Current Change Detection Elements Ocd, Ocd1 And Efd - Toshiba GRL100-701B Instruction Manual

detected maximum slip cycle is determined by the following equation:
f =
180° × T
where,
f = slip cycle
SY1θ = phase difference setting (degree)
T
SYN1

2.16.10 Current change detection elements OCD, OCD1 and EFD

As shown in Figure 2.16.10.1, the current change detection element operates if the vectorial
difference between currents I M and I N observed one cycle apart is larger than the fixed setting.
Therefore, the operating sensitivity of this element is not affected by the quiescent load current
and can detect a fault current with high sensitivity.
The OCD element is used for the VT failure supervision circuit.
The OCD1 and EFD are used as a fail-safe for current differential protection.
The operation decision is made by the following equation.
|I M − I N | > Is
where,
I M = present current
I N = current one cycle before
I s = fixed setting
2.16.11 Level Detectors
In addition to those explained above, GRL100 has overcurrent, overvoltage, and undervoltage
level detectors described below.
All level detectors except for undervoltage level detectors UVFS and UVFG, and overcurrent
level detector OCBF which require high-speed operation, operate in a similar manner.
That is, the operation decision is made by comparing the current or voltage amplitude with the
relevant setting.
Overcurrent detector OCH, OC and OC1
This detector measures A, B, and C phase currents and its sensitivity can be set. The detector OCH
is commonly used for the SOTF and stub protection. The detector OC is commonly used for
backup protection. The OC1 is used as a fail-safe for current differential protection.
SY1 θ
SYN1
= setting of synchronism check timer (second)
I N
I M
Figure 2.16.10.1 Current Change Detection
 147 
I s
6 F 2 S 0 8 5 0