Functions
6-897SJ62 Manual
C53000-G1140-C121-1
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
2perm prim
I
NMotor
----------------------------
I
NMotor
I
CT sec
I
CT prim
-------------------
⋅⋅
=
Pickup Setting
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