Motor Overload Protection; Settings And Diagnostics - ABB ACS880 Manual

94 Program features
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Motor overload protection

This section describes motor overload protection without using motor thermal protection
model, either with estimated or measured temperature. For protection with the motor
thermal protection model, see section Motor thermal protection (page 90).
Motor overload protection is required and specified by multiple standards including the
US National Electric Code (NEC), UL 508C and the common UL\IEC 61800-5-1 standard
in conjunction with IEC 60947-4-1. The standards allow for motor overload protection
without external temperature sensors.
The Motor overload protection fulfills standard IEC/EN 61800-5-1 ed. 2.1 requirements
for thermal memory retention and speed sensitivity. The estimated temperature is
retained over power down. Speed dependency is set by parameters.
The protection feature allows the user to specify the class of operation in the same
manner as the overload relays are specified in standards IEC 60947-4-1 and NEMA
ICS 2.
Motor overload protection requires that you specify a motor current tripping level. This
is defined by a curve using parameters 35.51, 35.52 and 35.53. The tripping level is the
motor current at which the overload protection will ultimately trip if the motor current
remains at this level continuously.
The motor overload class (class of operation), parameter 35.57, is given as the time
required for the overload relay to trip when operating at 7.2 times the tripping level in
the case of IEC 60947-4-1 and 6 times the tripping level in the case of NEMA ICS 2.
The standards also specify the time to trip for current levels between the tripping level
and the 6 times tripping level. The drive satisfies the IEC standard and NEMA standard
trip times.
Using class 20 satisfies the UL 508C requirements.
2
The motor overload algorithm monitors the squared ratio (motor current / tripping level)
2
and accumulates this over time. This is sometimes referred to as I t protection. The
accumulated value is shown in parameter 35.5.
You can define with parameter 35.56 that when 35.5 reaches 88%, a motor overload
warning will be generated, and when it reaches 100%, the drive will trip on the motor
overload fault. The rate at which this internal value is increased depends on the actual
current, tripping level current and overload class selected.
Parameters 35.51, 35.52 and 35.53 serve a dual purpose. They determine the load
curve for temperature estimate as well as specify the overload tripping level.

Settings and diagnostics

Parameters common to motor thermal protection and motor overload protection: 35.51
Motor load curve ... 35.53 Break point (page 361).
Parameters specific to motor overload protection: 35.5 Motor overload level (page 354),
35.56 Motor overload action ... 35.57 Motor overload class (page 363).