UPS system-generated error messages regarding, �Static Switch Thyristor Open� and �Static Switch Timeout A+B-�

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UPS system-generated error messages regarding, ?Static Switch Thyristor Open? and ?Static Switch Timeout A+B-?

CONFIDENTIAL TIBU4272-01

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TECHNICAL INFORMATION BULLETIN	August 11, 2004
Uninterruptible Power Supply	This Technical Information Bulletin replaces the June 16, 2004 UPS TIB, "UPS system-generated error messages regarding, "Static Switch Thyristor Open" and "Static Switch Timeout A+B-"". Disregard the June 16, 2004 UPS TIB. UPS 300 (CNJ, CPZ) UPS 301 (CSY) UPS 600 (CTX) UPS 900 (CRY) UPS 250 (APZ, CNM, BEE) UPS 500 (CSE) UPS 750 (CPM)
	Component Code: 7451

SUBJECT: UPS system-generated error messages regarding, "Static Switch Thyristor Open" and "Static Switch Timeout A+B-"

NOTE: This document applies to the UPS product equipped with the 199-5096 Static Switch Assembly, the 180-6221 SSI PWA, and the 200-8331 Gating Lead Harness.

PROBLEM:

Service technicians are improperly diagnosing the cause of the following UPS system-generated error messages: "Static Switch Thyristor Open" and "Static Switch Timeout A+B-". This misdiagnosed problem is resulting in improper repairs and invalid Warranty Claims.

SOLUTION:

The "Static Switch Thyristor Open" and/or the "Static Switch Timeout A+B-" error messages indicate a problem with the operation of a Silicon Controlled Rectifier (SCR) in the Static Switch Assembly (199-5096). There are six SCR components within the Static Switch Assembly. Refer to Illustration 1. Each SCR component has an associated Gating Lead wiring harness (200-8331, Illustration 3), which connects the SCR to the Static Switch Interface circuit board (SSI PWA) (180-6221). The typical cause for the "Static Switch Thyristor Open" or the "Static Switch Timeout A+B-" error message has been isolated to the Gating Leads or the Gating Lead connectors. Specifically, the problem has been primarily limited to the mating surface of the Gating Lead socket to the Plug Receptacle pin on the SSI PWA.

This document provides the service technician a proper trouble shooting guideline to determine the cause of the "Static Switch Thyristor Open" or the "Static Switch Timeout A+B-" error message and provide the appropriate corrective action. This trouble shooting guideline is to assist the service technician in locating a Short Circuit, High Impedance, Open Circuit, or Intermittent Circuit within the Static Switch assembly.

WARNING

Use of this document assumes that the service technician has successfully completed the formal service training program for the CAT UPS Series 300 Product as provided by the Caterpillar Corporate Training Center.

Use of this document also assumes that the service technician has been trained on the usage of special equipment such as meters and oscilloscopes and that these devices are calibrated to a standard recognized and traceable to the National Bureau of Standards.

When using an oscilloscope, only utilize an oscilloscope which provides electrical isolation between each channel and the trigger source. The use of an unapproved oscilloscope could result in equipment damage, de-energizing the load, personal injury, or death.

Hazardous voltages maybe present. Failure to follow appropriate safety procedures could result in personal injury or death.

When the flywheel is spinning, the following components are energized: the bus, the armature leads, and the flywheel armature fuses.

When Uninterruptible Power Supply (UPS) equipment must be in operation to make tests and/or adjustments, high voltage and current are present.

Improper use of test equipment may result in equipment damage, de-energizing the load, personal injury, or death.

When servicing or repairing UPS equipment, make sure all capacitors are discharged.

TOOLS

Examples of an oscilloscope and digital multimeter are:

Oscilloscope ? Tektronix THS720 with 600VAC 10x Probes

Digital Multimeter ? Fluke DMM 87111 or better

REFERENCE

For additional operational instructions and procedures, refer to the following publications:

RENR2476, Systems Operations, Testing and Adjusting, "UPS250, UPS300, UPS500, UPS750, and UPS900 Uninterruptible Power Supply"

SEBU7464, Operation and Maintenance Manual, "UPS250, UPS300, UPS500, UPS600, UPS750, and UPS900 Uninterruptible Power Supply"

Verify Gating Lead Connections

Before performing any electrical measurements or analysis type work, the service technician should "manipulate" the electrical conductors of each Gating Lead harness, one at a time, and monitor the result. If the result does not clear the error message, reseat the connectors between the Gating Lead harness and the SSI PWA circuit board. If the result clears the error message, you have determined the cause of the error messages and you should replace the Gating Lead harness (Cat p.n. 200-8331). If the result does not clear the error message, proceed with this troubleshooting guide.

Before beginning the procedure, ensure that each MMU has been de-energized or the Static Switch has been removed from the appropriate cabinet.

PROCEDURE:

Disconnect the six pairs of Gating Leads from the SSI PWA side only. Using a calibrated Digital Multi-Meter, at the Gating Lead connector measure the resistance between conductor sockets. You should record a value of 20 Ohms (+/- 4 Ohms). Note: Use extreme care when performing the resistance measurement. If you use excessive force when applying pressure with your DMM probes, against the connector sockets, you could "flare" the socket. The Gating Lead harness will have to be replaced if this occurs. Flaring the socket will result in an improper surface-to-surface mating between the connector socket and the SSI PWA connector pin.

Record the resistance value obtained in Step 1. Note the value as "A".

If the measured resistance value yields a Short Circuit condition, Open Circuit condition, or High Impedance (Greater than 24 Ohms) for any of the six Gating Lead harnesses, disconnect the Gating Lead connector from the SCR (203-2747). Using a calibrated Digital Multi-Meter at the SCR connector, measure the resistance between the connector pins. You should record a value of 20 Ohms (+/- 4 Ohms). If the measured resistance value is acceptable, you have a faulty Gating Lead harness and should change the Gating Lead harness. If the resistance value measured at the SCR connector yields either a Short Circuit condition, Open Circuit condition or High Impedance (Greater than 24 Ohms) then the respective SCR is defective. You will have to replace the Static Switch Assembly (199-5096).

If the measured resistance value recorded in Step 2 is acceptable and while the Gating Lead harness is disconnected from the SSI PWA, measure the resistance value of the resistor located on the SSI PWA. The resistor is located directly behind the SSI PWA connector plug. Refer to Illustration 2. You should record a resistance value of 43 Ohms (+/- 5 Ohms).

Record the resistance value obtained in Step 4. Note this value as "B".

Using the "A" and "B" values recorded in Steps 2 and 5, use the formula for parallel resistance and calculate the equivalent circuit resistance. The resultant of the calculation will be called "C". Therefore, the formula you are to use is C = (A*B)/(A+B). The calculated resistance value should be between 11.0 Ohms to 16.0 Ohms.

Reconnect the Gating Lead harness to the SSI PWA connector. Using a calibrated DMM, measure the resistance value across the SSI PWA resistor element from Step 4. You should record a resistance value equal to the "C" value calculated in Step 6 or at minimum within the resistance value of 11.0 Ohms to 16.0 Ohms.

With your DMM probes still placed across the SSI PWA resistor, manipulate the Gating Lead harness. View the DMM display to determine whether the resistance value changes as you manipulate the Gating Leads. If the resistance value can be varied by the manipulation of the Gating Leads, inspect the Gating Lead harness and the SSI PWA connector. Replace the faulty component.

Repeat Steps 1 thru 8 for each Gating Lead harness.

If the above process does not yield conclusive results in isolating the fault, proceed with the next step, Verifying Proper SCR Gating Signal.

Verifying Proper SCR Gating Signal

When the preceding instructions do not yield conclusive results in isolating the fault, this portion of the procedure is used to assist in further analyzing the "Static Switch Thyristor Open" and "Static Switch Timeout A+B-" error messages.

To conduct the following evaluation you will need to use an oscilloscope. Utilize only an oscilloscope that provides electrical isolation between each channel and the trigger source. De-energize the UPS or MMU before you connect, disconnect, or reconnect the oscilloscope leads. Once the leads have been properly landed, you can energize the UPS or MMU. The use of an unapproved oscilloscope could result in equipment damage, de-energizing the load, personal injury, or death.

This procedure is to confirm that all six of the "gating signals" between the SCR?s and the SSI PWA are similar to each other. The definition of similar is: "all SCR gating signals within a single MMU should have a frequency and amplitude within 20 percent of each other". The purpose of examining the gating signal is to determine if there is a single SCR that is not being gated properly, and thus causing the error messages.

Depending on the UPS firmware revision being utilized in your UPS, the gating signal "pattern" may differ from UPS to UPS. However, the gating signal will remain symmetrical within a complete UPS system.

The reference oscilloscope traces provided in this document are for "reference" only. The actual waveform signature of your UPS will be slightly different.

PROCEDURE:

Set the oscilloscope scaling as follows:

60Hz based UPS: 1 VDC per division, 5 mS time base and AC coupled.
50Hz based UPS: 1 VDC per division, 20 mS time base and AC coupled.

De-energize the UPS or MMU.

Connect the isolated oscilloscope leads across the SSI PWA Resistor. Refer to Illustration 2. DO NOT connect the Ground Lead to a Ground Reference point.

Energize the UPS or MMU.

As the UPS or MMU is energized, the K1 contactor will close, the Static Switch will begin to "gate" and charge the DC Bus in a slow and controlled manner. The initial gating of the Static Switch (when it begins to charge the DC Bus) will not produce an oscilloscope pattern like Oscilloscope Trace #1 or #2. The rationale is that the gating pattern will begin phasing from the "back" of the waveform and then begin moving "forward" as the SCR conducts more. Oscilloscope Trace #3 is an edited version of the anticipated waveform that should be seen during the initial charging of the DC Bus.

During the Static Switch "gating" process, capture the waveform with the oscilloscope.

Repeat Steps 2 through 7 for the remaining five SCR?s.

The absence of a Gating Signal on any SCR is the result of a faulty SSI PWA. Replace the faulty SSI PWA.

Review the characteristics from the six captured waveforms. Determine if there is a noticeable difference in amplitude or frequency of any one SCR. Again, the six waveforms should not have a variation in amplitude and frequency more than 20 percent of each other. A SCR that is outside of this range indicates an SCR that is not fully conducting. This faulty SCR is the cause of the error messages. You will then have to replace the entire Static Switch 199-5096.

Oscilloscope Trace #1 is an example of a properly functioning Static Switch SCR.