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13. SERVO AMPLIFIERS WITH A LARGE CAPACITY (30k TO 55kW)
13.9.8 Leakage current breaker
(1) Selection method
High-frequency chopper currents controlled by pulse width modulation flow in the AC servo circuits.
Leakage currents containing harmonic contents are larger than those of the motor which is run with a
commercial power supply.
Select a leakage current breaker according to the following formula, and ground the drive unit, servo motor,
etc. securely.
Make the input and output cables as short as possible, and also make the grounding cable as long as
possible (about 30cm) to minimize leakage currents.
Rated sensitivity current
10 {Ig1 Ign Iga K (Ig2 Igm)} [mA] ··········································· (13.2)
K: Constant considering the harmonic contents
Leakage current breaker
Type
Mitsubishi
products
K
Models provided with
harmonic and surge
reduction techniques
NV-SP
NV-SW
NV-CP
NV-CW
NV-HW
1
Ign
Noise filter
Cable
Ig1
NV
Converter
unit
Drive
unit
Cable
Iga
Ig2 Igm
M
General models
BV-C1
NFB
NV-L
3
Ig1: Leakage current on the electric channel from the leakage current breaker to the input terminals of the drive
unit (Found from Fig. 13.3.)
Ig2: Leakage current on the electric channel from the output terminals of the servo amplifier to the servo
motor (Found from Fig. 13.3.)
Ign: Leakage current when a filter is connected to the input side (4.4mA per one FR-BIF or FR-BIF-H)
Iga: Leakage current of the drive unit (Found from Table 13.7.)
Igm: Leakage current of the servo motor (Found from Table 13.6.)
Table 13.6 Servo motor’s leakage current
example (lgm)
Table 13.7 Converter unit
drive unit's leakage
current Example (Iga)
Servo motor power
[kW]
Leakage current
[mA]
Converter unit
Drive unit
Leakage current
[mA]
30 to 55 2.5
All series 5
120
100
80
60
40
20
0
2
3.5
5.5
8
14
22
38
80
150
30
60
100
Leakage current [mA]
Cable size
[
mm
2
]
120
100
80
60
40
20
0
2
3.5
5.5
8
14
22
38
80
150
30
60
100
Leakage current [mA]
Cable size
[
mm
2
]
a) 200V class b) 400V class
Fig.13.3 Leakage current example (lg1, lg2) for CV cable run in metal conduit