Thytronic NG10 User Manual

FUNCTION CHARACTERISTICS
57
NG10 - Manual - 04 - 2022
Three operating conditions with ideal and matched measurement CTs (pE1 = +1 and ME
(H)
=1) are
considered:
• Earth fault inside the protected zone, powered only from the starpoint
The trip current is equal to I
E1
while, being I
E(H)
= 0, the stabilization current is: I
ES(H)
= 4 · (I
E
- I
E
) = 0
The element trips when the fault current exceeds the minimum threshold set I
REF(H)
> (maximum
sensitivity for internal fault).
• Earth fault inside the protected zone, powered from both sides
The trip current is equal to I
E
while, assuming that I
EC
has the same module and is in phase ( = 0 °)
with I
E1
, hence:
I
ES
(H) = 4 · (|I
E
- I
E
| - |I
E
+ I
E
|) = - 8 I
E
< 0 => I
ES(H)
= 0
Since I
ES(H)
is zero, so that the element trips when the fault current exceeds the minimum threshold
set I
REF(H)
> (maximum sensitivity for internal earth fault).
• Earth fault outside the protected zone (external fault)
The trip current is still equal to I
E
, while being ideally I
E(H)
= -I
E
(residual current on the starpoint
grounding out of phase with the phase side H residual current, i.e  = 180 °), the stabilization cur-
rent is: II
ES(H)
= 4 · (|I
E
+ I
E
| - |I
E
- I
E
|) = 8 |I
E
|
that being positive and equal to eight times the tripping current, determines the stabilization ex-
ternal fault protection on increasing to infinity the trip threshold (maximum stability for external
earth fault). If any CT gets saturation, a displacement angle  <180 ° is introduced, weakening the
stabilization current.
In particular, the maximum stability on external fault is obtained with  ≥ 100 °. For  ≤ 90 ° however,
the stabilization current is nothing and protection has, therefore the maximum sensitivity.
For  increasing from 90 ° to 100 ° the sensitivity decreases from I
REF(H)
> to infinity.
The start of the 64REF side H threshold becomes active when the following condition are contempo-
raneously active:
A) I
ES(H)
≤ 4 · I
REF(H)
>
B) I
E
≥ I
ES(H)
+ [I
REF(H)
>/[1-(I
ES(H)
/4 · I
REF(H)
>)
20
] or in normalized form:
[I
E
/I
REF(H)
>] ≥ [I
ES(H)
/I
REF(H)
>] + [1 /[1-(I
ES(H)
/(4 · I
REF(H)
>))
20
]
C) 64
REF(H)
Enable = ON
D) 64
REF(H)
-BLK1 = OFF
where:
• 64
REF(H)
Enable is the enabling parameter of the 64REF element side H
• I
REF(H)
> is the minimum threshold setting (max sensitivity) of the 64REF element side H
• 64
REF(H)
-BLK1 is the output logic state for the logic block function of the 64REF element. side H.
After expiry of the associated delay time (t
REF(H)
>) a trip command is issued (TR I
REF(H)
); if instead the
A), B), C) and D) conditions current don’t remain valid, the element it is restored.
The restricted ground fault protection is then stabilized against external faults by increasing the
threshold of residual current measured at the grounding of the neutral current with increasing stabi-
lization in accordance with the following characteristics:
I
E

-I
E(H)
I
ES(H)
/4
I
E
-I
E(H)
I
E
+I
E(H)
I
E(H)

Thytronic NG10 Specifications

General

Brand	Thytronic
Model	NG10
Category	Protection Device
Language	English