Application - ABB 615 series Technical Manual

Section 4
Protection functions
4.5.4.5
4.5.4.6
634

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
The negative-sequence component current I
synchronous machine, is linearly proportional to the negative-sequence component
voltage V . When V is P% of V
2 2
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 picked up. This scheme
also prevents connecting the machine to the network if the phase sequence of the network
is not correct.
An appropriate value for the setting parameter Voltage pickup value is approximately 3
percent of V . A suitable value for the setting parameter Trip delay time depends on the
n
application. If the 47 operation is used as a backup protection, the trip time should be set
in accordance with the trip time of 46 used as the main protection. If the 47 operation is
used as the main protection, the trip time should be approximately one second.
Signals
Table 539: 47 Input signals
Name Type
V SIGNAL
2
BLOCK BOOLEAN
, drawn by an asynchronous or a
2
, I is typically about 5 x P% x I
n 2
Default Description
0 Negative phase sequence voltage
0=False Block signal for activating the blocking mode
1MAC059074-MB A
.
n
.
n
615 series ANSI
Technical Manual