Toshiba GR200 Series Instruction Manual page 40

where,
ΔId: Change in the differential current Id
(ΔIp + ΔIn): Change in the restraining current in the positive and negative half cycles
Id: Differential current
Ip: Sum of positive input currents
In: Sum of negative input currents
m, m-1, m-2: Sampling timing
The SE will operate when the sum of the absolute values of the difference between the
instantaneous values of current data at each CH from one cycle is greater than a specified
percentage of minDIF-I.
where,
I j : Current from CHj
minDIF-I: Minimum operating current in [DIFCH-I] and [DIFDZ-I]
n: Number of CHs
The SE discriminates a faulted state in the power system from that of the normal service
state and blocks the output of the WDE which otherwise may operate under normal service
conditions.
CT secondary current waveforms
(ii)
Figure 2.1-7 shows the current waveforms for the incoming and outgoing terminals in the
secondary circuit of the CTs; the differential current for an external fault with saturation of
the CT at the outgoing terminal is also shown.
Incoming
terminal current
Outgoing
terminal current
Differential
current
∆Id = | ���� | + | ����
− ����
�� ��−1
∆���� + ∆���� = | ���� − ����
�� ��−1
+ | ����
− ����
��
��
∑|�� − �� |
�� ( ��−24 )
����
��=1
Figure 2.1-7
Waveform for CT saturation
- 26 -
|
− ����
��−1 ��−2
| + | ���� − ���� |
��−1 ��−2
| + | ����
− ����
��−1 ��−1 ��−2
> 0.5 × min DIF– I
No change period
6F2S1931 (0.20)
(2.1-2)
(2.1-3)
|
(2.1-4)
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)