Hi, i am currently analysing a static exciter setup of which i included
the following link to the schematic:
It is a compound-source exciter, e.g. power to the generator field is
delivered by a voltage source (Power Potential transformer) and a
current source (Boost Current Transformer). This type of exciter is
very similar of the General Electric SCT/PPT exciter, with the
exception that the current transformer is not saturable.
A Basler whitepaper says the following: "The SCT-PPT excitation system
uses both a generator stator voltage source (PPT) and a generator
stator current source (SCT) as the power source for the main field.
When the generator is offline and not supplying current to a load, the
excitation field current is supplied by the 3-phase, power potential
transformer. When the generator is on-line and supplying current to the
system load, a portion of the excitation field current is supplied by
the three saturable current transformers. Since there is both a current
source and a voltage source used in this compound-type excitation
system, linear reactors are utilized to prevent the PPT from being
shorted when the SCTs are saturated. These three magnetic components
(PPT, SCTs and Linear Reactors) constitute the power magnetics for this
compound-type excitation system, all of which have been designed
specifically for each generator to ensure the correct amount of
excitation field current is available for all load conditions. This
makes the SCT-PPT compound-type excitation system very desirable." Why
does the SCT short the PPT?
Basler also claims the following: " Under normal steady-state
conditions, the phasor summation between the PPT/linear reactors and
the SCTs provides the correct compensated voltage and current to the
generator field for all loads at any power factor." Can someone explain
to me how this works?
The Boost Current Transformer is a pretty weird device. It essentially
is a wound CT with 1 primary coil (3 windings) and 2 secondary coils
(19 & 3 windings). They secondaries are series connected to eachother
in a sort of 'delta way'. Isn't it illegal to connect two current
sources in series. Does someone have a explanation of this arrangement?
There is a second 'current transformer' in the schematics, T1, which i
do not know the function of. The output of this transformer is also
essentially a current source. So you have a rectified current source
and a rectified voltage source, wich are added and put in the field.
Can someone explain how this thing works?
The field current is controlled by a thyristor setup which shunts
current from the middle phase of U2, essentially shorting the Current
Transformer for half a cycle. Is there some relation to coil L2?
16 years ago