Eli 3rd Year
An isolation transformer is routinely used where "clean power" is required to operate delicate electronic equipment such as computers.
True
Where a delta bank of three transformers is installed to serve a load that is comprised mostly of 120-volt loads (balanced), each power transformer must supply ___ required by the 120-volt loads.
about a third of the current
Power losses in transmission lines can be reduced by ___ voltage.
increasing
Temperature rise in a transformer is the ___ without damage occurring to the windings.
maximum temperature above the surrounding air temperature that can occur in the windings
Transformers are ___ efficient when the windings are cooled.
more
If a transformer "hums" after it is energized, ___.
the transformer is operating normally
When a 120/208-volt, 3Ø, 4-W supply system (typically a transformer) delivers power to a load, the coil (or winding) voltage equals ___.
EL ÷ 1.732
A 3Ø transformer supplies 120/240 volts to a 3Ø, 4-wire panelboard. From the breaker in space ___, there will be 208 volts to ground (or neutral).
10
Power losses in transmission lines can be reduced by ___ current.
decreasing
A liquid-filled transformer is cooled by immersion in a container that is filled with ___.
either a or b Oil or Silicone
___ are installed on dry-type distribution transformers to make them weather resistant and suitable for outdoor installations.
Weather shields
A 480 to 120/208 V transformer has a current in each wye-connected secondary winding of 102 amps. How much line current is the load drawing from the transformer?
102
A wye-connected transformer secondary has a line-to-line voltage of 208 volts. The voltage across each winding is ___ volts.
120
Refer to Figure 221.201. The transformer supplies 120/208 volts on its secondary ("X") windings. This means that each winding (X1 to X2 or X3 to X4) is supplying ___ volts.
120
In a 120/208-volt wye circuit, what is the voltage between BØ and ground?
120 volts
If the temperature rise of a transformer is 50ºC, this equals _____ºF.
122
Figure 221.201. This is a ___ connected bank.
Delta Wye
The primary of a 112.5 KVA transformer is 480-volt delta. The secondary is 240-volt delta and is delivering 100 amps to a 3Ø load. Given these conditions, ___ amps of current are flowing through each primary winding.
29
The delta-connected secondary of a transformer is delivering a line current of 54 amps. What is the phase (coil or winding) current? The secondary voltage is 240 volts line-to-line.
31.2 amps
Where a delta bank of three transformers is installed to serve a load that is comprised mostly of 120-volt loads, all three transformers must be the same size.
False
