3 CARRIER AIDED SCHEMES IMPLEMENTATION
With Aided Distance protection, tripping schemes are used to connect similar devices at different terminals on the
protected line to provide fast clearance for faults anywhere along the line.
For distance protection It is typical to set Zone 1 distance protection elements to cover only 80% of a line from the
relaying point. Faults on the other 20% of the line would generally be cleared by a delayed Zone 2 element, which
could be hundreds of milliseconds after the fault inception. There is, however, a limit to the amount of arc reistance
and tower footing resistance that can be adequately covered by distance IEDs, since the coverage is limited by
their ohmic reach. If extremely high values of ground fault resistance are expected, then an optional directional
comparison earth fault scheme (Aided DEF) can be used to complement the distance schemes.
Aided distance schemes assure fast clearance for faults on the entire circuit by communicating command signals.
For the the communication between local and remote terminals InterMiCOM 64 (IM64) can be used.
3.1
CARRIER AIDED SCHEME TYPES
This product has two independent Carrier Aided Schemes (Aided Scheme 1 and Aided Scheme 2). The two schemes
are independent, but the design of both is the same. Each of the two Carrier Aided Schemes provides the following
options:
● Permissive Underreaching Schemes (PUR, PUTT)
● Permissive Overreaching Schemes (POR, POTT)
● Blocking Scheme (Block 1)
● Blocking Scheme (Block 2)
● Unblocking POR Scheme
● Unblocking PUR Schemes
● Programmable
● Programmable Unblocking
The underreaching options can be used to implement Carrier Aided Distance schemes. The other options can be
used with any Carrier Aided scheme application.
The following diagram shows how the schemes can be assigned.
V03500
Aided 1Scheme
Scheme Category
Scheme Mode
Scheme Function
Underreaching
PUR PUR Unblocking POR POR Unblocking Block 1 Block 2 Prog Unblock Prog
Overreaching
Aided 2
Aided Distance Aided Distance Aided DEF Aided Delta*
*Not P445
Figure 70: Scheme Assignment
P446SV Chapter 8 - Carrier Aided Schemes
P446SV-TM-EN-1 169
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