pertanyaan dan jawaban lisan elektrik meo kelas 4

pertanyaan dan jawaban elektris kelas 4 meo

Listrik

Teknologi Elektro Kelautan Ditulis

Penyelamatan Motor

Tindakan apa yang akan Anda lakukan jika motor Anda terendam air laut dan Anda ingin menghidupkannya kembali?

Servis motor kena/tercuci air laut

Perangkat pengaman mesin kerek:

Lihat Jawaban Kopling selip.( Dipasang di antara motor hidrolik dan roda gigi)

Perjalanan beban berlebih.

Meger:

Lihat Jawaban Megger adalah ohmmeter untuk mengukur tahanan isolasi dalam jutaan ohm. (Kutub ke kutub, kutub ke bumi). Isolasi yang baik memiliki ketahanan yang tinggi; isolasi yang buruk, resistansi yang relatif rendah. Nilai resistansi yang sebenarnya dapat lebih tinggi atau lebih rendah, tergantung pada faktor-faktor seperti suhu atau kadar air dari insulasi (penurunan resistansi pada suhu atau kelembaban).

Tujuan Tes Megger:

Lihat Jawaban Untuk memverifikasi resistansi isolasi.

Untuk mendeteksi kesalahan isolasi.

Prosedur yang Benar untuk Memeriksa Megger:

Lihat Jawaban Matikan switchboard utama dengan pemutus arus &cabut sekring, beri label MEN AT WORK, putuskan sambungan dari stator, dot dengan Megger Meter. Ukur tahanan saat kondisi panas untuk pembacaan yang akurat.

Penguji isolasi Megger pada dasarnya adalah pengukur resistansi jarak tinggi (ohmmeter) dengan generator arus searah bawaan. Meteran ini memiliki konstruksi khusus dengan kumparan arus dan tegangan, memungkinkan ohm sebenarnya untuk dibaca secara langsung, terlepas dari tegangan aktual yang diterapkan.

Metode ini tidak merusak; yaitu, tidak menyebabkan kerusakan isolasi.

Bagaimana Anda tahu catu daya pantai benar atau tidak?

Lihat Jawaban Indikator urutan fase. (di dalam kotak koneksi pantai, putar searah jarum jam)

Operasikan kipas ventilasi E/R &periksa arah aliran udara.

Saat kehilangan eksitasi:

Lihat Jawaban Mengetuk dengan palu ke inti kumparan medan motor eksitasi.

Berikan energi dengan baterai.

Perjalanan preferensial:

Lihat Jawaban Jika kondisi kelebihan beban generator berkembang, perjalanan kelebihan beban preferensinya akan beroperasi untuk memberi energi pada relai pengatur waktu. Relai waktu kemudian beroperasi untuk memutuskan layanan yang tidak penting dalam urutan tertentu dan pada interval waktu tertentu.

Tidak ada yang penting (tanpa mempengaruhi operasi kapal.) 5 detik:

Penting (menjalankan kapal dengan benar) 5 detik:

Polaritas atas (propulsi, navigasi) 15 detik:

Listrik statis:

Lihat Jawaban Listrik yang dihasilkan pada bahan yang berbeda melalui kontak fisik &pemisahan

Keluar materi negatif, sisa materi positif.

Pembakaran spontan:

Lihat Jawaban Penyalaan bahan yang disebabkan oleh panas yang menghasilkan aktin kimia eksotermik di dalam bahan itu sendiri, tanpa paparan sumber pengapian eksternal. (kain basah berminyak, debu gergaji basah)

Reaksi jangkar.

Lihat Jawaban – Ketika generator DC atau motor beroperasi dengan beban, percikan api antara sikat karbon dan komutator terjadi karena Reaksi Jangkar. Reaksi jangkar terjadi ketika arus jangkar mengalir di dalam jangkar.

– Ketika arus mengalir dalam jangkar, inti jangkar dimagnetisasi oleh arus ini. Efek magnetisasi arus jangkar dapat dibagi menjadi dua efek:–

Efek magnetisasi silang atau distorsi.

Efek demagnetisasi atau pelemahan.

Untuk mengimbangi reaksi jangkar, Mesin Listrik modern dilengkapi dengan

Interpol

Kursi goyang sikat karbon.

Menetralisir Berliku.

Starter motor AC:

Lihat Jawaban Starter motor adalah peralatan yang digunakan untuk mengontrol start motor listrik.

Starter online langsung. (tanpa elemen pembatas arus)

Starter resistor atau reostatik. (dengan perangkat pembatas arus)

Starter delta bintang.

Starter Auto Transformer. (tegangan berkurang mulai 55%, 60%, 70%, tegangan penuh berjalan

Starter resistansi rotor. (start motor induksi slip ring)

Panci dasbor

Lihat Jawaban Perangkat mekanis untuk menghasilkan tindakan waktu tunda. Pengoperasian switch gear, arc lamp, motor starter, Electro magnetic bake, dll. Waktu tunda disesuaikan dengan kekentalan oli yang digunakan.

Lampu pendeteksi bumi

Lihat Jawaban Detektor gangguan bumi terdiri dari tiga lampu pijar yang dihubungkan secara bintang. Ketiga lampu ini disuplai dari sekunder tiga trafo step down satu fasa. Primer tiga transformator terhubung dalam bintang. Titik bintang dari pendahuluan dihubungkan dengan kerangka kapal. Primer transformator ini diumpankan dari fase merah, fase kuning dan fase biru dari pasokan kapal.

Memberikan sinyal visual dan buzzer akan berbunyi saat ada gangguan pembumian pada sistem yang terpasang.

Tiga lampu pijar yang dihubungkan secara bintang. Ketiga lampu ini disuplai dari sekunder tiga trafo step down satu fasa.

Primer dari ketiga transformator ini terhubung secara bintang. Titik bintang dari pendahuluan terhubung dengan Bingkai kapal. Primer transformator ini diumpankan dari fase Merah, Fase Kuning, dan Fase Biru dari suplai utama kapal.

Tidak Ada Kesalahan Pembumian dalam sistem, Lampu akan menyala dengan kecerahan yang sama.

Ketika gangguan pembumian terjadi pada salah satu fase, lampu pada fase tersebut akan menjadi gelap dan dua lampu lainnya akan menyala dengan kecerahan ekstra.

Gangguan pembumian dapat dilacak dengan mematikan pemutus arus satu per satu. Ketika sirkuit cabang dengan gangguan dimatikan, lampu pembumian akan kembali ke cahaya normalnya.

Catu daya darurat:

Lihat Jawaban Lampu darurat.

Lampu navigasi.

Peralatan komunikasi internasional.

Lampu penanda siang hari.

Peluit kapal.

Deteksi kebakaran dan pemasangan yang mengkhawatirkan.

Alarm kebakaran manual.

Sinyal darurat internal lainnya.

Pompa kebakaran darurat.

Perlengkapan kemudi.

Alat bantu navigasi dan perlengkapan lainnya.

Pentahapan tunggal:

Lihat Jawaban Pentahapan tunggal adalah istilah yang digunakan untuk menunjukkan kondisi yang timbul dalam rangkaian tiga fasa ketika satu fasa menjadi rangkaian terbuka.

Sirkuit terbuka dalam satu fase, sering kali karena sekering putus, kontak yang salah, atau kabel putus, akan mencegah motor untuk distarter tetapi motor yang sedang berjalan dapat terus beroperasi dengan gangguan.

Arus berlebih pada kabel suplai yang tersisa.

Distribusi arus yang tidak merata pada belitan motor.

Dapat dideteksi oleh perangkat yang kelebihan beban di jalur suplai atau melalui panas berlebih.

Panas berlebih pada motor yang mati atau berjalan akan menyebabkan koil kelebihan beban terbakar.

Pada motor yang dibebani ringan agar tetap tidak terdeteksi oleh perjalanan elektromagnetik pada jalur suplai yang hanya memantau arus. Meningkatkan perlindungan diberikan oleh termister yang ditempatkan di belitan untuk mengukur efek termal.

Sistem netral terisolasi

Lihat Jawaban Keuntungan

Sistem ini menghindari risiko kehilangan layanan penting mis. perangkat kemudi

Jika netral dibumikan dan korsleting pada satu fase menyebabkan sekering pada fase tersebut putus, sistem sekarang akan menggunakan satu fase dan dapat menyebabkan motor terbakar

Dalam netral terisolasi, satu gangguan pembumian tidak mengganggu suplai tetapi sistem deteksi kebocoran pembumian akan memberikan peringatan.

Arus gangguan pembumian yang rendah dalam sistem berinsulasi memberikan risiko kebakaran yang jauh lebih kecil.

Kekurangan

Pada sistem terisolasi tegangan ke bumi adalah 1,73 Vph mis. 440v vs 250v

Menelusuri gangguan pembumian lebih sulit karena meskipun tersandung selektif dapat melacak sirkuit yang dibumikan, posisi sebenarnya pada sirkuit mungkin masih sulit untuk ditemukan. Gangguan resonansi atau intermiten misalnya solenoid kontaktor atau transformator dengan netral terisolasi dapat menyebabkan tegangan diperbesar hingga 4 kali tegangan normal ke bumi (250v x 4 =1000v)

Catatan:kejutan listrik tidak dikurangi dengan menggunakan netral yang tidak dibumikan karena melibatkan tegangan yang besar. Kedua sistem sama-sama berbahaya

Sistem netral yang dibumikan

Lihat Jawaban Ketika sistem pembangkitan netral yang dibumikan digunakan, pembumian harus melalui resistor. Resistor harus sedemikian rupa sehingga membatasi arus gangguan pembumian ke nilai yang tidak lebih besar dari arus beban penuh dari generator terbesar pada bagian switchboard dan tidak kurang dari tiga kali arus minimum yang diperlukan untuk mengoperasikan perangkat apapun terhadap

Kembali E.M.F

Lihat Jawaban Ketika arus mengalir melalui konduktor dinamo motor, gaya akan diberikan pada konduktor. Gaya ini menghasilkan torsi, yang akan menyebabkan armature motor berputar.

Ketika konduktor jangkar bergerak melintasi medan magnet, konduktor ini akan memotong garis gaya magnet dan oleh karena itu menghasilkan E.M.F. Arah E.M.F yang dihasilkan ini berlawanan dengan tegangan yang diberikan motor. Karena E.M.F yang dibangkitkan di motor berlawanan dengan tegangan yang diberikan ke motor, E.M.F ini disebut E.M.F.

Tegangan Terapan =Penurunan tegangan ke tahanan jangkar + E.M.F balik

V =Ir + Eb

Pengatur tegangan otomatis (AVR):

Lihat Jawaban Lonjakan arus beban yang tiba-tiba (peningkatan besar yang tiba-tiba) (misalnya karena motor mulai) pada generator menyebabkan perubahan yang sesuai pada tegangan keluarannya. Hal ini disebabkan oleh penurunan tegangan internal pada belitan ac generator dan efeknya biasanya disebut 'penurunan tegangan'. Demikian pula, pelepasan beban (untuk menghilangkannya) akan menghasilkan tegangan berlebih pada bus-bar. Sistem eksitasi generator yang tidak diatur atau tidak digabungkan tidak akan realistis di atas kapal karena tegangan yang bervariasi yang disebabkan oleh permintaan beban yang berfluktuasi. Peralatan pengaturan tegangan otomatis (AVR) diperlukan untuk memperbaiki perubahan tegangan tersebut dengan cepat.

Pengatur tumpukan karbon.

Pengatur kontak getaran.

Keluaran alternator ditransformasikan, disearahkan dan dioutputkan melalui kumparan magnet terhadap pegas yang merupakan referensi tegangan dan berlaku untuk medan eksitasi dc dan rotor alternator.

Regulator tegangan otomatis statis.

Arus searah yang berasal dari output alternator melalui transformator &penyearah, diterapkan ke jembatan yang memiliki resistansi tetap pada dua lengan dan resistansi variabel (referensi tegangan dioda zener) pada dua lainnya. Ketika perubahan tegangan yang diterapkan, jembatan Whetstone menghasilkan sinyal kesalahan. Sinyal kesalahan dapat diperkuat dan digunakan untuk mengontrol eksitasi alternator dengan cara yang berbeda. (Thyristor, Transistor secara seri)

Dioda

Lihat Jawaban Perangkat elektronik yang memungkinkan elektron mengalir dalam satu arah tetapi sangat tahan terhadap aliran arus dalam arah yang berlawanan. (Sama halnya periksa di sistem perpipaan.)

Tujuan dioda adalah berfungsi sebagai penyearah osilasi frekuensi tinggi dan frekuensi rendah. Ini digunakan sebagai detektor di sirkuit penerima.

Dioda termionik terdiri dari pemanas, katoda, dan anoda, dalam katup yang dipanaskan secara tidak langsung.

Dioda semi konduktor dibangun dengan germanium kristal mono atau wafer silikon dengan dua lapisan berbeda doping; persimpangan 'pn' bertindak sebagai persimpangan penyearah.

Transistor

Lihat Jawaban Perangkat tiga lapis, baik NPN atau PNP

Memiliki emitor, kolektor &basis

Menggunakan daya sinyal kecil dari sirkuit samping yang mengontrol daya yang lebih besar di sirkuit lain. (Penguatan atau penguatan daya)

Thyristor

Lihat Jawaban Elemen kontrol daya. Perangkat multi-lapisan persimpangan P dan N alternatif.

Misalnya. Penyearah terkontrol silikon (SCR) ~ Perangkat empat lapis.

Triac ~ Jumlah yang lebih besar.

Thyristor adalah sakelar solid state, yang dihidupkan dengan penerapan tegangan sinyal tingkat rendah melalui koneksi pemicu yang dikenal sebagai elektroda gerbang

Tidak ada bagian yang bergerak untuk dipakai, atau kontak yang dapat rusak karena lengkung.

Ideal untuk operasi jarak jauh. Ukuran kecil ~ komponen sirkuit kontrol yang nyaman. Dapat mengontrol arus lebih besar dari 1000 amp dan tegangan lebih dari 1000 volt. Ganti sakelar konvensional yang besar.

Kecepatan operasi lebih cepat (25.000 kali per detik).

Pemicu:

Ini adalah generator DC kecil. Ini memasok arus yang menarik ke rotor generator A.C.

Arus eksitasi diperlukan untuk menciptakan medan magnet apa pun.

Equaliser

Equalizer adalah koneksi antara generator dengan kapasitas berbeda yang berjalan secara paralel sehingga beban berjalan dibagi secara proporsional di antara keduanya.

Beban DC pada sistem pelayanan kapal AC:

Sistem alarm umum.

Pencahayaan darurat.

Daya radio darurat.

Memperbaiki untuk pengisian daya baterai.

Perawatan motor:

Jaga saluran udara tetap bersih.

Menghilangkan timbunan debu, minyak dan lemak.

Lakukan pembacaan tahanan isolasi.

Mencegah percikan pada sikat dan komutator.

Pemeriksaan mekanis pada bantalan, kopling penahan baut.

Pemeriksaan rutin pada starter dan pengontrol motor, pemeliharaan kontak, resistansi, dan sambungan.

Galvanometer:

Ini adalah alat untuk mengukur arus listrik kecil dengan besar dan arahnya.

Resistor:

Ini adalah perangkat yang menghantarkan listrik tetapi mengubah sebagian energi listrik menjadi panas.

Resistivitas:

Ini adalah resistansi suatu material dan dinyatakan dalam ohm/satuan panjang.

Reostat

Ini adalah resistor, yang dilengkapi dengan sarana untuk menyesuaikan resistansi dengan mudah.

Pemadaman kebakaran di switchboard

Pertama-tama pemutus sirkuit harus diputus. Kemudian dipadamkan dengan api dengan alat pemadam portabel CO2.

Setelah api berhenti, papan sakelar menjadi dingin

Semua sistem kabel harus dilacak dan uji kontinuitas.

Setelah menelusuri dan memperbarui semua fitting, switchboard dapat digunakan kembali.

Pencegahan Kebakaran:

Gunakan sekering yang benar.

Semua kontak pemutus sirkuit dan sakelar terhubung dengan baik.

Semua sambungan kabel terhubung dengan baik.

Penyebab Kebakaran:

Kontak longgar.

Sekering salah.

Kerusakan isolasi

Magnetisme sisa:

Saat menghidupkan generator, magnet yang diperlukan disediakan oleh inti besi dari kutub medan. Magnetisme ini dikenal sebagai magnet sisa.

Pemasangan baterai dan langkah-langkah keamanan:

Memerlukan ventilasi yang baik untuk melibatkan H2. Memerlukan cat yang sesuai untuk mengeluarkan saluran ventilasi. Saluran masuk ventilasi harus di bawah level baterai.

Lampu telanjang dan merokok dilarang di ruang baterai.

Luka pangkuan. Rangkaian multi paralel di angker.

Gelombang luka Dua sirkuit paralel di angker.

Gagal menggairahkan:

Hilangnya sisa magnet.

Resistansi terlalu tinggi di sirkuit medan.

Motor universal:

Luka seri.

Fase tunggal.

Baik A.C atau D.C dapat digunakan.

Daya pecahan (sangat kecil). (Kurang dari 1 HP.)

Digunakan pada mesin jahit, bor portabel, dll.

(Bila motor dihubungkan ke saluran DC, arus searah sepanjang waktu. Dalam saluran AC, arus bolak-balik sendiri setiap siklus.)

Apa kemungkinan konsekuensi dari upaya untuk menutup pemutus sirkuit udara (ACB) pendapatan ketika generator tidak sinkron?

Pada saat pemutus arus ditutup, perbedaan fasa tegangan menyebabkan arus sirkulasi yang besar antara mesin yang menghasilkan gaya magnet yang besar untuk 'menarik' generator ke dalam sinkronisasi. Ini berarti percepatan yang cepat dari satu rotor dan perlambatan yang lain. Kekuatan besar dapat secara fisik merusak generator dan penggerak utamanya dan arus sirkulasi yang besar dapat membuat setiap pemutus generator tersandung. Hasil? Pemadaman, bahaya, dan rasa malu!

Sinkronisasi:

Sinkronisasi

Menyinkronkan lampu:

Metode lampu 'Gelap'. (2 lampu)

Metode lampu 'terang'. (2 lampu)

Metode 'Urutan'.(3 lampu)

Bagaimana Anda bisa memantau saat yang tepat untuk sinkronisasi tanpa bantuan Synhroscope atau lampu sinkronisasi?

Hubungkan sepasang probe voltmeter 500 V di satu fase pemutus arus mesin yang masuk. Sesuaikan kecepatan generator hingga voltmeter perlahan berfluktuasi dari nol hingga maksimum. Tutup pemutus saat voltmeter melewati nol.

Apa arti posisi yang berbeda dari jarum sinkroskop; apa perbedaan antara jam 6 dan jam 12?

Jam 6 berarti tidak sinkron. Kami tidak dapat memparalelkan generator yang masuk. Pukul 12 berarti kondisi sinkronisasi yang sempurna (tegangan, frekuensi, dan urutan fase cocok).

Mengapa kita menutup sakelar pada jam 11 dan bukan pada jam 12?

Ketika synchroscope mendekati jam 12 "slip" (diferensial) antara gelombang sinus mendekati minimum (slip adalah nol ketika synchroscope berada pada jam 12) dan perbedaan tegangan antara fase minimal (itu nol ketika sinkroskop pada jam 12). Karena waktu yang dibutuhkan untuk menutup sakelar sinkronisasi, biasanya dilakukan pada jam 11. Karena keterlambatan penutupan yang kecil, dengan melakukan pada jam 11, kami mencapai penutupan mendekati jam 12.

Mengapa Megger digunakan untuk uji insulasi dan bukan multimeter?

Dengan megger, tegangan tidak kurang dari 500 volt DC digunakan untuk menguji tahanan isolasi belitan. Dengan multimeter, tegangan yang digunakan tidak lebih dari 3 volt DC. Megger menggunakan pengujian impedansi tinggi dan karenanya lebih akurat daripada multi-meter

Apa saja keamanan di MSB?

Pemutus arus, sekering, dan relai arus lebih digunakan. Panel mati panel depan, yaitu, kami tidak dapat membuka panel untuk pemeliharaan sampai kami mematikan daya ke panel dengan pemutus arus.

Kapan daya Reverse mengalir?

Situasi generator adalah memberi makan sistem melalui sakelar gigi yang memiliki beberapa generator yang terhubung secara paralel dengan generator ini. Aliran arus pada saat sistem berjalan normal adalah dari generator ke switch gear. Jika salah satu generator mengalami masalah dan tegangan terminalnya turun di bawah tegangan sistem, generator akan bertindak sebagai motor, seperti halnya motor dapat bertindak sebagai generator, dan arus akan mengalir dari switch gear ke generator. Ini adalah kekuatan terbalik. Efeknya dapat berkisar dari kecil hingga ekstrem jika terjadi kegagalan mekanis total pada generator yang gagal.

Apa salahnya jika arus listrik terbalik?

Asumsikan bahwa generator secara normal menghasilkan sejumlah daya yang sama dengan P, dan bahwa ketika beroperasi sebagai motor, generator akan menyerap jumlah yang sama, P. Oleh karena itu, efek bersih pada jaringan akan sama seperti jika mengalami kenaikan bertahap. dalam beban sama dengan 2P. Bergantung pada ukuran jaringan dan kekuatan pembangkit yang tersisa, peningkatan 2P secara bertahap dapat mengakibatkan perubahan frekuensi yang signifikan pada jaringan.

Mungkin ada kerusakan penggerak utama dalam beberapa kasus (terutama turbin uap).

Bagaimana perlindungan terhadap daya balik diberikan?

Perlindungan daya terbalik digunakan untuk anti-motoring. Fungsi ini digunakan untuk proteksi prime mover bukan generator. Hal ini dapat memotong pasokan bahan bakar dan menghentikan penggerak utama.

Bagaimana Anda menguji perjalanan daya terbalik?

Ketika dua generator bekerja secara paralel dan satu generator dapat membawa beban, perjalanan daya terbalik dapat diuji dengan pemindahan beban menggunakan kontrol gubernur. Ketika beban telah bergeser cukup dan generator off-loaded membawa sebagian kecil beban, pemutus trip dan suplai bahan bakar ke penggerak utama terputus. Ini berarti relai daya terbalik telah beroperasi. Relai dapat diuji dengan simulasi (menggunakan tombol tekan uji pada relai) untuk melihat apakah relai memulai sinyal trip.

Apa bentuk lengkap dari ACB?

Pemutus sirkuit udara. Biasanya digunakan pada 400V dan aplikasi arus yang lebih tinggi (pemutus generator).

Jika Anda menekan tombol Tutup ACB pada generator yang menganggur, apa yang akan terjadi?

Biasanya, pemutus tidak akan menutup sampai Anda menyinkronkan, jadi bahkan jika Anda menekan pemutus dekat, itu tidak akan menutup. Pemutus memiliki perlindungan tegangan rendah yang tidak akan membiarkan Anda menutupnya.

Apa yang dimaksud dengan perlindungan tegangan rendah?

Ini mencegah penutupan pemutus karena kesalahan, atau generator yang datang dengan beban selama operasi paralel. Ini juga memberikan perlindungan terhadap kehilangan tegangan saat mesin terhubung ke switchboard.

Apa yang dimaksud dengan perjalanan preferensial? Mengapa disediakan?

Trip preferensial adalah sejenis pengaturan kelistrikan di kapal yang dirancang untuk memutuskan sirkuit non-esensial yaitu beban non-esensial dari bar bus utama jika terjadi kegagalan sebagian atau kelebihan suplai utama. Ini memungkinkan beban kritis berjalan (seperti perangkat kemudi) dan mendorong beban yang tidak penting (seperti AC dan dapur) dan merupakan fitur keselamatan.

Apa tujuan indikasi gangguan pembumian pada papan sakelar?

Ini mendeteksi dan menunjukkan gangguan fase ke bumi pada sirkuit.

Jika Anda mendapatkan alarm gangguan bumi, apa yang akan Anda lakukan?

Kesalahan dapat diselidiki dengan terlebih dahulu mengidentifikasi area kapal yang memiliki kemungkinan besar terjadinya gangguan tanah (misalnya pencahayaan dek atau peralatan dapur) dan kemudian mematikan pasokannya satu per satu untuk melihat apakah alarm hilang. Saat beban tertentu menghilangkan alarm, kami tahu bahwa sirkuit tersebut mengalami gangguan pembumian dan kami dapat memperbaikinya.

Apa itu Arus Langsung?

Aliran arus searah.

Apa itu arus bolak-balik?

Aliran arus dua arah dalam bentuk sinusoidal dengan puncak positif dan negatif.

Apa yang dimaksud dengan fase dalam AC?

Dua atau lebih tegangan atau arus AC yang tidak selangkah satu sama lain. Puncak dan titik nol mereka tidak cocok pada titik waktu yang sama. Ini yang dimaksud dengan fase.

Apakah ada fase di DC?

Tidak

Mengapa DC tidak banyak digunakan sekarang?

Generator AC adalah teknologi yang lebih baik dan transformasi tegangan (dengan transformator) dapat dilakukan dengan mudah di AC dan bukan di DC.

Di mana Anda cenderung melihatnya digunakan?

DC bertenaga baterai umumnya digunakan dalam sistem navigasi, kontrol, dan keselamatan terutama dalam navigasi, radar, sistem keselamatan, antena dan sistem komunikasi, serta penerangan darurat.

Apa yang dimaksud dengan arus tiga fase?

Tiga bentuk gelombang sinusoidal arus yang besarnya sama tetapi dengan pergeseran fasa 120 derajat.

Apa itu nilai rms?

Nilai akar rata-rata kuadrat adalah nilai puncak dibagi dengan akar kuadrat 2.

What is the meaning of power factor?

Power factor is the cosine of the angle between voltage and current waveform.

What is the usual value you see onboard?

Usually 0.8.

What is the best value possible?

1 is the best value possible. That is possible with a purely resistive load.

What is the benefit of improving power factor?

Power factor close to 1 means for the same real power in kW, the load current is less and hence the I2R losses are less. The system efficiency is higher as the losses are lower. Improved voltage regulation is achieved.

How can it be improved?

Power factor improvement capacitor banks are used if the loads are mainly resistive.

What is the meaning of saying I and V are in phase?

The angle between the I and V waveform is zero which means the load is purely resistive.

Why are motor ratings given in KW and that of alternator and transformer given in KVA?

kW is the output mechanical power of a motor and is expressed in kW.

kVA is the net (apparent) power input to the transformer. This input power is the output + losses.

kW =kVA x system power factor

Where does reactive power go?

Reactive power is not ‘lost’. It is delivered to the motor where it sustains the electric field that enables the motor to convert the real power (electrical) into mechanical torque.

What is a semi conductor?

Substance as germanium or silicon whose electrical conductivity is intermediate between that of a metal and an insulator; its conductivity increases with temperature and in the presence of impurities

What is doping?

Doping intentionally introduces impurities into an extremely pure (also referred to as intrinsic) semiconductor for the purpose of modulating its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly and moderately doped semiconductors are referred to as extrinsic. A semiconductor doped to such high levels that it acts more like a conductor than a semiconductor is referred to as degenerate.

What happens to insulation when temperature rises?

For insulators, an increase in temperature will cause their resistance to decrease -which is why excessive temperature is often the main reason why insulation fails

What happens to resistance of conductors when temperature rises?

For conductors an increase in temperature will cause their resistance to increase.

What is an induction motor?

An induction motor is an alternating current motor in which the primary winding on one member (usually the stator) is connected to the power source and a secondary winding or a squirrel-cage secondary winding on the other member (usually the rotor) carries the induced current.

What is “slip”?

An AC (Amplitude Current) induction motor consists of two assemblies – a stator and a rotor. The interaction of currents flowing in the rotor bars and the stators’ rotating magnetic field generate a torque. In an actual operation, the rotor speed always lags the magnetic field’s speed, allowing the rotor bars to cut magnetic lines of force and produce useful torque. This speed difference is called the slip.

What is a synchronous motor?

A constant-speed motor, the speed being dependent on the frequency of the ac supply and the number of poles for which it is designed.

Where is it used?

Synchronous motors find applications in all industrial applications where constant speed is necessary. Improving the power factor as Synchronous condensers. Electrical power plants almost always use synchronous generators because it is important to keep the frequency constant at which the generator is connected. Low power applications include positioning machines, where high precision is required, and robot actuators.

How do you use a multi-meter?

What is an AVO meter?

The Avometer was a British brand of multimeter, latterly owned by Megger. It is often called simply an AVO and derives its name from the first letter of the words amperes, volts, ohms

How do you check continuity?

Set the multi-meter in resistance mode and then check with probes the resistance between the points or circuit under check. If the resistance is low or zero, it means continuity. If it is high or infinite, it means open circuit.

What limits the electrical load?

The available power is fixed and the voltage is fixed, so the setting of the breaker or fuse is the normal current of the load. If the load exceeds the rated current, then the breaker or fuse will operate and limit the load.

What is the voltage used in a meggar?

500V DC.

How does current flow during welding?

The current flows through the electrode and to the clamp. That’s how it flows in MIG, stick, flux cored. On Tig, the electricity flows through the electrode also except that now that’s the only function of it, the rod is held in your hand and electrode in the other.

What do we use for welding on ships? AC or DC?

What is the voltage?

What is the voltage used for ignition in boilers/incinerators etc.?

Normally 10,000V (10kV).

Why is it different from that for welding?

It is higher as the ignition requires break down of air gap for park to occur. The air breaks down at this high voltage of 10kV. Therefore, it is higher than normal welding voltage.

Does current flow through hull during welding?

Yes I think.

If so why don’t you get a shock?

. Because the whole hull is at the same potential, so there is no potential difference to get a shock.

What is safe voltage to prevent shock?

Normally 50V. It depends on the body resistance and how conducting the path is (example use of insulating boots or mat may allow slightly higher voltage to be safe)

What is the meaning of earthing in a ship?

What is the meaning of Star winding/ Delta winding?

Refer Dennis T Hall

Is the ship’s alternator Star wound or Delta wound?

Refer Dennis T Hall

What is the meaning of ACB, MCCB, NFB?

Air circuit breaker for 400V higher current ratings.

Moulded case circuit breaker for 400V medium current ratings.

No Fuse Breaker – 75 A capacity

What is a magnetic contractor? Where is it used?

A contractor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.

Contractors are used to control electric motors, lighting, heating, capacitor banks, and other electrical loads.

What is a relay? How is it different from a magnetic contractor?

Contractor is a heavy duty switch whereas the relay is light duty switch. Relays can be as simple as 12 V DC solenoids with 12 V, 0.5 A rated contacts. They are used to detect faults on the power system and signal a local or remote switching device (breaker) to trip the circuit.

Can you draw a DOL starter circuit?

Refer to DOL diagram in Dennis T Hall

What is the meaning of overload?

An overload is a current over and above the normal load current (over the load).
In other words greater than the original design current. This can be a momentary overload such as the starting current for a motor which is usually ignored or it can be a sustained overload such as plugging in too many appliances at once or a motor that has faulty bearings or gets jammed

What is meaning of short circuit?

A short circuit occurs when conductors are connected (shorted) together by a fault. This is normally phase to phase fault due to failure of insulation by something cutting the wires, fires, etc.

How is protection provided for OL and SC?

Damage from short circuits and overloads can be reduced or prevented by employing fuses, circuit breakers, or other overload protection, which disconnect the power in reaction to excessive current. The tripping time is much less (in milli seconds) for short circuit due to very high currents but can higher (a few seconds) due to currents say 1.1 to 1.5 times the normal current.

What is the function of a fuse?

Fuse places a limit on the amount of current that can be drawn by an electric circuit by opening (blowing or melting) when the current exceeds a preset limit. This protects the circuit and the surroundings from fire or damage in the case of an overload or short circuit.

What is the normal setting of overload relays?

Normally 90-100% of rated normal current. Sometimes can be set to 105% of rated current.

How does a thermal overload relay work?

The bi-metallic strip in the relay heats up by the over load current and the movement in the bi-metallic strip causes the breaker to trip. The breaker has to be reset (turn off) before turning on again. Sometimes it takes a time delay for the bi-metallic strip to cool down after which the breaker can be reset and switched on.

What is single phasing?

Single phasing is a condition in three phase motors and transformers wherein the supply to one of the phases is cut off.

How can it happen?

Single phasing is caused by the use of single-phase protection devices such as fuses. Three phase loads should be protected by devices which cause the interruption of power to all three phases simultaneously when a fault occurs. Defective contacts or loose connections in three phase breakers can also cause single phasing.

What is the harm caused by this?

Single phasing causes higher than rated currents in the healthy phases of loads such as motors causing over heating of the motor and consequently motor failure.

Single phasing can sometimes cause excessive noise and vibration in motors.

What protection is provided against this?

Single phasing can be identified by special protective relays which can identify and isolate the connected loads. Smaller motors rely on over current and negative phase sequence relays. Motor protection relays for larger motors come readily fitted with protection against single phasing.

Why is it necessary that incoming alternator frequency is more than bus bar?

Prior to paralleling alternators together, the frequency of the incoming alternator is made slightly higher. This is to ensure that the incoming generator will take some of the bus load. If the incoming generator is slow it will become motorized and will add load onto the bus. If this happens it is possible to cause other generators to trip off line.

What is dark lamp and bright lamp method for synchronizing? How is the connection made?

Formerly, three light bulbs were connected between the generator terminals and the system terminals. As the generator speed changes, the lights will rise and fall in intensity at a rate proportional to the difference between generator frequency and system frequency. When the voltage at the generator is opposite to the system voltage (either ahead or behind in phase), the lamps will be bright. When the voltage at the generator matches the system voltage, the lights will be dark. At that instant, the circuit breaker connecting the generator to the system may be closed and the generator will then stay in synchronism with the system.

Apart from renewing bearings is there any reason for opening up motors for maintenance?

Insulation checks and renewal (example using insulation spray on stator winding insulation).

Why is this reverse power used instead of reverse current in alternators?

It is extremely difficult to detect reverse current with an alternating current system, reverse power can be detected and protection can be provided by reverse power relay.

What is the meaning of excitation in an alternator?

An electric generator or electric motor consists of a rotor spinning in a magnetic field. The magnetic field may be produced by permanent magnets or by field coils. In the case of a machine with field coils, a current must flow in the coils to generate the field, otherwise no power is transferred to or from the rotor. The process of generating a magnetic field by means of an electric current is called excitation.

Is the field current in an alternator AC or DC ?

DC. To confirm check Dennis T Hall.

Is the field rotating or stationary?

Rotating. To confirm check Dennis T Hall.

How is it supplied?

The rotor’s magnetic field is supplied by a rotor winding energized with direct current through slip rings and brushes.

What is a brush less alternator?

A brushless alternator is composed of two sections:main alternator and the smaller exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wearing parts. The main alternator has a rotating field as described above and a stationary armature (power generation windings).

How is the excitation achieved in this?

Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.

What is the meaning of residual magnetism?

Residual magnetism is a property in which certain amount of excitation remains back in the conductor even after the removal of the magnets.

Why is an air compressor started unloaded?

The air pressure inside the compressor cylinder offers resistance to the movement of the piston. Hence started unloaded. Ask 4/E or 2/E in ship.

How is the speed of a 3-phase induction motor varied?

The speed of a normal 3-phase induction motor is a function of the frequency of the supply voltage. Changing the speed of such a motor hence requires building a 3-phase power frequency convertor. This can be realised by using power MOSFETs (or IGBTs) capable of handling high voltages and fast switching speeds.

How is the direction of rotation varied?

By changing the phase sequence (from say R-Y-B to R-B-Y)

How does this cause a rotation to change?

Due to the change in phase sequence, the rotating magnetic field changes direction and the rotor rotates in the opposite direction.

How is the speed of a DC motor varied?

To vary the speed of a DC motor we need a constant voltage power supply with a series POT resistor of higher watt rating. A Pulse Width Modulator (PWM) can be used.

How is the direction varied?

A general purpose DC motor can be reversed by changing the polarity of either the armature or the field but not both.

What is a diode?

In electronics, a diode is a two-terminal electronic component with asymmetric transfer characteristic, with low (ideally zero) resistance to current flow in one direction, and high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is acrystalline piece of semiconductor material with a p-n junction connected to two electrical terminals

What is a zener diode?

A zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, “zener knee voltage” or “zener voltage.”

What is a thyristor? What is an SCR?

A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased (that is, while the voltage across the device is not reversed).

A silicon-controlled rectifier (or semiconductor-controlled rectifier) is a four-layer solid state device that controls current. It is a type of thyristor.

How does an inverter work?

An inverter converts DC supply into AC by use of electronic devices such as diodes and thyristors.

How does a tube light work?

It is well explained in Dennis T Hall

When voltage is applied to the fluorescent lamp, here’s what happens:

The starter (which is simply a timed switch) allows current to flow through the filaments at the ends of the tube.

The current causes the starter’s contacts to heat up and open, thus interrupting the flow of current. The tube lights.

Since the lighted fluorescent tube has a low resistance, the ballast now serves as a current limiter.

When you turn on a fluorescent tube, the starter is a closed switch. The filaments at the ends of the tube are heated by electricity, and they create a cloud of electrons inside the tube. The fluorescent starter is a time-delay switch that opens after a second or two. When it opens, the voltage across the tube allows a stream of electrons to flow across the tube and ionize the mercury vapor.

Without the starter, a steady stream of electrons is never created between the two filaments, and the lamp flickers. Without the ballast, the arc is a short circuit between the filaments, and this short circuit contains a lot of current. The current either vaporizes the filaments or causes the bulb to explode.

What is the function of the choke?

The choke has two main functions. In conjunction with the starterit causes the tube to ignite by using the back emf to create a plasma in the tube and it controls the current through the tube when it is ignited.

Where is a slip ring used and where is a commutator used?

Slip rings are commonly found in slip ring motors, electrical generators for alternating current systems and alternators. They can be used on any rotating object to transfer power.

A commutator is a common feature of direct current rotating machines. By reversing the current direction in the moving coil of a motor’s armature, a steady rotating force (torque) is produced.

What is capacitance?

Capacitance is the ability of a body to store an electrical charge. Any body or structure that is capable of being charged, either with static electricity or by an electric current exhibits capacitance. C =Q/V where Q is the charge and V is the voltage

Does current flow though a capacitor?

No. Current (or more specifically, charge) flows into one plate, and an opposing current (charge) flows out of the other plate, but the current (except for leakage current) does not flow across the dielectric. The result is that there is a charge differential between the plates.

What is the unit for capacitance ?

Farad

What is a neutral?

In multiphase circuits, the conductor used to carry unbalanced current. In single-phase systems, the conductor used for a return current path.

What is the difference between neutral and earth?

The ground or “earth” wire is a circuit’s safety protective wire that normally carries no current.

What is a synchronous condenser?

A synchronous condenser is a device identical to a synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid’s voltage, or to improve power factor.

Where and why is it used?

Used for power factor correction as a synchronous capacitor.

If a motor is wound star and you want to change to delta what should you do?

Open the terminal connection box. Remove the shorting link connecting the common connection (star) point of A2, B2 and C2. With the 3 phase windings marked A1A2, B1B2, C1C2, connect A2 to B1, B2 to C1 and C2 to A1.

If the AVR, is defective, when additional loads come on will the generator be able to take it?

No. and refer to Dennis T Hall.

How do you test reverse power trip, high current trip, preferential trip?

Reverse power trip – refer answer for question 11..

High current (over load trip) – Set your overload relay high current trip setting to say 75% of the rated current. Run the motor. The relay will trip the breaker. Another way of testing it is pushing the trip button on the relay which trips the breaker.

Preferential trip – With one generator running, try to switch on additional loads to overload the generator. Preferential trip will trip all the non-critical loads..

What is residual magnetism? Where is it important?

Residual magnetism is a property in which certain amount of excitation remains back in the conductor even after the removal of the magnets.

It is required as we need some magnetism to start off the generation before the field winding has power to produce the full field.

Sometimes, when you change the running direction of a E/R blower (from supply to exhaust) it trips. Why?

If the flaps of the blower are not set or opened properly or the filters are clogged, the air supply is affected and the blower may be overloaded causing it to trip. Ask E/O for more information.

What is the function of the friction clutch mechanism used in purifiers?

It is a mechanical question.

What is the regular maintenance done on batteries?

Every week the cell voltage is checked. The specific gravity is monitored using the battery hydrometer. The terminals are lubricated to prevent corrosion. Sometimes load tests are done on the batteries.

What safety precautions need to be taken during maintenance on batteries?

The room needs to be ventilated to prevent explosions due to gases generate by the battery. Protective clothing, gloves and eye protection should be used to prevent acid splash over. No flames or ignition sources should be brought near batteries. Never short both positive and negative terminals as this will cause short circuit and high energy flashover. When disconnecting batteries, always disconnect negative terminals first and vice versa when reconnecting.

Why is special lighting used in battery rooms?

Spark proof lighting is used as explosive gases may be generated during battery charging and so there should be no sparks in the room.

What is the voltage available from each cell in a lead acid battery?

2 V DC.

What is the full battery voltage ?

24 V DC.

How is this voltage achieved?

By connecting 12 cells in series. 12 x 2 V =24 V is total battery bank voltage.

What is the meaning of a normally open contact?

The contact is open in the normal (de-energised condition).

How does a Salinometer function?

It detects the salinity in parts per million (ppm) and provides a alarm signal and also initiates a command to the bypass valve of a fresh water generator. Ask E/O and look in your ship Fresh water generator manual for more details.

How does the air compressor start and stop automatically?

The air reservoir has pressure switch which is set for cut-off and cut-in depending on the pressure desired. When the pressure drops below the cut-in setting, the switch energises the contactor coil and the compressor starts. When the pressure reaches the cut-off setting, the switch opens its closed contact in series with the power circuit to contactor and cuts supply to the contactor.

How is the cold room temperature maintained?

The cold room has temperature switch (thermostat) which has a cut-in and cut-off temperature setting. Depending on the setting, the compressor cuts when the temperature rises and cuts-off when the temperature cools down to the set value.

What is a self-monitoring alarm circuit?

It self monitors the health of the alarm circuit. That is, it senses whether the power supply to the alarm circuit is healthy and all the relays and contacts are functioning normally. Check with E/O for more details.

Out at sea, if there is a black out during your watch, what action will you take?

After a black out the emergency generator comes on; On restoring the main supply we are closing the circuit breaker of the main generator without bothering about synchronizing. How is this possible?

There is a power link connection breaker between the main generator and the emergency generator. During black out, this breaker trips. The emergency generator starts and its breaker closes and feeds only the emergency loads. During restoration, the main generator is started again and its breaker is closed. As the link breaker is still open, there is no paralleling between main and emergency generator.

How does the emergency generator start automatically?

It is activated by a under voltage relay. When there is blackout, the under voltage relay senses loss of voltage and starts up the emergency generator. Similarly when the power is restored, the relay stops the emergency generator.

If all your air bottles are at low pressure and there is a blackout how do you start the generators?

If main air bottles are empty, the emergency air bottle can be used to start the main generator. If even the emergency air bottle is empty, then it can be filled by running emergency air compressor (powered by emergency generator). Once the emergency air bottle is filled, this air can be used to start the main generator.

What is a shaft generator?

A shaft generator is coupled to the main engine. It uses the main engine as its prime mover and has a frequency converter (thyristor controlled) that converts the variable engine speed to near constant speed and produces electrical power. It can only be employed at sea speed (full speed) and not at manoeuvring speed.

Even though the main engine runs at varying speeds, how does the alternator maintain constant frequency?

By use of thyristor controlled frequency (rpm) converters.

Is the alternator connected star or delta

Look up in Dennis T Hall. Normally star.

Why is 440 V used for motors and 110/220 V used for lighting?

Motor load currents are large. Motors are 3-phase loads. A higher 440V voltage means lesser current for the same power and hence losses and size of cable wires is lower. Lighting is single phase loads and its load currents are small, hence lower voltage means less insulation in the cable wires.

For a given line voltage, four heating coils will produce maximum heat when connected in-

Parallel

The unit of absolute permittivity of a medium is-

Farad/ metre

Explain 3 phase motor working principle ?

How emergency generator comes on load after blackout ?
Explain induction &synchronus , difference between the two construction and operational ?

Explain testing of emergency generator ?
Induction motor working principle ?

How static charge is produced ?

Emergency steering procedure ?

Explain 3 phase motor working principle ?

What is slip ring motor ? Where it is used ?

Emergency generator where it supplies ?

What is the significance of Air gap ?

Transformer in your ship , what is its type and working ?

Parts of brushless alternator ?

What are the advantages of earthed neutral system ?

Explain parallel operation of alternator ?

What are the types of fuses ?

Parts of brushless alternator ?

What are the advantages of earthed neutral system ?

what is AVR ? and its function , how does it works ?

Explain parallel operation of alternator ?

Difference between ME/MC ?

What are the types of earthing system ?

What is mutual induction and which machine works on mutual induction ?

What are the voltages in your ship ?

Advantages of earthed neutral system ?

What is mutual induction and which machine works on mutual induction ?

what is AVR ? and its function , how does it works ?

Parts of brushless alternator ?

What are the advantages of earthed neutral system ?

Explain parallel operation of alternator ?

What are the types of earthing system ?

What place you take insulation test in motor ?

What is avr function ?

What is steering gear electrical safety in dudes and cables ?

What is essential load ?

What is the value of motor insulation ?

Explain AE preferential trip?

Explain Pv breaker and pv valve ?

Explain Earth fault ? Action

Explain Generator mounting and connection ?

Explain Power calculation ?

What is Rms value ?

What is insulation resistance ?

Explain Power calculation ?

What is insulation resistance ?

What are MSB safeties ?
What is kw and kva

Explain Earth fault ? Action