Mitsubishi NF-S Series User Manual

12
Total
clearing
time
Latching
(relay)
time
Electromagnet
oparating
time
Time for
contacts to
open
Arc-
extinguishing
time
Mechanical
delay
time
Arcing
time
Fig. 4.3 Instantaneous Tripping Sequence
4.3 Effects of Mounting Attitudes
Instantaneous tripping is negligibly affected by mount-
ing attitude, for all types of MCCB. Delay tripping is
also negligibly affected in the thermal types, but in
the hydraulic-magnetic types the core-weight effect
becomes a factor. Fig. 4.4 shows the effect, for verti-
cal-surface mounting and for two styles of horizontal-
surface mounting.
(vertical plane)
100%
93%
ON
ON
ON
ON
ON
ON
ON
ON
90%110%
93%
107%
107%
100%
Fig. 4.5 Effects of Nonvertical-Plane Mounting on Current
Rating
4.4 DC Tripping Characteristics of AC-Rated MCCBs
Table 4.2 DC Tripping Characteristics
Trip unit
Thermal
magnetic
Hydraulic
magnetic
Long delay
No effect below 630A
frame. Above this, AC
types cannot be used
for DC.
DC minimum-trip
values are 110~140%
of AC values.
Instantaneous
DC inst.-trip current is
approx. 130% of AC
value.
Tripping curve
AC
DC
Overcurrent
Tripping time
AC
DC
Tripping time
Overcurrent
4.5 Frequency Characteristics
At commercial frequencies the characteristics of
Mitsubishi MCCBs of below 630A frame size are vir-
tually constant at both 50Hz and 60Hz (except for the
E Line models, the characteristics of MCCBs of 2000A
frame and above vary due to the CT used with the
delay element).
At high frequencies (e.g., 400Hz), both the current
capacity and delay tripping curves will be reduced by
skin effect and increased iron losses.
Performance reduction will differ for different types;
at 400Hz it will become 80% of the rating in breakers
of maximum rated current for the frame size, and 90%
of the rating in breakers of half of the maximum rating
for the frame size.
The instantaneous trip current will gradually in-
crease with frequency, due to reverse excitation by
eddy currents. The rise rate is not consistent, but
around 400Hz it becomes about twice the value at
60Hz. Mitsubishi makes available MCCBs especially
designed for 400Hz use. Apart from operating char-
acteristics they are identical to standard MCCBs (S
Line).
Floor-mounted
Overcurrent
Tripping time
Ceiling-mounted
Wall-mounted
(horiz. or vert. attitude)
Fig. 4.4 Effect of Mounting Attitude on the Hydraulic-
Magnetic MCCB Tripping Curves

Mitsubishi NF-S Series Specifications

General

Brand	Mitsubishi
Model	NF-S Series
Category	Circuit breakers
Language	English