• When MeasurCurrent = RMS (default); the maximum true RMS current value
from the three-phase input currents is used as the measured quantity for the stator
overload protection.
• When MeasurCurrent = PosSeqNegSeq; the weighted sum of positive and
negative sequence stator currents in primary amperes is used as the measured
quantity for the stator overload protection. This current value is calculated from
the connected three-phase input currents, see Figure
214.
The weighted sum of positive and negative sequence stator currents is calculated as
per the following equation.
2 2
1 2
PosSeqFactor NegSeqFactorI I I= × + ×
GUID-8768BBBF-3EF7-4D4A-9FF6-DF4A07272812 V1 EN (Equation 99)
Where:
I is current value in primary amperes used by the overload function
I
1
is stator positive sequence current in primary amperes
I
2
is stator negative sequence current in primary amperes
PosSeqFactor
is a setting factor to multiply the positive sequence current and its default value is 1.0
NegSeqFactor
is a setting factor to multiply the negative sequence current and its default value is 6.0
The measured current used by the function is available as a service value.
Overload characteristics
Stator winding temperature increases with the current. Thus, it is logical to apply over
current elements with inverse time-current characteristics for overload protection.
The function operating characteristic is designed in accordance with the American
standard IEEE-C50.13. This standard specifies the following operating points:
Table 254: Operate time in accordance with IEEE-C50.13 standard
Current (% of IBase)
Trip time (s)
116 120
130 60
154 30
226 10
In order to obtain such operating characteristic the stator overload function utilizes the
following formula in order to calculate the operate time:
1MRK502052-UEN B Section 8
Current protection
457
Technical manual
To Next Page
Loading...
