Sudden, pressure relay supervisory apparatus

In a power system network of at least one phase including:

• at least one power transformer disposed in a sealed enclosure and susceptible to internal and external faults, said power transformer including a plurality of windings for said power system phase;
• means for measuring the current in each winding of said transformer associated with said phase and for generating signals correspondingly representative thereof;
• a differential protective relay unit for generating a restraint signal from each generated current signal and for selecting the generated restraint signal having the greatest amplitude;
• a sudden pressure relay (SPR) operative to detect a faulty condition of said transformer and to generate a fault signal indicative thereof;
• and a breaker for each winding of said transformer associated with said phase, said breakers operative conditionally in response to said SPR generated fault signal to isolate the windings corresponding thereto from said power system network, a sudden pressure relay supervisory unit comprising:
• means responsive to an event including the occurrence of said selected restraint signal, associated with said power system phase, exceeding a predetermined level to block said SPR generated fault signal from operating said breakers, said blocking means being operative to relieve said blocking condition when said selected restraint signal is rendered below said predetermined level;
• and
• means for delaying relief from said blocking condition for a predetermined time period from the occurrence of an event including said selected restraint signal rendered below said predetermined level.

In a three-phase power system network including:

• at least one power transformer disposed in a sealed enclosure and susceptible to internal and external faults, said power transformer including a plurality of windings for each phase of said network;
• a corresponding plurality of current measuring means for each phase, each for generating a signal representative of the current in its corresponding winding;
• a differential protective relay unit (DRU) for each phase, each DRU responsive to the generated current representative signals corresponding to the phase associated with said DRU to generate corresponding restraint signals and to select from said generated restraint signals the one with the greatest amplitude;
• a sudden pressure relay (SPR) operative to detect a faulty condition of said transformer and to generate a fault signal indicative thereof;
• and breaker means operative conditionally in response to said SPR generated fault signal to isolate the transformer from said power system network, a sudden pressure relay supervisory unit comprising:
• first, second and third means corresponding to the three phases of the power system network, each of said first, second and third means being responsive independently to an event including the occurrence of the phase corresponding selected restraint signal exceeding a predetermined level to initiate a phase corresponding blocking condition to block said SPR generated fault signal from operating said breaker means, each of said first, second and third means being operative to relieve solely the blocking condition initiated thereby when the phase corresponding selected restraint signal is rendered below said predetermined level;
• and
• means for delaying relief from said blocking condition for a predetermined time period from the occurrence of an event including all of said selected restraint signals rendered below their corresponding predetermined levels.