Digital Distance Protection Relay

The distance protection is a multi-system device with functions for protecting overhead lines and cables at all voltage levels from 5 to 765 kV. All types of neutral point treatment (resonant earthing, isolated, solid or low-resistance earthing) are reliably coped with. The unit can issue three-pole OFF commands as well as ON commands. The unit can be used as backup protection for all differential protection devices.

Protection functions

• Overload protection (ANSI 49)
• Distance protection with excitation I> (ANSI 21, 21N)
• Overvoltage protection /undervoltage protection U>, U< (ANSI 59, 27)
• Frequency protection (ANSI 81)
• Sensitive earth fault current measurement

Five independent distance zones and one separate overreach zone are available. The integrated fault locator calculates the fault impedance and the distance-to-fault. The results are displayed in ohms, kilometres (miles) and in percent of the line length. Parallel line compensation and load current compensation for high-resistance faults is also available.

The unit provides extensive information on the fault history with time stamp. The following information is stored in a fail-safe manner:

• Fault logs
  The last eight fault events are stored. The assignment of individual events is accurate to the millisecond.
• Event messages
  All events that are not directly connected to a network fault (e.g. monitoring messages, switching actions) are stored in the event memory.

Large, easy to-read backlit display is provided. The serial RS232 PC interface accessible from the front of the unit permits quick access to all parameters and fault event data. The use of the optional DIGSI 4 operating program is particularly advantageous during commissioning.