Overspeed Limit 2-103
Overspeed Limit The Overspeed Limit is a user programmable value that allows operation at
maximum speed but also provides an “overspeed band” that will allow a
speed regulator such as encoder feedback or slip compensation to increase
the output frequency above maximum Speed in order to maintain maximum
Motor Speed.
Figure 2.14 illustrates a typical Custom V/Hz profile. Minimum Speed is
entered in Hertz and determines the lower speed reference limit during
normal operation. Maximum Speed is entered in Hertz and determines the
upper speed reference limit. The two “Speed” parameters only limit the
speed reference and not the output frequency.
The actual output frequency at maximum speed reference is the sum of the
speed reference plus “speed adder” components from functions such as slip
compensation.
The Overspeed Limit is entered in Hertz and added to Maximum Speed and
the sum of the two (Speed Limit) limit the output frequency. This sum
(Speed Limit) must is compared to Maximum Frequency and an alarm is
initiated which prevents operation if the Speed Limit exceeds Maximum
Frequency.
Figure 2.14 Typical V/Hz Curve for Full Custom (with Speed/Frequency Limits
Frequency
Output Voltage
Note 1: The lower limit on this range can be 0 depending on the value of Speed Adder
Overspeed
Limit
Frequency Trim
due to Speed
Control Mode
Maximum
Voltage
Motor NP
Voltage
Run
Boost
Break
Voltage
Start
Boost
Allowable Output Frequency Range - Normal Operation
1
Allowable Speed Reference Range
Allowable Output Frequency Range -
Bus Regulation or Current Limit
Maximum
Frequency
Motor NP Hz0 Break
Frequency
Maximum
Speed
Minimum
Speed
Output
Frequency
Limit
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