Characteristic Value
Reset ratio Typically 1.04
Retardation time Total retardation time when the impedance
returns from the operating circle <40 ms
Operate time accuracy ±1.0% of the set value or ±20 ms
Suppression of harmonics -50 dB at f = n × f
n
, where n = 2, 3, 4, 5,…
4.7.3.11 Technical revision history
Table 957: UEXPDIS Technical revision history
Product
connectivi
ty level
Technical
revision
Change
PCL4 C Added support for settable blinder in offset mho characteristic.
4.7.4 Three-phase underimpedance protection UZPDIS (ANSI
21G)
4.7.4.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Three-phase underimpedance pro-
tection
UZPDIS Z<G 21G
4.7.4.2 Function block
Figure 569: Function block
4.7.4.3 Functionality
The three-phase underimpedance protection UZPDIS is generally applied as a
backup protection for generators and transformers against short circuit faults.
The protection is based on the origin-centric circular characteristics on the
impedance plane. The function calculates the impedance value from the voltage
and current phasors. If the impedance vector enters the origin-centric circle, the
function produces the operating signal after a set delay. The operating time
characteristics are according to definite time (DT).
However, it is also possible to enable separate zones of offset-mho based
protection with multiple instances of the function.
Protection functions
1MRS759142 F
1026 REX640
Technical Manual
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