Thermal Overload Protection, One Time Constant Lcpttr/Lfpttr; Thermal Overload Protection, Two Time Constant Trpttr; Breaker Failure Protection Ccrbrf; Pole Discordance Protection Ccpdsc - ABB RET670 Product Manual

Transformer protection RET670 2.0
Product version: 2.0
Sensitive directional residual overcurrent and power
protection SDEPSDE
In isolated networks or in networks with high impedance
earthing, the earth fault current is significantly smaller than the
short circuit currents. In addition to this, the magnitude of the
fault current is almost independent on the fault location in the
network. The protection can be selected to use either the
residual current or residual power component 3U0·3I0·cos j,
for operating quantity with maintained short circuit capacity.
There is also available one nondirectional 3I0 step and one 3U0
overvoltage tripping step.
No specific sensitive current input is needed. 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 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.

Thermal overload protection, two time constant TRPTTR

If a power transformer reaches very high temperatures the
equipment might be damaged. The insulation within the
transformer will experience forced ageing. As a consequence of
this the risk of internal phase-to-phase or phase-to-earth faults
will increase.
The thermal overload protection estimates the internal heat
content of the transformer (temperature) continuously. This
estimation is made by using a thermal model of the transformer
with two time constants, which is based on current
measurement.
Two warning levels are available. This enables actions in the
power system to be done before dangerous temperatures are
reached. If the temperature continues to increase to the trip
value, the protection initiates a trip of the protected
transformer.
The estimated time to trip before operation is presented.
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Breaker failure protection CCRBRF

Breaker failure protection (CCRBRF) ensures a fast backup
tripping of surrounding breakers in case the own breaker fails to
open. CCRBRF can be current-based, contact-based or an
adaptive combination of these two conditions.
Current check with extremely short reset time is used as check
criterion to achieve high security against inadvertent operation.
Contact check criteria can be used where the fault current
through the breaker is small.
CCRBRF can be single- or three-phase initiated to allow use
with single phase tripping applications. For the three-phase
version of CCRBRF the current criteria can be set to operate
only if two out of four for example, two phases or one phase
plus the residual current start. This gives a higher security to the
back-up trip command.
CCRBRF function can be programmed to give a single- or
three-phase re-trip of the own breaker to avoid unnecessary
tripping of surrounding breakers at an incorrect initiation due to
mistakes during testing.

Pole discordance protection CCPDSC

An open phase can cause negative and zero sequence currents
which cause thermal stress on rotating machines and can
2
t
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.
Directional over/underpower protection GOPPDOP/
GUPPDUP
The directional over-/under-power protection GOPPDOP/
GUPPDUP can be used wherever a high/low active, reactive or
apparent power protection or alarming is required. The
functions can alternatively be used to check the direction of
active or reactive power flow in the power system. There are a
number of applications where such functionality is needed.
Some of them are:
• detection of reversed active power flow
• detection of high reactive power flow
Each function has two steps with definite time delay.
Broken conductor check BRCPTOC
The main purpose of the function Broken conductor check
(BRCPTOC) is the detection of broken conductors on protected
power lines and cables (series faults). Detection can be used to
give alarm only or trip the line breaker.
1MRK 504 141-BEN C
ABB