Hitachi Relion REL670 Product Manual page 42

Line distance protection REL670
Version 2.2
No specific sensitive current input is needed. Sensitive
directional residual overcurrent and power protection
(SDEPSDE) can be set as low 0.25% of IBase.
Thermal overload protection, one time constant
LCPTTR/LFPTTR
The increasing utilization of the power system closer to the
thermal limits has generated a need of a thermal overload
protection for power lines.
A thermal overload will often not be detected by other
protection functions and the introduction of the thermal
overload protection can allow the protected circuit to
operate closer to the thermal limits.
The three-phase current measuring protection has an I
characteristic with settable time constant and a thermal
memory. The temperature is displayed in either Celsius or
Fahrenheit, depending on whether the function used is
Thermal overload protection (LCPTTR) (Celsius) or
(LFPTTR) (Fahrenheit).
An alarm level gives early warning to allow operators to take
action well before the line is tripped.
Estimated time to trip before operation, and estimated time
to reclose after operation are presented.
Breaker failure protection CCRBRF
Breaker failure protection (CCRBRF) ensures a fast backup
tripping of the surrounding breakers in case the own
breaker fails to open. CCRBRF measurement criterion can
be current based, CB position based or an adaptive
combination of these two conditions.
A current based check with extremely short reset time is
used as check criterion to achieve high security against
inadvertent operation.
CB position check criteria can be used where the fault
current through the breaker is small.
CCRBRF provides three different options to select how t1
and t2 timers are run:
1. By external start signals which is internally latched
2. Follow external start signal only
3. Follow external start signal and the selected
FunctionMode
CCRBRF can be single- or three- phase initiated to allow its
use with single phase tripping applications. For the three-
phase application of the CCRBRF the current criteria can be
set to operate only if "2 elements operates out of three
phases and neutral" for example; two phases or one phase
plus the residual current start. This gives a higher security
to the backup trip command.
The CCRBRF function can be programmed to give a single-
or three- phase retrip to its own breaker to avoid
42
unnecessary tripping of surrounding breakers at an
incorrect initiation due to mistakes during testing.
Stub protection STBPTOC
When a power line is taken out of service for maintenance
and the line disconnector is opened in multi-breaker
M12020-4 v14
arrangements the voltage transformers will mostly be
outside on the disconnected part. The primary line distance
protection will thus not be able to operate and must be
blocked.
The stub protection (STBPTOC) covers the zone between
the current transformers and the open disconnector. The
three-phase instantaneous overcurrent function is released
from a normally closed, NC (b) auxiliary contact on the line
2
t
disconnector.
Overcurrent protection with binary release BRPTOC
Overcurrent protection with binary release (BRPTOC) is a
simple, non-directional three-phase overcurrent protection
function with definite time delay. A single step is available
within the function. The current pickup level and definite
time delay can be set independently. It is possible to
release the function operation via a binary signal. If the
binary signal is not connected, the function will
automatically operate in a continuous mode of operation.
Several function instances are available.
From the measured three-phase currents, various types of
M11550-6 v19
measurement modes such as DFT, Peak, and Peak-to-peak
can be selected for the BRPTOC operation.
Peak and Peak-to-Peak measurement mode allow this
function to be used as instantaneous over-current protection
as well. If required by application, short time delay can also
be applied.
BRPTOC can be used for different line and transformer
protection applications. If required, it can also be used to
supervise on-load tap-changer operation.
Pole discordance protection CCPDSC
An open phase can cause negative and zero sequence
currents which cause thermal stress on rotating machines
and can cause unwanted operation of zero sequence or
negative sequence current functions.
Normally the own breaker is tripped to correct such a
situation. If the situation persists the surrounding breakers
should be tripped to clear the unsymmetrical load situation.
The Pole discordance protection function (CCPDSC)
operates based on information from auxiliary contacts of the
circuit breaker for the three phases with additional criteria
from unsymmetrical phase currents when required.
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