Tulisan ini membahas tentang pembuatan generator axial-flux permanent magnet (AFPM) yang dapat menghasilkan dua buah tegangan tiga-fasa dengan pergeseran sudut 30° ataa lazim dikenal sebagai tiga-fasa ganda. Tipe generator AFPM yang dibuat adalah double sided internal rotor yang memiliki sebuah piringan rotor untuk menempatkan kutub-kutub magnet generator yang diapit oleh dua buah piringan stator yang digunakan untuk menempatkan dua buah belitan jangkar tiga-fasa. Generator ini memiliki 18 kutub magnet sehingga jarak antara dua buah kutub magnet yang saling berdekatan adalah 20° mekanik. Oleh karenanya, untuk menghasilkan tegangan keluaran tiga-fasa maka, belitan-belitan fasa R, S dan T pada masing-masing piringan stator akan berjarak 13,3° mekanik. Lebih lanjut, untuk menghasilkan pergeseran fasa 30° diantara kedua buah tegangan keluaran tiga-fasa generator maka belitan tiga-fasa pada piringan stator pertama dan kedua harus diberi pergeseran sudut sebesar 3,3° mekanik. Hasil uji laboratorium menunjukkan bahwa generator AFPM yang dibuat mampu menghasilkan dua buah tegangan tiga-fasa berfrekuensi 50 Hz pada putaran 339 rpm (rotation per-minute) yaitu R1 = 44,9 Ð0° V, S1 = 39,8Ð-118° V dan T1 = 44,0Ð-237° V dengan total harmonic distortion (THD) sebesar 3,4% serta R2 = 42,82Ð-32° V, S2 = 42,7Ð-153° V dan T2 = 42,6Ð-272° V dengan THD sebesar 2,1%. Hasil pengujian ini menunjukkan bahwa generator mampu membangkitkan dua buah tegangan keluaran tiga-fasa yang memiliki bentuk gelombang mendekati sinusoidal murni dengan keseimbangan magnitudo dan fasa cukup baik karena rata-rata penyimpangannya masing-uasing hanya sebesar 1,5 V (2,5%) dan 2,4° (1,7%).

This paper presents design of phase shifting transformer to reduce source current harmonic generated by using of variable speed drive (VSD) in textile industry. Nine VSDs are used in a stenter machine of a selected textile industry. Each of these VSD generates source current total harmonic distortion (THD) in range of 43.91% to 50.34%, which contains all odd order harmonics except the triplen ones. The first method to reduce this source current harmonic is by using arrangement of three phase shifting transformers, which requires one Yy three-phase winding connection to produce 0° phase shifting, one Yz(+) three-phase winding connection to produce 20° phase shifting and one Yz(-) three-phase winding connection to produce –20° phase shifting. The second method is by using arrangement of nine phase shifting transformers, which requires one Yy three-phase winding connection with 0° phase shifting, four Yz(+) three-phase winding connections with 6.67°, 13.34°, 20° and 26.67° phase shifting respectively and four Yz(-) three-phase winding connections with –6.67°, –13.34°, –20° and –26.67° phase shifting respectively. Simulation results using MATLAB SIMULINK show that source current THD successfully reduced to 1.99% and 1.74% respectively when arrangements of three phase shifting transformers and nine phase shifting transformers are used.

Using variable speed drive for controlling speed of three-phase induction motor in industrial sector gives an advantage of reducing consumption of electrical energy; on the other hand, it also causes a disadvantage of source current harmonic.  To solve the problem of source current harmonic, a method of using phase-shifting transformer is applied. This method may be applied in a system with two VSDs or more connected to a three-phase power supply. The application of this phase-shifting transformer method could be as simple as using of two transformer with Y-y (wye-wye) and Y-d (wye-delta) three-phase winding connections to give a phase-shifting of 30 or more complex as it uses two transformer with Y-y and Y-z (wye-zigzag) three-phase winding connections to give a phase-shifting less than 30. This paper proposes design of five different phase-shifting transformer configurations to produce 30, 20, 15, 12 and 10 phase-shifting. Simulation on a computer-based software, Simulink Matlab, then confirmed that the proposed phase-shifting transformer design gives a very accurate result regarding to phase-shifting and magnitudes of input and output voltage of the phase-shifting transformers.

Almost all today electrical loads are considered non-linear such as switch mode power supply (SMPS) for powering computer and mobile phone or variable speed drive (VSD) for driving home and industrial electric motors. These loads generate ac non-sinusoidal current containing a lot of harmonics as indicated by its high total harmonics distortion (THD) figure. Current harmonics bring negative effects into all electrical power system components, including three-phase generator. This paper provides analysis of load current harmonics effects on vibration of three-phase generator. Three different laboratory experiments have been conducted i.e. three-phase linear resistive loading, non-linear loading with a three-phase ac/dc converter and non-linear loading with three single-phase capacitor filtered ac/dc converters. Results show that the higher load current harmonics content the higher is vibration of the three-phase generator. Non-linear loading with a three-phase ac/dc converter that generate about 24.7% THD gives an increase of 4.3% and 5.5% in average of vertical and horizontal vibrations of the three-phase generator respectively. Further, non-linear loading with three single-phase capacitor filtered ac/dc converters that generate THD as high as 74.9% gives significant increase of 28.1% and 23.6% in average of vertical and horizontal vibrations respectively.

This paper discusses the design of the low-speed single-phase AC permanent magnet generator through the modification of a squirrel cage single-phase AC induction motor. Both rotor and stator of the single-phase AC induction motor are modified. Eight permanent magnet poles are embedded in the rotor so that generator will rotate at a relatively low speed of 750 rpm and produce an sinusoidal AC voltage with a frequency of 50 Hz. The total number of stator windings and slots remains the same: four stator windings and 36 stator slots. However, the number of turns for each stator winding is increased to 600 turns. Therefore, each stator slot is housing 150 conductor turns. The permanent magnet generator is expected to generate an sinusoidal AC output voltage with a magnitude in the range of 110 -115 V when it rotates at 750 rpm. Laboratory tests with a constant speed of electric motor drive have been conducted. Results of the no-load test show that generator output voltage is 110 V when it rotates at 749.3 rpm. However, the output voltage generated is not sinusoidal as indicated by its total harmonic distortion (THD) value of 15.8%. Results of the on-load test show that generator voltage drops vary from 8.2% to 29.1% and 4.5% to 26.4% respectively on linear resistive and non-linear load. On the same loading condition, the generator efficiency varies from 53.5% to 66.7% and 32.6% to 67.5%.