Voltage Protection; Capacitor Bank Protection (Cbpgapc); Negative Sequence Time Overcurrent Protection For Machines; Two Step Undervoltage Protection Uv2Ptuv/Ov2Ptov - ABB RET670 Product Manual

Transformer protection RET670 2.0
Product version: 2.0
Voltage-restrained time overcurrent protection VRPVOC
Voltage-restrained time overcurrent protection (VRPVOC)
function can be used as generator backup protection against
short-circuits.
The overcurrent protection feature has a settable current level
that can be used either with definite time or inverse time
characteristic. Additionally, it can be voltage controlled/
restrained.
One undervoltage step with definite time characteristic is also
available within the function in order to provide functionality for
overcurrent protection with undervoltage seal-in.

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
2
=
I t K
generator as defined in standard IEEE C50.13.
2
where:
I is negative sequence current expressed in
2
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
ABB
NS2PTOC has a wide range of
capability of detecting and tripping for negative sequence
currents down to the continuous capability of a generator.
In order to match the heating characteristics of the generator a
reset time parameter can be set.
A separate definite time delayed output is available as an alarm
feature to warn the operator of a potentially dangerous
situation.

6. Voltage protection

Two step undervoltage protection UV2PTUV
Undervoltages can occur in the power system during faults or
abnormal conditions. Two step undervoltage protection
(UV2PTUV) function can be used to open circuit breakers to
prepare for system restoration at power outages or as long-
time delayed back-up to primary protection.
UV2PTUV has two voltage steps, each with inverse or definite
time delay.
UV2PTUV has a high reset ratio to allow settings close to
system service voltage.
Two step overvoltage protection OV2PTOV
Overvoltages may occur in the power system during abnormal
conditions such as sudden power loss, tap changer regulating
failures, and open line ends on long lines.
Two step overvoltage protection (OV2PTOV) function can be
used to detect open line ends, normally then combined with a
directional reactive over-power function to supervise the
system voltage. When triggered, the function will cause an
alarm, switch in reactors, or switch out capacitor banks.
OV2PTOV has two voltage steps, each of them with inverse or
definite time delayed.
OV2PTOV has a high reset ratio to allow settings close to
system service voltage.
Two step residual overvoltage protection ROV2PTOV
Residual voltages may occur in the power system during earth
faults.
Two step residual overvoltage protection ROV2PTOV function
calculates the residual voltage from the three-phase voltage
input transformers or measures it from a single voltage input
transformer fed from an open delta or neutral point voltage
transformer.
ROV2PTOV has two voltage steps, each with inverse or definite
time delay.
Reset delay ensures operation for intermittent earth faults.
1MRK 504 141-BEN C
K settings and the sensitivity and
31