Transformers Equations

Question 1

Nameplate calculations: volt drop?

Answer 1

Our nameplate impedance in decimal form (e.g.) 3.8 impedance means a 3.8% volt drop which turns to 0.038 and our nameplate voltage of eg 415 it will be 415x0.038 = 15.77, so 415 - 15.77 = 399 V which will be our volt drop

Question 2

MVA rating?

Answer 2

We take our name plate KVA e.g 200 KVA and times by 1000 to turn to Get 200,000 then divide by our decimal impedance so e.g 0.038 which gives us 200,000/0.038 which gives us a big number but we push ENG on calculator which will give us our awnser 5.26 MVA

Question 3

ISPCC?

Answer 3

Our secondary or our LT current ( low tension ) / impedance in decimal form e.g 278/ 0.038 which equals a big number then push ENG which gives 7.3 KA

Question 4

What is S

Answer 4

VA

Question 5

Single phase: how to calculate secondary voltage?

Answer 5

Use the primary voltage and use the ratio to divide and get ur awnser. E.g ratio 19:1 and ur voltage 230 it will be 230 divided by 19 to get 12v secondary voltage

Question 6

Single phase: Primary and secondary current?

Answer 6

Use formula S= V x I but transpose to I= s/v our s is our given VA e.g 25 over our primary voltage of e.g 230 so 25/230 equals 0.11, from here we calculate our secondary current with the ratio and multiplying it. Eg ratio 19:1 so 0.11 x 19 giving us 2.09 a

Question 7

Auto transformer?

Answer 7

An auto transformer is a single winding transformer where both the primary and secondary are formed from a common winding the primary and secondary windings are connected electrically and magnetically. Advantages: simple construction. Cheapest/ smaller. Less I 2 R losses

Question 8

If low tension current not given what formula do u use?

Answer 8

S / (£3 x VL) x impedance decimal form