SRMP Electric Power Generation SRMP Generator Caterpillar

Illustration 1	g00610379
Varistor CR7

Varistor CR7 can be checked with a megohmmeter or equivalent meter. Use the megohmmeter in order to measure the clamping voltage between the terminals.

Note: For testing rectifier blocks with integral varistor CR7, refer to Testing and Adjusting, "Rotating Rectifier - Test".

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Personal injury or death can result from improper troubleshooting and repair procedures. The following troubleshooting and repair procedures should only be performed by qualified personnel familiar with this equipment.

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Personal injury or death can result from high voltage. When power generation equipment must be in operation to make tests and/or adjustments, high voltage and current are present. Improper test equipment can fail and present a high voltage shock hazard to its user. Make sure the testing equipment is designed for and correctly operated for high voltage and current tests being made. When servicing or repairing electric power generation equipment: Make sure the unit is off-line (disconnected from utility and/or other generators power service), and either locked out or tagged DO NOT OPERATE. Make sure the generator engine is stopped. Make sure all batteries are disconnected. Make sure all capacitors are discharged.

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Shut off engine and remove key before performing maintenance or repair work. Failure to do so may result in personal injury due to inadvertant machine operation. Do not start the engine or move any of the controls if there is a “Do Not Operate” or similar warning tag attached to the start switch or controls.

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Do not connect generator to a utility electrical distribution system unless it is isolated from the system. Electrical feedback into the distribution system can occur and could cause personal injury or death. Open and secure main distribution system switch, or if the connection is permanent, install a double throw transfer switch to prevent electrical feedback. Some generators are specifically approved by a utility to run in parallel with the distribution system and isolation may not be required. Always check with your utility as to the applicable circumstances.

Procedure

The two following procedures test the ability of the normal state of two different varistors. The following procedures are to be used for the 9Y-9412 Varistor (CR7) and the 4P-6009 Varistor (CR7. Determine which varistor is being used in your application, then use the appropriate procedure. If any meter reading does not fall within the given ranges, replace the varistor (CR7).

9Y-9412 Varistor (CR7)

1. Remove all of the leads that are connected to varistor (CR7) block.

2. Place the 500 VDC or the 1000 VDC megohmmeter test leads on the varistor (CR7). The varistor (CR7) device is not polarity sensitive.

3. If the megohmmeter is not capable of reading DC voltage, then hook up a 500 VDC voltmeter across the CR7 terminals.

4. Select either 500 VDC or 1000 VDC setting of the megohmmeter. Apply the voltage to the varistor (CR7).

   Note: Do not apply voltage to the varistor for more than 3 seconds.

5. Megohmmeter readings should be between 354 VDC and 429 VDC.

   • If the readings are greater than 430 VDC, the varistor (CR7) is OPEN.

   • If the readings are less than 353 VDC, the varistor (CR7) is SHORTED or DEGRADED.
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   NOTICE
   Do not over torque. Applying torques greater than the listed torques may cause damage to the components.

6. Install leads. Apply the following torques.

   • Terminal connections - 1.4 N·m (12 lb in) to 1.7 N·m (15 lb in)

   • Varistor mounting to heat sink - 8.1 N·m (72 lb in) to 16.3 N·m (144 lb in)

   Note: If the varistor (CR7) is found to be faulty, then the varistor (CR7) most likely failed due to a transient voltage surge on the main rotor. Varistor failure is not usually a component failure. Root causes of varistor (CR7) failure include:

   • Incorrect paralleling or loss of synchronism

   • Reverse VAR or reverse power event

   • High ambient temperature (or other application error)

   • Large sudden load application

4P-6009 Varistor (CR7)

1. Remove all of the leads from the varistor (CR7) block.

2. Place 1000 VDC megohmmeter test leads on the varistor (CR7). The varistor (CR7) device is not polarity sensitive.

3. If the megohmmeter is not capable of reading DC voltage, then use a voltmeter that is able to check 1000 VDC. Connect the voltmeter across the CR7 terminals.

4. Select the 1000 VDC setting of the megohmmeter. Apply the voltage to the varistor (CR7).

   Note: Do not apply voltage to the varistor (CR7) for greater than 3 seconds..

5. Megohmmeter readings should range from 735 VDC to 910 VDC.

   • If the readings are greater than 911 VDC, the varistor (CR7) is OPEN.

   • If the readings are less than 735 VDC, the varistor (CR7) is SHORTED or DEGRADED.
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   NOTICE
   Do not over torque. Applying torques greater than the listed torques may cause damage to the components.

6. Install leads. Apply the following torques.

   • Terminal connections - 1.4 N·m (12 lb in) to 1.7 N·m (15 lb in)

   • Varistor mounting to heat sink - 8.1 N·m (72 lb in) to 16.3 N·m (144 lb in)

   Note: If the varistor (CR7) is found to be faulty, the varistor (CR7) most likely failed due to a transient voltage surge on the main rotor. Varistor failure is not usually a component failure. Root causes of varistor (CR7) failure include:

   • Incorrect paralleling or loss of synchronism

   • Reverse VAR or reverse power event

   • High ambient temperature (or other application error)

   • Large sudden load application