Homework 225

When properly connected to deliver 208 volts from a 190-volt supply circuit (affected by voltage drop), a ___ kVA (standard size) 120 x 240 - 12/24-V transformer can operate a 29 amp load without being overloaded.

.75

A ___ kVA 240 × 480 - 24/48-V transformer that is connected to a 277-volt circuit should be used to operate a 230-volt 1Ø motor that draws 25 amps.

1

Which connection diagram, shown in Figure 224.108, should be used where the Supply Circuit is from a 1-pole breaker 120/240-volt, 3-ph, 4-W panelboard? The load is rated to operate at 12 volts. The transformer is a 120 × 240 — 12/24 volt.

1

Each winding set in a Group III, B-B transformer has a turns ratio of ___.

10:1

Buck-boost transformers are available with secondary windings that are rated to deliver voltages of ___.

12, 16, 24, 48

Which connection diagram, shown in Figure 224.108, should be used where the Supply Circuit is from a 2-pole breaker 120/240-volt, 3-ph, 4-W panelboard? The load is rated to operate at 12 volts. The transformer is a 120 × 240 — 12/24 volt.

2

Panel K, shown in Figure 225.102, is 120/240V, 3Ø, 4-W. The Control Panel requires 208 volts. Using a 120/240V-16/32V Group II transformer, the calculated voltage that would be applied to the Control Panel is ___ volts where the proper connections are made and the input voltage is exactly 240 volts.

212

Panel K, shown in Figure 225.102, is 120/240V, 3Ø, 4-W. The Control Panel requires 208 volts. Using a 120/240V-12/24V Group I transformer, the calculated voltage that would be applied to the Control Panel is ___ volts. Assume that proper connections are made and the input voltage is exactly 240 volts.

218

The supply circuit shown in Figure 225.104 is from a 2-P breaker in a 120/208-V, 3Ø, 4W panel. The foreign-made equipment is rated to operate at 220 volts. The supply-circuit voltage is 206 volts where it enters the B-B transformer. If Connection Diagram 3 from the Buck Boost Transformer Chart is used to connect a 120/240V-16/32V Group II transformer, the equipment will be supplied with ___ volts.

220

The supply circuit shown in Figure 225.104 is from a 2-P breaker in a 120/208-V, 3Ø, 4W panel. The foreign-made equipment is rated to operate at 220 volts. The supply-circuit voltage is 206 volts where it enters the B-B transformer. If Connection Diagram 4 from the Buck Boost Transformer Chart is used to connect a 120/240V-12/24V Group I transformer, the equipment will be supplied with ___ volts.

227

Refer to Figure 225.102. Panel K is 120/208V, 3Ø, 4-W. The Control Panel requires 230 volts. Where the proper connections are made and the input voltage is exactly 208 volts and a 120/240V-12/24V Group I transformer is used, the calculated voltage that would be applied to the Control Panel is ___ volts.

229

The supply circuit shown in Figure 225.104 is from a 2-P breaker in a 120/208-V, 3Ø, 4W panel. The foreign-made equipment is rated to operate at 220 volts. The supply-circuit voltage is 206 volts where it enters the B-B transformer. If Connection Diagram 4 from the Buck Boost Transformer Chart is used to connect a 120/240V-16/32V Group II transformer, the equipment will be supplied with ___ volts.

233

Refer to Figure 225.102. Panel K is 120/208V, 3Ø, 4-W. The Control Panel requires 240 volts. Using a 120/240V-16/32V Group II transformer, assuming the proper connections are made and the input voltage is exactly 208 volts, the calculated voltage that would be applied to the Control Panel is ___ volts.

236

Without being overloaded, a .5 kVA 120 × 240 - 12/24-V transformer can carry a maximum of ___ amps at 12 volts.

41.6

The circuit you have available to supply a 240-V, 150 A load is 208 volts. The rating for a B-B transformer that can operate the load at its rated voltage is ___ kVA.

5.0

Smaller transformers, typically 50 kVA and smaller, operating at 600 volts and below are normally wound for ___ polarity.

Additive

When buck-boost transformers are connected to boost the input voltage, the primary and secondary voltages are ___.

Additive

When supply voltage is to be changed ± 15%, a buck-boost transformer is connected as ___ to deliver the proper voltage to the load.

An autotransformer

Is this an example of an autotransformer, isolation transformer, or a distribution transformer.

Autotransformer

When buck-boost transformers are connected to ___ the input voltage, the primary and secondary voltages are additive.

Boost

When buck-boost transformers are connected to ___ the input voltage, the primary and secondary voltages are subtractive.

Buck

For a buck-boost transformer, the output voltage depends on the ___ used.

Connection diagram and input voltage

Buck boost transformers should only be used for voltage drop correction when the load is ___.

Constant

If the coils of a buck-boost transformer are connected in parallel, the voltages are added together.

False

A buck-boost transformer cannot be used as an isolating (insulating) transformer to supply power to low voltage control circuit. True or False

Flase

To produce an output of 12 volts, a 120 × 240-volt primary - 12/24-volt secondary transformer is connected as a(n) ___.

Isolating transformer

Generally, polarity is a term associated with ___ transformers.

Single-phase

Larger capacity and higher than 600-volt transformers are typically wound for ___ polarity.

Subtractive

When buck-boost transformers are connected to buck the input voltage, the primary and secondary voltages are ___.

Subtractive

An autotransformer has windings that are electrically connected to each other.

True

Buck-boost transformers can be used for voltage drop correction, but only if the load is constant. True or False

True

Where the circuit voltage is 208 volts, a buck-boost transformer can be used to operate a load that is rated to operate at 240 volts. True or False

True

Where the circuit voltage is 240 volts, a buck-boost transformer can be used to operate a load that is rated to operate at 12 volts. True or False

True