Ano ang mga pagsusulit na kailangang gawin sa mga current transformers?

Ni Oliver, 8 Taon sa Industriya ng Elektrisidad

Kamusta lahat, ako si Oliver, at nagsisilbing tagapagtustos sa industriya ng elektrisidad para sa 8 taon.

Mula sa mga unang araw ng pagkakomisyon ng kagamitan ng substation hanggang sa pamamahala ng mga konfigurasyon ng proteksyon at pagsusukat para sa buong sistema ng distribusyon, isa sa mga pinaka madalas kong ginagamit na aparato sa aking trabaho ay ang Current Transformer (CT).

Kamakailan, isang kaibigan na nagsisimula lang ang kanyang karera ay nagtanong sa akin:

“Paano mo itest ang current transformers? May simpleng at epektibong para ba para malaman kung wasto silang gumagana?”

Magandang tanong! Marami ang nagsasabing ang pagtest ng CTs ay nangangailangan ng mahiwagang kagamitan at mahigpit na proseso, ngunit ang totoo — maraming karaniwang isyu na maaaring matukoy gamit ang pangkaraniwan na kasanayan at kagamitan.

Ngayon, ibabahagi ko sa inyo sa madaling salita — batay sa aking karanasan sa nakaraang ilang taon — kung paano:

Itest ang current transformers, kilalanin ang mga karaniwang kamalian, at ano ang dapat babantayan sa panahon ng pag-aayos o inspeksyon.

Walang teknikal na termino, walang walang katapusang pamantayan — kung hindi praktikal na kaalaman na maaari mong gamitin sa bawat araw.

1. Ano Talaga ang Current Transformer?

Bago tayo magpatuloy sa pagtest, ipaalala muna natin ang kanyang tungkulin.

Ang current transformer ay tumutugon bilang isang translator sa sistema ng kuryente — ito ay nagbabago ng malaking primarya na kuryente sa mas maliit na secondarya na kuryente na maaring ligtas na gamitin ng mga protective relays, measuring instruments, at metering devices.

Karaniwang ito ay nakainstalo sa switchgear, outgoing lines ng transformer, o sa transmission lines. Ito ang pundasyon ng proteksyon at pagsusukat.

Kaya, kung ang CT ay mabigo, maaaring hindi gumana ang iyong proteksyon, at maaaring mali ang iyong pagsusukat.

2. Pitong Karaniwang Kamalian sa Current Transformers

Batay sa aking 8 taon ng karanasan sa field at troubleshooting, ang mga sumusunod ang mga pinaka karaniwang problema na makikita mo sa CTs:

2.1 Bukas na Secondary Circuit — Ang Pinakamapanganib na Isyu!

Ito ang isa sa mga pinaka karaniwan at mapanganib na pagbigo ng CT.

Sa normal na operasyon, ang secondary side ay dapat sarado. Kung ito ay bukas, maaaring lumitaw ang napakataas na voltages — minsan nasa libo-libong volts — na maaaring mapanganib sa mga tao at maaaring sirain ang kagamitan.

Typical na sintomas:

• Sparkling o arcing sounds;

• Ang mga meters ay walang reading o erratic values;

• Misoperation o failure to operate ng proteksyon;

• Overheating o even smoking ng CT.

Bakit ito nangyayari?

• Loose terminals;

• Broken o disconnected wiring;

• Relay coil failure;

• Forgetting to short-circuit during maintenance.

Ang aking payo:

• Laging ishort ang secondary bago anumang live inspection;

• Gamitin ang dedicated test terminals;

• Regular na i-check ang tightness ng terminal block.

2.2 Maliang Polarity — Ang Hidden Killer

Ang maliang polarity ay maaaring magdulot ng:

• Maliang direksyon ng power flow;

• False differential protection alarms;

• Reverse meter readings;

• Confused protection logic.

Paano ito nangyayari?

• Wiring error during installation;

• Failure to recheck after replacement;

• Primary conductor installed in the wrong direction.

Paano i-check:

• DC method: Battery + multimeter momentary connection;

• Or use a polarity tester;

• In operation, check via power flow direction.

2.3 Ratio Mismatch — Affects Metering Accuracy

Kung ang aktwal na ratio ay hindi tugma sa nameplate, ito ay nagdudulot ng mga error sa pagsusukat.

Halimbawa: Ang CT na may rating na 100/5 ay nagpapakita lamang ng 4.7A output — ibig sabihin ang tunay na ratio ay mas mataas kaysa sa label, na nagdudulot ng under-metered energy readings.

Mga sanhi:

• Manufacturing tolerance;

• Core saturation;

• Wrong number of primary turns;

• High secondary load causing accuracy drop.

Mga paraan ng pagtest:

• Use a CT ratio tester;

• Or apply primary current and measure secondary;

• Compare with nameplate data.

2.4 Poor Excitation Characteristics — Impacts Protection Reliability

Lalo na para sa protection-grade CTs, ang mahinang excitation performance ay maaaring magdulot ng delayed o failed protection.

Ano ang excitation characteristic? Sa simple, ito’y ang magnetization curve ng core sa iba’t ibang voltages — na nagpapakita ng linear range at saturation point.

Paano i-test:

• Use an excitation characteristic tester;

• Check if knee-point voltage meets protection setting requirements;

• 5P10, 5P20, etc., should meet certain minimum knee-point voltages.

2.5 Aging or Moisture Damage — Especially in Harsh Environments

Sa mainit, dusty, o malamig na kapaligiran, ang CTs ay maaaring mabawasan ang insulation o magkaroon ng moisture sa loob.

Mga sintomas:

• Reduced insulation resistance;

• Increased partial discharge;

• Heating or strange smell;

• Fails dielectric withstand test.

Mga solusyon:

• Regular insulation resistance testing;

• Drying treatment or replace seals;

• Consider space heaters in tropical areas;

• Ensure proper cabinet sealing.

2.6 Mechanical Damage or Deformation — Caused by External Forces

Minsan, ang pisikal na pinsala sa katawan ng CT o deformation ng primary conductor ay nakakaapekto sa performance.

Common causes:

• Improper installation;

• Handling impact;

• Vibration from switching operations;

• Corrosion causing structural distortion.

Testing methods:

• Visual inspection of housing;

• Check for bent primary conductors;

• Measure core hole diameter for fit;

• Repair or replace if necessary.

2.7 Wiring Errors or Disordered Connections

Sa multi-winding CTs, ang maliang wiring ay maaaring magdulot ng:

• Mixed use of windings for protection, measurement, and metering;

• Signal interference between circuits;

• Abnormal monitoring data.

Ang aking payo:

• Clearly define winding functions (protection, measurement, metering);

• Label connections clearly;

• Double-check wiring after installation or replacement;

• Use a tester to verify each winding output.

3. Common Tools and Steps for On-Site Testing

Common Testing Tools:

On-Site Testing Procedure (Summary):

• Visual inspection for damage or burn marks;

• Measure insulation resistance (primary to ground, secondary to ground, primary to secondary);

• Check polarity correctness;

• Test current ratio against nameplate;

• Test excitation characteristics (especially for protection windings);

• Verify wiring correctness and tightness;

• Monitor operation under load (if possible).

4. My Final Recommendations

As someone with 8 years of hands-on experience in this field, I want to remind all professionals:

“The CT may be small, but its role is huge. Don’t wait until a trip happens to realize it had a problem.”

Especially in critical circuits like main transformer differential, feeder protection, and metering points, regular testing and careful maintenance are essential.

Here are my recommendations for different roles:

 For Maintenance Personnel:

• Learn to read CT nameplate information;

• Master basic testing techniques (insulation testing, polarity check);

• Recognize common fault symptoms;

• Report abnormalities promptly.

For Technical Staff:

• Understand CT selection and calculation;

• Know protection winding characteristics;

• Interpret system short-circuit parameters;

• Analyze excitation curves.

For Managers or Procurement Teams:

• Define clear technical specifications;

• Choose reliable manufacturers;

• Request full test reports from suppliers;

• Maintain equipment records for traceability.

5. Closing Thoughts

Though small, current transformers are the eyes and ears of the entire power system.

They’re not just about reducing current — they form the basis of protection, the foundation of metering, and the guarantee of safety.

After 8 years in the electrical field, I often say:

“Details determine success or failure, and proper testing ensures safety.”

If you ever run into difficulties testing CTs, dealing with frequent protection misoperations, or unsure if your parameters are suitable, feel free to reach out — I’m happy to share more hands-on experience and solutions.

May every current transformer operate stably and accurately, safeguarding the reliability of our power grid!

— Oliver