Maximum Actual Transmission Time (Tac); Security - ABB ETL600 Instruction Manual

ABB Switzerland Ltd
Signal evaluation time
The nominal transmission times for the three applications are:
•
Blocking
•
Permissive Tripping
•
Direct Tripping
3.6.6.2.2.

Maximum actual transmission time (Tac)

The user can choose one of three programmable applications for each
command. This determines the level of security for the evaluation of
the related
interferences) on the transmission path may occasionally introduce an
additional delay of a few milliseconds compared to the nominal
transmission time T0. This delay is generally higher at the same
signal-to-noise ratio (SNR) for commands with higher security
requirements.
The maximum actual transmission time Tac is the maximum
transmission time encountered under noisy channel conditions for a
defined dependability and SNR. It is measured with continuous white
noise applied to the RF input of the ETL600 receiver.
Commands which are not received within a certain Tac are considered
as lost or missed commands (refer also to section 3.6.6.4
'Dependability').
The actual transmission time of the NSD600 is measured, for example,
by means of the manual or cyclic loop tests, refer to section 3.6.8.13
and 3.6.8.14.
3.6.6.3.

Security

The NSD600 with its dynamic adaptation of the receiver provides the
best security / dependability trade-off for the chosen command
application at lowest possible transmission time.
Security is expressed as the "worst case" false signal rate (probability
of unwanted commands P
"Worst case" is defined as the level of interference at which the guard
signal is completely suppressed.
The security level P
applications.
The internal security settings for tripping signal evaluation are:
Security Measurements
3-68
1KHW001489-EN
Tev1: 4.125 ms
Tev2: 8.25 ms
Tev3: 16.5 ms
T0 = 10 ms
T0 = 11 ms
T0 = 12 ms
tripping signals.
) for blocks of noise of 200 ms duration.
uc
is fixed for each of the possible command
uc
Blocking
Permissive Tripping
Direct Tripping
November 2005
Severe disturbances
Puc < 1E-04
Puc < 1E-06
Puc < 1E-09
Structure and Function
ETL600
(noise or