Thermal Model with Speed Biasing

This feature acts as an additional check of the amortisseur, or squirrel

cage winding rotor heating. This feature uses estimated speed-dependent

thermal capacity used (actual value ‘’ and compares this value to the

Thermal Capacity Used calculated by the current-based and RTD Bias

(when Enabled) methods. The larger of the three values is used from that

point onward.

RTD Biasing

The Multilin 869 supports up to 13 programmable RTD inputs that can

be configured for an Alarm or Trip. The RTD voting option gives additional

reliability to ignore any RTD failures.

The RTDs can be assigned to a group for monitoring the stator, bearing and

ambient temperatures.

The Thermal Model is also biased by the RTD’s temperature feedback. This

feature allows the relay to protect the motor against unusual high ambient

temperatures or abnormal heating due to overvoltage or damaged

bearings. The RTD biasing feature can correct for this temperature rising

by forcing the TCU register up to the value appropriate to the temperature

of the hottest stator RTD.