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Appendix a: trip curves & equations, A.3 definite inverse equation – Siemens ISGS SG8158-00 User Manual

Page 61

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Appendix A: Trip Curves & Equations

Siemens Energy & Automation, Inc.

55

Figure A.7 Extremely Inverse Curve (SEA6)

Figure A.8 Slightly Inverse Curve (SEA7)

0.01

0.1

1

10

100

1000

1

10

50

9.9

7.0

5.0

3.0

1.5

0.5

0.1

Multiples of Pickup

T

ime to T

rip (Seconds)

T

ime Dial

0.01

0.1

1

10

100

1

10

50

9.9

7.0

5.0

3.0

1.5

0.5

0.1

Multiples of Pickup

T

ime to T

rip (Seconds)

T

ime Dial

A.3 Definite Inverse Equation

Equation A.2 The ISGS provides an emulation of the

popular CO-6 Definite Inverse characteristic. This curve is

defined by the equations shown in Equation A.3.

Equation A.3 Definite Inverse Equation

In Equation A.3, the time dial term 6.33D + 0.37 is neces-

sary to convert the time dial range defined by Westinghouse

and the range that Siemens is using.

Equation (1) is valid for values of I/Ip greater than 1.5 and

equation (2) is valid for values of I/Ip between 1.0 and 1.5

(note that the equation is undefined at I/Ip = 1.0).

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
tr = reset constant = 1.0394
N = inverse constant = 2.54096

For

i

ip

-----

1.5

T

785

671

i

ip

----

N

1.19

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

+

6.33D 0.37

+

24000

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

×

=

>

For1.0

i

ip

-----

1.5:

T

785

671

i

ip

----

N

1.19

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

+

6.33D 0.37

+

24000

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

×

=

<

<

For

i

ip

-----

1:

T

t

r

D

i

ip

----

N

1

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

=

<

i

ip

-----

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A

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