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Percentage-Differential Powered By Docstoc

                                                  For the protection of AC rotating
                                                machinery and power transformers.

Features and Benefits                                Protection and Control
I   Single- and three-phase units                    I   Fixed slope percentage-differential
I   Various percentage slopes available
I   Electrically operated target seal-in unit
I   Restraint current matching taps (IJD53)
I   Drawout case

I   AC rotating machines (IJD52)
I   Power transformers (IJD53)

                                                                               GE Multilin       1
    IJD Percentage-Differential

    Application                             Rotating machine current trans-        For transformers rated 2000 kva
                                            formers should be selected so          and above, any voltage, high-
    The IJD relay is an induction disk      that the “difference” current will     speed differential relays are
    unit that should be applied as          not exceed 5 per cent of the           recommended (see Type BDD,
    follows:                                current that may be encountered        STD).
    For Ac Rotating Machines IJD52A         during normal or abnormal oper-        Above recommendations also
    is recommended for ratings as           ation of the machine. This             apply to power autotransformers
    indicated in Table 1.                   includes all currents up to the        having equivalent physical capac-
    Differential protection is also         maximum fault current which can        ities.
    recommended for smaller                 be delivered by the machine in
    machines, under the following           case of an external fault. This
    conditions:                             calculation must be based on the       Desensitizing
      (1)      Machines which operate in    actual     current-transformer         Equipment
         parallel on the same bus with      secondary burden including the
         differentially protected           leads.                                 In some instances differential
         machines.                                                                 relays will operate on magnetiz-
                                            In general, it is recommended
      (2)      Machines, regardless of                                             ing inrush currents when the
                                            that current transformers for IJD
         size, which are important to the                                          power transformer is first ener-
                                            differential protection be used for
         operation of the system. The                                              gized. This condition can be
         decision governing this applica-   no other purpose.
                                                                                   overcome by the addition of
         tion is based on the actual        For power transformer s, it is         auxiliary desensitizing equip-
         importance of the machine, and     recommended that percentage-           ment. To avoid this problem, the
         the degree of relaying required    differential    protection   be
         for the particular application.                                           Type STD harmonic restraint
                                            provided for transformers rated        relay should be considered.
    For generators rated 2000 kva           10 0 0 kva and above if circuit
    and above or motor s and                breakers are provided for each
    synchronous condensers rated            winding into which power can           General
    3000 hp (or kva) and above, high-       flow when an internal fault             (a For most installations a hand
    speed product-restraint relays,         occurs, and for all transformers           reset multi-contact auxiliary
    Type CFD are recommended.               rated 5000 kva and above even if           relay is required.
    NOTE: In order to provide               it requires the purchase of the         (b)     Short-circuit duty:
    complete percentage protection,         necessary circuit breakers.            Where short-circuit current avail-
    it is necessary that both ends of       Differential protection is also        able from the bus is sufficient to
    each machine winding be                 recommended for transformers           result in line current transformer
    brought out to the terminal             rated below 1000 kva that oper-        secondary current in excess of 50
    board. This construction should         ate in parallel with differentially    A, a Thyrite® voltage limiter
    be specified when purchasing the        protected transformers and have        should be connected across the
    machine, since those of lower           circuit breakers for all parallel-     secondary of each line current
    voltages or lower hp or kva             connected windings. If a fault         transformer secondary.
    ratings may not ordinarily have         occurring in a small parallel
    this feature.                           connected transformer is not
    The IJD52A relays protect against       promptly removed, it may prove
    phase-to phase and phase-to-            just as damaging to service as a
    ground faults within the machine        similar fault in a large bank.
    and leads within the differential       The IJD53C relay is used for
    zone, provided the fault current is     protection of two-winding power
    above the relay minimum pickup          transformer s. This relay has
    value. They will not protect            tapped operating and restraining
    against open circuits or turn-to-       coils, making it possible to
    turn faults. If the neutral of the      balance secondary currents from
    system is not grounded, protec-         the two sets of current transform-
    tion against grounds in the             ers.
    machine winding is provided only
                                            Percentage-differential relays are
    upon the occurrence of a second
                                            recommended for transformers
    fault in another phase of the
                                            rated 1000 up to 1999 kva, below
                                            15,000 volts.

                                                                                                     IJD Percentage-Differential

Fig. 1. Typical machine connections                               Table 1
                                                                  Ratings of ac rotating machines for which percent-
                                                                  age-differential protection using IJD52A relays is


Internal Connection Diagrams
Fig. 3. Internal connections for IJD52A, front view (6209677)   Fig. 4. Internal connections for IJD53C, front view (6556496)                                                                                                      3
    IJD Percentage-Differential

    SELECTION GUIDE Single-Phase 0.2/2A Target Seal-in