ABB 615 Series ANSI, Техническое руководство, Страница: 249 / 713

Section 4
1MAC050144-MB C
Protection functions
242 615 series ANSI
Technical Manual
Timer
Once activated, the timer activates the PICKUP output. The time characteristic is
according to DT. When the operation timer has reached the value set by Trip delay time,
the TRIP output is activated if the overvoltage condition persists. If the negativesequence
voltage normalizes before the module trips, the reset timer is activated. If the reset timer
reaches the value set by Reset delay time, the trip timer resets and the PICKUP output is
deactivated.
The timer calculates the pickup duration value PICKUP_DUR which indicates the ratio of
the pickup situation and the set trip time. The value is available through the Monitored data
view.
Blocking logic
There are three operation modes in the blocking functionality. 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 IED.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the
trip timer is frozen to the prevailing value. In the "Block all" mode, the whole function is
blocked and the timers are reset. the "Block TRIP output" mode, the function operates
normally but the
TRIP
output is not activated.
4.2.4.5 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 V
n
.
The negative-sequence component current I
2
, drawn by an asynchronous or a synchronous
machine, is linearly proportional to the negative-sequence component voltage V
2
. When
V
2
is P% of V
n
, I
2
is typically about 5 x P% x I
n
.
The negative-sequence overcurrent 46 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 47 function, monitoring the voltage unbalance of
the busbar.
If the machines have an unbalance protection of their own, the 47 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 47 operation has started. This scheme also prevents
connecting the machine to the network if the phase sequence of the network is not correct.