ANSIEQUATION1431 V1 EN (Equation 27)
The type B curve is described as:
2.0
480
0.055
Vpickup < -V
32 0.5
Vpickup
TD
t
×
= +
× -
<
æ ö
ç ÷
è ø
EQUATION1608 V1 EN (Equation 28)
The lowest voltage is always used for the inverse time delay integration. The details of
the different inverse time characteristics are shown in section 19.3 "Inverse time
characteristics".
Trip signal issuing requires that the undervoltage condition continues for at least the
user set time delay. This time delay is set by the parameter t1 and t2 for definite time
mode (DT) and by some special voltage level dependent time curves for the inverse
time mode (TUV). If the pickup condition, with respect to the measured voltage ceases
during the delay time, the corresponding pickup output is reset.
8.1.7.3 Blocking
It is possible to block Two step undervoltage protection (UV2PTUV ,27) partially or
completely, by binary input signals or by parameter settings, where:
BLOCK:
blocks all outputs
BLK1: blocks all pickup and trip outputs related to step 1
BLK2: blocks all pickup and trip outputs related to step 2
8.1.7.4 Design
The voltage measuring elements continuously measure the three phase-to-neutral
voltages or the three phase-to-phase voltages. Recursive fourier filters or true RMS
filters of input voltage signals are used. The voltages are individually compared to the
set value, and the lowest voltage is used for the inverse time characteristic integration.
A special logic is included to achieve the 1 out of 3, 2 out of 3 and 3 out of 3 criteria to
fulfill the PICKUP condition. The design of Two step undervoltage protection
UV2PTUV (27) is schematically shown in Figure 51.
1MRK 505 277-UUS C Section 8
Voltage protection
127
Technical Manual
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