Del Unit 28
If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a _____.
three-phase bank
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
11.55:1
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary line current?
1.6 A
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.
one-line
In an open delta with a center-tapped transformer, label the two ends of the center-tapped transformer as L2 and L3 and label the high leg as L1. The current flow in the neutral (center tap) is equal to _____.
AN = A1 + (A2 - A3)
What function is performed by dielectric oil?
All of the above
A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?
480 V
An open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____.
86.6 kVA
In an open delta with single-phase loads, the high leg must be identified by _____.
both a and b
When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. The correct voltage reading is _____.
zero volts
A delta-wye transformer has a turns ratio of 9:1. The primary line voltage is 3600 V. What is the secondary line voltage?
692.8 V
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?
8.66:1
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.
H; X
An open delta connection is made using _____ single-phase transformers.
two
A delta-wye transformer has its _____ connected as a delta and its _____ connected as a wye.
primary; secondary
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.
primary; secondary
A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
20:1
An open delta transformer is assembled from two 150 kVA transformers. The output power of the open delta is _____.
259.8 kVA
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the secondary phase current?
3.2 A
A wye-delta transformer has a secondary phase voltage of 480 V. A delta-connected resistive load has a resistance of 12 Ω in each leg. What is the current in each load leg?
40 A
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the current flow is in each load resistor?
5.54 A
For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides a(n) _____ three-phase transformer.
open delta with one transformer center tapped
When using an open delta with a center tapped transformer, one wire is the high leg. The high leg is the one that _____.
has the highest voltage
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary phase current?
1.6 A
When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced.
False
