American Standard CH530 manual Current Overload Protection, Overload trip time versus percent RLA

Machine Protection

and Adaptive

Control

Current Overload Protection

Motor currents are continuously monitored for over current protection and locked rotor protection. This protects the Chiller itself from damage due to current overload during starting and running modes but is allowed to reach full load amps. This overload protection logic is independent of the current limit. The overload protection will ultimately shut the unit down anytime the highest of the three phase currents exceeds the time-trip curve. A manual reset diagnostic describing the failure will be displayed.

Overload protection for the motor starts based on the Maximum Time to Transition permitted for a particular motor .

Running Over Current Protection

In the run mode, a “time-to-trip” curve is looked at to determine if a diagnostic should be called. The UCP continuously monitors compressor line currents to provide running over current and locked rotor protection. Over current protection is based on the line with the highest current. It triggers a manually resettable diagnostic shutting down

the compressor when the current exceeds the specified time-trip curve. The compressor overload time trip curve is expressed as a percent of the Rated Load Amps of the compressor and is not adjustable:

Overload Must Hold = 102 Percent RLA.

Overload Must Trip in 20 (+0 -3) seconds = 112 Percent RLA (Note the above gives a nominal 20 second must trip point of 107 Percent RLA.)

Overload Must Trip in 1.5 seconds = 140 Percent RLA (Nominal)

The linear time-trip curve is as follows:

Figure 30. Overload trip time versus percent RLA

The Maximum Acceleration Time Setting and Current Transformer Setting are factory set however can be set with the service tool;

CDHF-SVU01C-EN 73