twenty times the set current pickup value. Note that the operating time value is dependent on the
selected setting value for time multiplier k.
In addition to the ANSI and IEC standardized characteristics, there are also two additional inverse
curves available; the RI curve and the RD curve.
The RI inverse time curve emulates the characteristic of the electromechanical ASEA relay RI. The
curve is described by equation
233:
[ ]
=
- ×
æ ö
ç ÷
ç ÷
ç ÷
ç ÷
è ø
0.339 0.235
td
t s
Pickupn
i
EQUATION1647 V1 EN-US (Equation 233)
where:
Pickupn is the set pickup current for step n
td is set time multiplier for step n
i is the measured current
The RD inverse curve gives a logarithmic delay, as used in the Combiflex protection RXIDG. The
curve enables a high degree of selectivity required for sensitive residual ground-fault current
protection, with ability to detect high-resistive ground faults. The curve is described by
equation
234:
[ ]
= - ×
×
æ ö
ç ÷
è ø
5.8 1.35 ln
i
t
td Pickupn
s
EQUATION1648 V1 EN-US (Equation 234)
where:
Pickupn is the set pickup current for step n,
td is set time multiplier for step n and
i is the measured current
If the curve type programmable is chosen, the user can make a tailor made inverse time curve
according to the general equation
235.
[ ]
= ×
-
+
æ ö
ç ÷
ç ÷
ç ÷
æ ö
ç ÷
ç ÷
ç ÷
è ø
è ø
P
A
t td
i
C
Pickupn
s B
EQUATION1640 V1 EN-US (Equation 235)
Section 26 1MRK 502 066-UUS B
Inverse time characteristics
1386
Technical manual
To Next Page
Loading...
