PIN 5J1825 - Caterpillar

All SR4 and SR4B Generators,Description of Change: Resistive thermo devices (RTDs) and type J thermocouples are typically installed in Caterpillar generators in the stator windings on the drive end. In factory installation, these devices are embedded among the strands of copper magnet wire. Thermocouples are commonly used on random wound generators and RTDs are used on form wound generators. When the thermocouples or RTDs need to be replaced, this procedure provides a method of field replacement. Adaptable To: For field installation, the thermocouples or RTDs should be mounted on the surface of the varnished windings. It should be noted however, that surface mounting will not give the same value as an embedded device and also a coefficient does not exist to convert one reading to the other. The alarm and shutdown limits outlined in the manuals are based on embedded devices. The following procedure should be used when adding these monitoring devices to an existing generator. This procedure is applicable to all SR4 and SR4B generators equipped with thermocouples or RTDs.
1. For the 3500 only, remove the generator shell to allow access to the windings at the drive end of the generator.2. Install six thermocouples/RTDs per generator among the stator coils on the flywheel (exhaust air) end of the unit. Install the thermocouples/RTDs 2 per phase starting in the 12 o'clock area. To determine the mounting location of the other 2 pair, use the following formula to calculate the spacing between phases. n = # of coils (slots) between phases or,
n = # of total coils (slots) ÷ # of poles ÷ # of phases.
The "Rewind Data" will provide the number of slots, poles, and phases for a particular generator. For example: If a generator was four pole, three phase, and had 72 slots;
n = 72 ÷ 4 ÷ 3
n = 6 coils (slots)
From this first pair installed at the 12 o'clock position, count n coils toward the 11 o'clock position and n coils toward the 1 o'clock position. Mount a pair of thermocouples/RTDs in each location (six total).
3. Clean the surface area of the coil where the devices are to be mounted. Apply epoxy adhesive to the thermocouple/RTD and press it on to the coil surface. Cover the device with a piece of polyester felt pad or similar insulating material. Secure this pad with a nylon cable tie.4. Run the thermocouple/RTD leads back down the top center of the generator to the end mounted terminal box.5. For the 3500 only, reinstall the generator shell.Within the parts system, no means presently exists to order these parts.