Anong Mga Pagsusulit Ang Kailangan Tanggapin ng Isang Nakapagpapatunay na AIS Current Transformer

Kamusta sa inyong lahat, ako si Oliver, may 10 taong karanasan sa industriya ng power system. Ngayon, pag-uusapan natin ang isang napakapraktikal na paksa — paano malalaman kung ang current transformer (CT) na ginagamit sa Air Insulated Switchgear (AIS) ay talagang kwalipikado? Hindi ito tungkol lamang sa pagtugon sa mga teknikal na espesipikasyon; ito ay direktang nauugnay sa kaligtasan ng kagamitan, estabilidad ng grid, at wastong pagsukat.Bumaba tayo — batay sa aking tunay na karanasan.

Panimula

Sa mga substation o distribution systems, ang mga current transformers ay gumaganap ng mahalagang papel. Ito ay nagpapalit ng mataas na primary currents sa manageable secondary signals para sa pagsukat, proteksyon, at kontrol.

Upang masiguro na sila ay makapagpapahayag ng maasahan sa lahat ng kondisyon, kinakailangan ang serye ng mga test — mula sa factory testing hanggang sa on-site commissioning at long-term maintenance.

Kaya ano ang mga essential na test na ito?

Hayaan akong ilarawan sa inyo ang mga ito step by step.

Bahagi 1: Basic Performance Testing Bago ang Factory Delivery
(1) Insulation Resistance Test

Ito ang isa sa pinakabatang — ngunit mahalagang — mga test.

• Layunin: Upang suriin kung ang insulation sa pagitan ng primary winding, secondary winding, at housing ay buo.

• Paraan: Gamitin ang megohmmeter (insulation tester) upang sukatin ang resistance.

• Standard: Karaniwan ay dapat na ito ay higit sa 500 MΩ, bagaman ang eksaktong halaga ay depende sa espesipikasyon ng manufacturer at standards tulad ng IEC o IEEE.

Ang mababang reading ay maaaring ipakita ang moisture ingress, aging insulation, o manufacturing defects.

(2) Power Frequency Withstand Voltage Test (Dielectric Test)

Tinatawag din itong "hi-pot" test.

• Layunin: Upang patunayan na ang CT ay maaaring tumanggap ng mataas na voltages nang walang breakdown sa normal na operasyon o transient overvoltages.

• Prosedura: Ilapat ang voltage na ilang beses na mas mataas kaysa sa rated (halimbawa, 3 kV para sa 1 kV-rated CT), karaniwang para sa 1 minuto.

• Ano ang Pansinin: Anumang mga senyas ng arcing, flashover, o insulation failure.

Ito ay sigurado na ang CT ay maaaring tumanggap ng electrical stress nang ligtas.

(3) Ratio Error Test

Ang pangunahing tungkulin ng CT ay ang wastong pagpapalit ng current.

• Layunin: Upang kumpirmahin na ang aktwal na current ratio ay tugma sa nameplate value.

• Paano Ginagawa:

• Sukatin ang primary at secondary currents sa iba't ibang loads.

• Kalkulahin ang error percentage.

• Tanggap na Range:

• Para sa metering CTs: ±0.5%

• Para sa protection CTs: ±1% o higit pa, depende sa application.

Mahalaga ang accuracy — lalo na kapag ang billing o protection logic ay nakasalalay dito.

(4) Polarity Check

Ang mga polarity errors ay maaaring magdulot ng seryosong isyu, lalo na sa differential protection circuits.

• Layunin: Upang kumpirmahin ang tama na direksyon ng current flow sa pagitan ng primary at secondary windings.

• Mga Paraan:

• DC method: Briefly apply a DC voltage and observe the deflection on a voltmeter.

• AC method: Use a standard CT to compare phase angles.

• Best Practice: Always double-check after installation.

Don’t skip this — it’s easy to mess up and hard to catch later.

Bahagi 2: Functional Testing After On-Site Installation
（1）Grounding Resistance Test

Ang tamang grounding ay mahalaga para sa kaligtasan at performance.

• Tool: Ground resistance tester.

• Target: Karaniwan ay bababa sa 4 ohms, bagaman ang mas mahigpit na requirements ay maaaring lumitaw sa sensitive environments.

• Why It Matters: Poor grounding can lead to electric shock risks, equipment damage, or false tripping.

Lalo na importante sa outdoor AIS setups na exposed sa weather at environmental factors.

(2) Secondary Loop Continuity Test

Ensures there are no open circuits or loose connections in the secondary wiring.

• Method: Use a multimeter to check for continuity across terminals.

• Importance:

• An open circuit can cause dangerously high voltages.

• Loose connections may result in signal loss or overheating.

Never energize a CT with an open secondary!

(3) Temperature Rise Test

Overheating can degrade insulation and shorten the life of a CT.

• Process: Run the CT at rated current for a set time and monitor temperature rise.

• Limits: Must stay within specified thermal limits (e.g., 55K rise for Class B insulation).

• Tools: Infrared thermography or embedded temperature sensors.

Helps identify poor contact points or inadequate cooling.

(4) Dynamic Response Test

Checks how well the CT responds to sudden changes in current, such as short circuits.

• Method: Inject a simulated fault current and observe secondary output behavior.

• Goal: Ensure fast, stable response for reliable protection triggering.

Crucial for applications involving relay protection systems.

Bahagi 3: Periodic Maintenance During Long-Term Operation
(1) Partial Discharge Detection

Early signs of insulation degradation often appear as partial discharges.

• Technique: Use ultrasonic or ultra-high frequency (UHF) sensors to detect discharge activity.

• Frequency: At least once a year for critical systems.

• Benefits: Early warning before major insulation failures occur.

Especially useful for aging equipment or units operating in harsh conditions.

(2) Accuracy Calibration

Over time, due to aging or environmental effects, CT accuracy may drift.

• Approach: Remove key CTs periodically and recalibrate in a lab setting.

• Interval: Varies by usage, but typically every 3–5 years for metering CTs.

Ensures continued compliance with standards and avoids billing disputes.

(3) Visual Inspection & Cleaning

Simple but effective.

• Checklist:

• Cracks or discoloration on housing

• Corrosion on terminals

• Dust buildup or blockage in ventilation

• Action: Clean with dry cloth, tighten connections, replace damaged parts.

Combine with regular patrols for early detection of issues.

Final Thoughts

Testing a current transformer in air insulated switchgear isn’t something you can afford to take lightly. From basic factory checks to field commissioning and long-term monitoring — every step plays a vital role in ensuring safe, stable, and accurate operation.

Here’s a quick recap of the key tests:

If you're working with AIS CTs and have questions about any of these tests — or need help interpreting results — feel free to reach out anytime. I’d be happy to share more hands-on tips and troubleshooting techniques.

Let’s keep our CTs running strong — silently guarding our power systems behind the scenes.

— Oliver