Ashida ADR241B, Instruction Manual

Page: 99 / 272

ADR241B
Doc ID : ADR241B-DO_IM_01
Ref ID : ADR241B/IM/PLF
Rev No. : 06
Page No. : 99 of 272
4.6 Negative Sequence Over current (46)
Negative sequence Over-current function operates for a set value of current with time delay
(IDMT/DT). This function provided with two stages, Where Stage 1 (I2>1) can be
programmed as IDMT or Definite Time (DT) provided with the Range of 1% to 250% in step
of 1%. All major international IDMT curves as well as Definite Time and User Define curves
are available. The Stage 2 (I2>2) can be programmed as Instantaneous or Definite Time
(DT) provided with the Range of 5% to 3000% in step of 1%.
The Negative sequence current is calculated from the three phase currents as shown below
Negative sequence current I2 = (IA+a
2
IB+aIC)/3 Where a = 1
∟120
o
.
The following diagram figure 11 explains about Negative sequence over current protection
function.
&
IDMT/
DT
I2>1T
I2 Negative
Sequence Current
+
-
I2>1P
I2>1
I2>1 Enable = Yes
Figure 11: Logic Diagram for the Negative sequence over current
Where n=1 to 2 stages of Negative Sequence Over Current.
The calculated Negative Sequence Over Current logic checks the Negative Sequence Over
Current is exceed the pickup value (I2>n) and calculated operating time based on the curve
selected in the I2>n Curve setting and I2>n TMS or tI2>n DT parameter settings. After
satisfied all the above condition the IED generates the negative sequence over current trip.
4.7 IDMT Characteristics
4.7.1 IDMT Characteristics for Phase, Ground and Negative Sequence OC
ADR241B relay provides inverse time over current characteristic for phase over current,
ground over current, residual over current and negative sequence over current elements.
The phase and ground over current elements are independently settable with inverse time or
definite time characteristic. The following tripping characteristics curves are available
•
IEC Standard Inverse 1 Curve (C1) for 3s
•
IEC Standard Inverse 2 Curve (C2) for 1.3s
•
IEC Very Inverse Curve (C3)
•
IEC Extremely Inverse Curve (C4)
•
IEC Long time Inverse Curve (C5)