Training and Development
LESSON PLAN
SEPT 2012
COURSE
2nd Year Apprenticeship
SUBJECT AND TIME
Transformers Class #4
(2 Hrs)
OBJECTIVE
1. Define :Balanced 3 phase system WYE
2. State the phase relationship for the 3 phase voltages in a three-phase system
WYE
3. State and Verify by connection the relationship between phase and line for a
WYE
a. Current
b. Voltage
4. Describe Vectors and connections for WYE
5. Determine given nameplate information, the supply voltage and required load
voltage, the connection requires
6. Determine the expected secondary voltage using a vector
7. Determine Total KVA of Bank
INSTRUCTIONAL MATERIAL
3 Phase Alternators PP
WYE PP
REFERENCE MATERIAL
N/A
ASSIGNMENTS
Transformers
1
Training and Development
Instruction:
1. Go through alternator PP
2. GO through WYE PP
3 Phase WYE Connections PRIMARY
1. Explain and Draw 3 Phase WYE connection from the generator to the xfmr
a. On the board draw 3 phase generator connected in WYE Fig 1
b. Draw windings over the primary vector and show how they are
connected
i. Note Phase –Grnd x 1.732 ex. 14.4 x 1.732=24940KV
ii.
Transformers
2
Training and Development
c. Add Grnd to connection to the star point of the WYE to create 3 Phase
4W WYE 14.4/25 KV Primary Fig 5
d. Flatten Vector and Draw in the Primary Windings Fig 6
Transformers
3
Training and Development
WYE Connected Secondary
2. Explain that in order to get 208 V L-L the connection requires 120 V P-G
a. The secondary windings of each transformer are paralled to provide 120V
P-G at full KVA Capacity of the xfmr
3. Draw a vector for WYE Secondary
a. Show secondary windings (X1,X2 and X3)
b. Identify XFMRS
c. Identify A,B and C phases
d. NOTE P-G x 1.732 EG. 120V x 1.732 =208V
e. Add the ground in Last
4. Flatten the vector and draw secondary windings (WYE –WYE)
Transformers
4
Training and Development
ONLY DISCUSS IF
QUESTION COMES UP
Secondary windings not paralleled
P-G x 1.732 = L-L = 240 x 1.732 = 416V
Transformer Bank Sizing & Capacity
 WYE connected banks each transformer takes 1/3 of the load so all 3 xfmrs
are equal in KVA rating
 For our purpose we do not serve a single phase load from a WYE Bank
Ex 3- 10kva 14400/120/240V XFMR in a WYE Bank
3ø KVA Cap (St)= S x 3-xfmrs
= 10 kva x 3
= 30 KVA
 To size the bank for proper kva of each transformer
St/3 = 30 KVA/3(xfmrs) = 10 KVA
Transformers
5
Training and Development
Board Exercise #1 (Half up to white board other half draw on paper)
 Line 25 KV
 3 x 14400/120/240 15 KVA
 Require 120/208 V 3 Phase 4W
 Total KVA? (45)
Board Exercise #2
 Phase 2400V
 3 x 2400/120/240 25KVA
 Require 120/208V 3 Phase 4 W
 Total KVA? (75)
End Class
Transformers
6