Harmonics

INTRODUCTION

In recent years, with the increasing use of power electronics, the quality of electricity supply, together with energy efficiency, has become a key issue, and company energy responsibles are more and more aware of the benefits of paying attention to that.

The main representation of power quality is the harmonic distortion, which represents the deviation between the ideal sinusoidal waveform the network voltage or the load current should have, and what really it is.

Some of the effects the harmonic can cause, to the equipment, to the installation, or both, are:

• Added efficiency losses to the system composed by electrical installation and equipment.
• Unexpected resonances.
• Disturbances in electronic equipments, causing “logical” faults in digital circuits.
• Unwanted overload (or need to oversize) for transformers, wirings.
• Malfunctions of motors and generators.
• Unwanted Circuit Breakers tripping or Fuses blowing.

The harmonics mitigation can report quantifiable benefits for industry critical processes, IT systems, datacenters, etc., in terms of overall installation cost, energy bill reduction, and protection against process interruptions and equipment faults.

What is harmonics and what do you mean by harmonics

Harmonics can be described as the distortion or deviation of perfect sinusoidal waveform. It can also be explained as currents or voltages with frequencies that are integer multiples (H=0, 1, 2,…N) of the fundamental power frequency. The power panels would become mechanically resonant with the magnetic fields. generated by the harmonics, if the presence of harmonic frequency is high, because of this the panel vibrates and makes a buzzing sound. Harmonics are the by-product of modern electronic equipment, such as laptops, battery chargers, UPS, and any other equipment powered by the switched-mode power supply. The switched-mode power supply is non-linear loads. These non-linear loads will generate harmonics that they are sensitive to. The non-linear loads are classified into two types, single-phase, and three-phase. We can see single-phase non-linear loads in modern offices and three-phase non-linear loads in many factories and industrial plants.

 What is harmonics in electrical

Harmonic distortion can be seen in both current and voltage, most current distortion is generated by electronic loads also called non-linear loads. Harmonics can be caused by any distortion in the current or voltage waves. Current distortion is conducted through normal system wiring, it creates voltage distortion according to the ohm’s law. The current distortion travels only along the power path of the non-linear load, while the voltage distortion would affect all loads connected to the particular phase. Current distortion would affect the power system and distribution equipment, it may directly or indirectly cause the destruction of loads or loss of product.

What is 3rd, 9th, and 15th harmonics and what is triplen-harmonics

Electronic components generate more than one frequency, a computer could generate 3rd, 9th, and 15th harmonics, and these are called triplen harmonics. These harmonics can cause many damages because they can do more than distort voltage waveforms. Triplen harmonics can do the overheating of building wiring, tripping, transformer overheating, and equipment failure.

Effects of Harmonics to Electronic Equipment 

The Effects of Harmonics to Electronic Equipment are experienced in various ways depending on the type of device - from slight to serious consequences. Ironically, it is a known fact that most electronic equipment is prone to misoperation due to harmonic distortion, even though it is a harmonic generator itself. In this post, these common effects will be briefly discussed.

Power Electronic Equipment

This equipment is reliant upon accurate determination of voltage zero crossings or other facets of the voltage wave shape. Unfortunately, harmonics can shift the voltage zero crossing, or the point at which one phase-to-phase voltage becomes greater than another phase-to-phase voltage. These are both significant points for many types of electronic circuit controls, and the unwanted shifts can lead to equipment misoperation.

Medical Instruments

Malfunctioning medical instruments present the most serious negative effect of harmonics to electronic devices. This is because it may place a person’s life in jeopardy. For this reason, many medical instruments are provided with line-conditioned power and protected by proper power quality devices.

In addition, less dramatic interference effects of harmonics can sometimes be observed in radio and television equipment, as well as in video recorders and audio reproduction systems.

Computers and Other Electronic Devices

Computers and allied equipment like programmable controllers typically require AC sources that have no more than a 5% harmonic voltage distortion factor, with the largest single harmonic being no more than 3% of the fundamental voltage.

Harmonic distortion levels that exceed standard limits may result to malfunctioning equipment, which in some cases, have serious consequences. It must be noted that electronic devices can be disturbed by the transmission of AC supply harmonics via the equipment power supply or through magnetic coupling of harmonics into equipment components.

Moreover, other electronic instruments can be affected by harmonics by giving incorrect data or unpredictable performance (i.e. digital energy meters).

Voltage Notching

Most electronic devices are installed at the low voltage level of its associated power distribution system. As a result, they also become exposed to the effects of voltage notching. Voltage notches often introduce frequencies, both harmonic and non-harmonic, which are much higher than those exhibited in 5 kV and higher voltage distribution systems.

Subsequently, these frequencies are in the radio frequency (RF) range, which can lead into detrimental effects associated with spurious RF, such as signal interference introduced into communication or logic circuits. Sometimes, the voltage notching effect is of adequate power to overload electromagnetic interference (EMI) filters and similar high-frequency sensitive capacitive circuits.

What are the benefits of eliminating or reducing harmonics

• Avoidance of frequent capacitor failures
• Safeguards neutral conductors
• Reduces system losses
• Reduces neutral current
• Reduces local neutral to ground voltage
• Resonance elimination
• Improves voltage stability
• Shunts harmonic currents
• Reduces transformer overloading

What is total harmonic distortion

It is the number of harmonics in a distorted wave as a percentage of the fundamental. It can be described as the degree to which a waveform deviates from a purely sinusoidal.

What is harmonic blocking

If the harmonic is less, then the blocking technique is used to protect the most affected equipment an example for this is capacitor bands which are used for power factor correction offers very low impedance to high-frequency harmonics, so it could be damaged because of large current drawn due to thermal break down. So inductors or damping resistors can be connected in series to protect the capacitor bank.

How do you know if you have a harmonic problem

• Frequent tripping of circuit breaker and fuse blowing
• Capacitor failures
• Transformer neutral overloading
• Sever lamp flicker
• Excessive equipment heating
• Overvoltage
• Electrical interference

How can we reduce or remove the harmonics

Certain methods can be used to reduce harmonics they are

• Delta-Delta and Delta-wye transformers
• Isolation transformers
• Use of reactors
• Passive harmonic filters
• Active filters
• 12-pulse converter front end

Delta-Delta and delta wye transformers

In this type, it uses two separate utility feed transformers with equal non-linear loads. This shifts the phase relationship to various six pulse converters through cancellation techniques

Isolation transformers

Isolation transformers provide a good solution in many cases to mitigate harmonics generated by non-linear loads. Isolation transformers can reduce the third harmonic which is created due to the usage of the delta to a star configuration

Use of reactors

Reactors can be used to reduce the harmonics created by non-linear loads and reactors are better than isolation transformers to reduce harmonics. Reactors or inductors are used in loads such as variable and speed drives. Because of this, the AC line reactor reduces the total harmonic voltage distortion on its line side.

Passive harmonic filters

It is also called harmonic trap filters and they are capable to handle harmonics that is in lower-order like the 5th, 7th, and 11th. This can be used larger non-linear loads and single-phase smaller non-linear loads. This filter has an L-C circuit and resistor is used for damping. The L-C circuit will be tuned to a specific harmonic frequency that needs to be reduced. The entire operation is related to the resonance phenomenon and this takes place by the variations in frequency in inductors and capacitors

Active filters

Active filters are widely used, in many industrial applications. These filters can reduce harmonics and reactive power compensation. These filters are unaffected by the changes in source impedance. The active filters consist of the IGBT bridge and DC bus architecture.

12 pulse converter front end

In this, the bridge rectifier uses twelve diodes instead of six. This device can reduce the 5th and 7th harmonics and it can also reduce the higher-order harmonics like 11th and 13th. This will not eliminate the harmonics but it reduces the magnitude of the harmonics.