HUW1
Series Intelligent Universal Circuit Breaker
14
Ground fault protection mode and electrical schematic diagram
Mode 1 (difference type)
TN-C, TN-C-S and TN-S distribution systems use three-pole circuit
breakers without neutral current transformers.
●
The vector sum of the three-phase current is taken for the
ground fault protection signal.
●
The protection characteristics are fixed time or inverse time
protection.
Mode II (difference type)
The four-pole circuit breaker with built-in neutral current transformer
is used in the TN-S distribution system.
●
The vector sum of the four-phase current is taken for the ground
fault protection signal.
●
The protection characteristics are fixed time or inverse time
protection.
Mode III (difference type)
The three-pole circuit breaker with external neutral current
transformer is used in the TN-S distribution system.
●
The vector sum of the three-phase current and the N-phase
current is taken for the ground fault protection signal.
●
The protection characteristics are fixed time or inverse time
protection.
Note: The conductor length of the neutral current transformer is not
more than 2 meters.
Mode IV (ground current type)
The three-pole circuit breaker with external ground current
transformer is used in the ground current protection distribution
system.
●
Provided with additional special current transformer.
●
The distance between the special current transformer and the
circuit breaker is not more than 10 meters.
6.4.6
Neutral line protection
The cable and current characteristics used in the neutral phase are often quite different from those of other three
phases, and intelligent controllers implement different protections for the neutral phase according to different
applications. When the neutral line is thin, it can be protected by semi-fixed value method; when the neutral line is the
same as other phases, it can be protected by full fixed value; and when the harmonics in the power grid are serious,
double fixed value or 1.6 times fixed value can be used for protection.
Action current set
value I
N
(0.5, 1.0) In + OFF
Current tolerance
±10%
Action time T
N
Same as overload long time delay duration
6.4.7
Current imbalance protection
The current imbalance protection protects the open-phase and three-phase current imbalance, and performs
protection actions according to the imbalance rate between the three-phase currents. When the execution mode is
“
Alarm
”
, its action principle is the same as that of grounding protection.
Transformer
Transformer
Transformer
Transformer
Intelligent
controller
Intelligent
controller
Intelligent
controller
Intelligent
controller