Energy Systems Ch. 2

Front 1

Is the turns ratio of the transformer the same as the ratio of voltages across the transformer?

Back 1

yes for an ideal transformer.
a = Np/Ns

Front 2

what is the leakage flux in a transformer?

Back 2

both the primary and secondary fluxes taking a path through the air. this causes an inductance to be produced in the transformer windings also know and the leakage inductance.

Front 3

copper losses

Back 3

(I^2)R losses
-resistive heating losses in the primary and secondary winding of the transformer

Front 4

eddy current losses

Back 4

-resistive heating losses but are in the core of the transformer.

Front 5

hysteresis losses

Back 5

-in the transformer core, due to the rearrangement of the magnetic domains in the core during each half cycle. also depends on voltage applied to transformer

Front 6

leakage flux

Back 6

-either primary or secondary flux which escapes the core and passes through transformer windings. produces leakage inductance. inductance produces a loss

Front 7

why does the power factor of a load affect the voltage regulation of a transformer?

Back 7

PF=p/vi so when the power factor is low the current is high.

Front 8

why does the short circuit test show only copper losses and not excitation losses in a transformer?

Back 8

-short circuit test has to be conducted at its full rated current of the transformer so the short circuit test is done on the high voltage side. Since in the short circuit test the applied voltage is 10% to 15% the core losses in the transformer are a small fraction of the total losses obtained in the short circuit test. so the core losses are neglected leaving only copper losses as a primary loss

Front 9

why does the open-circuit test essentially show only excitation losses and not cooper losses.

Back 9

-open circuit test has to be conducted at its full rated voltage so its customary to conduct open circuit test on low voltage side. the no load current will be very small so there will very little copper losses. leaving core losses

Front 10

how does the per-unit system of measurement eliminate the problem of different voltage levels in a power system?

Back 10

-each quantity is measured as a decimal fraction of some base level.

Front 11

what are transformer taps?

Back 11

-electrical connections on the transformer winding, each tap position give different voltage from the other. permits small changes in the turns ratio.

Front 12

what are the problems associated with the Y-Y three phase transformer connection?

Back 12

-if loads on the transfomer circuit are unbalanced, then the voltages on the phases of the transformer can become severely unbalanced.
- third harmonic voltages are very large

Front 13

what is a TCUL transformer?

Back 13

-with this transformer we are able to change the tap position on the secondary of the transformer without disconnecting the load.

Front 14

Can a 60-Hz transformer be operated on a 50-Hz system? what actions are necessary to enable this operation?

Back 14

...rocky? trevon?

Front 15

what happens to a transformer when it is first connected to a power line?

Back 15

- a large amount of magnetizing current is drawn from the supply lines

Front 16

what is a potential transformer?

Back 16

-special wound transformer with a high voltage primary and a low voltage secondary. more primary turns less secondary turns.

Front 17

what is a current transformer?

Back 17

-transformer with higher primary current ratings and lower secondary current ratings.

Front 18

why does one hear a hum when standing near a large power transformer?

Back 18

-the vibration of the laminated plates of the transformer core.