Avtron ADDvantage-32, Manual, Page: 94 / 290

Control Block Description
ADDvantage-32
4-32
4.23 CURRENT LIMIT
This block provides the user with a feature for selecting an automatic taper back of the
drive current limits by two events or using fixed current limits.
The first event, if enabled by P***:BYPASS I2R = ZERO BIT (DEFAULT), prevents
the drive from faulting on a MOTOR (II) T fault. The current limit block accomplishes
this by lowering the current limit when A***:IIR INTEGR is > to 25 counts. The
MOTOR (II) T fault indicates a motor thermal overload condition where the motor
armature current was above 100% for more than the time specified by X***:Thermal TC.
The motor will be allowed to operate at 150% armature current for 60 seconds if the
Thermal TC is set to 60.0 (DEFAULT). The motor could operate up to 200% armature
current, but the MOTOR (II) T fault would occur much sooner than 60 seconds. The user
can increase the Thermal TC value up to a maximum of 3,000 seconds.
The drive will fault on a BRDGE (II) T fault when drive armature current is 150% of the
drive D.C. MAX CONT nameplate current for 60 seconds. This is an Underwriters
Laboratories (UL) mandated fault where the magnitude and time cannot be altered by
users.
When actual motor armature current rises above 110% motor nameplate, IIR INTEGR
will count up from zero when current is rising and count down when current falls below
110%. The IIR INTEGR is used to calculate motor temperature. The rate at which IIR
INTEGR counts is determined by the magnitude of armature current above 100% and the
thermal TC value.
The current limit taper feature can be disabled by setting P***:BYPASS I2R = ONE BIT.
In this nontaper mode, IIR INTEGR will continue counting when motor armature current
is above 110% until it reaches the maximum count of 100 and faults the drive on a
MOTOR (II) T fault.
The second event provides automatic taper back of the drive current limit to prevent
commutation faults due to overcurrenting the armature above base speed. The current
limit should be set below 150% at maximum motor speed to prevent flashovers.
The user can configure the motor current limits using parameters P***:MAX I LIMIT
and P***:MIN I LIMIT. These parameters are defaulted to C***:POS CUR LMT = 100
and C***:NEG CUR LMT = 100 respectively. The user can enter different current limits
by entering a new value for the "C" parameter corresponding to the POS CUR LMT or
NEG CUR LMT. The value is entered as a percentage of the motor nameplate armature
current. It is assumed the user has correctly scaled the motor armature current to the
drive D.C. MAX CONT nameplate current by setting X***:MOTOR IARM.