ABB RELION REX640, Техническое руководство, Страница: 873 / 1960

Timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is
available in the Monitored data view.
Blocking logic
The binary input
BLOCK
can be used to block the function. The activation of the
BLOCK
input deactivates all outputs and resets internal timers.
4.5.4.6 Application
A sudden power loss, tap changer regulating failures and open line ends on long
lines are abnormal conditions which cause overvoltage in a power system. PSPTOV
is applied to power system elements, such as generators, transformers, motors and
power lines, to detect overvoltage conditions.
PSPTOV can be used in combination with low-current signals or a directional
reactive overpower function to identify the distribution line with an open remote
end. PSPTOV can also be used to initiate voltage correction measures, such as
insertion of shunt reactors or switching out capacitor banks, to control the voltage.
Overvoltage faced by the power transformer can lead to an overexcitation problem.
Overexcitation normally occurs when the voltage-to-frequency ratio increases much
above the design value resulting into transformer operation under a nonlinear
region. A transformer can be in such an overvoltage situation during a sudden loss
of load due to underfrequency load shedding. Overexcitation results in an increase
of the exciting current which leads to core heating and thus to transformer damage.
PSPTOV along with the underfrequency protection can be used for the protection of
the transformer during overexcitation.
Some common reasons leading to positive-sequence overvoltages are:
• Broken conductor falling to a crossing overhead line, transformer flash overfault
from high-voltage winding to low-voltage winding
• Malfunctioning of a voltage regulator or wrong settings under manual control
(symmetrical voltage increase)
• Low load compared to the reactive power generation (symmetrical voltage
increase)
PSPTOV prevents sensitive equipment from running under overvoltage conditions
which cause equipment overheating or stress on insulation material.
4.5.4.7 Signals
PSPTOV Input signals
Table 814: PSPTOV Input signals
Name Type Default Description
U3P SIGNAL - Three-phase voltages
BLOCK BOOLEAN 0=False Block signal for acti-
vating the blocking
mode
1MRS759142 F Protection functions
REX640
Technical Manual
873