Effect of Harmonics on Electric Power System
Harmonics are periodically distorted waves that occur in voltage, current, or power waves consisting of sine waves whose frequency is a multiple of the fundamental frequency of the source, so the shape is not sinusoidal. The relationship between harmonic and fundamental frequencies can be written as follows:
f_h = nf_i \ ldots(1)
With f_h is the harmonic frequency, nis the wave multiplier (integer), and f_i is the fundamental frequency. This harmonic wave will ride on the fundamental wave so that the wave will be distorted. This is due to the summing effect of the harmonic wave with its fundamental wave. This harmonic wave can be described in the following Fourier series:
f (t) = \ frac {a_0} {2} + \ sum_ {h + 1} ^ {\ infty} \ {a_h \ cos (h \ omega_0t) + b_h \ sin (h \ omega_0t) \} \ ldots(2)
with:
a_0 = \ frac {1} {T} \ int_ {0} ^ {T} f (t) dt \ ldots(3)
a_h = \ frac {2} {T} \ int_ {0} ^ {T} f (t) \ cos (h \ omega t) dt \ ldots(4)
b_h = \ frac {2} {T} \ int_ {0} ^ {T} f (t) \ sin (h \ omega t) dt \ ldots(5)
a_0 is a DC component, whereas Ah and b_h is an AC component.
The role of harmonics in electrical power systems is quite large, especially in the tools contained in the power system. Harmonics will cause some impacts such as excess heat on some devices such as generators and transformers because of the tendency of harmonics to flow to places with lower impedances. Some other impacts will be explained in this article. The harmonic magnitude parameter is expressed in Total Harmonic Distortion (THD) which can be written as:
For voltage,
THD_V = \ frac {\ sqrt {V_2 ^ 2 + V_3 ^ 2 + V_4 ^ 2 + \ cdots + V_n ^ 2}} {V_1} \ ldots(6)
For the current,
THD_I = \ frac {\ sqrt {I_2 ^ 2 + I_3 ^ 2 + I_4 ^ 2 + \ cdots + I_n ^ 2}} {I_1} \ ldots(7)
Based on the agreement agreed upon by the international community, THD received is when it is worth under 5% of the voltage or current fundamentalnya.Apabila above the limit then the electronic devices should not be used.
The effects of harmonics can not be eliminated completely, but can be reduced. There are several ways commonly used in reducing harmonics, namely by the use of passive filters such as the installation of capacitors, the addition of the number of phases, and compensation or injection of negative harmonics.
There are three kinds of sequence of phase and sequence of harmonics are:
The positive phase sequence, the order of the phase is the RST between the separate phase 120 0 . The order of harmonization is n = 1, 7, 13, ....
The negative phase sequence, the order of the phase is the RTS between the separate phase 120 0 . The order of harmonization is n = 5, 11, 17, ...
A zero sequence that has phase difference equals zero (in phase). The order of harmonization is n = 3, 9, 15, .... There are two types of load on the system ketenagalistirikan.Beban consists of linear load and non- linear load. The load is called linear if the current value is linearly proportional to the load voltage. Means the current waveform will be the same as the voltage waveform.
The load is called a non-linear load if the current waveform is not equal to the voltage waveform (distorted). Non-linear load-pulled currents are not sinusoidal but periodic. Non-periodic waveforms can be described based on fundamental components and harmonic components. Non linear loads such as semi conductors are used as switching devices. This non linear load serves as a source of harmonics in electrical systems .
In electric power system non linear load sources are derived from static converter, nonlinear transformer magnetization, engine speed AC current, capacitor bench and others.
INFLUENCE OF HARMONISA IN POWER SYSTEM
Protection System
In protection system equipment, harmonics can cause:
Decreased rating (derating) due to warming that occurred.
Causes increased heating and switchgear losses, thus reducing current-carrying capability and shortening the life of some isolator components.
The emergence of mechanical vibrations in electrical panels which are mechanical resonance vibrations due to high frequency current harmonics.
Harmonics may induce additional torque on kWh-meter electromechanical type using rotating induction disks, consequently faster disc rotation or measuring error at kWh-meter because the induction disk is designed only to operate at the base frequency.
Triple harmonics on neutral wire can provide harmonic induction which disrupts the telecommunication system.
The load breaker may work under its rated current or may not work on the rated current. For the power system, the current on the neutral wire is enlarged (mainly due to the emergence of the 3rd harmonic multiplier) and the touch tension of the enlarged and dangerous equipment for the operator.
