Cracking of PMG Capacitor Cases Due to Prolonged Elevated Temperatures in Certain High Voltage Generators (Kato).

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Cracking of PMG Capacitor Cases Due to Prolonged Elevated Temperatures in Certain High Voltage Generators (Kato).

CONFIDENTIAL TIBU3821-00

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TECHNICAL INFORMATION BULLETIN	April 02, 2003
High Voltage Generators on Caterpillar Gensets	24Z, 25Z, 7RN, 8RM, 2JW, 6HN, 6WN, BPJ, BRK, CMC, CMD, CMJ, CMB, CMJ, CNB, CRN, CSZ, CWW, CWY, FDN, PPS
	Component Code: 1404

SUBJECT: Cracking of PMG Capacitor Cases Due to Prolonged Elevated Temperatures in Certain High Voltage Generators (Kato)

PROBLEM:

The PMG capacitors installed in certain Caterpillar high voltage generators (Kato SR4B-HV 12 and 13 kV generators) may develop cracks on the surface of the capacitor body. These capacitors are installed in the generator exciter under the side cover. On generator frame sizes 2410 through 2480, the capacitors are located above the space heaters. This proximity to the space heaters along with site conditions and high ambient temperature make heat-related failure the leading suspect. These capacitors, when needed, aid in providing a low impedance power source for proper voltage regulator operation. In most cases the generator will operate satisfactorily with a cracked capacitor or without capacitors. Only in the case of shorted capacitors will the generator fail to operate.

SOLUTION:

This problem continues to be investigated by Caterpillar and the generator supplier. In the interim, Caterpillar recommends the following procedure:

Inspect the generator PMG capacitors (Cat p/n 161-4498 Capacitor) at the first scheduled maintenance interval.
Turn off the generator space heater. Avoid coming in contact with hot surfaces when working in the generator exciter area.
Remove the exciter side cover. See the Illustration 1 for the typical capacitor location.
Cut the tie-wraps securing the capacitors to the bracket and inspect each capacitor.
Rotate the capacitors by hand and look for any large cracks in the black plastic body of the capacitor.
If the cracked capacitors are found, and if the SR4B High Voltage Generator is using the KCR 760 regulator, disconnect and remove the capacitors.

Illustration 1. Typical capacitor loction.

PMG capacitors are not necessary for satisfactory operation. Replacement of the cracked capacitors with new capacitors of the same design is likely to lead to similar failures. The SR4B-HV generators have been tested while using a KCR 760 voltage regulator. The tested generators operated satisfactorily both with and without the capacitors across the PMG. Additional tests are being conducted on SR4B-HV generator using a Basler DECS regulator to verify the performance of this combination.

Note: In order to be consistent, the Caterpillar supplier installed capacitors on their entire line of PMG generators and voltage regulators. Due to the wide variety of voltage regulators and generator designs that they produce, these capacitors were installed regardless of whether they were necessary for system operation.