ABB RELION 620 Series Technical Manual page 696

Section 8
Power quality measurement functions
690
GUID-D61DBDF6-7C1B-492E-94CB-C6A2EC7C1463-ANSI V1 EN
Figure 350: Duration and voltage magnitude limits for swell, dip and interruption
measurement
Voltage dips disturb the sensitive equipment such as computers connected to the power
system and may result in the failure of the equipment. Voltage dips are typically caused
by faults occurring in the power distribution system. Typical reasons for the faults are
lightning strikes and tree contacts. In addition to fault situations, the switching of heavy
loads and starting of large motors also cause dips.
Voltage swells cause extra stress for the network components and the devices connected
to the power system. Voltage swells are typically caused by the earth faults that occur in
the power distribution system.
Voltage interruptions are typically associated with the switchgear operation related to the
occurrence and termination of short circuits. The operation of a circuit breaker
disconnects a part of the system from the source of energy. In the case of overhead
networks, automatic reclosing sequences are often applied to the circuit breakers that
interrupt fault currents. All these actions result in a sudden reduction of voltages on all
voltage phases.
Due to the nature of voltage variations, the power quality standards do not specify any
acceptance limits. There are only indicative values for, for example, voltage dips in the
European standard EN 50160. However, the power quality standards like the international
standard IEC 61000-4-30 specify that the voltage variation event is characterized by its
duration and magnitude. Furthermore, IEEE Std 1159-1995 gives the recommended
practice for monitoring the electric power quality.
1MAC504801-IB E
620 series ANSI
Technical Manual