Thytronic NA20, Руководство пользователя, Страница: 56 / 208

FUNCTION CHARACTERISTICS
56 NA20 - Manual - 04 - 2022
Negative sequence current / positive sequence current ratio - I2/I1
Preface
One adjustable operation threshold ( I
2
/ I
1
)> with definite time adjustable delay ( t
21
>).
Operation and settings
The negative and positive sequence currents are computed as:
I
1
=( I
L1
+e+
j120°
· I
L2
+e
-j120°
· I
L3
)/3
I
2
=( I
L1
+e-
j120°
· I
L2
+e
+j120°
· I
L3
)/3
where e
-j120°
=-1/2-j√3/2, e
j120°
=-1/2+j√3/2.
The negative sequence-positive sequence currents ratio is compared with the setting value. Ratio
above the associated pickup value is detected and a start is issued. After expiry of the associated
operate time ( t
21
>) a trip command is issued; if instead the it drops below the threshold, the element
is restored.
The element can be enabled or disabled by setting
ON
or
OFF
the
State
parameter inside the Set \
Profile A(or B) \ Negative sequence current/positive sequence current ratio-I2/I1 \ I 21> Element \ Def-
inite time menu.
The element can produce the Breaker Failure output if the (
I2
/
I1
)
> BF
parameter is set to
ON.
The parameter is available inside the Set \ Profile A(or B) \ Negative sequence current/positive
sequence current ratio-I2/I1 \ I 21> Element \ Setpoints menus.
[1]
A block from the second harmonic restraint may be set by setting
ON
the parameter inside the Set \
Profile A(or B) \ Negative sequence current/positive sequence current ratio-I2/I1 \ I 21> Element \ Set-
points menu .
If the CLP function (Cold Load Pick-up) is enabled for element blocking, the selected threshold may
be blocked for an adjustable time interval, starting from the circuit breaker closure.
This operating mode may be select by setting
ON-Element blocking
the
I2
/
I1
)
CLP> Mode
pa-
rameter.
If the CLP function (Cold Load Pick-up) is enabled for threshold change, the selected threshold may
be changed for an adjustable time interval, starting from the circuit breaker closure.
This operating mode may be select by setting
ON-Change setting
the
I2
/
I1
)
CLP> Mode
param-
eter, whereas the operating thresholds within the CLP may be adjusted inside the Set \ Profile A(or
B) \ Negative sequence current/positive sequence current ratio-I2/I1 \ I 21> Element \ Definite time
menu.
For both operating modes the CLP Activation time parameter (
t21CLP>
) may be adjusted in-
side the Set \ Profile A(or B) \ Negative sequence current/positive sequence current ratio-I2/I1 \
I 21> Element \ Setpoints menu.
Note 1 The common settings concerning the Breaker failure protection are adjustable inside the Breaker Failure - BF menu.
t-int-I2-I1.ai
I
2
/
I
1
t
21
>
(
I
2
/
I
1
)
>
t
TRIP
General operation time characteristic for Negative sequence-positive sequence ratio element - I2/I1
General logic diagram of the negative sequence-positive sequence ratio element - I2/I1
all-FI2-I1.ai
(I2/I1)
(I2/I1)> Element
Start (I2/I1)>
Start (I2/I1)>
Trip (I2/I1)>
t
21
>
def
(I2/I1)>
def
Enable (I2/I1)>
Block1
BLK1(I2/I1)>
&
I<<BLK1
&
Start I2ndh>
&
(I2/I1)>2ndh-REST