Toshiba GR200 Series - 2.29.1 Overcurrent element (OCFS); 2.29.2 Phase current change detector element (OCDFS); 2.29.3 Earth fault current element (EFFS)

6F2S1914 (0.49)
GRL200 (Soft 033 & 037)
- 360 -
2.29.1 Overcurrent element (OCFS)
Three overcurrent elements consist for the three-phases: OCFS-A, OCFS-B, and OCFS-C.
Their pick values of those elements are determined by a setting [OCFS]. Those element can
operate when On is set for scheme switch [OCFS-EN].
2.29.2 Phase current change detector element (OCDFS)
Three elements consist for three-phases and they are used to detect changing currents per
phase: OCDFS-A, OCDFS-B, and OCDFS-C. Figure 2.29-1 shows that those elements operate
if vectorial differences (between currents I
M
and I
N
) are being observed in a cycle, and their
differences are larger than setting [OCDFS]. Because the quiescent load current does not affect
the operating sensitivity of OCDFS elements, they can detect a fault current precisely.
I
s
I
M
I
N
Figure 2.29-1 Current change detection
They can operate based on the following equation.



 




(2.29-1)
where,
I
M
= present current
I
N
= current one cycle before
Is = setting [OCDFS]
Those settings are determined by a setting [OCDFS], and those elements can operate when On
is set for its scheme switch [OCDFS-EN]. They, additionally, have off-delay timers. A setting
[TOCDFS] is provided to adjust those timers.
2.29.3 Earth fault current element (EFFS)
Residual current is measured in an earth fault current element, so an earth fault is detected
if the residual current gets over a setting level [EFFS]. Its elements can operates when On is
set for the scheme switch [EFFS-EN].
If its earth fault current is significant, because of unbalance in the network, Off should
be set for that [EFFS-EN] to disable the operation of the EFFS.