Siemens ISGS SG8158-00 User Manual download pdf (Page 62)

Appendix A: Trip Curves & Equations

56 Siemens Energy & Automation, Inc.

Figure A.9 Definite Inverse Curve (SEA8)

A.4 I-Squared-T Curve

The ISGS provides an I-Squared-T characteristic in addition

to the standard inverse curves.

Equation A.4 I-Squared-T Equation

0.01

0.1

100

11050

9.9

7.0

5.0

3.0

1.5

0.5

0.1

Multiples of Pickup

Time to Trip (Seconds)

Time Dial

Trip Characteristic

Reset Characteristic

T = time to trip, in seconds

= multiple of pickup setting

D = time dial setting, 0.1 to 9.9 in steps of 0.1

= reset constant = 7.4

50.7D 10.14+

----





-------------------------------------=

For

-----

1 : T

----









1–

-----------------------

-----







Figure A.10 I-Squared-T Curve

A.5 Custom Protective Curve

The custom curve consists of up to 60 current-time pairs

corresponding to points on the time-current characteristic

curve. Current refers to multiple-of-pickup value (I/Ip) on the

horizontal axis, and time refers to time-to-trip values on the

vertical axis. Each point consists of two values (I/Ip and t),

loaded in order from lowest to highest value of I/Ip via the

SEAbus or local ports. Siemens Wisdom software is required

in order to load a custom curve. Time-to-trip has a range of

0.00 to 655.35 seconds in steps of 0.01 seconds. I/Ip has a

range of 1.1 to 20.00 in steps of 0.01. The first point in the

data set must be I/Ip=1.1, the last point must be I/Ip=20.

Points in between these two limits can be for any values of I/

Ip and t as long as the slope (

∆t/(∆I/Ip)) of the curve

described by the points is between 0 (horizontal) and -

∞ (ver-

tical). For input current in excess of 20 x Ip, the relay will

enter a definite time mode and the curve will be considered

to be flat (constant time) at the time value associated with I/

Ip=20. Once loaded, a custom curve is not adjustable, that is

there is no time dial adjustment.

A.6 Over/Undervoltage Curves

The ISGS provides a moderately inverse overvoltage and a

moderately inverse undervoltage protection defined by the

equation in Equation A.5 and Equation A.6. Their charac-

teristics are provided in Figure A.11 and Figure A.12.

Multiples of Pickup

Time to Trip (Seconds)

Time Dial

1000

100

0.1

0.01

9.9

7.0

5.0

3.0

1.5

0.5

0.1

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