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Edvard

Testing Procedures for HV Voltage Transformers

Te sting Pro ce d ure s fo r HV Vo ltag e Transfo rme rs (p ho to cre d it: hvcafrica.co m)

Content:

1. Equipment required

Following equipment is necessary to perform testings:

Polarity test kit

Megger 500-5000V

Ohmmeter

Multimeter

Autotransf ormers & Step-up transf ormers

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2. General inspection

Mechanical checks

General visual inspection and compliance with the drawings and manuals.

Check nameplate ratings and HV, LV terminal markings.

Check that all parts of the transf ormer are properly assembled and tight.

Check the HV connections are tight.

Check the cable connections on the LV side and the markings.

Check the oil levels and inspect f or leakage. (Where applicable)

Capacitor dividers type

Check that all parts of the transf ormers are properly assembled.

Electromagnetic type

Check the installation of dif f erent sections.

Electrical Checks

Check the equipment grounding (Continuity and connection)

Check the f use rating of secondary side.

Perf orm the operation described in the f ollowing

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Insulat ion Resistance Test

To obtain values as close as possible to the manuf acturer ’s specif ications the insulators must be veryclean. Select the megger range corresponding to the ratings of the equipment under test.

For Primary side, apply voltage depending on rating of voltage rating of VT.

For 6.6 kV VT (example), apply 2.5 kV and

For 132 kV VT (example), apply 5.0 kV.

Fig ure – Me asure me ntb e twe e n p rimary and

se co nd ary

Fig ure – Me asure me nt b e twe e n p rimary and g ro und

Fig ure – Me asure me nt b e twe e n se co nd arie sand b e twe e n se co nd ary and g ro und

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Polarity Test

The polarity is checked using the flick method (application of direct current)and check of def lection on a bi-directional milliammeter. The test is also usedto check primary and secondary circuit continuity.

When switch k is closed, the milliammeter pointer def lects posit ive.

When the circuit is opened, the milliammeter pointer def lects in thenegative direction.

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Transformer Turns rat io test

A variable AC source is applied on the primary side. Theprimary and secondary voltages are measured todetermine the ratio V2/V1

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132kv Substation

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Reference: Contract specific procedure for testing of electricalequipment and 132kV OHL

Edvard - Electrical engineer, programmer and f ounder of EEP.Highly specialized f or design of LV high power busbar trunking(<6300A) in power substations, buildings and industry f ascilit ies.Designing of LV/MV switchgears. Prof essional in AutoCADprogramming and web-design. Present on Google+.

Fig ure – VT Po larity te st

Fig ure – Transfo rme r Turns ratio te st