t
tr
is triptime in seconds
TD1 is a multiplier (it shall have default value of 33.8 in order to get the operating points as prescribed by the
standard, see Table331)
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 Figure318.
t_MinTripDelay
tCutOff
t_MaxTripDelay
IPickupIBase
t (s)
I (A)
1
2
IBase
I
TD1
tr
t
ANSI12000011-1-en.vsd
ANSI12000011 V1 EN-US
Figure 318: Operating characteristic for the overload function
As shown in Figure 318 it is possible to define the maximum (
t_MaxTripDelay
) and minimum
(
t_MinTripDelay
) trip time for the function regardless of the level of the measured current. In
addition to this it is also possible to specify the cut-off time below which the IDMT curve defined
by the above equation will be used. Note that
tCutOff
shall be always set to the smaller value than
t_MaxTripDelay
.
The trip time of the rotor overload function is calculated by using the integration principle (see
Chapter “Inverse time characteristics” in the Technical Manual for more information). As a service
value from the rotor overload function regarding this integration process the Theta parameter,
proportional to the rotor heating content, is provided. This parameter has value of 100% when
function issues the trip signal. Thus, in simple words, it represent a percentage of the function trip
level. As soon as the measured current is above the pick-up level
IPickup
and no block signal is
present, the output signal PICKUP is activated and the Theta parameter is incremented following
the inverse characteristic given in Figure 319. When theta has reached value 100%, the output
signal TRIP is set. The minimum trip signal duration is defined by the parameter
tPulse
. Note also
that the BLKRECL signal will remain one as long as Theta >
ReclsLevTheta
. Thus the parameter
1MRK 502 066-UUS B Section 8
Current protection
593
Technical manual
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