3BHB006338R0001 ABB Excitation control of medium and high voltage frequency conversion board

Description

When a motor or generator is stationary, there is no forced
cooling and the cooling time constant is much longer. The time
constant at standstill is defined by the setting of the factor “k”.
The time constant is switched when the current falls below a
given value and the external signal “Stillst.-Inp” is being applied
at the same time.
The universal model enables overtemperature to be monitored
on the basis of a general function, which describes the temperature rise for a given current change. Fig. 3.5.19.1 shows the
response of the general function s (t) to a step change in the
current. The general function s (t) is divided into 40 sections. The
mean values h1, h2 … h40, which define the steps of the impulse
response, are determined graphically from the derivation of the
function s (t) for the individual sections in relation to time. These
instantaneous values of the impulse response are entered as
h[1] to h[40] when using the universal model. The
“ResponseTime”, i.e. the duration of the impulse response, must
also be entered. Zero must be entered for the thermal time constant “TimeConstant”.
The reduced cooling of a motor or generator at standstill is taken
into account by extending the impulse response by the factor “k”
when an external signal coincides with operation of the low-current monitor.