1 The transformer is connected up as shown. The line to line voltage on the outp
ID: 2250005 • Letter: 1
Question
1 The transformer is connected up as shown. The line to line voltage on the output is 192V. How should the transformer be wired to result in a 208 line voltage from the secondary? 1. SQUARE D ENERGY EFFICIENT LOW VOLTAGE DISTRIBUTION TRANSFORMER, DRY TYPE CAT NO.: EX1ST3H STYLE NO.: NVE7091103 KVA:15 PHASE: 3 FREQ: 60 %IZ: 4.18 PRI (H) VOLTS: 480D SEC (X) VOLTS 208Y/120 PRI (H) AMPS:18 SEC (X)AMPS: 418 RISE: 150 SERAL NO: 1012517014 DATE CODE: 1704 WEIGHT:196 LBS TYPE: S0 AMB 40 INS CLASS: 220 c EFFICIENCY EFF. 9789% @ 35% LOAD & 75C MEETS FINAL RULE U.S. 10 CPR 431 APR 201s NCL 17K TYPE 1 TYPE SR WHEN 7 TO BE IN ACCORDANCE WITH THE NATIONAL ELECTRIC CODE SECTION 450.9, AND UL1561, MAINTAIN MINIMUM CLEARANCE OF 0S INCH TO WALL OR OTHER OBSTRUCTIONS BASIC MODEL NO. 024EX0015T480020RYA-004 TAP POSITIONS PRI TAP VOLTS 1 504 2 491 3 480 4 467 5 456 6 443 x1 2. What is the turns ratio of the transformer if tap 3 is used? 3. Explain the operating principles of a DC motorExplanation / Answer
1)
For line voltage VL-L = 192 V
Primary is connected to tap = ?
Turns ratio = Vp / Vs (Phase Voltages)
Given transformer rating is 480 V : 208 V (Line-Line Voltage)
From the tap setting table primary should be connected to tap 3 to get primary line voltage 480 V and secondary line voltage to 208 V.
As we know for Delta side line voltage is equal to phase voltage and for star side phase voltage is line voltage by 1.732.
Turns ratio n = 480 / (208/1.732) = 4
Tap setting for 192 V line voltage on secondary is Vs = 192/1.732 = 110.851 V
Primary line voltage is equal to phase voltage Vp = 4*110.851 = 443 V (Line to Line)
Tap = 6 ; from tap setting table.
2)
Turns ratio for tap=3 is
480 : 120
n = 480/120 = 4 ; .................. turns ratio
3)
Operating principle of DC motor which obeys fleming left-hand rule i.e when a current carrying conductor is placed in a magnetic field, mechanical force is experienced on the conductor. This force acts perpendicular to current and induced flux. The conductor starts moving in the direction of the force.
Fleming left-hand rule direction of current is given by center finger, induced flux is given by forefinger and force is given by thumb. The rotor of DC motor starts rotating in the direction of thumb.
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