PHASE ANGLE REGULATOR - PROTECTION
Electromechanical type Differential Protection
In the past, the differential protection for the PAR
(Fig.2) would require six single phase
electromechanical type transformer differential relays -
three for the primary differential system - 87P, and
another three for the secondary differential system ~
87s. A single phase differential electromechanical
relay is set to respond on per-phase differential current,
that may result from summation of the electrically
connected source, load and exciting unit primary
currents, as part of the primary differential protection.
A single phase differential electromechanical relay is
also set on per phase basis, and respond on differential
current, that may appear during internal for the series
and exciting unit secondary winding faults, as includes
the source, load and exciting unit secondary winding
currents. To set electromechanical relays for protection
of the primary differential system, no special treatment
is required, as it is similar to providing differential
protection on autotransformer. However, applying
electromechanical relays for protection of the
secondary differential system, (Figure 3) would require
the load and source side CTs to be connected in delta,
interposing auxiliary CTs for magnitude compensation,