Nini kipengele kinachopaswa kuzingatika wakati wa chaguo la transforma ya mawimbi kwa mzunguko wa transforma ya stesheni ya 10kV

Ushiriki wa Taaluma kutoka kwa Mfundi wa Umeme katika Nyanja
Na James, Miaka 10 katika Sanaa ya Umeme

Habari zenu wote, mimi ni James, na nimekuwa nikifanya kazi katika sanaa ya umeme kwa miaka 10.

Tangu uanachama mapema katika uzakata wa substation na chaguo la vifaa, hadi baadaye kusimamia uzinduzi wa mfano wa relay protection na muhimu wa system za automation kwa majukumu yote, moja ya vifaa vilivyotumika sana katika kazi yangu ni current transformer (CT).

Karibu, rafiki yangu ambaye amefanikiwa tu alinisuluhisha:

“Nini ninapaswa kusikiliza wakati wa kutagua current transformers kwa circuits za station transformer za 10kV?”

Swali nzuri! Wengi wanadhani kuwa kutagua CT ni kuhusu kianzisho cha current ratio tu — lakini kwa kutoa maanani kwa circuit, unahitaji kutathmini viwango vingine vipimo.

Leo, nitawaelezea kwa lugha rahisi — kulingana na tajriba yangu ya miaka mingi — vitu muhimu vinavyohitajika kutumia CTs kwa circuits za station transformer za 10kV, maana ya kila parameter, na jinsi ya kutatua sahihi.

Hakuna maneno magumu, hakuna masharti mengi — tu maarifa yanayoweza kutumika katika maisha halisi.

1. Kwanini Ni Muhimu Kutagua CTs Kwa Circuits Za Station Transformer?

Ingawa station service transformer haipo kama transformer mkuu wa nguvu, anachukua nafasi muhimu katika kutumia nguvu ndani ya substation — ikizingatia nguvu za kudhibiti, robo, nguvu za huduma, na systems za UPS.

Ikiwa station transformer hufeli au usalama wake huenda kushindwa, inaweza kusababisha:

• Kupoteza nguvu za kudhibiti;

• System DC kupoteza uwezo wa charging;

• Substation nzima kufungwa.

Na tangu current transformer ni muhimu kwa usalama na utambuzi, chaguo lake lisilo sahihi linaweza kusababisha usalama usiwe upendelei na utambuzi usiwe usahihi.

Kwa hivyo, kutagua CT sahihi = usalama + uelewa + gharama nzuri.

2. Vitu Viwili Vya Muhimu Wakati Wa Kutagua CTs Kwa Circuits Za Station Transformer Za 10kV

Kulingana na miaka 10 yangu katika nyanja na malengo yangu ya kazi, hapa ni masuala sita muhimu zaidi:

Kitu 1: Current Rasmi na Secondary Inayotegemea

Maana: Hakikisha CT anafanya kazi vizuri na anasikia matarajio ya usalama.

Hii ni parameter asili na muhimu zaidi.

Mizizi ya karibu:

• Current rasmi: 50A, 75A, 100A, 150A (kulingana na ukubwa wa station transformer)

• Current secondary: 5A au 0.5A (vifaa vyenye ubunifu vya mwishoni mvuke 0.5A)

Msaada wangu:

• Chagua current rasmi kama mara 1.2~1.5 ya current rasmi ya station transformer;

• Kwa vifaa vyenye ubunifu, chagua output 0.5A ili kuridhisha ongezeko la secondary;

• Sisite chagua rating kubwa sana — ingawa accuracy itakuwa duni kwenye current madogo, kusababisha matarajio ya usalama yasikie.

Kitu 2: Kisasa Kilichozi Kwa Tumaini

Maana: Hakikisha faida tofauti (kama usalama, utambuzi, metering) hutumia signals sahihi.

Matumizi tofauti hunahitaji standards tofauti.

Classes ya karibu:

• Measurement winding: Class 0.5

• Metering winding: Class 0.2S

• Protection winding: 5P10, 5P20, 10P10, etc.

Tajriba yangu:

• Circuits za station transformer hazitoshi kwa utambuzi mkubwa isipokuwa kunapokutana na billing;

• Winding za usalama lazima ziwape linear katika short circuits;

• CTs wenye windings kadhaa hutoa uwekezaji mkubwa zaidi na zinapendekezwa.

Kitu 3: Output Capacity Rasmi (Thamani ya VA)

Maana: Hakikisha CT anaweza kudrive vifaa vilivyotenganishwa au vifaa vya usalama.

Capacity duni inaweza kusababisha voltage drop, kusababisha accuracy ya utambuzi au kazi ya usalama.

Formula ya hisabati:

Total Load = Impedance ya Cable + Input Impedance ya Instrument/Protection Device

Msaada wangu:

• Marurumo chagua kati ya 10–30 VA;

• Vifaa vyenye ubunifu vya microprocessor vinatumia nguvu chache — capacity chache inaweza kuwa inapatikana;

• Ikiwa cable ya secondary ni refu (kama zaidi ya 50 mita), ongeza capacity kwa kutosha;

• Usisite chagua capacity kubwa sana — chukua hatari ya core saturation.

Kitu 4: Check ya Thermal na Dynamic Stability

Maana: Hakikisha CT anaweza kudumu kwenye current ya short-circuit bila kufeli.

Katika systems za 10kV, current za short-circuit zinaweza kufikia thousands of amps.

Jinsi ya kufanya:

• Check maximum short-circuit current (Ik);

• Verify CT thermal stability current (It) and dynamic stability current (Idyn);

• Generally, It ≥ Ik (for 1 second), Idyn ≥ 2.5 × Ik

Case halisi: Mara nyingi CT ilikuwa ina explode baada ya short circuit — ilikuwa dynamic stability current haijafanikiwa kusikia mikakati ya system. Kutumia CT na rated current kubwa sana iliyosolve tatizo.

Kitu 5: Installation Method na Structure Type

Maana: Hakikisha CT ni rahisi kutumia na kudhibiti, na inafanya kazi na nafasi inayopo.

CT types common:

• Core-type (common in switchgear)

• Post-type (suitable for outdoor use)

• Bushing-type (often used on transformers)

Msaada wangu:

• Katika switchgear za 10kV, CTs za core-type ni zinazotumika zaidi;

• Hakikisha ukubwa wa conductor unaofanana na ukubwa wa core hole;

• Kwa nafasi zifuatazo, angalia CTs za split-core kwa installation na removal rahisi;

• Katika mazingira ya moisture au corrosion, chagua models zenye resistance ya moisture au corrosion.

Kitu 6: Polarity na Wiring Method

Maana: Hakikisha direction ya signal kwa relays za usalama na instruments ni sahihi, kurejesha misjudgment.

Polarity si sahihi inaweza kusababisha:

• Misoperation au failure ya usalama;

• Wrong power flow direction judgment;

• False alarms in differential protection.

Tajriba yangu:

• All CTs should clearly mark polarity terminals (P1, P2);

• Use subtractive polarity connection consistently;

• Always perform a polarity test after installation or maintenance;

• Use a dedicated polarity tester or DC method for verification.

3. Other Practical Tips

In addition to the six key points above, here are some other important notes:

Multi-winding Configuration：

• Separate windings for protection, measurement, and metering to avoid interference;

• Reserve spare windings for future expansion.

Excitation Characteristics：

• Especially for protection windings, good excitation characteristics improve protection reliability;

• If possible, perform an excitation curve test to confirm core performance.

Sample Selection Reference for a 50kVA Station Transformer

4. My Final Suggestions

As someone with 10 years of field experience, I want to remind all professionals:

“Don’t just look at the model number — always consider the actual circuit, protection setup, and installation environment when selecting a CT.”

Especially in seemingly "simple" 10kV station transformer circuits, improper selection often leads to serious consequences.

Here are my recommendations for different roles:

For Maintenance Personnel:

• Learn how to read CT nameplate information;

• Understand basic parameter meanings;

• Be familiar with polarity testing methods;

• Report any abnormalities promptly.

For Technical Staff:

• Master CT selection calculation methods;

• Understand protection winding characteristics;

• Know how to interpret system short-circuit parameters;

• Be able to analyze excitation curves.

For Managers or Procurement Teams:

• Clearly define technical specifications;

• Choose reputable manufacturers with stable quality;

• Request full test reports from suppliers;

• Maintain equipment records for traceability.

5. Closing Thoughts

Current transformers may look small, but they are the eyes and ears of the entire power system.

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

After 10 years in the electrical field, I often say:

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

If you ever run into difficulties selecting 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 safely, safeguarding the accuracy and reliability of our power grid!

— James