5.4.9 Direction of Motor Rotation
The default setting is clockwise rotation with the frequency converter
output connected as follows.
Terminal 96 connected to U-phase
Terminal 97 connected to V-phase
Terminal 98 connected to W-phase
The direction of motor rotation is changed by switching two motor pha-
ses.
Motor rotation check can be performed using par. 1-28
Motor Rotation
Check
and following the steps shown in the display.
5.4.10 Motor Thermal Protection
The electronic thermal relay in the frequency converter has received the UL-approval for single motor protection, when par. 1-90
Motor Thermal Protec-
tion
is set for
ETR Trip
and par. 1-24
Motor Current
is set to the rated motor current (see motor name plate).
5.4.11 Motor Insulation
For motor cable lengths
≤
the maximum cable length listed in the General
Specifications tables the following motor insulation ratings are recom-
mended because the peak voltage can be up to twice the DC link voltage,
2.8 times the mains voltage, due to transmission line effects in the motor
cable. If a motor has lower insulation rating it recommended to use a du/
dt or sine wave filter.
Nominal Mains Voltage
Motor Insulation
U
N
≤
420 V
Standard U
LL
= 1300 V
420 V < U
N
≤
500 V
Reinforced U
LL
= 1600 V
500 V < U
N
≤
600 V
Reinforced U
LL
= 1800 V
600 V < U
N
≤
690 V
Reinforced U
LL
= 2000 V
5.4.12 Motor Bearing Currents
It is generally recommended that motors of a rating 110kW or higher operating via Variable Frequency Drives should have NDE (Non-Drive End) insulated
bearings installed to eliminate circulating bearing currents due to the physical size of the motor. To minimize DE (Drive End) bearing and shaft currents
proper grounding of the drive, motor, driven machine, and motor to the driven machine is required. Although failure due to bearing currents is low and
very dependent on many different items, for security of operation the following are mitigation strategies which can be implemented.
Standard Mitigation Strategies:
1.
Use an insulated bearing
2.
Apply rigorous installation procedures
Ensure the motor and load motor are aligned
Strictly follow the EMC Installation guideline
Reinforce the PE so the high frequency impedance is lower in the PE than the input power leads
Provide a good high frequency connection between the motor and the frequency converter for instance by screened cable which has a 360°
connection in the motor and the frequency converter
5 How to Install
VLT
®
HVAC Drive Design Guide
110
MG.11.B9.02 - VLT
®
is a registered Danfoss trademark
5