When a surge impinges on the line-end coil
of a machine winding, see Figure 1b, it breaks
up into transmitted surges moving away from the
overhang region and a reflected surge travelling
back into the surge source network. As mentioned,
a coil of a machine winding consists of two slot
sections and two end connections, having each of
these regions different electrical characteristics.
The transmitted surges propagate along the overhang
section until they reach the slot entry, where
they encounter a change in surge impedance; this
change causes further reflections and refractions.
Each turn of the coil may be regarded as a single
conductor transmission line coupled to its neighbour
turns, being the end of one turn the start of
the next turn, and the coil can be regarded as a
multiconductor transmission line in that all the
turns run in parallel, see Figure 1. One phase of
the armature winding consists of series connection
of the separate coils of the phase. The complete
model of a machine consists of the models of the
winding phases which can be either delta or star
connected.
Small and large rotating machines behave
differently under high frequency transient voltages.
Small machines, which have many turns or
coils in the same stator slot, have high capacitances
between turns and coils as well as high
mutual inductances, so under transient conditions
they behave like transformers. Larger machines,
which have fewer and longer turns per slot, have
both smaller capacitances between turns and
smaller mutual inductances, and their behaviour
is closer to that of transmission lines (Chowdhuri,
2004).
The number of stator coils in series in formwound
induction and synchronous machines varies
over a considerable range; from a minimum
of three or so in large low-voltage machines to
more than 20 in small high-voltage machines.
A generator, in general, has more coils than a
transformer, but they are connected in parallel.
Generator coils, on the other hand, have relatively
few turns. Hydro generators are different from
turbo generators in that the slots are shorter and
the end regions longer. In addition, they have
more turns per coil than turbo generators. In
general, a generator is connected to its step-up
transformer and the concern is with transients
caused by switching and lightning surges on the
power system that reach the generator through the
step-up transformer, and with disturbances such
as faults and circuit breaker operations occurring
on the generator bus
When a surge impinges on the line-end coil
of a machine winding, see Figure 1b, it breaks
up into transmitted surges moving away from the
overhang region and a reflected surge travelling
back into the surge source network. As mentioned,
a coil of a machine winding consists of two slot
sections and two end connections, having each of
these regions different electrical characteristics.
The transmitted surges propagate along the overhang
section until they reach the slot entry, where
they encounter a change in surge impedance; this
change causes further reflections and refractions.
Each turn of the coil may be regarded as a single
conductor transmission line coupled to its neighbour
turns, being the end of one turn the start of
the next turn, and the coil can be regarded as a
multiconductor transmission line in that all the
turns run in parallel, see Figure 1. One phase of
the armature winding consists of series connection
of the separate coils of the phase. The complete
model of a machine consists of the models of the
winding phases which can be either delta or star
connected.
Small and large rotating machines behave
differently under high frequency transient voltages.
Small machines, which have many turns or
coils in the same stator slot, have high capacitances
between turns and coils as well as high
mutual inductances, so under transient conditions
they behave like transformers. Larger machines,
which have fewer and longer turns per slot, have
both smaller capacitances between turns and
smaller mutual inductances, and their behaviour
is closer to that of transmission lines (Chowdhuri,
2004).
The number of stator coils in series in formwound
induction and synchronous machines varies
over a considerable range; from a minimum
of three or so in large low-voltage machines to
more than 20 in small high-voltage machines.
A generator, in general, has more coils than a
transformer, but they are connected in parallel.
Generator coils, on the other hand, have relatively
few turns. Hydro generators are different from
turbo generators in that the slots are shorter and
the end regions longer. In addition, they have
more turns per coil than turbo generators. In
general, a generator is connected to its step-up
transformer and the concern is with transients
caused by switching and lightning surges on the
power system that reach the generator through the
step-up transformer, and with disturbances such
as faults and circuit breaker operations occurring
on the generator bus
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