Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.8.2.6
REX640
Technical Manual
Timer
Once activated, the Timer activates the START output. The time characteristics are
according to DT. When the operation timer has reached the value of Operate delay
time, the OPERATE output is activated. If a drop-off situation happens, that is, the
value of power drops below Start value before the operate delay is exceeded, the timer
reset state is activated. If the reset timer reaches the value set by Reset delay time, the
operate timer resets and the START output is deactivated.
The Timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time (DT). The value is
available in the Monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting Configuration/System/
Blocking mode, which selects the blocking mode. The BLOCK input can be controlled
by a binary input, a horizontal communication input or an internal signal of the
protection relay's program. The influence of the BLOCK signal activation is
preselected with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode,
the operate timer is frozen to the prevailing value. In the "Block all" mode, the whole
function is blocked and the timers are reset. In the "Block OPERATE output" mode,
the function operates normally but the OPERATE output is not activated.

Application

DOPPDPR is used to provide protection against an excessive power flow in the set
operating direction. The main application is the protection of generators and turbines.
It can also be used in feeder protection applications, for example, the ring network.
DOPPDPR in the forward direction can be used to protect the generators or motors
from delivering or consuming excess power. For example, the generator overpower
protection can be used to shed a noncritical feeder load or to start parallel generators.
A synchronous motor may start consuming more reactive power in case of loss of
excitation, in which case the forward overpower protection is used to detect such
condition.
The DOPPDPR function has many applications when used as reverse power
protection. A generator in a power plant converts mechanical energy to electrical
energy. Sometimes the mechanical power from a prime mover may decrease to a limit
that it does not cover the internal losses. The synchronous generator becomes a
synchronous motor and starts importing power from the system. The effect of a
generator acting as a motor implies no risk to the machine but can cause damage to the
prime mover. The extent of the damage depends on the type of the prime mover.
Steam turbines become overheated easily if the steam flow drops too low or if the
steam ceases to flow through the turbine. The break of a main steam pipe, damage to
Section 4
Protection functions
965