Power Transformer Failures Due to Overburden of the Medium Voltage Power Transformers

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Power Transformer Failures Due to Overburden of the Medium Voltage Power Transformers

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TECHNICAL INFORMATION BULLETIN	October 24, 2001
Engines Generator Sets	3508 (23Z, 69Z, 70Z, 96Y, 3LS, 5XM) 3508B (6PN, 4GM, 2HW) 3512 (24Z, 66Z, 67Z, 6PM, 3MS, 50Y) 3512B (8RM, 6WN, 5AW, 4AW) 3516 (29Z, 25Z, 72Z, 73Z, 4XF 5SJ, 4MJ, 7KM, 3NS) 3516B (7RN, 6HN, 2JW, 1NW) G3508 (2JF, 4WD, 9TG, 2TJ) G3512 (4KC, 5JD, 7NJ) G3516 (3RC, 8LD, 4EK) 3516 (8TW) 3516B (8NW) G3508 (CPJ, CPS) G3512 (CSP, CRN) G3516 (CPG, CSZ)
`	Component Code(s) 1409

SUBJECT: Power Transformer (PT) Failures Due to Overburden of the Medium Voltage Power Transformers

PROBLEM: The 149-3403 Transformer is a medium voltage power transformer that is rated at 5 VA maximum output. On a 149-3403 Transformer with 240 volt load-share module sensing, the load puts a total burden of approximately 6.47 VA on phase two of the three-phase transformer configuration. This can lead to early failure of the solder connection and can cause corona damage inside the generator cabinet.

SOLUTION: Using the 35:1 PT secondary leads instead of the 17.5:1 leads, rewire the load-share-sensing voltage to the 120 VAC input. At 120 VAC sensing, the VA rating of the Woodward load-share-sensing circuit drops to approximately 2.35 VA per phase.

Perform the following steps in order to reduce the load on the transformers and to provide long-term reliable operation.

Remove the load share sensing leads from terminals 20, 22, and 24. Re-attach these leads to terminals T1, T3, and T2 on the 170-5400 Terminal Strip Group. Refer to Illustration 1, Illustration 2, and Illustration 3.
Locate the leads of the TX1 secondary output and the TX2 secondary output. The leads of the TX1 secondary output and the TX2 secondary output are black with white tracers. These leads should be connected to terminal T1 and terminal T3 on the 170-5400 Terminal Strip Group.
Install a 14 gauge jumper wire from terminal 24 (170-5400 Terminal Strip Group) to terminal T2 (170-5400 Terminal Strip Group). This will bring the total burden on the potential transformers to approximately 4 VA.
If main the Terminal Strip does not have T2, refer to Illustration 3 in order to connect the Load Share Module.

Note: When medium voltage generator transformer sensing leads are attached to the bus bars, apply an equal amount of torque to connections T1, T2, T3, and T0. If equal torque is not applied to these connections, voltage losses across the poor connections could cause voltage readout accuracy errors on the EMCPII.

During operation, there should be approximately 120 ACV across any two of the following 170-5400 Terminal Strip terminals: T1, T2, and T3. Refer to Table 1.