Functions
6-89
7SJ63 Manual
C53000-G1140-C120-1
Logic
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.
6.7.2
Programming Settings
General
Negative sequence protection is configured at address
. If only the definite
time elements are desired, address
should be set to
'HILQLWH7LPHRQO\
.
If both definite time and inverse time elements are to be used, address
should
be set to
7LPH2YHUFXUUHQW&XUYH$16
I, and if negative sequence protection is
not needed, address
should be set to
'LVDEOHG
.
Negative sequence protection is switched
21
or
2))
at address
)&7
.
Refer to phase rotation via binary input section 6.1.1.1 and 6.16.
The default pickup settings and delay settings of the negative sequence time-overcur-
rent relay elements are generally sufficient for most applications. If the device is used
to protect a motor, and data is available from the manufacturer regarding the allowable
long-term load imbalance and the allowable load imbalance per unit of time, this data
should be used as the basis for selecting the pickup and delay settings. In this situa-
tion, it is important to ensure that the values given by the manufacturer represent the
primary values for the motor. For example, if the long-term allowable thermal inverse
current (with respect to the nominal motor current) is given, this value is used to cal-
culate the settings for the negative sequence time-overcurrent element. For this situ-
ation:
Definite Time Ele-
ments
The pickup and delay settings associated with the 46-1 element are set at addresses
3,&.83
and
'(/$<
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
where I
2 perm prim
Permissible Thermal Inverse Current of the Motor
I
N Motor
Nominal Motor Current
I
CT sec
Secondary Nominal Current of the Current Transformer
I
CT prim
Primary Nominal Current of the Current Transformer
I
2
I
2 perm prim
I
NMotor
----------------------------
I
NMotor
I
CT sec
I
CT prim
-------------------
⋅
⋅
=
Pickup Setting
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