# Horrible Harmonics!

T

#### Tanty

Jan 1, 1970
0
I put together a small three-phase, star connected, synchronous generator
and measured a signal with nineth order harmonics and peak of 0.8 volts. The
signal looks allot like a roughly approximated square wave. My problem is
that after rectification using a three-phase full wave bridge rectifier, i
get a dc voltage of 1.1v. I expect to get root three times the peak (0.8V)
minus the two 0.7 volt drops. Does the fact that the generated signals are
not pure sinusoids have an effect on the voltage after rectification. If so
why?
Any ideas

L

#### litw

Jan 1, 1970
0
Yes, the squre wave is more "full" if you look at the output of the
rectifier. The average of the rectifier output from a square will be
larger than that from a sinusoid.
litw

T

#### Tony Williams

Jan 1, 1970
0
I put together a small three-phase, star connected, synchronous
generator and measured a signal with nineth order harmonics and
peak of 0.8 volts. The signal looks allot like a roughly
approximated square wave.

Three-phase F.W rectifiers are tricky, because the
line currents are drawn as rectangular current pulses,
of peak value equal to Idc.

If the source is Star connected then the winding
currents are also the direct line currents. The
winding will have a source impedance, and the
rectangular current-draw can flatten the output
voltage.
My problem is that after rectification
using a three-phase full wave bridge rectifier, i get a dc
voltage of 1.1v. I expect to get root three times the peak (0.8V)
minus the two 0.7 volt drops. Does the fact that the generated
signals are not pure sinusoids have an effect on the voltage
after rectification. If so why? Any ideas

You don't say what the dc-load is on the output of
the bridge and whether there is any smoothing-C.

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