8. PT disconnection check
The device has a PT disconnection check function. It will send an alarm signal when detects
the PT is disconnected.
PT
disconnection
criterion
:
①
There
is
a
phase
voltage
less
than
a
fixed
value
,
and
a
phase
current
is
greater
than
0
.
04In
,
used
to
detect
three
-
phase
voltage
loss
and
asymmetric
disconnection
;
②
The negative sequence voltage is greater than the fixed value, used to detect asymmetric
disconnection.
After
satisfying
any
of
the
above
conditions
,
the
device
reports
that
the
PT
is
disconnected
after
3s
delay
.
The
criterion
①
is
mainly
used
to
determine
the
symmetry
three
-
phase
disconnection
,
also
as
supplement
of
the
asymmetric
disconnection
at
the
same
time
.
The
current
blocking
condition
is
added
to
prevent
the
protection
device
falsely
transmitting
an
alarm
signal
when
no
voltage
is
applied
during
the
debugging
process
.
The criterion
②
is
specifically
used
to
determine
whether
there
is
PT
asymmetric
disconnection
.
9.
Low
frequency
load
shedding
function
The device is equipped with low-frequency load shedding function with low voltage blocking, current
blocking and slip blocking. When the device is put into operation, if the frequency exceeds its
normal range (45Hz-55Hz), the low frequency load shedding function is blocked. If the voltage is too
low, it may be a fault state. The protection device should trip and block the low frequency load
shedding function. If the current is too small, it may not be caused by the frequency reduction
caused by this circuit. Even if the current is reduced, it still won't be functioning, so the protection
device will block the low frequency load shedding function too. The A and C phases of the device
with larger currents will be blocked. When the circuit is started with a large load such as a motor,
the system frequency is rapidly reduced, so the slip lock is used.
10.
Control
loop
disconnection
The device is equipped with a control loop disconnection monitoring function, which uses the
combined contacts of the closing and tripping relays to judge whether the control loop is normal
through software. It is constituted by . When the fault occurs, the protection device
will send control loop disconnection alarm signal after 0.5 second delay.
11.
About Bus coupler
This device can be used for the bus coupler protection. If there are special requirements, pls tell us
before ordering.
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