ABB 615 Series ANSI, Техническое руководство, Страница: 677 / 713

Section 11
1MAC050144-MB C
General function block features
670 615 series ANSI
Technical Manual
The user can define the curves by entering the parameters using the standard formula:
(Equation 86)
t[s] trip time in seconds
A the set value of Curve parameter A
B the set value of
Curve parameter B
C the set value of Curve parameter C
D the set value of
Curve parameter D
E the set value of Curve parameter E
V measured voltage
V> the set value of Pickup value
k the set value of
Time multiplier
11.3.1.3 IDMT curve saturation of overvoltage protection
For the overvoltage IDMT mode of operation, the integration of the trip time does not start
until the voltage exceeds the value of
Pickup value . To cope with discontinuity
characteristics of the curve, a specific parameter for saturating the equation to a fixed value
is created. The
Curve Sat Relative setting is the parameter and it is given in percents
compared to Pickup value . For example, due to the curve equation B and C, the
characteristics equation output is saturated in such a way that when the input voltages are
in the range of
Pickup value to Curve Sat Relative in percent over Pickup value , the
equation uses Pickup value * (1.0 + Curve Sat Relative / 100 ) for the measured voltage.
Although, the curve A has no discontinuities when the ratio V/V> exceeds the unity, Curve
Sat Relative is also set for it. The Curve Sat Relative setting for curves A, B and C is 2.0
percent. However, it should be noted that the user must carefully calculate the curve
characteristics concerning the discontinuities in the curve when the programmable curve
equation is used. Thus, the
Curve Sat Relative parameter gives another degree of freedom
to move the inverse curve on the voltage ratio axis and it effectively sets the maximum trip
time for the IDMT curve because for the voltage ratio values affecting by this setting, the
operation time is fixed, that is, the definite time, depending on the parameters but no longer
the voltage.
11.3.2 IDMT curves for undervoltage protection
In the inverse-time modes, the trip time depends on the momentary value of the voltage,
the lower the voltage, the faster the trip time. The trip time calculation or integration starts
immediately when the voltage goes below the set value of the
Pickup value setting and the
PICKUP
output is activated.
The
TRIP
output of the component is activated when the cumulative sum of the integrator
calculating the undervoltage situation exceeds the value set by the inverse-time mode. The
set value depends on the selected curve type and the setting values used. The user
determines the curve scaling with the
Time multiplier setting.
t s
k A
B
V V
V
C
D
E
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