**3. Harmonic mitigation**

212 Power Quality Harmonics Analysis and Real Measurements Data

Harmonic distortion may or may not create a problem for own facility. A plant may have harmonics present, but experience no adverse effects. However, as harmonic levels increase,

To make matters worse, harmonics can sometimes be transmitted from one facility back through the utility's equipment to neighbouring businesses, especially if they share a common transformer. This means harmonics generated in one facility can stress utility

Electric utilities have recognized this problem and are adopting standards, like the Institute of Electrical and Electronics Engineers (IEEE) Standard 519 which defines allowable harmonic distortion at customer service entrances. This standard is designed to protect both businesses and utilities, many other standards are also available and set limits for such

Harmonic analysis, load flow analysis, and power factor correction in Metal Scrab plant in Saudi Arabia, were considered for two reasons: 1) the planned installation of a new Induction furnace; and 2) the correction of the overall plant power factor to a value above

The voltage across an electric arc, which is relatively independent of current magnitude, consists of three components, anode drop, cathode drop and arc column component; which

Typical values of arc voltages are in the range of 150-500 volts. Since the arc is extinguished at current zero, the power factor plays an important role on arc re-ignition. The figure 1. shows how arc voltage, power factor, input power; arc power and reactive power vary with arc current for a particular tap setting on the furnace transformer. The furnace is normally

operated near maximum arc power, which corresponds to a power factor of 70% [9].

the likelihood of experiencing problems also increases. Typical problems include:

Overheating in neutral conductors, transformers, or induction motors

equipment or cause problems in other neighbour's facility and vice versa.

Deterioration or failure of power factor correction capacitors

Pronounced magnetic fields near transformers and switchgear

Malfunctioning of microprocessor-based equipment

Erratic operation of breakers and relays

0.90 lagging to eliminate utility penalties.

**2. The behavior of electric arc furnace** 

amount to about 12 volts/cm of arc length.

Fig. 1. Electrical Characteristics of Electric Arc Furnace

harmonic penetration.

Several methods of mitigating harmonics have been developed over the years. The most common method is using filter, either passive or active. Passive filter block certain harmonic bandwidth while active filter injects current into the system to cancel the current harmonic waveforms. Both methods have their advantages and disadvantages, for example, advantage of passive filter is easy to design and active filter can monitor many frequencies simultaneously while disadvantage of passive filter is bulky in size and active filter is costly. Harmonic filters are useful and practical to be implemented by consumer near the proximity of the non-linear load at the low voltage system. Another method which is normally used by consumers is using phase cancellation method using twelve pulse converters instead of six pulse converters [12].

Similar application using filters for utility at higher voltage level such as distribution network requires extensive economic consideration. This is due to the size and cost of the equipment while most of harmonic pollutant is caused by consumer. There is little study on a feasible and cost effective means for utility to mitigate harmonic, especially harmonic voltage. A study was conducted on method using shunt harmonic impedance which can act like a central damper to reduce harmonic at distribution network [13]. This method is considered to be less expensive compared to active filter. The method uses power electronic to emulate resistive behavior for harmonic. However, the method is still under further study. Currently, all harmonic mitigation techniques involve equipment required to be installed on the system. There is yet a study on using other factors which can affects harmonic voltage distortion such as network impedance. Optimizing network impedance to mitigate harmonic can be cost effective for utility to apply. Because of mitigating harmonic is expensive, many utility company have resorted in imposing penalty to consumer for injecting current harmonic above the standard steady state limit into the system. This process requires method of determining harmonic contribution by the consumers and the equipment need to be installed at all consumers' feeder which is very costly[13].

Harmonics Effect in Industrial and University Environments 215

1 230.00 1.00 0.00 1.24 0.98 2 34.50 0.99 -2.30 2.95 0.99 3 34.50 0.99 -2.30 2.95 0.99 5 34.50 0.99 -2.30 2.95 0.99 45 0.48 0.95 -4.00 2.92 0.97 46 0.48 0.95 -4.10 2.92 0.97

Single-tuned filters were designed for the metal plant system according to the next paragraph theories and its input data are provided in table 2. The results of load flow, total harmonic distortion, and power factor of buses 1, 2, 3, 5, 45, and 46 after installing filter are shown in table 3. Also the spectrum and waveform of bus 34.5 kV is provided in figure 3.

Harmonic filters are designed to suppress system harmonics as well as to improve power factor. They allow a system to meet IEEE Standard 519 harmonic limits while avoiding power factor penalties. Filter designs are tailored to individual project objectives such as meeting a harmonic limit and/or a power factor level. This is a complex and involved engineering task, where alternative designs are checked to ensure that the final one will

Typically, single tuned shunt filters are designed with a reactor and capacitor in series, connected as a shunt load on the system. In more complex studies, other types of filters, like 2nd or 3rd order, C-type, and/or double tuned filters are designed. In a complex filter design,

LF Angle (deg)

THD

(%) Pf

LF Voltage (p.u)

Bus #

Nominal Voltage (KV)

Table 3. Load Flow, THD, and Power Factor Results

Fig. 3. Spectrum of voltage at bus 34.5 kV

**5. Filter design** 

meet study objectives [14].
