ABB REG670 - Page 476

In order to obtain such operating characteristic the rotor overload function utilizes the
following formula in order to calculate the operate time:
1
2
1
op
k
t
I
IBase
=
æ ö
-
ç ÷
è ø
GUID-E050AB5E-B2A4-4838-9E0F-C8133A63DF54 V1 EN (Equation 103)
Where:
t
op
is operate time in seconds
k1 is a multiplier (it shall have default value of 33.8 in order to get the operating points as prescribed by
the standard, see Table254)
I is measured current by the function
IBase is base current (rotor winding rated current when DC current is used as measured current)
In addition to this equation based operating characteristic, the rotor overload function
has some additional cut-off features. The actual overall operating characteristic of the
rotor overload function is shown in Figure221.
tMin
tCutOff
tMax
i>IBase
t (s)
I (A)
-
÷
ø
ö
ç
è
æ
=
1
2
1
IBase
I
k
op
t
IEC12000011-1-en.vsd
IEC12000011 V1 EN
Figure 221: Operating characteristic for the overload function
Section 8 1MRK502052-UEN B
Current protection
470
Technical manual