262
NVA100X-D - Manual - 02 - 2016
FUNCTION CHARACTERISTICS
Second Harmonic Restraint - 2ndh-REST
Preface
When a power transformer is energized, as well know an inrush current fl ow in the side that have
been energized with an amount and duration that depend by many factors which:
Instantaneous value of the supply voltage at the time where the transformer is energized
Transformer design, magnetization characteristic and size
Residual fl ux
The maximum amount of the inrush current is produced by energizing the transformer at the zero
point of the voltage wave, when it increase or decrease with the residual fl ux respectively positive
or negative. Moreover the ratio between the maximum amount of the inrush current and the nominal
current of the transformer decrease if the size of transformer increase, whereas the duration of the
inrush current increase with the size of transformer.
Some types of instantaneous protections as overcurrent, residually connected ground fault and dif-
ferentials, are affected by this inrush current and their unwanted tripping can occur on transformer
energizing.
The second harmonic restraint is available to restraint any selected threshold of protective relay:
Negative sequence overcurrent for motor - 46M
Phase overcurrent - 50/51
Residual overcurrent - 50N.1/51N.1
Residual overcurrent - 50N.2/51N.2
Calculated residual overcurrent - 50N(Comp)/51N(Comp)
Moreover one or more output contacts may be allocated to the 2NDH-REST function in order to block
any external protection relays where second harmonic restraint is not available.
Operation and settings
Each second harmonic component of phase currents (
I
L1-2nd
,
I
L2-2nd
,
I
L3-2nd
) is compared with the
I
2ndh>
adjustable threshold.
When one or more currents overcome the setting threshold a start is issued.
The start may be employed to block-off one or more of 46M, 50/51, 50N.1/51N.1, 50N.2/51N.2 and
50N(Comp)/51N(Comp) elements or to block-off external protections by means output relays (this
can be usefully used in order to restraint external protection relays where second harmonic restraint
is not available).
For the purpose to keep in block state the selected elements, an adjustable
t
2ndh>RES
reset delay is
provided.
The setting of
I2ndh>
and
t2ndh>RE
S parameters are available inside the
Set \ Profi le A(B) \
Second Harmonic Restraint
menu.
The second harmonic element may be enabled or disabled; to enable it, the
I2ndh>
parameter must
be set to
ON
inside the
Set \ Profi le A(B) \ Second Harmonic Restraint-2ndh-REST
menus.
All the parameters can be set separately for
Profi le A
and
Profi le B
.
The output may be assigned to the selected
I2ndh>-ST-K
output relays inside the
Set \ Profi le A(B) \ Second Harmonic Restraint-2ndh-REST
menu; the same for addressing the LED
indicators (
I2ndh>-ST-L
).
When output relays are programmed for second harmonic element output, the
t
TR
time delays must
reset to zero; the operation mode must be set with self reset (
No-latched
inside
Set \ Relays
sub-
menu) and the
Logic
parameters (
Energized
/
De-energized
) must be programmed in the same
way of the related binary input connected with-it.
—
•
•
•
•
•
•
•
•
2NDH-REST-diagram.ai
I
L 1-2nd
t
2ndh>RES
T
0
≥
1
t
2ndh>RES
Start I2ndh>
ON
≡
Enable
I2ndh> Enable
&
I2ndh>ST-K
I2ndh>ST-L
I
2 n d h >
I
L 1-2nd
≥
I
2 n d h >
I
L 2-2nd
I
L 2-2nd
≥
I
2 n d h >
I
L 3-2nd
I
L 3-2nd
≥
I
2 n d h >
TRIP
P
ING
M
ATRIX
(LED
+R
EL
AY
S
)
Logic diagram concerning the second harmonic restraint function - 2NDH/REST
