What is the turns ratio?

[franko26]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

[lester mcmanaway]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

Is the 7200 line or phase voltage ?

[franko26]

Is the 7200 line or phase voltage ?

I copied and pasted the question at the top of the comment, your guess is as good as mine.

[lester mcmanaway]

I copied and pasted the question at the top of the comment, your guess is as good as mine.

My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.

[franko26]

My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.

i think the point i was trying to make is that the answer is 20:1, even though, grammatically, it should be 1:20 per the study guide that I included. I really hope the real test is not like this. Whats the point of having questions that will trick you, they really should be testing our knowledge. Though I think this website is excellent for getting your mind thinking in the right direction, some of the questions are questionable. There was another one: what is the fla for a single phase 115vac 1hp motor? the answer according to test guy is 16a, this is correct per nec table 430.28. remember though, the code book is only a guide. if you use the formula P=I xE or I=P/E, with P=to 746, the answer is 6.49 which is close to the 8a answer thy included. I dont believe they are going to let us use the nec on the test, so you have to figure it out mathematically.

[iwanttotest]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

Wouldn't 1:20 be a step-up transformer? The transformer in question is a step-down.

If the secondary winding has fewer turns than the primary, a lower voltage will be induced in the secondary. This type of transformer is called a step-down transformer.

A secondary coil with twice as many turns as the primary will be cut twice as many times by the magnetic flux, and twice the applied primary voltage will be induced in the secondary. This transformer is known as a step-up transformer.

My answer would be 11.55:1 assuming 7200 is the line voltage.

[10beers]

Wouldn't 1:20 be a step-up transformer? The transformer in question is a step-down.

If the secondary winding has fewer turns than the primary, a lower voltage will be induced in the secondary. This type of transformer is called a step-down transformer.

A secondary coil with twice as many turns as the primary will be cut twice as many times by the magnetic flux, and twice the applied primary voltage will be induced in the secondary. This transformer is known as a step-up transformer.

My answer would be 11.55:1 assuming 7200 is the line voltage.

Keep in mind, some transformers are both step up and step down, For example, a power plant uses grid power for back feed when it is not producing power. In this case, the Generator Step Up (GSU) transformer also acts as a step down transformer when the Generator Circuit Breaker (GCB) is open. When the generator is shut down (GCB open), the 230kv grid voltage is stepped down to 19kv through the GSU and the 19kv is stepped down again to 4160v with the auxiliary transformer to provide medium voltage back feed to power all plant loads while the turbine generators are shut down. I hope this was not too confusing and keep in mind, these are common voltages but all will vary depending on the location and plant configuration.

[iwanttotest]

Keep in mind, some transformers are both step up and step down, For example, a power plant uses grid power for back feed when it is not producing power. In this case, the Generator Step Up (GSU) transformer also acts as a step down transformer when the Generator Circuit Breaker (GCB) is open. When the generator is shut down (GCB open), the 230kv grid voltage is stepped down to 19kv through the GSU and the 19kv is stepped down again to 4160v with the auxiliary transformer to provide medium voltage back feed to power all plant loads while the turbine generators are shut down. I hope this was not too confusing and keep in mind, these are common voltages but all will vary depending on the location and plant configuration.

Great point and I would also add that the same could be said for just about any transformer. I've seen 480-208/120 transformers used backwards as step ups many times, it just depends on which side you energize.

As for the original question, it did specify that the primary voltage was 7200.

[gzafarabadi]

i think the point i was trying to make is that the answer is 20:1, even though, grammatically, it should be 1:20 per the study guide that I included. I really hope the real test is not like this. Whats the point of having questions that will trick you, they really should be testing our knowledge. Though I think this website is excellent for getting your mind thinking in the right direction, some of the questions are questionable. There was another one: what is the fla for a single phase 115vac 1hp motor? the answer according to test guy is 16a, this is correct per nec table 430.28. remember though, the code book is only a guide. if you use the formula P=I xE or I=P/E, with P=to 746, the answer is 6.49 which is close to the 8a answer thy included. I dont believe they are going to let us use the nec on the test, so you have to figure it out mathematically.

I think, to answer this question you need to dived first voltage by the second one: 7200/360= 20 so the ratio is 20:1. If first one was 360 and the second one 7200, then the answer would be 1:20. so for this question 20:1 is the right answer.
regarding your fla question, you forgot to consider PF: P=I*E*PF.

[MaurerAdam]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

[MaurerAdam]

I copied and pasted the question at the top of the comment, your guess is as good as mine.


I copied and pasted the question at the top of the comment, your guess is as good as mine.

I've seen and worked on this voltage before on a temporary transformer with primary and secondary taps.

7200 if i remember is a rural voltage. (Line to neutral) Ph-Ph will be 12,456v. Odd looking voltage I know but I'm sure this is what you will see on the nameplate.

So if the 7200 is Line-neutral than 1:20 is correct.

Unless for whatever strange reason they want an "indirect ratio or percent ratio" (a test equipment i have which i hate) Then the math is as follows.

360 / 7200 = 0.05x100% = 5 ; 1:5

[gzafarabadi]

I've seen and worked on this voltage before on a temporary transformer with primary and secondary taps.

7200 if i remember is a rural voltage. (Line to neutral) Ph-Ph will be 12,456v. Odd looking voltage I know but I'm sure this is what you will see on the nameplate.

So if the 7200 is Line-neutral than 1:20 is correct.

Unless for whatever strange reason they want an "indirect ratio or percent ratio" (a test equipment i have which i hate) Then the math is as follows.

360 / 7200 = 0.05x100% = 5 ; 1:5

Based on my knowledge, I think for turn ratio here is the rule:

1- we need to just consider ph-ph voltages not ph-ground; so we don't care about delta or wye configuration.
2- turn ratio is always dividing primary over secondary not secondary over primary.

in this case, primary is 7200 and secondary is 360 so ratio is 20:1.

just we need to pay attention which one is primary and which one is secondary.

[stevenl569]

Wouldn't 1:20 be a step-up transformer? The transformer in question is a step-down.

If the secondary winding has fewer turns than the primary, a lower voltage will be induced in the secondary. This type of transformer is called a step-down transformer.

A secondary coil with twice as many turns as the primary will be cut twice as many times by the magnetic flux, and twice the applied primary voltage will be induced in the secondary. This transformer is known as a step-up transformer.

My answer would be 11.55:1 assuming 7200 is the line voltage.

You are 100% correct on this. 7,200V (Line) WYE = 4,160V (Phase). On the Delta side Vline=Vphase. You should always use the phase voltages to get a ratio, especially when dealing with a WYE-Delta configuration. Using phase voltages your math should be 4,160V/360V = 11.55:1 Ratio not 1:11.55. Turns ration is stated with the Primary Turns First. So in this case the Primary voltage is higher so the ratio will begin with the higher number of turns.

[todgayle]

My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.

I would have to agree with the 11.55:1 Ratio. I'm pretty sure in a WYE/DELTA you have to divide the primary by the square root of 3 first to get the correct ratio.

[hy3533]

I would have to agree with the 11.55:1 Ratio. I'm pretty sure in a WYE/DELTA you have to divide the primary by the square root of 3 first to get the correct ratio.

i agree.

[Lestracy31]

Wouldn't 1:20 be a step-up transformer? The transformer in question is a step-down.

If the secondary winding has fewer turns than the primary, a lower voltage will be induced in the secondary. This type of transformer is called a step-down transformer.

A secondary coil with twice as many turns as the primary will be cut twice as many times by the magnetic flux, and twice the applied primary voltage will be induced in the secondary. This transformer is known as a step-up transformer.

My answer would be 11.55:1 assuming 7200 is the line voltage.



If not stated its always assumed line voltage and what your suggesting is correct. I am not sure why they would do 20:1 as a correct answer in this problem or if that answer is confirmed or assumed correct. but who knows. ;)

[bmguster]

If not stated its always assumed line voltage and what your suggesting is correct. I am not sure why they would do 20:1 as a correct answer in this problem or if that answer is confirmed or assumed correct. but who knows. ;)

I just got the question and selected the 20:1 response and it was wrong.

[Kalbi_Rob]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

This post took a very strange turn of events, as most people got stuck on the turns ratio vs how to actually solve the question.

The turns ratio is the ratio of turns of the primary to the number of turns to the secondary of a SINGLE PHASE TRANSFORMER. Since this is a Wye/Delta transformer, we know it is 3 phase, and will have to convert the voltages to phase-to-ground (single phase) voltages to perform the ratio.

The Mnemonic I use is WIDE, which stands for Wye transformers I is equal between Line and Phase, and Delta transformers E (electromagnetic force which is measured in volts) is equal between Line and Phase.
To find the opposite I (current) or E (voltage), you must divide by square root of 3 (or simplified to 1.732).

The high side is WYE at 7200V, thus we must divide by 1.732 to find Phase Voltage.
7200V/1.732=4157V
The low side is DELTA at 360V, thus Phase Voltage equals Line Voltage at 360V.

Turns ratio is derived from the equation, where A=turns ratio: A=N1/N2=V1/V2=I2/I1 thus A=V1/V2. (https://www.electricalclassroom.com/transformer-ratio-calculator-online/)
A=V1/V2
A=4157V/360
A=11.55
or stated as turns ratio is equal to 11.55:1 (the first number represents N1 or Primary winding turns, and the second number represents N2 or the secondary winding turns. A=N1/N2)

[Miller1085]

My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.

WYE-DELTA
H side would be 7200, you would divide /by 1.732 get you L-L of 4157.044 divide this by your sec voltage of 360. 11:55:1. Good Stuff

[Kalbi_Rob]

WYE-DELTA
H side would be 7200, you would divide /by 1.732 get you L-L of 4157.044 divide this by your sec voltage of 360. 11:55:1. Good Stuff

I would disagree on one point. 7200V would be your VL-L and 4157.044V would be your VL-G. Anytime you read voltage on a WYE system, phase to phase (line to line) will be a larger number than your phase to ground (line to ground).

(VL-L/sqrt(3)) = VL-G

[RabbleRabble]

I would disagree on one point. 7200V would be your VL-L and 4157.044V would be your VL-G. Anytime you read voltage on a WYE system, phase to phase (line to line) will be a larger number than your phase to ground (line to ground).

(VL-L/sqrt(3)) = VL-G

Great answer thank you. I think line to neutral voltages can be confusing.

[Izeldeen]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

7200/1.732=4157
4157/360=11.5

[Izeldeen]

You are 100% correct on this. 7,200V (Line) WYE = 4,160V (Phase). On the Delta side Vline=Vphase. You should always use the phase voltages to get a ratio, especially when dealing with a WYE-Delta configuration. Using phase voltages your math should be 4,160V/360V = 11.55:1 Ratio not 1:11.55. Turns ration is stated with the Primary Turns First. So in this case the Primary voltage is higher so the ratio will begin with the higher number of turns.

thats right

[ranniery100]

I believe this question is wrong. On D-D system there's only Line voltage. So the answer it's a direct division between the two available voltages 7200/360 = 20:1.

On Y-D, you must divide the Line voltage on the primary to get the related phase voltage. In the secondary there's only one available voltage, which is the Phase one. So, the \TTR would be 7200/sqrt(3) / 480 = 11.55:1