Alstom MiCOM P546 - 2.4.10 Delta scheme POR - permissive overreach transfer trip (Distance option only); 2.4.11 Delta blocking scheme (Distance option only); 2.4.12 Delta schemes current reversal guard timer (Distance option only); 2.5 Loss of load accelerated tripping (LoL) (Distance option only)

P54x/EN AP/La4 Application Notes
(AP) 6-36 MiCOM P543, P544, P545 & P546
AP
2.4.10 Delta scheme POR - permissive overreach transfer trip (Distance option only)
This scheme is similar to that used in the LFDC relay.
Send logic:  Fault Forward
Permissive trip logic:  Fault Forward plus Channel Received.
The Delta Delay trip time setting should be set to zero, for fast fault clearance.
2.4.11 Delta blocking scheme (Distance option only)
This
scheme is similar to that used in the LFDC relay.
Send logic:  Fault Reverse
Trip logic:  Fault Forward, plus Channel NOT Received, delayed by Tp.
Recommended Dly setting = Max. signaling channel operating time + 6 ms.
2.4.12 Delta schemes current reversal guard timer (Distance option only)
Similarly to t
he distance protection schemes, current reversals during fault clearance on an
adjacent parallel line need to be treated with care. In order to prevent misoperation (mal-
tripping) of the protection on the unfaulted line, a current reversal guard timer must be set.
The recommended setting for both POR and BLOCKING schemes is:
tREVERSAL GUARD = Maximum signaling channel reset time + 35 ms
2.5 Loss of load accelerated tripping (LoL) (Distance option only)
For ci
rcuits with load tapped off the protected line, care must be taken in setting the loss of
load feature to ensure that the I< level detector setting is above the tapped load current.
When selected, the loss of load feature operates in conjunction with the main distance
scheme that is selected. In this way it provides high speed clearance for end zone faults
when the Basic scheme is selected or, with permissive signal aided tripping schemes, it
provides high speed back-up clearance for end zone faults if the channel fails.
2.6 Phase fault overcurrent protection
Settings for the time delayed ove
rcurrent element should be selected to ensure
discrimination with surrounding protection. Setting examples for phase fault overcurrent
protection can be found in the Network Protection and Automation Guide (NPAG), a
comprehensive reference textbook available from ALSTOM Grid.
Caution: The IEEE C.37.112 standard for IDMT curves permits some
freedom to manufacturers at which time dial (TD) value the
reference curve applies. Rather than pick a mid-range value, for
the MiCOM P54x the reference curve norm applies at a time dial
of 1. The time dial is merely a multiplier on the reference curve,
in order to achieve the desired tripping time. Take care when
grading with other suppliers' relays which may take TD = 5, or TD
= 7 as a mid-range value to define the IDMT curve. The
equivalent MiCOM P54x setting to match those relays is achieved
by dividing the imported setting by 5 or 7.