GE 531X302DCIBAG1 Gas Turbine System Gas Turbine Card

Description

The 489 has six phase current transformer inputs (three output side and three neutral end), each with an isolating transformer. There are no internal ground connections on the CT inputs. Each phase CT circuit is shorted by automatic mechanisms on the 489 case if the unit is withdrawn. The phase CTs should be chosen such that the FLA is no less than 50% of the rated phase CT primary. Ideally, the phase CT primary should be chosen such that the FLA is 100% of the phase CT primary or slightly less. This will ensure maximum accuracy for the current measurements. The maximum phase CT primary current is 50000 A.

The 489 will measure correctly up to 20 times the phase current nominal rating. Since the conversion range is large, 1 A or 5 A CT secondaries must be specified at the time of order such that the appropriate interposing CT may be installed in the unit. CTs chosen must be capable of driving the 489 phase CT burden (see SPECIFICATIONS for ratings). Verify that the 489 nominal phase current of 1 A or 5 A matches the secondary rating and connections of the connected CTs. Unmatched CTs may result in equipment damage or inadequate protection. Polarity of the phase CTs is critical for phase differential, negative sequence, power measurement, and residual ground current detection (if used).

The 489 has a dual primary isolating transformer for ground CT connections. There are no internal ground connections on the ground current inputs. The ground CT circuits are shorted by automatic mechanisms on the case if the unit is withdrawn. The 1 A tap is used for 1 A or 5 A secondary CTs in either core balance or residual ground configurations.

If the 1 A tap is used, the 489 measures up to 20 A secondary with a maximum ground CT ratio of 10000:1. The ground CT must be capable of driving the ground CT burden. The HGF ground CT input is designed for sensitive ground current detection on high resistance grounded systems where the GE Multilin HGF core balance CT (50:0.025) is used. In applications such as mines, where earth leakage current must be measured for personnel safety, primary ground current as low as 0.25 A may be detected with the GE Multilin HGF CT. Only one ground CT input tap should be used on a given unit.

The HGF CT has a rating of 50:0.025. However if the HGF CT is used in conjunction with the 489, the relay assumes a fixed ratio of 5:0.0025. Therefore, the pickup level in primary amps will be Pickup × CT, where CT is equal to 5.

The external faults of the card or module need to be checked and analyzed step by step. Common fault diagnosis methods include:
(1) Direct judgment method: Directly analyze and determine the cause and location of the fault based on the fault phenomenon, scope, characteristics, and records of the fault occurrence, and identify the fault.
(2) External inspection method: For some obvious faults with external characteristics, external inspection is used to determine the fault location, such as loose plugs, broken wires, touching wires, short circuits, component heating and burning, faulty soldering, and desoldering. Some faults, especially temporary faults, can be detected by manual shaking and tapping.
(3) Replacement comparison method: For suspected faulty components, replace them with spare parts or the same card or module, or compare them with each other. However, it should be noted that before replacing, analyze and eliminate some hazardous faults, such as power abnormalities, load short circuits, and other faults that cause component damage. If not eliminated first, the replaced card or module will continue to be damaged.
(4) Segmental search method: When the scope and cause of the fault are unknown, the relevant components and circuits can be segmented, analyzed, inspected, tested, and replaced section by section.
(5) Isolation method: It can be combined with segmented search method to temporarily disconnect certain parts or lines, observe the changes in fault phenomena, gradually reduce the suspected objects, and ultimately identify the faulty parts for processing or replacement.