Application - ABB RELION REX640 Technical Manual

1MRS759142 C
4.5.5.6
REX640
Technical Manual
The 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
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in 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 operation timer is frozen to the prevailing value, but the OPERATE output is not
deactivated when blocking is activated. 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

A continuous or temporary voltage unbalance can appear in the network for various
reasons. The voltage unbalance mainly occurs due to broken conductors or
asymmetrical loads and is characterized by the appearance of a negative-sequence
component of the voltage. In rotating machines, the voltage unbalance results in a
current unbalance, which heats the rotors of the machines. The rotating machines,
therefore, do not tolerate a continuous negative-sequence voltage higher than
typically 1-2 percent x U
The negative-sequence component current I
synchronous machine, is linearly proportional to the negative-sequence component
voltage U . When U is P% of U
2 2
The negative-sequence overcurrent NSPTOC blocks are used to accomplish a
selective protection against the voltage and current unbalance for each machine
separately. Alternatively, the protection can be implemented with the NSPTOV
function, monitoring the voltage unbalance of the busbar.
If the machines have an unbalance protection of their own, the NSPTOV operation can
be applied as a backup protection or it can be used as an alarm. The latter can be
applied when it is not required to trip loads tolerating voltage unbalance better than the
rotating machines.
If there is a considerable degree of voltage unbalance in the network, the rotating
machines should not be connected to the network at all. This logic can be implemented
by inhibiting the closure of the circuit breaker if the NSPTOV operation has started.
This scheme also prevents connecting the machine to the network if the phase
sequence of the network is not correct.
.
n
, drawn by an asynchronous or a
2
, I is typically about 5 x P% x I
n 2
Section 4
Protection functions
.
n
793