Performance Criteria; General; Transmission Time - ABB ETL600 Instruction Manual

ABB Switzerland Ltd
3.6.6.

Performance criteria

3.6.6.1.

General

A fundamental requirement in all the applications that teleprotection
equipment is used in, is that command signals are communicated
reliably at the highest possible speed (transmission time). In the event
of a fault on the protected unit, the command signals must be received
at the remote end in the shortest possible time even if the channel is
disturbed by the fault (dependability).
On the other hand, interference on the communications channel must
never cause unwanted operation of the protection by simulating a
tripping signal when there is no fault on the power system (security).
The most important features of a teleprotection equipment are
therefore transmission time, dependability and security. From the
communications engineering point of view, the bandwidth or data rate
a teleprotection equipment uses must also be taken into account.
By security is understood that the receiver does not generate spurious
tripping signals in the presence of interference on the communications
channel. Dependability characterizes the receiver's ability to recognize
a genuine tripping signal within a given time in spite of interference on
the communications channel. It is obvious that to demand maximum
security at the same time as maximum dependability is contradictory
and one can only be increased at the expense of the other.
The NSD600 uses dual tone command signals. This transmission type
prevents an unintended tripping by a discrete sine tone.
Note:
3.6.6.2.

Transmission time

Traditional teleprotection have a set of fixed signal evaluation times for
which the equipment delivers the requested performance (trans-
mission time, dependability and security).
For example three different evaluation times could be found: one for
blocking (T1, fast), one for permissive tripping (T2, medium) and one
for direct tripping (T3, slow), each selection being compliant with the
requested security and dependability for the given application.
Once the equipment is programmed for direct tripping (T3, slow) for
example, it will not trip very fast even if the actual prevailing channel
conditions would permit to do so.
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1KHW001489-EN
much higher dependability when the channel is
disturbed (which is usually the case while commands
have to be transferred).
Maloperation can mean both fail to trip (sometimes
called underfunction) and false trip (sometimes called
overfunction).
November 2005
ETL600
Structure and Function