NR Electric PCS-9611, Instruction Manual

Page: 48 / 300

3 Operation Theory
PCS-9611 Feeder Relay
3-12
Date: 2014-04-08
for the stage 1 overcurrent protection is shown as below. The logic diagrams of voltage control
elements of phase B and phase C can be gotten on the analogy of this.
[VTS.En]
[50/51P.En_VTS_Blk]
[VTS.Alm]
Ubc(present measure)
Ia (present measure)
[50/51P1.Opt_Dir] ≠ 0
Ubc(in memory)
Phase A
Direction
Check
&
50/51P1.Dir_A
[ BI_En_VT ]
Figure 3.3-8 Logic diagram of the OC1 phase A directional element
Where:
[50/51P1.Opt_Dir] is the setting which is used to select the directional mode (non-directional,
forward, reverse) of the directional element for the stage 1 overcurrent protection;
[VTS.En] is the logic setting of the protection voltage transformer supervision function;
[50/51P.En_VTS_Blk] is the logic setting of the function which can block all the OC protective
elements that relate to the voltage measurement when the voltage transformer is failed;
[BI_En_VT] is the binary input for denoting the local VT is in service;
[VTS.Alm] is the alarm signal of the protection voltage transformer supervision.
3.3.5 Harmonic Blocking Element for Overcurrent Protection
To prevent maloperation of the overcurrent protection when the transformer is energized without
any load, this relay provides a 2
nd
harmonic blocking function for resolving such a problem.
The percent threshold of the 2
nd
harmonic blocking element to the fundamental wave can be set
through the setting [50/51P.K_Hm2].
The harmonic blocking mode can be selected through the setting [50/51P.Opt_Hm_Blk].
Setting Value
Harmonic Blocking Criterion
Phase A Phase B Phase C
1 Phase blocking Ia
2
/ Ia
1
> Ib
2
/ Ib
1
> Ic
2
/ Ic
1
>
2 Cross blocking (Ia
2
/ Ia
1
>) or (Ib
2
/ Ib
1
>) or (Ic
2
/ Ic
1
>)
3 Ma ximum blocking Ma x(Ia
2
, Ib
2,
Ic
2
)/ Ia
1
> Ma x(Ia
2
, Ib
2,
Ic
2
)/ Ib
1
> Ma x(Ia
2
, Ib
2,
Ic
2
)/ Ic
1
>
When the fundamental current is greater than the setting [50/51P.I_Rls_HmBlk], the harmonic
blocking element of the corresponding phase is released.
The following figure shows the logic diagram of the harmonic blocking element of phase A for the
stage 1 overcurrent protection. The logic diagrams of the harmonic blocking elements of phase B
and phase C can be gotten on the analogy of this.