ABB RELION 670 Series Product Manual page 34

Transformer protection RET670 2.1 IEC
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
2
=
I t K
as defined in standard IEEE C50.13.
2
where:
I is negative sequence current expressed
2
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 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.
34
K settings and the
M13789-3 v11
M13798-3 v14
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.
Overexcitation protection OEXPVPH
When the laminated core of a power transformer or
generator is subjected to a magnetic flux density
beyond its design limits, stray flux will flow into non-
laminated components that are not designed to carry
flux. This will cause eddy currents to flow. These eddy
currents can cause excessive heating and severe
damage to insulation and adjacent parts in a relatively
short time. The function has settable inverse operating
curves and independent alarm stages.
Voltage differential protection VDCPTOV
A voltage differential monitoring function is available. It
compares the voltages from two three phase sets of
voltage transformers and has one sensitive alarm step
and one trip step.
Loss of voltage check LOVPTUV
Loss of voltage check LOVPTUV is suitable for use in
networks with an automatic system restoration
function. LOVPTUV issues a three-pole trip command to
the circuit breaker, if all three phase voltages fall below
the set value for a time longer than the set time and the
circuit breaker remains closed.
The operation of LOVPTUV is supervised by the fuse
failure supervision FUFSPVC.
7. Frequency protection
Underfrequency protection SAPTUF
Underfrequency occurs as a result of a lack of
generation in the network.
Underfrequency protection SAPTUF measures frequency
with high accuracy, and is used for load shedding
1MRK 504 155-BEN F
M13808-3 v10
M13319-3 v9
SEMOD153862-5 v7
SEMOD171457-5 v7
M13349-3 v12
ABB