impact on the peak asymmetrical current during such a fault, which is why accurate modeling of this parameter is essential, as highlighted in the video.

💡Power System Engineers

Power system engineers are professionals who design, analyze, and maintain electrical power systems. The video is aimed at these engineers, providing them with guidance on how to accurately model transformers in simulation software, which is a critical skill in their field.

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