NET PHENOMENA WE ENCOUNTER EVERY DAY

Network quality is not a new topic, although it has come more and more into focus in recent years due to an increasingly high-tech and also more vulnerable world. The consideration and the limits for the electrical phenomena are derived from the standardisation for electromagnetic compatibility (EMC) according to IEC 61000-x-x.

Even though at first glance we have a very reliable supply of electrical energy, every day we encounter phenomena in the electrical grid that can become serious problems for people, machines and the environment, either individually or collectively. In 2007, a study put the economic damage caused by network phenomena at 157 billion euros per year, with a strong upward trend.

The network phenomena according to IEC61000-x-xx (EMC) in detail

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network frequency


In the event of an oversupply of electrical power, the grid frequency increases; in the event of an undersupply, it decreases. Normally, these deviations are minimal in the Western European interconnected grid and are less than 0.2 Hz. If there is a massive imbalance between the supply and demand of electrical power due to non-compensable faults, correspondingly strong grid frequency fluctuations are the result.

Causes:

  • Omission of power generators
  • Large load changes

Possible consequential problems

  • Instability of the supply grid

Power supply voltage level


A change in the network load can lead to a (short-term) change in the level of the supply voltage,

Causes:

  • Changes in the network load

Possible consequential problems

  • Malfunction of operating equipment
  • System shutdown
  • Data loss

Flicker

Frequent rapid voltage changes result in light fluctuations called flicker, which can cause eye fatigue, discomfort and dizziness in humans.

The causes of flicker are often welding machines, arc furnaces, X-ray equipment, wind turbines as well as drives with shock loads

Causes

  • Frequent load changes
  • Engine start

Possible consequential problems

  • Flickering of the lighting
  • Impairment of the work performance of exposed persons

Dips / surges in the supply of the voltage. Rapid Voltage Changes (RVC)


In the event of voltage dips (often interpreted as transients), the voltage rms value drops to values between 1% and 90% of the nominal voltage, caused by short-term, high mains loads, especially in networks with low short-circuit power. This is caused by high starting currents of large motors, which are many times the rated current. The same applies to motors that have to start under high load.

Cause

  • Large load changes
  • Short circuit, earth fault
  • Thunderstorm
  • Overload of the power supply
  • Feeding in renewable energies such as wind or photovoltaics

Possible consequential problems

  • Malfunction of operating equipment such as controls or drives
  • Interruption of service
  • Data loss in control systems and computers

Voltage interruptions


An interruption refers to the complete loss of voltage or current. A distinction is made between a long-term interruption (longer than 3 min.) and a short-term interruption (up to and including 3 min.)

Causes

  • Short circuit
  • Blown fuses
  • Component failure
  • Planned interruption of supply

Possible consequential problems

  • Loss of production
  • Process interruptions
  • Data loss in control systems and computers

Unbalance of the supply voltage

Due to uneven distribution of single-phase loads and the operation of two-phase loads, transformers are asymmetrically loaded. The active load of the consumers is responsible for uneven phase voltages and the reactive load ensures deviations of the phase shifts from the ideal 120 degrees.

Causes:

  • Unequal load on the phases due to single-phase or two-phase consumers

Possible consequential problems

  • Current in the neutral conductor
  • Overload / overheating of equipment
  • Increase in harmonics

Harmonic voltages


Harmonics are sinusoidal components superimposed on the voltage or current fundamental. They arise from non-linear consumers in the grid. The ratio of the harmonic frequency to the network frequency is called the ordinal number h. Integer multiples of the mains frequency are called harmonics. If the result is a non-integer multiple, then one speaks of intermediate harmonics.

Causes:

Non-linear loads such as frequency converters, rectifiers, switching power supplies, arc furnaces, computers, fluorescent tubes, etc.

Possible follow-up problems:

  • Reduction of machine efficiency
  • Increased energy losses
  • Overload / overheating of equipment
  • Current in the neutral conductor

Interharmonic voltages, voltages for signal transmission


Interharmonics are sinusoidal oscillations whose frequency is not an integer multiple of the fundamental frequency of 50 Hz.

Causes:

  • Frequency inverters and similar control devices

Possible follow-up problems:

  • Flicker
  • Ripple control failure

Transient

Transient overvoltages, often confused with rapid voltage change (RVC), are high-frequency events with the duration of less than one network period. Voltage peaks of up to several kV occur. These only last for a few milliseconds. In addition, a key characteristic of transients is that the waveform of the sinusoid is significantly affected for a short duration.

Transients are mainly caused by operational switching events on the grid, lightning strikes and short-circuit tripped fuses and circuit breakers.

Acquisition of fast transients, e.g. according to IEC61000-4-4, usually requires a cost-intensive separate measuring channel with a very high sampling rate.

Possible causes:

  • Lightning, switching operations

Possible follow-up problems:

  • Destruction of equipment
  • Data loss
  • System shutdown