UNIT 28-3 PHASE TRANSFORMERS

Which of the following are considered "triplen" harmonics?

3rd, 9th, 15, 21st

Three phase vs single phase loads

3 phase transformer connections (ideal conditions occur when connecting to a well balanced 3 phase load)

A 3-phase transformer bank has the secondary connected in a wye configuration. The center-tap is used as a neutral conductor. If the voltage across any phase conductor and the neutral is 120 volts, how much voltage would be applied to the 3-phase load connected to the secondary of this transformer bank?

208

A 3-phase transformer connection has a delta-connected secondary, and one of the transformers has been center-tapped to form a neutral conductor. The phase-to-neutral value of the center-tapped secondary winding is 120 volts. If the high leg is connected to a single-phase load, how much voltage will be applied to that load?

208

A 3-phase transformer connection has a delta-connected primary and a wye-connected secondary. The center tap of the wye is used as a neutral conductor. If the line-to-line voltage is 480 volts, what is the voltage between any one phase conductor and the neutral conductor?

277

What is the frequency of the 2nd harmonic?

120 hertz

A 3-phase transformer bank has the primary and secondary windings connected in a wye configuration. The secondary center tap is being used as a neutral to supply single-phase loads. Will connecting the center-tap connection of the secondary to the center-tap connection of the primary permit the secondary voltage to stay in balance when a single-phase load is added to the secondary?

yes

A positive-rotating harmonic is more harmful to an induction motor than a negative-rotating harmonic.

False

An open-delta 3-phase transformer system has one transformer center-tapped to provide a neutral for single phase voltages. The voltage from the line to center tap is 277 volts. If a single phase load is connected across the two line conductors and a neutral of the transformer, and one of the lines has a current of 80 amps the other line has 68 amps, The total current flowing in the neutral is 148 amps.

False

Construction of a 3 phase transformer

Three single phase transformers wound on a single core.

Scott connection

Used to convert 3 phase power to 2 phase. Using two single phase transformers

A 22.5 kVA single phase transformer is tested with a true-RMS ammeter and an ammeter that indicates the peak value. The true-RMS reading is 94 amps.The peak reading is 204 amps. Should this transformer be derated?

Yes