Voltage dips and interruptions

Voltage dips and interruptions

Fig.: Example: Voltage dips due to bird droppings
Fig.: Example: Voltage dips due to bird droppings

Voltage drops can lead to huge complications – for example the failure of production processes – and to quality problems. Such voltage drops arise much more frequently than interruptions. The commercial effects of voltage drops are seriously underestimated time and again.

What is a voltage drop?

According to the European standard EN 50160 a voltage drop is a sudden lowering of the effective voltage value to a value of between 90% and 1% of the stipulated nominal value, followed by the immediate reinstatement of this voltage. The duration of a voltage drop lies between a half period (10 ms) and one minute.

If the effective value of the voltage does not drop below 90% of the stipulated value then this is considered to be normal operating conditions. If the voltage drops below 1% of the stipulated value then this is considered an interruption.

A voltage drop should therefore not be confused with an interruption. An interruption arises, for example, after a circuit breaker has tripped (typ. 300 ms).The mains power failure is propagated throughout the remaining distribution network as a voltage drop.

The diagram clarifies the difference between a drop, a short interruption and an undervoltage situation.

Voltage variations are caused by:

  • Short circuits
  • Switch-on and switch-off processes with large loads
  • Starting drives (larger load)
  • Load changes with drives
  • Pulsed power (oscillation package controls, thermostatic controls) • Arc furnaces
  • Welding machines
  • Switching on capacitors
  • Construction works
  • Bird droppings
Fig.: Critical voltage dip with production standstill
Fig.: Critical voltage dip with production standstill

Voltage drops can lead to the failure of computer systems, PLC systems, relays and frequency converters. With critical processes just a single voltage drop can result in high costs, continuous processes are particularly impacted by this. Examples of this are injection moulding processes, extrusion processes, printing processes or the processing of foodstuffs such as milk, beer or beverages.

The costs of a voltage drop are comprised of:

  • Loss of profits due to production stoppage
  • Costs for catching up with lost production
  • Costs for delayed delivery of products
  • Costs for raw materials wastage
  • Costs for damage to machinery, equipment and moulds
  • Maintenance and personnel costs
Fig.: Motor start-up currents can lead to a voltage dip
Fig.: Motor start-up currents can lead to a voltage dip

Sometimes processes run in unmanned areas in which voltage drops are not immediately noticed. In this case an injection moulding machine, for example, could come to a complete standstill unnoticed. If this is discovered later there will already be a large amount of damage.The customer receives the products too late and the plastic in the machine has hardened off.

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