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HKB SINGLE POLE
Fig
!-Vectors for Normal Balanced Conditions and for a
Phase-A-to-Ground Fault.
120°
essentially
out-of-phase with the respec
tive zero sequence phase B and C components.
For
phase faults not
HQS
type
relay
does not
sequence currents are zero.
HZM-3
The type
relay is connected to receive
s�ar current and the delta voltage which leads
this
current.
With
proper
setting,
the
operate
on phase
faults
line
to
ground faults,
the
leading delta
voltage are approximately,
120°
apart as shown in Figure
This
figure
shows
conJitions.
When
a
fault
occurs,
V a collapses
fault
current
I a lags
system
angle
shown
delta voltage
V ab is reduced slightly and now
leads the relay current by approximately
R
X
On
an
and
impedance diagram as shown in
Figure
2,
the
type
HZM-3
faults
in
the
shaded
quadiant.
By off setting and shifting the ohm
circle
so
that
the
90
180°
region of
to
lag
relay
can
be
made
faults.
It
should
be
remembered
impedance
seen
by
the
inherently
higher for
2
RELAY CURRENT
involving ground,
the
operate as the zero
this
connection
and by
relay
can
be
made
to
only.
For close-iD
the
star current and
1.
V a ,
V b , V c
for normal
phase
a
line-to-ground
to
V a , and
the
this
voltage
by the
60°
in the figure.
The
120°.
relay sees
ground
area
in
the
second
relay
response
in the
is very limited,
the
inoperative
on
ground
that
the scalar
distance
relay
is
ground faults than for
-X
Fig. 2-0perating Characteristics of the Type HZM-3 Relay
on Single-Line-to-Ground Faults plotted on an
Diagram.
On
phase faults.
phase faults the delta relay
voltage
is
almost
completely
compared
to
a collapse
for
ground
faults.
Thus
ground faults
the impedance seen by the relay
will be outside the relay setting.
The
three poles
of the breaker are tripped
as follows for the various faults.
nal single line-to-ground the type
relays operate to trip only the faulted phase.
phase A to ground faults,
In
other words for
HKB
the
relay
contacts
HQS
phase
selector relay contacts
phase A
trip
pole.
For
&s
R
fault,
contact
and
pole, and
for a phase-C-to-ground fault, con
3c
R
tacts
and
close
For these
faults
contacts
HZM-3
the type
relay should not operate.
For
any
internal
three-phase,
phase,
or
two-phase to-ground fault contact
and
one or more
of the type
tacts ZA, Z B ,
or Zc close and energize CSl and
CS2
contactor
switches.
all three poles of the breaker.
to..., g round
faults
the phase
associated with the unfaulted phase will oper
ate
and initiate tripping of
simultaneously CSl and CS2 will also trip this
phase as well as the other two.
a-X
collapsed
as
57%
of not more than
for heavy close-in
For inter
HQS
HKB
and
R
close, and the type
S
A close to
a phase B-to-ground
close to trip phase B
to
trip
phase C pole.
Z A , A B ,
and Zc of
phase-to
R
HZM-3
relay con
These
in turn trip
On
two phase
selector contact
this phase,
but
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