3rd year level 1 lesson 14 transformers- 3 phase connections II

False

An open wye-open delta transformer bank will operate with a floating or grounded primary neutral bus.

False

Closed transformer banks that deliver 240-volt, 3-phase and 120/240-volt, single-phase power operate with fewer losses than open banks that supply similar loads.

2400 volts

Transformers installed on a 4.16-kilovolt, 4-wire wye system can have primary voltage ratings of 4,160 volts or ? .

False

Transformers with primary windings in a delta configurations can only be connected to delta 3-wire primary circuits.

True

Two delta-wye transformer banks can be paralleled if voltages and angular displacements are the same.

347 V/Y

To provide a 347/600-volt, 3-phase service, transformers with a secondary voltage rating of ? must be ? banked.

277 V

To supply 480-volt, 3-phase power with the transformer secondary coils banked in a wye configuration, the transformer secondary voltage ratings must be ? .

True

The grounded primary neutral of an open wye-open delta transformer bank carries full primary current.

36 A

A closed 150-kVA delta-wye bank is connected to a 2,400-volt, 3-wire line. The three transformers are operating at full load. The current through the primary leads is ? . (Round the FINAL answer to the nearest whole number.)

30 KVA

A closed transformer bank supplies 240-volt, 3-phase and 120/240-volt, single-phase power. With a single-phase load of 30 kVA and a 3-phase load of 60 kVA, the total load on each of the power pots is ? .

60 kva

A closed wye-delta transformer bank supplies 240-volt, 3-phase and 120/240-volt, single-phase power. With a single-phase load of 45 kVA and a 3-phase load of 90 kVA, the total load on the lighter transformer is ? .

24 kva

A closed wye-delta transformer bank supplies 240-volt, 3-phase power and 120/240-volt, single-phase power on a 4-wire service line. If the single-phase load is 36 kVA, the transformer with the grounded X2 bushing will supply ? of that load.

True

A transformer bank provides 240-volt, 3-phase and 120/240-volt, single-phase power. A vector line drawing of the secondary shows the 208-volt wild leg is at the point farthest from the grounded X2 terminal.

43.3 kva

An open transformer bank supplies 3-phase power on a 3-wire service line. The transformers are each rated at 25 kVA. The power rating of this bank is ? .

True

If a CSP transformer is used in a closed wye-delta transformer bank as the lighter, there is a risk of an open neutral condition on the single-phase, 120/240-volt circuit if the secondary circuit breaker is opened or trips.

heads to tails

The secondary vector lines of a wye-delta phasor drawing are connected ? .

True

Transformers with secondary coil ratings of 120/240 volts can supply a 240/416-volt service with the secondary coils connected in series and banked in a wye configuration.

parallel/ wye

Transformers with secondary voltage ratings of 120/240 volts can be used to supply a 120/208-volt load when the secondary coils are connected in ? and ? banked.

34.6 A

Under a balanced load condition, the primary transformer coils of a closed delta bank each draw 20 amperes. The current through each of the primary leads is ? .

240 v

Which one of the following 3-phase service types requires a delta secondary configuration?

False

Wye-delta transformer banks can be connected with either 30° or 120° angular displacements.

86.6 %

An open wye-open delta bank with equally sized transformers has a kVA rating of ? of the combined transformer power ratings.

173 kva

A 100-kVA transformer of a 300-kVA wye-delta bank has failed. Power has been restored by converting the system to open wye-open delta. The power rating of the open bank has been reduced to ? .

271 A

A 225-kVA delta-wye transformer bank feeds a 480-volt secondary circuit. The secondary windings draw 271 amperes at full load. The current through each of the two X terminal to star point conductors is ? .

361 A

A 300-kVA transformer bank with the secondary windings configured in wye feeds a balanced 480-volt load. At full load, or 100% of the power rating, the current through each of the secondary load lines is ? .

90 A

A 75-kVA closed wye-delta transformer bank feeds a 3-wire, 480-volt load. When operating at full rated capacity, the current on each of the three load lines is ? . (Round the FINAL answer to the nearest whole number.)