Nominal Transmission Time (T0) - ABB ETL600 Instruction Manual

ETL600
For the NSD600, this disadvantage can be avoided by using patented
dynamic adaptation. Inside the NSD600 three receivers are connected
in parallel: a fast one (T1), a medium one (T2) and a slower one (T3).
All three comply with the requested security for a given application
(user programmable) such as blocking, permissive tripping or direct
tripping.
If now the actual channel condition during command transmission is
good, the NSD600 will decide to trip with its fast receiver (T1) and not
wait for the medium (T2) or slower one (T3). If the actual channel
condition is worse, it will not trip with receiver T1 but wait for receiver
T2 or even T3 to trip.
With this in mind, shorter transmission times can therefore be
expected on average, compared with traditional solutions.
Moreover, the decision threshold for accepting a trip is permanently
and smoothly adapted to the actual prevailing received noise power:
from "low" for good channels to "high" for noisy channels. This
prevents noise from producing unwanted trips.
3.6.6.2.1.

Nominal transmission time (T0)

The nominal transmission time T0 is the transmission time measured
under noise-free transmission conditions i.e. there is no interference
on the channel. It is measured with nominal signal levels at the
transmitter output and the receiver input. The ETL600 RF terminals
are connected back-to-back via an artificial line with nominal
attenuation.
T0 is the time elapsed between the instant of change of state at the
input terminals of the teleprotection interface type G4AI and the instant
of the corresponding change of state at the output terminals.
The nominal transmission time T0 is composed of three terms:
T
I/O
T
g
T
ev
Structure and Function
1KHW001489-EN
T0 = T
Switching times of the teleprotection interfaces at the
transmitting and receiving end, T
state output is used or approx. 8 ms if a relay contact is used
for the command.
ETL600 internal delay (group delay of the filters, SSB
conversion, TDM-bus, etc; approx. 4 to 5 ms).
Signal evaluation time in the NSD600 receiver. It depends on
the settings of the command application. Since there is no
channel interference when measuring T0, the dynamic
adaptation is not in operation and the fastest receiver (Tev1)
will always become effective.
+ T + T
I/O g ev
approx. 1 ms if a solid
I/O
November 2005
ABB Switzerland Ltd
3-67