Overcurrent Protection Configuration
24
5 Overcurrent Protection
Configuration
5.1 Protective Functions Menu
The SB Energy-Comm trip unit provides configurable overcur-
rent protection functions that can trip the SB circuit breaker.
The user can easily accommodate load changes and other
protection requirements while still assuring optimum coordina-
tion. A standard feature of the SB Energy-Comm trip unit is
RMS current sensing. As opposed to peak-current sensing,
RMS sensing measures the true heating potential of the current
waveform. This allows more accurate overcurrent protection
and eliminates nuisance tripping that results from harmonic
distortion of the current waveform. The current transformers
(CTs) in the circuit breaker provide operating power as well as
current level data. When the circuit breaker is carrying load
currents, the trip unit requires no external connections or con-
trol power to perform the basic overcurrent protective func-
tions.
To set the overcurrent protection, from the
Main Menu
, select
Protective
and press Enter . This displays the
Protective
Menu
, which includes the functions for setting the characteris-
tics of the time-current curve.
Long time overcurrent protection is always enabled. For the
models with ground fault protection, this protective function is
similarly always enabled. The short time and instantaneous
protective functions can be enabled or disabled from the
System Configuration
menu; either the short time or instanta-
neous protection must be enabled. Refer to Short Circuit Pro-
tection in
4.2, Setting System Configuration Parameters.
The
Time Current Curve
, which displays a graphical represen-
tation of the time-current curve is available only on trip units
with software version 3.00 or later.
Figure 5.1
shows a typical time-current curve that summarizes
the protection. The settings in the
Protective Menu
allow the
user to define this overall curve by selecting parameters that
define parts of that curve. The overall curve is then a summa-
tion of the individual parts. This gives the user the maximum
flexibility in defining the appropriate protection for a specific
application.
Figure 5.1
Time-Current Curve
For each part of the curve, there is a set of adjustable parame-
ters. When each set of parameters is adjusted, if security is
inactive, press Escape and the verification screen appears.
Press Enter to accept the changes (accept the settings you
have entered). If you want to quit without saving these
changes, press Escape .
Each of the menu options available for the
Protective Menu
is
discussed next. Note that chapters 6 and 7 are devoted
entirely to alarms and protective relays, respectively.
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