Logic Control; Logic Control (Lc); Extreme Running Conditions - GE AF-650 GP Design And Installation Manual

Application Set-Up Examples

6.7 Logic Control

6.7.1 Logic Control (LC)

Logic Controller (LC) is a sequence of user-defined actions
(see parameter LC-52 Logic Controller Action [x]) executed by
the LC when the associated user-defined event (see
parameter LC-51 Logic Controller Event [x]) is evaluated as
TRUE by the LC.
The condition for an event can be a particular status or
that the output from a logic rule or a comparator operand
becomes TRUE. That leads to an associated action as
shown in Illustration 6.25.
Events and actions are each numbered and linked in pairs
(states). This means that when event [0] is fulfilled (attains
the value TRUE), action [0] is executed. After this, the
conditions of event [1] is evaluated and if evaluated TRUE,
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action [1] is executed, and so on. Only one event is
evaluated at any time. If an event is evaluated as FALSE,
nothing happens (in the LC) during the current scan
interval and no other events are evaluated. This means
that when the LC starts, it evaluates event [0] (and only
event [0]) each scan interval. Only when event [0] is
evaluated TRUE, the LC executes action [0] and starts
evaluating event [1]. It is possible to program 1–20 events
and actions.
When the last event/action has been executed, the
sequence starts over again from event [0]/action [0].
Illustration 6.25 shows an example with 4 event/actions:
Illustration 6.25 Order of Execution when 4 Events/Actions are
Programmed
Comparators
Comparators are used for comparing continuous variables
(output frequency, output current, analog input, and so on)
to fixed preset values.
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Illustration 6.26 Comparators
Logic rules
Combine up to 3 boolean inputs (TRUE/FALSE inputs) from
timers, comparators, digital inputs, status bits, and events
using the logical operators AND, OR, and NOT.
Illustration 6.27 Logic Rules

6.8 Extreme Running Conditions

Short circuit (motor phase – phase)
The frequency converter is protected against short circuits
by current measurement in each of the three motor phases
or in the DC link. A short circuit between two output
phases causes an overcurrent in the inverter. The inverter is
turned off individually when the short circuit current
exceeds the permitted value (Alarm 16 Trip Lock).
Switching on the output
Switching on the output between the motor and the
frequency converter is fully permitted. Switching on the
output does not damage the frequency converter in any
way. However, fault messages may appear.
Motor-generated overvoltage
The voltage in the DC link is increased when the motor
acts as a generator.
This occurs in following cases:
1. The load drives the motor (at constant output
frequency from the frequency converter), i.e. the
load generates energy.
2. During deceleration if the moment of inertia is
high, the friction is low and the decel time is too
short for the energy to be dissipated as a loss in
the frequency converter, the motor, and the
installation.
3. Incorrect slip compensation setting may cause
higher DC-link voltage.
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