Information for using the motors
7.11 Insulated bearings (NDE) (option L27)
1PH7 induction motors (Machine tools)
Configuration Manual, (APH7W), 04/2009, 6SN1197-0AD72-0BP0
233
7.11 7. 11 Insulated bearings (NDE) (option L27)
Relevant, additional bearing currents
When compared to a pure sinusoidal supply, the pulsed output voltage of a frequency
converter results in additional motor bearing currents. The relevant additional bearing
currents are:
● Circulating currents
● EDM currents
● Rotor ground currents
Factors that influence bearing currents
Above a certain magnitude, bearing currents result in localized melting at the bearing rings
and rolling assemblies as well as lubricant wear. This reduces the bearing lifetime. Essential
influencing factors include:
● Motor speed and associated operating time
● Pulse frequency of the frequency converter
● Grounding relationships between the motor and the connected load
Application for option L27
At speeds < 500 rpm, the load due to bearing currents increases significantly. Option L27 is
always required if the motor is operated in the speed range between 0 ... 500 rpm for a
longer period of time. Without option L27, the total operating time in the speed range 0 ...
500 rpm may be a maximum of 800 h (for an assumed bearing change interval (t
LW
) of the
bearings of 20,000 h.
Table 7- 8 Measures that are required for operation in the speed range < 500 rpm
Shaft height Bearing change interval (t
LW
) for lifetime
lubrication [h]
1)
Options that are
required
Remarks
100 - 160
- Due to the experience from the
field (in practice) no dangers
have been identified due to
bearing currents
180 L27 Insulated NDE bearings
225
20000
_ Generally insulated NDE
bearings
1) Definition, refer to the table "Recommended bearing change intervals (standard bearing design)"
To Next Page
Loading...
