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Profibus; Over Current Protection Functions; Long Time; Short Time - GE EntelliGuard TU Installation, Operation And Maintenance Manual

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09/25/08

ProfiBus

This protocol is integral to EntelliGuard G Trip Units.
ProfiBus DP over RS485 is supported.

OVER CURRENT PROTECTION FUNCTIONS

The Trip Unit provides the following over current
protections:

Long Time

Short Time

Instantaneous
Reduce Let Through Energy Instantaneous (RELT)
Ground Fault Internal Summation
Ground Fault CT External Summation
Override (HSIOC)
Making Current Release (MCR)
Long Time
Long Time Pickup
This setpoint establishes the breaker's nominal ampere
rating, xLT, as a fraction of the rating plug value, xIn (xLT
= LT multiplier x xIn).
The adjustment range for long time pickup settings is
0.50 to 1.00 times xIn in steps of 0.05. The pickup value
tolerance band has a 10% tolerance. The band is drawn
at 1/(1+10%) and 1/1-10%). The actual long time pickup is
increased by 12% over the nominal so that 100%
nominal current may be carried indefinitely. So a 1000 A
setting is placed at 1120 A with the minimum pickup
drawn (left side of band) is 1120 A/1.1, and the maximum
pickup (right side of band) is drawn at 1120 A/0.9. Figure
5 shows the Long Time pickup setting.

Figure 5: Long Time Pickup Setting

Long Time Delay
The trip unit makes up to 44 different long time bands
available. Not all circuit breakers have all bands available.
There are 22 bands using a logarithmic type curve that
resembles the thermal portion of a thermal magnetic
circuit breaker. There are 22 bands that are a straight line
that simulate a fuse curve. The Entelliguard circuit
breaker is able to use all 44 bands. Power Break I, Power
© 2008 General Electric All Rights Reserved
Courtesy of NationalSwitchgear.com
Section 1 – General Information
Break II, WavePro and AKR circuit breakers use the 19
lower thermal CB-type bands and the 22 fuse-type
bands.
Short Time
Short Time Pickup
The Short Time Pickup function establishes the current at
which short time trip is activated. Short Time Pickup is
coupled with Long Time Pickup and the choices of pickup
settings are from 1.5 to 12.0 times the Long Time setting,
xLT, in steps of 0.5 xLT.
The maximum pickup depends on breaker type and
frame as shown in Table 2 below:
Table 2. Short Time Breaker Type and Frame
Breaker
PowerBreak I, PowerBreak II,
WavePro, AKR conversion kits
EntelliGuard G Frame 1 and 2
EntelliGuard G Frame 3
The Short Time Pickup value tolerance band is -9% to
+11% of the set point based on a 10% current sensing
accuracy with the pickup calculated with 1/(1+Tolerance).
The time current curve of short time pickup is shown in
Figure 6.

Figure 6: Short Time Pickup Time Current Curve

Short Time Delay
The Short Time Delay setting consists of both a slope
setting and a fixed delay band setting. The slope and
delay are independently selectable. The slope setting
2
consists of three I
T slopes (minimum (1), intermediate (2)
and maximum (3)) and fixed delay. The fixed delay bands
consist of 11 constant time bands. The width of the bands
varies by circuit breaker and with frequency. See Table 3.
EntelliGuard®TU Trip Unit
Available Settings
1.5 to 9, steps of 0.5
1.5 to 12, steps of 0.5
1.5 to 10, steps of 0.5
9

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