Induksion motorlarda sirpanish chastotasini tushunish
Slip frequency — bu induksion motorning stator magnit maydonining aylanish tezligi bo'lgan sinxron tezlik va rotorning haqiqiy aylanish tezligi o'rtasidagi farq bo'lib, gerts birligida ifodalanadi. U magnit maydonining rotor o'tkazgichlari bo'ylab qanchalik tez "sirpanishini" o'lchaydi va aynan shu nisbiy harakat moment hosil qiladigan rotor tokini induktsiya qiladi. Sirpanish chastotasi induksion motorning ishlash tamoyilining asosi bo'lib, u motor diagnostikasi, because — through the qutb o'tish chastotasi (slip frequency × number of poles) — it sets the sideband spacing in the vibration va tok imzolarini belgilaydi rotor sterjen nuqsonlari.
Odatiy yuklanish ostida ishlayotgan motor uchun sirpanish chastotasi odatda quyidagi diapazonida bo'ladi: 0.5–3 Hz. U yuklanish oshishi bilan ko'tariladi, bu esa motorning qanchalik intensiv ishlayotganini bilvosita, ammo qulay tarzda o'lchash imkonini beradi. Motor tebranish spektrini to'g'ri o'qish — va undan elektromagnit nosozliklarni aniqlash — sirpanishni tushunishga bog'liq.
1. Induksion motorlarda sirpanish qanday ishlaydi
Induksiya tamoyili
Induksion motor elektromagnit hodisalar zanjiri orqali moment hosil qiladi:
- Stator chulg'amlari sinxron tezlikda aylanadigan magnit maydon hosil qiladi.
- Bu maydon rotordan biroz tezroq aylanadi.
- Maydon va rotor chiviqlar o'rtasidagi nisbiy harakat rotorda tok induktsiya qiladi.
- Induktsiya qilingan tok rotorda’ o'z magnit maydonini hosil qiladi.
- Stator va rotor maydonlarining o'zaro ta'siri moment hosil qiladi.
- Key point: agar rotor sinxron tezlikka yetsa, nisbiy harakat bo'lmaydi, induksiya bo'lmaydi va shunga ko'ra moment ham bo'lmaydi.
Nima uchun sirpanish zarur
- Induksiya yuz berishi uchun rotor sinxron tezlikdan sekinroq aylanishi shart.
- Sirpanish qanchalik katta bo'lsa, shuncha ko'p tok induktsiya qilinadi va shuncha ko'p moment hosil bo'ladi.
- Yuklanishsiz ishlashda sirpanish minimal — taxminan 1%.
- To'liq yuklanishda u yuqoriroq — odatda 3–5%.
- Siljish — dvigatelning o'z momentini yukka avtomatik moslashtirish mexanizmidir.
2. Siljish chastotasini hisoblash
Asosiy formula
fs = (Nsync − Nactual) / 60
where fs = siljish chastotasi (Hz), Nsync = sinxron tezlik (RPM) va Nactual = rotorning haqiqiy aylanish tezligi (RPM).
Siljish foizidan foydalanish
- Slip (%) = [(Nsync − Nactual) / Nsync] × 100
- fs = (Slip% × Nsync) / 6000
Three related quantities are easily confused, so it pays to keep them apart: the slip frequency fs defined above (the speed difference in Hz — the convention used throughout this glossary); the electrical slip frequency s·fline (the frequency of the currents induced in the rotor, where s is the per-unit slip); and the qutb o'tish chastotasi FP = number of poles × fs = 2·s·fline, which is the sideband spacing actually observed in rotor-bar diagnostics. The synchronous speed itself follows from the supply line frequency va qutblar soniga bog'liq. Agar uni qo'lda hisoblashni istamassangiz, Motor siljishi & haqiqiy AYM kalkulyatori nominal plastinkadagi ma'lumotlarni siljish va ishlash tezligiga to'g'ridan-to'g'ri aylantiradi.
Amaliy misollar
4 qutbli, 60 Hz dvigatel bo'sh yuklama rejimida:
- Nsync = 1800 RPM, Nactual = 1795 RPM (engil yuklama)
- fs = (1800 − 1795) / 60 = 0.083 Hz; slip = 0.3%
Xuddi shu dvigatel to'liq yuklama rejimida:
- Nsync = 1800 RPM, Nactual = 1750 RPM (nominal tezlik)
- fs = (1800 − 1750) / 60 = 0.833 Hz; slip = 2.8%
2 qutbli, 50 Hz dvigatel:
- Nsync = 3000 RPM, Nactual = 2950 RPM
- fs = (3000 − 2950) / 60 = 0.833 Hz; slip = 1.7%
3. Vibratsiyon diagnostikada siljish chastotasi
Rotor sterjenidagi nuqsonlar uchun yon zoqlar oralig'i
Bu siljish chastotasining eng muhim diagnostik qo'llanilishidir. Singan yoki yoriq rotor sterjenida elektromagnit assimetriya paydo bo'lib, 1× ishchi tezlikda peak, producing sidebands spaced at the pole-pass frequency FP = poles × fs:
- Pattern: sidebands around 1× running speed at ±FP, ±2FP, ±3FP.
- Example: a 4-pole, 1750 RPM motor (29.2 Hz) with fs = 0.83 Hz, so FP = 4 × 0.83 = 3.33 Hz.
- Sidebands at: 25.8 Hz and 32.5 Hz around the 29.2 Hz peak, plus 22.5 Hz and 35.8 Hz, and so on.
- Diagnosis: bu simmetrik yon chastotalar ko'rsatadi singan yoki yoriq rotorli sterjenlar.
- Amplitude: yon chastotalarning amplitudasi singan sterjenlarning soni va darajasini aks ettiradi.
Joriy Signaturani Tahlil Qilish
Dvigatel toki spektrlari (MCSA) ta'minot liniyasi chastotasi atrofida o'xshash naqshni ko'rsatadi:
- Rotorli sterjen nuqsonlari liniya chastotasi atrofida yon chastotalar hosil qiladi.
- Pattern: fline ± 2·s·fline, where s is the per-unit slip — the same ±FP spacing as in vibration, since 2·s·fline = FP.
- For the 4-pole 60 Hz motor above (s = 50/1800 ≈ 2.8%, FP = 3.33 Hz), the sidebands sit at 56.7 Hz and 63.3 Hz.
- Bu tebranish orqali aniqlangan rotorli sterjen diagnostikasini mustaqil ravishda tasdiqlaydi. Motor Elektr Nosozliklari Chastotasi Kalkulyatori har qanday dvigatel uchun kutilayotgan tok yon chastotalarini belgilab beradi.
4. Sirpanish Yuklanish Ko'rsatkichi Sifatida
Sirpanish Yuklanishga Qarab O'zgaradi
- No load: 0,2–1% sirpanish (odatiy dvigatellarda 0,1–0,5 Hz).
- Half load: 1–2% sirpanish (0,5–1,0 Hz).
- Full load: 2–5% sirpanish (1–2,5 Hz).
- Overload: 5% dan ortiq sirpanish (2,5 Hz dan ko'p).
- Starting: 100% sirpanish — sirpanish chastotasi liniya chastotasiga teng bo'ladi, chunki rotor bir lahza harakatsiz turadi.
Yuklanishni Baholash uchun Sirpanishdan Foydalanish
- Motorning haqiqiy aylanish tezligini aniq o'lchang.
- Sinxron tezlik bilan farqdan sirpanishni hisoblang.
- Uni nom taxtasidagi nominal to'liq yuklanishdagi sirpanish bilan taqqoslang.
- Motor yuklanishini foiz sifatida baholang.
- Bu, ayniqsa, to'g'ridan-to'g'ri quvvat o'lchash imkoniyati mavjud bo'lmagan hollarda juda foydali.
5. Sirpanishga Ta'sir Etuvchi Omillar
Design Factors
- Rotor qarshiligi: yuqori qarshilik kattaroq sirpanishga olib keladi.
- Motor konstruksiya sinfi: NEMA konstruksiya harfi sirpanish xarakteristikasini belgilaydi.
- Voltage: kuchlanishning pasayishi ma'lum bir yuklanishdagi sirpanishni oshiradi.
Ish Sharoitlari
- Load torque: sirpanishning asosiy aniqlovchi omili.
- Ta'minot kuchlanishi: past kuchlanish sirpanishni oshiradi.
- Chastota o'zgarishi: ta'minot chastotasidagi o'zgarishlar sinxron tezlikni, shuningdek, sirpanishni ham o'zgartiradi.
- Temperature: qizigan rotor yuqori qarshilikka ega bo'ladi, bu esa sirpanishni oshiradi.
Motor Holati
- Rotoр sterjenlarining sinishi sirpanishni oshiradi, chunki moment hosil qilish samaradorligi pasayadi.
- Stator chulg'ami muammolari siljishi mumkin.
- Ishqalanishni oshiradigan podshipnik muammolari siljishni biroz ko'taradi.
6. Siljish chastotasini o'lchash usullari
To'g'ridan-to'g'ri tezlikni o'lchash
- Use a tachometer yoki stroboskop yordamida haqiqiy AYD qiymatini o'qish.
- Sinxron tezlikni identifikatsion plitadan oling (qutblar soni va chastota).
- Siljishni f sifatida hisoblangs = (Nsync − Nactual) / 60.
- Bu eng aniq usul hisoblanadi.
Tebranish spektridan
- 1× ishchi tezlik cho'qqisini aniq aniqlang.
- Ushbu cho'qqi chastotasini ishchi tezlikka aylantiring.
- Sinxron tezlik bilan farqdan siljishni hisoblang.
- Bu yuqori aniqlikdagi FFT; the FFT ajratish qobiliyati kalkulyatori siljish bo'yicha joylashgan cho'qqilarni ajratish uchun yetarli chiziqlar sonini belgilashga yordam beradi.
Yon chastota oralig'idan
- Agar rotor panjarasi nuqsonining yon chastotalari mavjud bo'lsa, ular orasidagi oraliq is the pole-pass frequency; dividing it by the number of poles gives the slip frequency directly.
- Qulay — ammo faqat nuqson paydo bo'lgandan keyin mavjud bo'ladi.
Amaliyotda ushbu o'lchovlar ko'chma ikki kanalli asbob yordamida joyida amalga oshiriladi. Balanset-1A records the vibration spectrum at the motor bearing while its optical laser tachometer reads true shaft speed, so you can pin down the exact 1× frequency, compute slip, and search for the pole-pass-spaced sidebands that betray rotor bar damage — all without taking the motor off line. Because slip changes with load, the most revealing measurements are taken with the machine under its normal duty.
7. Amaliy diagnostik qo'llash
Siljishning normal qiymatlari
- Har bir dvigatel uchun bir necha yuklanish darajasida asosiy siljish qiymatini qayd eting.
- To'liq yuklanishdagi odatiy siljish 1–3% ni tashkil etadi — har doim zavod plitasini tekshiring.
- Zavod plitasidagi qiymatdan yuqori siljish dvigatelning haddan ortiq yuklanganligini yoki nosozligini ko'rsatishi mumkin.
- Berilgan yuklanishdagi kutilgan qiymatdan past siljish elektr nosozligini ko'rsatishi mumkin.
Siljishning g'ayritabiiy ko'rsatkichlari
- Haddan ortiq siljish: dvigatel haddan ortiq yuklanishi, rotor shtangalari singan yoki rotor qarshiligi yuqori.
- Variable slip: yuklanish o'zgarishlari yoki elektr ta'minoti beqarorligi.
- Yuklanishdagi past siljish: stator muammosi yoki kuchlanish bilan bog'liq nosozlik bo'lishi mumkin.
Slip frequency sits at the heart of both induction-motor operation and induction-motor diagnostics. As the basis of the pole-pass sideband spacing that reveals rotor bar defects, and as a stand-in for motor loading, it carries a great deal of condition information in a single number. Determining it accurately is what lets an analyst interpret motor vibration and current signatures correctly — and tell normal running apart from a developing fault.
