Perhaps you didn’t know that the Bitronics 70 Series Single Line Recorders have the ability to provide a distance-to-fault determination. The 70 Series Recorders employ an impedance based Modified Takagi Method, as described in ANSI C37.114 to calculate a distance-to fault, and this value is provided as a register or point value that can also be displayed on the optional 70 Series display. This Modified Takagi Method has the following characteristics:

• Well-recognized, standardized implementation
• Single-ended impedance-based algorithm
• Simple, doesn’t require knowledge of source impedance
• Good for about ±5% accuracy on dead-short faults
• Good for line-line and line-ground faults

How does it work? The user fills in some information on the line settings page of the 70 Series Configurator software program. This includes the line length, direct line impedance and phase angle magnitude, and the zero sequence compensation magnitude and phase angle.

The user then sets up triggers on the trigger page for each phase (triggers can include exceeding RMS threshold values, status inputs from other devices like protection relays, or logical combinations of event conditions) and selects “Fault Analysis” for the corresponding trigger(s). The phase that the trigger condition applies to is indicated in the “Fault Distance” Box. Other recordings (waveform capture, disturbance recording, Sequence of Event) can be selected as well with each trigger.

 

Logic for the typical condition shown above is shown in the following table:

 

Imbalance, either line-line OR line-ground as indicated by the Sequence Magnitudes, asserts Virtual Output 1 (VO1), a “soft
point.” High IA AND the soft point representing imbalance (VO1), asserts VO2. This in turn triggers the Fault Analysis calculation, disturbance recordings, and an entry in the SOE Log. The B and C phases would be setup similarly using VO3 andVO4 respectively.

What is the Outcome?

When triggered, the recorder determines:

• Distance-to-fault
• Type of fault (line-line, line-ground, phases involved)
• Peak fault current

The outputs from the distance-to-fault calculation can include:

• Local display
• DNP3 SCADA Points
• Binary targets (discrete I/O, communications)
• SOE Log entry