Programming Settings - Siemens SIPROTEC 7SJ62 Instruction Manual

Logic
6.7.2

Programming Settings

General
Definite Time Ele-
ments
7SJ62 Manual
C53000-G1140-C121-1
Figure 6-42 shows the logic diagram for negative sequence protection. The protection
may be blocked via a binary input.
When the negative sequence protection criteria are no longer satisfied (i.e. all phase
currents drop below 10 % of the nominal relay current or at least one phase current is
greater than four (4) times the nominal device current, the tripping time delay is imme-
diately reset.
Negative sequence protection is configured at address  . If only the definite
time elements are desired, address  should be set to 'HILQLWH 7LPH RQO\.
If both definite time and inverse time elements are to be used, address  should
be set to 7LPH 2YHUFXUUHQW &XUYH $16I, and if negative sequence protection is
not needed, address  should be set to 'LVDEOHG.
Negative sequence protection is switched 21 or 2)) at address  )&7 .
Refer to phase rotation via binary input section 6.1.1.1 and 6.16.
The default pickup settings and delay settings of the negative sequence time-overcur-
rent relay elements are generally sufficient for most applications. If the device is used
to protect a motor, and data is available from the manufacturer regarding the allowable
long-term load imbalance and the allowable load imbalance per unit of time, this data
should be used as the basis for selecting the pickup and delay settings. In this situa-
tion, it is important to ensure that the values given by the manufacturer represent the
primary values for the motor. For example, if the long-term allowable thermal inverse
current (with respect to the nominal motor current) is given, this value is used to cal-
culate the settings for the negative sequence time-overcurrent element. For this situ-
ation:
Pickup Setting
where I Permissible Thermal Inverse Current of the Motor
2 perm prim
I Nominal Motor Current
N Motor
I Secondary Nominal Current of the Current Transformer
CT sec
I Primary Nominal Current of the Current Transformer
CT prim
The pickup and delay settings associated with the 46-1 element are set at addresses
  3,&.83 and   '(/$< respectively while the pickup and delay
settings for the 46-2 element are set at address   3,&.83 and  
 '(/$< respectively. Typically the 46-1 element is set with a lower pickup value and
higher time delay than the 46-2 element. This allows the 46-1 element to act as an
alarm while the 46-2 element will initiate fast tripping for severe imbalances.
If the 46-2 element is used for fast tripping against severe imbalances, the pickup val-
ue should be set at 60 % of the nominal phase current. This will ensure pickup for the
complete loss of one phase. On the other hand, because the loss of a phase could be
I
  I
2perm prim
⋅
--------------------------- -
I
=
 
2 NMotor
I
NMotor
Functions
I
CT sec
⋅
------------------ -
I
CT prim
6-89