Distance Protection Relay, ANSI 21 (SYMAP®)

Distance protection (ANSI 21), impedance-based line protection

Distance protection (ANSI 21) measures the impedance between the relay location and a fault, and provides fast, selective tripping based on line impedance and zone reach. It is the primary protection for MV lines where simple overcurrent does not provide adequate selectivity, including lines feeding industrial plants.

SYMAP^® Y-D uses ANSI 21 BP (Backup Protection) impedance protection with two independent circular zones in the R/X diagram, intended as backup impedance protection rather than full line distance protection. Full distance protection (ANSI 21) with five impedance zones (Z1, Z5) is provided by SYMAP^® Compact+ in the F3/F4/+F3/+F4/+GC configurations with the 21 option.

Typical applications

MV distribution lines

Overhead and cable MV lines with polygonal or circular characteristic. Impedance zones Z1, Z5 with project-specific zone reach and timing per coordination study.

MV lines feeding industrial plants

MV lines feeding refineries, steel mills and other industrial plants. Distance with power-swing blocking, switch-onto-fault and out-of-step logic.

Tee-tap and parallel-line configurations

Tee-tap lines with infeed from multiple sources, parallel lines with cross-coupling. Specialised zone reach and directional logic per system study.

Cable lines and mixed overhead/cable

Distance protection on cable lines and mixed overhead/cable circuits, with cable-specific impedance settings and reach correction.

Backup protection for line differential

Distance as backup to primary line-differential protection (87LD). Coordinated trip times, communication-aided tripping schemes (POTT, DCB, DCUB).

HIMAP-D retrofit

For legacy HIMAP-D distance panels, a project-specific retrofit is coordinated with HQ Hamburg, with the same panel cut-out and a modern distance algorithm.

Compact+ or classic SYMAP^®?

SYMAP^® Y-D provides ANSI 21 BP backup impedance protection with two independent circular zones in the R/X diagram, not full line distance protection. SYMAP^® Compact+ (+F3 or +F4 with 21 OPTION) suits applications where distance is one of several functions in a compact feeder or connection bay.

Products covering this application

Need detailed technical specifications?

For exact protection function coverage, settings ranges, ANSI device numbers, CT/VT specifications, communication protocols and configuration support, contact our team to receive the relevant datasheet and engineering proposal.

Request datasheet Engineering inquiry

Availability of individual functions depends on the selected SYMAP^® / SYMAP^® Compact+ variant, Order Code, measuring inputs, CT/VT/PT configuration, binary inputs and outputs, communication options and project verification. For every specific application the single-line diagram, CT/VT ratios, line parameters, network earthing, coordination study and required communication scheme must be checked.

Distance protection (ANSI 21)