Reliable Electrical Power

First of all, deterioration of electrical equipment is normal, and this process begins as soon as the equipment is installed.  If deterioration is not checked, it can cause electrical failures, malfunctions, downtime, loss of production and loss of profits.  Maximize your uptime!  Deterioration of electrical equipment is not limited to switchgear; it does include the most vital power distribution equipment, the transformer.   And, oil diagnosis and insulation resistance testing of transformers is not a complete test.   Oil D and insulation resistance testing is the minimum preventive test performed on transformers. 

Electrical test and oil diagnosis for transformers

 1. Perform Insulation resistance test, winding-to-winding and windings-to-ground utilizing a megohmeter at appropriate voltage.  Test duration shall be for 10 minutes with resistances tabulated at 30 seconds, 1 minute, and 10 minutes.

2. Perform a “turns ratio” test between windings at a designated tap position. The tap position is to be determined by the Plant Engineer.

 3. Perform insulation power factor, dissipation factor or Doble tests on all windings and bushings. Overall dielectric and power factor shall be determined.  Test voltages should be limited to the line-to-ground voltage rating of the transformer winding.

 4. Perform individual excitation current tests on each phase.

 5. Oil diagnosis

OCPD Failures                            Primary disconnect

over current protection devices    secondary disconnect

short circuit

ground fault

looses connections

improper maintenance

no maintenance

sized incorrectly

Oil Diagnosis Transformers

A.)  Distribution Package (economical package)

        Oil screen:                    appearance and sediment (visual examination)

Dissolved gas:             monitors the operational integrity of the equipment

        Moisture content:          moisture is a contaminant in electrical equipment that affects the potential

                                  for dielectric failure.

B.)    Power package includes distribution package plus oxidation inhibitor, power factor

         Oxidation inhibitor        "early warning" oil aging, oxidation of oil test

liquid power factor        monitors oil aging and oxidation, other contaminations

C.)    Other packages call for more info

Transformer Inspection and Maintenance

Proper maintenance of the transformer should include:

1.  Routine inspection and repair

2.  Transformer liquid-maintenance(oil diagnosis) and testing

3.  Transformer winding insulation maintenance and testing

Routine Inspection and Repair

Load current

Voltage

Liquid level

Temperature

Protective Devices

Protective alarms

Ground Connections

Lightning Arrestors

Pressure-relief devices

Breather

Auxiliary Devices

External Inspections

Internal Inspections

Transformer Fluids

Transformer Diagnostic Guide

Overtemperature

Winding Insulation Failure

Incorrect Secondary Voltage

Discoloration of Transformer Liquid

Internal Arcing

Core Failure

High Exciting Current

Low Dielectric Strength

Oxidation of Oil

PSI-relief Diaghragm Broken

Bushing Failure

Leakage of Transformer Liquid

Moisture Condensation

Gas-sealed Transformer Troubles

Transformer Switching Equipment Troubles

Transformer winding insulation and maintenance

Insulation Resistance tests

Insulation Power Factor Tests

Transformer Turns Ratio Test