Vita vya Vyamaapi Lisabu ya AIS Inayohitajika Kupitia
Salamu, mimi ni Oliver, mwaka 10 katika uchumi wa umeme. Leo tutakusaidia kuelewa jinsi ya kutambua ikiwa transformer wa current (CT) unatumika kwenye Air Insulated Switchgear (AIS) una uwezo wa kutosha. Hii si tu kuhusu kutumaini spec za teknolojia; ni kuhusu usalama wa vifaa, ustawi wa grid na upimaji sahihi.Hebu tufanye hii — kutegemea na tajriba yangu ya kweli.
Mwanzo
Katika substations au mifumo ya uzinduzi, transformers wa current wanajihisi maana muhimu. Wanabadilisha mikasi ya asili yenye ukubwa kwa ishara zenye ukubwa wa sekondari kwa ajili ya kupima, kupambana na kukidhibiti.
Kutokae waweze kufanya kazi kwa imani siku zote, inahitaji kuwa na majaribio mengi — kutoka kutajaribu kwenye factory hadi kutayarisha on-site na huduma la muda mrefu.
Basi, ni nini hayo majaribio muhimu?
Ningependa nikushirikishe wao hatua kwa hatua.
Sehemu 1: Majaribio ya Msingi Kabla ya Kutumia Factory
(1) Jaribio la Resistance ya Insulation
Hii ni moja ya msingi zaidi — lakini muhimu — majaribio.
Lengo: Kukagua ikiwa insulation kati ya primary winding, secondary winding, na housing yametisha.
Njia: Tumia megohmmeter (insulation tester) kutathmini resistance.
Standard: Mara nyingi inapaswa kuwa juu ya 500 MΩ, ingawa thamani sahihi zinategemea kwa spec za manufacturer na standards kama IEC au IEEE.
Ukaguzi chache kunaweza kuonyesha entry ya maji, aging ya insulation, au matatizo ya manufacturing.
(2) Jaribio la Withstand Voltage la Power Frequency (Dielectric Test)
Inatafsiriwa pia kama "hi-pot" test.
Lengo: Kutathmini ikiwa CT inaweza kukagua voltage kubwa bila kutumika wakati wa operation normal au transient overvoltages.
Mfano: Tumia voltage mara kadhaa kubwa kuliko rated (mfano, 3 kV kwa 1 kV-rated CT), mara nyingi kwa dakika moja.
Nini Kutazama: Ishara yoyote ya arcing, flashover, au failure ya insulation.
Hii hutathmini ikiwa CT inaweza kukagua stress ya electrical safely.
(3) Jaribio la Ratio Error
Core function ya CT ni kubadilisha current kwa kutosha.
Lengo: Kuthibitisha ikiwa actual current ratio inafanana na thamani ya nameplate.
Jinsi Itasafanuliwa:
Pima primary na secondary currents kwa tofauti za loads.
Hitungu percentage ya error.
Range Inapatikana:
Kwa CTs za metering: ±0.5%
Kwa CTs za protection: ±1% au zaidi, kutegemea na application.
Usahihi unahitajika — hasa wakati billing au protection logic inategemea.
(4) Kutathmini Polarity
Matatizo ya polarity yanaweza kutoa shida, hasa katika circuits za differential protection.
Lengo: Kuthibitisha direction sahihi ya current flow kati ya primary na secondary windings.
Njia:
DC method: Tumia DC voltage kidogo na angalia deflection kwenye voltmeter.
AC method: Tumia standard CT kutafuta phase angles.
Best Practice: Angalia mara mbili baada ya installation.
Usisite hii — ni rahisi kuyaburudisha na ngumu kuyapata baadae.
Sehemu 2: Majaribio ya Functional Baada ya Installation On-Site
（1）Jaribio la Grounding Resistance
Grounding sahihi ni muhimu sana kwa ajili ya usalama na performance.
Zana: Ground resistance tester.
Target: Mara nyingi chini ya 4 ohms, ingawa requirements zifuatazo zinaweza kutumika kwenye mazingira sensitive.
Nini Inaumia: Grounding chache kunaweza kuongeza risasi ya shock, damage ya vifaa, au false tripping.
Imehitajika sana katika AIS setups za nje zinazoendelea kusikia weather na environmental factors.
(2) Jaribio la Secondary Loop Continuity
Hutathmini ikiwa hakuna open circuits au loose connections kwenye secondary wiring.
Njia: Tumia multimeter kutathmini continuity across terminals.
Importance:
Open circuit anaweza kutoa voltage kubwa.
Loose connections zinaweza kutoa signal loss au overheating.
Usifunike CT na open secondary!
(3) Jaribio la Temperature Rise
Overheating inaweza kuboresha insulation na kurudisha miaka ya CT.
Mchakato: 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) Jaribio la Dynamic Response
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.
Sehemu 3: Huduma la Muda Mrefu Wakati wa Operation La Muda Mrefu
(1) Detection ya Partial Discharge
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
