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44  Mentor MP User Guide
www.controltechniques.com                     Issue: 3
Table 4-16 Mentor MP size 1 drive thyristor I
2
t rating for 
semiconductor fusing
Table 4-17 Mentor MP size 2 drive thyristor I
2
t ratings for 
semiconductor fusing
4.6.3     Internal field fuses
The internal field fuses provide protection to the field controller. The 
fuses can rupture if there is a fault in the field circuit. The user should 
check the internal field fuses if the drive is tripping field loss (FdL) and 
the field controller is enabled.
Figure 4-9 Removing the internal field fuses
Insert a flat-head screwdriver into the groove as shown above and lever 
downwards to remove the fuse cover. Refer to section 4.6.1 Ferraz 
Shawmut fuses on page 40 for fuse types.
4.7      External suppressor resistor
The Mentor MP range of drives provide internal suppression of the 
voltage overshoots created by commutation of the thyristors in the power 
stage during the operation of the product. The internal suppression is 
suitable for typical applications using recommended line reactors as 
defined in section 4.4 Line reactors on page 37. The Mentor MP drives 
provide the facility to allow for extra suppression for applications at the 
boundaries of the drive's operating area. Applications which may require 
an external suppression resistor to be installed have some or all the 
following characteristics:
1. Supplies rated ≥10kA with less than the recommend line reactance.
2. High line-to-line voltage
The recommended external suppressor resistor selections are shown in 
Table 4-18.
Table 4-18 Recommended external suppressor resistors
The following diagram shows the location of the external suppressor 
resistor terminals above the L1 and L2 terminals:
Model
Thyristor I
2
t (A
2
s)
Field fuses 400
MP25A4 MP25A5 1030
MP45A4 MP45A5 3600
MP75A4 MP75A5 15000
MP25A4(R) MP25A5(R) 1030
MP45A4(R) MP45A5(R) 3600
MP75A4(R) MP75A5(R) 15000
MP105A4 MP105A5
80000
MP155A4 MP155A5
MP210A4 MP210A5
MP105A4(R) MP105A5(R)
MP155A4(R) MP155A5(R)
MP210A4(R) MP210A5(R)
Model
Thyristor I
2
t 
(A
2
s)
Field fuses 400
MP350A4(R) MP420A4(R) MP550A4(R) 320000
MP350A6(R) MP470A5(R) MP470A6(R) 281000
MP700A4(R) MP825A4(R) MP900A4(R) 1050000
MP700A6(R) MP825A5(R) MP825A6(R) 1200000
MP1200A4(R) MP1200A5(R) MP1200A6(R)
2720000
MP1850A4(R) MP1850A5(R) MP1850A6(R)
Isolate the power before removing the internal field fuses.
Model
Resistance
Power
rating
Voltage
rating
Isolation
voltage
kΩ WVVrms
MP25A4(R)
8.2 150 1100 2500
MP45A4(R)
MP75A4(R)
MP105A4(R)
MP155A4(R)
MP210A4(R)
MP25A5(R)
15 150 1400 2500
MP45A5(R)
MP75A5(R)
MP105A5(R)
MP155A5(R)
MP210A5(R)
MP350A4(R)
4.1 300 1100 2500
MP420A4(R)
MP550A4(R)
MP700A4(R)
MP825A4(R)
MP900A4(R)
MP1200A4(R)
MP1850A4(R)
MP350A5(R)
MP350A6(R)
8.6 300 1600 2500
MP470A5(R)
MP470A6(R)
MP700A5(R)
MP700A6(R)
MP825A5(R)
MP825A6(R)
MP1200A5(R)
MP1200A6(R)
MP1850A5(R)
MP1850A6(R)