ABB RET670 Product Manual page 16

Transformer protection RET670
Customized
Product version: 1.2
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 CCRPLD
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 Polediscordance protection function CCRPLD
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. Reset times for both steps can be set as
well.
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.
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1MRK 504 117-BEN D
Capacitor bank protection (CBPGAPC)
Shunt Capacitor Banks (SCB) are used in a power
system to provide reactive power compensation
and power factor correction. They are as well
used as integral parts of Static Var Compensators
(SVC) or Harmonic Filters installations. Capacitor
bank protection (CBPGAPC) function is specially
designed to provide protection and supervision
features for SCBs.
Negative sequence time overcurrent protection
for machines NS2PTOC
Negative-sequence time overcurrent protection
for machines NS2PTOC is intended primarily for
the protection of generators against possible
overheating of the rotor caused by negative
sequence current in the stator current.
The negative sequence currents in a generator
may, among others, be caused by:
• Unbalanced loads
• Line to line faults
• Line to earth faults
• Broken conductors
• Malfunction of one or more poles of a circuit
breaker or a disconnector
NS2PTOC can also be used as a backup
protection, that is, to protect the generator in
case line protections or circuit breakers fail to
clear unbalanced system faults.
To provide an effective protection for the
generator for external unbalanced conditions,
NS2PTOC is able to directly measure the negative
sequence current. NS2PTOC also has a time
delay characteristic which matches the heating
characteristic of the generator
defined in standard IEEE C50.13.
where:
I is negative sequence current
2
expressed in per unit of the rated
generator current
t is operating time in seconds
K is a constant which depends of
the generators size and design
NS2PTOC has a wide range of
sensitivity and capability of detecting and tripping
2
=
I t K
as
2
K settings and the
ABB