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SR469-P5-HI-A20-E-H Relay protector

Analog input is used when the field current is measured or controlled. When controlling an AI-based field exciter, it is also necessary to transfer the reference to the field exciter. This can be done by means of connecting one analog output channel to the signal F1 CURR REF (11301). The scaling of the used analog output must be arranged so that the value 4096 corresponds to the rated nominal excitation value as a voltage reference. The field current actual signal must also be scaled so that the scaled input value is 4096 with rated field current. Calculation Example For example, the field exciter nominal current is 32.5A, which corresponds to the 7V field current actual measurement. The connected analog input channel is AI3.For more information on how to scale the AI/AO, see paragraph Digital and Analog I/O.

Two Field Exciters at the same time

 When the same converter controls two motors as a "shared motion", the armature unit is switched between two motors by means of an extra contactor. Both motors have still their own field exciters. In the documents the main motor field exciter is called the "first field exciter" and that of the second motor the "second field exciter". Only the "first field exciter" can be current controlled and gets it´s current reference from the EMF CONTROL function block. The "second field exciter" always uses either a fixed field current level or a variable one, generated by an analog input or a similar function. Motor standstill heating function can be used on the not-used motor by giving a small field current reference to the field exciter. Field Current Settings The nominal field current must be given to the program in order to have a correctly controlled field. Usually there is no need to change maximum and minimum levels.

Free Wheeling Function

 Ext. DCF50x-0050 has a free-wheeling function to give a path for the current if the AC-input voltage disappears for some reason, e.g. the field contactor opens. When this happens, the current does not stop but tends to increase the voltage of the field excitation unit very rapidly . Trigger Point Setting of the Free Feeling Function The AC input voltage is measured, and if the value changes too fast, the field excitation unit fires two selected thyristors continuously open to provide a path for the current. The sensitivity for starting the free-wheeling function can be adjusted by means of the following parameters The initial value is 10 % which means that the free-wheeling function starts if the two successive AC-voltage measurements in field exciter differ more than 10 %.