Siemens SG8158-00 manual Definite Inverse Equation, Figure A.7 Extremely Inverse Curve SEA6

Appendix A: Trip Curves & Equations

1000
	100
(Seconds)	10
TimetoTrip	1		TimeDial
			9.9
			7.0
			5.0
			3.0
	0.1		1.5
			0.5
			0.1
	0.01
	1	10	50

Multiples of Pickup

Figure A.7 Extremely Inverse Curve (SEA6)

100
	10		TimeDial
(Seconds)
			9.9
			7.0
toTrip	1		5.0
			3.0
Time			1.5
			0.5
0.1
			0.1
0.01
	1	10	50

Multiples of Pickup

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.

Trip Characteristic

For

--i--

> 1.5

ip

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

671

×

6.33------------------------------D + 0.37

T =

785 +

⎛

i

⎞

N

24000

⎝ ---ip

⎠

–

1.19

For1.0 < --i--< 1.5:

ip

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

671

×

6.33---------------------------------D+ 0.37

T =

785 +

⎛

i

⎞

N

24000

⎝ i---p

⎠

–

1.19

Reset Characteristic

For

i

<

1:

T =

trD

----

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

ip

⎛ i

⎞

N

⎝ ip ⎠---

– 1

T = time to trip, in seconds

⎛ --

i--

⎞

⎜

⎟ = multiple of pickup setting

⎝ i

p

⎠

D = time dial setting, 0.1 to 9.9 in steps of 0.1 tr = reset constant = 1.0394

N = inverse constant = 2.54096

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).

A

Figure A.8 Slightly Inverse Curve (SEA7)
Siemens Energy & Automation, Inc.	55