What is harmonics and how can we reduce harmonics

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 are the effects of harmonics and what are the problems created by harmonics

In an electrical distribution system, harmonics can create large load current in the neutral wires of a three-phase system and this would overheat the neutral wire and could result in a fire hazard. Harmonics can overheat the electrical supply transformers and it would affect the transformer life and it would be damaged quickly. It can create overheating and mechanical oscillations in the motor load system.

Problems created by harmonics

  • Produces rotating magnetic field, which is opposite to the fundamental magnetic field
  • Neutral and ground conductors would be damaged and also causes overheating
  • Malfunction of sensitive Tele-control and protection relaying
  • False or spurious relay operations and trips of circuit breakers
  • Mal operation instability of voltage regulator
  • Failure of communications circuits in DC motor drives and AC drives
  • Capacitor bank would act as a sink for higher harmonic current

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.

What are the loads that produce harmonics and sources of harmonic generation

Loads producing harmonics

  • Electronic lighting ballasts/controls
  • Adjustable speed motor drives
  • Electric arc welding equipment
  • Solid-state industrial rectifiers
  • Industrial process control systems
  • Uninterrupted power supply systems
  • Saturated inductors/transformers
  • LAN/computer networks

Sources of harmonics generation

Transformers are the source of voltage harmonics, it causes a magnetic saturation or magnetic distortion due to the presence of a DC component. Converters in the HVDC system could generate harmonics in AC and DC. Harmonics are caused by firing angle errors, negative sequence components in the converter bus AC voltage, and unequal converter transformer leakage impedances.

What is linear and non-linear loads

A linear load is a load that has a linear relationship between the current and voltage. When a sinusoidal voltage is applied linear loads it absorbs a sinusoidal current. If this linear relationship is not verified, the load is termed non-linear. It absorbs a non-sinusoidal current and thus harmonic currents, even when it is supplied by a purely sinusoidal voltage.

What causes 3rd, 5th, and 7th harmonics

Mostly third harmonics are created by electronic components, it is the current harmonics and is created due to the non-linear loads. The 5th and 7th harmonics are mostly created by synchronous machines.

Fundamental frequency 50Hz (the lowest frequency)

Third harmonics: 150 Hz (3*50Hz)

Fifth harmonics: 250 Hz (5*50Hz)

By measuring the harmonics we could know the distortion of voltage or current. This distortion can be produced by magnetic saturation in the core of transformers or by the switching of thyristors or IGBT’s electronic drive.

How can we wire electrical distribution system for harmonics

  • Use double size neutral wire or separate neutral for each phase
  • Specify a full separate size insulated ground wire rather than relying on the conduit alone as a return ground path
  • We can use isolated ground wire for sensitive electronic and computer equipment in a branch circuit
  • Oversize phase wires to minimize voltage drops on branch circuits
  • Shorten the distance on branch circuit from the power panel to minimize voltage drop
  • Segregate sensitive electronic and computer loads on a separate branch circuit all the way back to the electrical panel

How harmonics are generated and what are the main causes of harmonics

Harmonics are produced by non-linear loads, and these loads will create harmonics by drawing current in a short pulse, rather than in a smooth sinusoidal manner. Harmonics are created when there is a large number of electronic devices such as personnel computers, UPS, etc. The electronic devices work by converting the incoming AC-DC and it is done by using solid-state power switching supplies.

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.