Voltage Dip

According to internationally adopted definition (under European standard EN 50160), a voltage dip occurs when the voltage drops to a level below 90% of standard power supply voltage
Most voltage dips last for less than 0.1 second before the standard power supply voltage is restored
During a voltage dip, the power supply is not interrupted

A voltage dip can be triggered by a variety of factors: (see illustration below)

Overhead transmission lines intervened by external factors, such as adverse weather, overgrown vegetation and wild animals, etc.
Underground cables damaged by third party
Failures of power supply equipment

No power systems over the world can completely avoid voltage dips.

Some customers may experience momentary dimming or flickering of their lights
Some electrical installations sensitive to voltage fluctuation, such as lifts, may trip as a result of the activation of the equipment’s protection mechanism
Under special circumstances, loss of electricity supply may occur especially in very hot summer when families are using air conditioners. When voltage levels return to normal, the simultaneous reactivation of air conditioners will spike up the electricity current to three to seven times above the normal level. This may cause the main power switch of buildings to trip and result in power outage

CLP encourages customers to opt for equipment that has “ride-through” capabilities, e.g. an Uninterruptible Power Supply (UPS), a voltage stabiliser and an appropriate protection device
If a voltage dip leads to power interruption, CLP advises customers to turn off power supply of their electrical appliances like air conditioners and seek help from the building management office. If the main power switch of the building has been tripped, it should be reset by a qualified electrician to restore normal supply
CLP’s Power Quality Team is happy to offer professional advice to interested customers