If a starter element picks up, the associated DDB signal is asserted. These can be used to block the current
differential protection. These DDB signals are:
● I1 Lo Start (Positive phase-sequence fixed threshold start)
● Del I1 Lo Start (Rate-of-change of positive phase-sequence current)
● I2 Lo Start (Negative phase-sequence fixed threshold start)
● Del I2 Lo Start (Rate-of-change of negative phase-sequence current)
If elements are set to Disabled, then the DDB signals cannot be asserted.
If elements are set to Enabled, then the DDB signals will be asserted if appropriate conditions are met. This will
allow you to use PSL to customize supervision of Current Differential protection operation. These signals do not
directly affect the operation of the Current Differential function. In order to directly influence the operation of the
current differential function you need to set one or more of the starter elements to Idiff Permit.
If elements are set to Idiff Permit, then the DDB Start signals will also be asserted if the appropriate
conditions are met, so you can use the PSL to customise supervision of Current Differential protection operation. In
addition however, if any one or more elements are set to IDiff Permit, then fixed internal logic is employed to
produce an internal signal (Permit CDiff) that supervises the Current Differential protection by either inhibiting it or
permitting it.
P543i/P545i Chapter 18 - Supervision
P54x1i-TM-EN-1 463
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