Received 4 March 2016; accepted 7 May 2016; published 10 May 2016
Construction of three-phase transformer is basically a single-phase transformer that is arranged into three pieces in the iron core. A transformer consists of a coil and an iron core. Usually there are two coils, namely the primary coil and the secondary coil. The two coils is not related physically but connected by a magnetic field  .
By the standards of IEC (International Electro technical Commissioning) 1000.4 - 11, they’re classified into harmonic interference waveform distortion   . In this phenomenon changes the waveform of the wave base. Harmonics are sinusoidal voltage or current wave having a frequency which is the product of the integer (integer) of the fundamental frequency, wherein the supply system is designed to operate (typically 50 or 60 Hz). Basically harmonics are symptom formation of waves at different frequencies. It is called frequency harmonics arising from the original waveform, while integer multiplier fundamental frequency is called harmonics sequence number. Here is an example of a comparison of the basic waveform and harmonic wave   .
The level of disability in harmonics often expressed with Total Harmonic Distortion (THD), Total Harmonic Distortion, used as a gauge to see how much influence the overall presence of harmonics has to the sine signal. Because it is so large and varied effects of harmonics on equipment and systems are technical and economical, it is necessary to standardize the harmonics. Standards governing the harmonic distortion are the IEEE 512-1992 standard, this standard set of harmonics allowable limits (Table 1)  .
Saturation is a condition in which the magnets are fully transformer cores and generate maximum magnetic flux. This usually happens if the transformer is not big enough for the application. While some parts affect the resilience and create distortions that can harm the heart. Core saturation can also increase the temperature and magnetization current transformer. In saturation, as the transformer core and current harmonics generation sources, some of it will flow directly to the primary and secondary windings. Results of previous studies show that the harmonic content increases significantly when the current no-load and high magnetic flux density injects. Today many transformers are widely disturbed by harmonics. Harmonic components have caused losses in the transformer which allows fails to operate.
2. Research Method
2.1. Material Research
Specifications transformer is used as the test material is as follows  :
The manufacturer: PT. Trafoindo Prima Perkasa
Power (s): 630 kVA
Number of phase: 3 phase
Impedance (Z): 4%
Cooling System: ONAN
Primary voltage: 20 KV
Secondary Voltage: 400/230 V
Core material: laminate M4 grain-oriented electrical steel (H1-Carlite)
Thickness of laminate: 0.27 mm thickness
Table 1. IEEE Standard 512-1992, harmonic current limitation  .
2.2. Measuring Instrument
Measurements were made with the simplest tool in measuring current and voltage that is ampere meter and voltmeter. Ampere meter used to measure the current value of the magnetization in the transformer. While the volt meter is used to measure the value of the voltage on the transformer. VVVF used as a voltage regulator and also the frequency at this time of measurement. Where the input voltage is connected with the core and frequencies connected to the secondary side of the transformer in Figure 1.
2.3. Circuit Testing
Testing is done by measuring the transformer core, where the ampere meter is connected to the input voltage and variable frequency (VVVF). On the secondary side of the transformer and on the primary side is connected to the VVVF and volt meter. Transformer testing lowered the ratio of 1.1. Measurements were performed with different flux density, which is done by varying the input voltage while the frequency is kept constant (fixed). Measurements were taken at each phase that is phase R, S, T, so that the measurement results has equal value or balanced on each phase. The series of measurements carried out as Figure 2.
2.4. Collect of Data
From the measurement results obtained:, then Irms is as follows:
From the calculation Irms = 2.69136 A, the total harmonic current distortion (THDi) is as follows:
Figure 1. Sanwa PC 720 M digital multimeter and variable voltage variable frequency (VVVF)  .
Figure 2. The measuring circuit transformer core  .
3. Results and Discussion
The phenomenon of harmonics in this case distorted total harmonic currents (THD) and the magnetization current (Io) of the transformer in the magnetic flux density that varies at a frequency of 50 Hz shown in Table 2.
The relationship between the magnetization current and total harmonic current distortion (THDi) of the magnetic flux density at a frequency of 50 Hz is shown in Figure 3 and Figure 4. While the curve of the power factor of the magnetic flux density is shown in Figure 5.
The evaluation results magnetization current (Io), total harmonic current distortion (THDi) and power factor are shown in Table 2. Stimulation magnetization current Io on the flux density B = 1.7 T (i.e., Io = 0.95 A) almost doubled compared to 1.5 T (Io = 0.698). Meanwhile, THDi increases when the transformer that is charged with a magnetic flux density is higher. On the condition of flux density of 1.5 T and 1.7 T waveform is not sinusoidal currents that occur, as happened in Figure 5. While the flux density of 0.1 - 1.4 T shape of the current waveform is sinusoidal or perfect. This indicates that the flow has been distorted. Characterized by the core saturation current waveform is not sinusoidal or irregular.
Increased THD is very significant when a flux density of 1.5 T density change-1.9 T. This indicates that the core of transformer laminations experiencing burnout. Figure 3 and Figure 4 also shows that the pattern of Io and THDi the density flux density is almost the same with the B-H curve of a magnetic material. Besides saturation characterized by the value of the magnetic flux THD at 1.5 T with a value 25.93%. Where the value of THD
Figure 3. Curves total harmonic current distortion (%) of the magnetic flux density.
Figure 4. Power factor curve of the magnetic flux density.
Figure 5. Magnetization current curve of the magnetic flux density.
allowable standards for electrical appliances maximum is 25% (IEEE 519-1992). As mentioned in Equation (7), the power factor is inversely proportional to THDi. This phenomenon is shown in Table 2 or Figure 4 It is clear that the power factor decreases significantly when a changing magnetic flux density of 1.5 T to 1.9 T. This can also be an indication that core transformer laminations have been experiencing burnout.
1) Analysis of the test data show a high magnetic flux density contributing more to the magnetization current, the phenomenon of high harmonics and power factor is low on the magnetic flux density that occurs in the normal operation of the actual transformer which is 1.5 Tesla or 1.7 Tesla.
2) The pattern of magnetization current and total harmonic distorted the magnetic flux density is almost the
Table 2. The calculation result THDi and power factor on the flux density that varies.
same as the curve B - H of the magnetic material (shown in the image above).
3) THDi of the transformer. When the 1.5 Tesla magnetic flux exceeds the standard IEEE 519-1992 i.e. 25% of the capacity of the transformer, then the transformer experiencing saturation condition is characterized by the onset of heat on the transformer.
4) This phenomenon can be used as an indicator to show that a 1.5 Tesla transformer core material has led to saturation.