Siemens SG8158-00 manual Squared-T Curve, Custom Protective Curve, Over/Undervoltage Curves

Appendix A: Trip Curves & Equations

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

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

Multiples of Pickup

Figure A.9 Definite Inverse Curve (SEA8) Figure A.10 I-Squared-T Curve

A

A.4 I-Squared-T Curve

The ISGS provides an I-Squared-T characteristic in addition to the standard inverse curves.

		Trip Characteristic
		50.7D + 10.14
		T = -------------------------------------
		⎛		i	⎞ 2
		⎝	---		⎠
			i	p
		Reset Characteristic
		i						trD
		For ----< 1:		T =
						----------------------
		ip				⎛	i	⎞	2
						⎝	---	⎠	– 1
T = time to trip, in seconds							ip
⎛		⎞
⎜ --i--		⎟ = multiple of pickup setting
⎝ i	p	⎠

D = time dial setting, 0.1 to 9.9 in steps of 0.1 tr = reset constant = 7.4

Equation A.4 I-Squared-T Equation

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

0.00to 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 (Δt/(ΔI/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.

56 Siemens Energy & Automation, Inc.