Characteristic
Value
Operate time accuracy in definite time mode
±1.0% of the set value or ±20 ms
Suppression of harmonics
DFT: -50 dB at f = n × f
n
, where n = 2, 3, 4, 5,…
4.4.3.10
Technical revision history
Table 562: PREVPTOC Technical revision history 46R Technical revision history
Technical revision
Change
B
Internal improvement
4.4.4
Negative-sequence overcurrent protection for machines
MNSPTOC
4.4.4.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Negative-sequence overcurrent
protection for machines
MNSPTOC
I2>M
46M
4.4.4.2
Function block
Figure 327: Function block
4.4.4.3
Functionality
The negative-sequence overcurrent protection for machines function MNSPTOC
protects electric motors from phase unbalance. A small voltage unbalance can
produce a large negative-sequence current flow in the motor. For example, a 5
percent voltage unbalance produces a stator negative-sequence current of 30
percent of the full load current, which can severely heat the motor. MNSPTOC
detects the large negative-sequence current and disconnects the motor.
The function contains a blocking functionality. It is possible to block the function
outputs, timers or the function itself, if desired.
4.4.4.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of MNSPTOC can be described by using a module diagram. All the
modules in the diagram are explained in the next sections.
1MRS757644 H
Protection functions
620 series
Technical Manual
623
