ABB DCS 500B Description

Also see for DCS 500B: Operating instructions Service manual Service manual

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ABB DCS 500B Description Manual pdf 59 page image

Functional Software descriptionDCS 500 Software Description 51Internal Field ExciterSDCS-FEX-2Internal field exciter FEX2 is a half controlled bridge that can controlthe field current in one (positive) direction. Because of the nature ofthe half controlled bridge, a very small amount of current (5...10%)flows always through the bridge if the field contactor is closed.SDCS-FEX-2 is controlled via a serial communication link. FEX2measures the field current and sends the value to the drive via se-rial communication.Acknowledge The measured field current is used to form an acknowledge signal.If the field current exceeds the overcurrent limit, the drive will trip tothe fault FIELD EX 1 OVERCURR. A low level of field currentblocks the controllers immediately, but the low level must be activeat least 6 seconds before the drive will trip to the fault: NO FIELDACK.External Field ExciterDCF503-0050For the control point of view the DCF503-0050 is similar to SDCS-FEX-2. The differences are that DCF503-0050 can handle a higherfield current than SDCS-FEX-2, and its mechanical size is larger.The control board type is SDCS-FEX-32.External Field ExciterDCF504-0050External field exciter DCF504-0050 can control the field current ei-ther to the positive or negative direction. The direction is selectedby the sign of the field current reference. A positive sign means"forward" bridge and negative sign "reverse" bridge.The field current supervision logic is handled in the same way as inSDCS-FEX-2. The control board type is SDCS-FEX-31.AI/DI ConnectedField ExcitersWhen modifying existing machines ("revamping") the old field ex-citers are often reused. In this case an acknowledge signal must beformed in order to supervise the field function. This can be doneusing either digital or analog input.When a digital input is used to form the acknowledge signal, thefunction is similar to that used with FEX1, the diode field exciter.AcknowledgeSelectionThe acknowledge signal is selected with the same parameter thatis used for selecting the field exciter type. Acknowledge signal isconnected to input [F1 ACK] (1304)FEXC SEL (505)...5 = [FIELD ACK VIA DI]field acknowledge through DI6 = [FIELD ACK VIA AI]field acknowledge through AI