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    Static Relays

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    Bharathwaj Sreedhar
    Static relays are solid state relays that use electronic, magnetic, or optical components instead of mechanical parts to operate. They consist of an input circuit to measure a value, a comparator to compare it to a threshold, an optional time delay, and an output circuit. The main advantages of static relays over electromechanical relays are their compact size, accuracy, programmability, and ability to perform multiple functions. However, they require auxiliary power and can be affected by interference.

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    Static Relays

    Uploaded by

    Bharathwaj Sreedhar
    779 views11 pages
    Static relays are solid state relays that use electronic, magnetic, or optical components instead of mechanical parts to operate. They consist of an input circuit to measure a value, a comparator to compare it to a threshold, an optional time delay, and an output circuit. The main advantages of static relays over electromechanical relays are their compact size, accuracy, programmability, and ability to perform multiple functions. However, they require auxiliary power and can be affected by interference.

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    Static relays are solid state relays that use electronic, magnetic, or optical components instead of mechanical parts to operate. They consist of an input circuit to measure a value, a comparator to compare it to a threshold, an optional time delay, and an output circuit. The main advantages of static relays over electromechanical relays are their compact size, accuracy, programmability, and ability to perform multiple functions. However, they require auxiliary power and can be affected by interference.

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    779 views11 pages

    Static Relays

    Uploaded by

    Bharathwaj Sreedhar
    Static relays are solid state relays that use electronic, magnetic, or optical components instead of mechanical parts to operate. They consist of an input circuit to measure a value, a comparator to compare it to a threshold, an optional time delay, and an output circuit. The main advantages of static relays over electromechanical relays are their compact size, accuracy, programmability, and ability to perform multiple functions. However, they require auxiliary power and can be affected by interference.

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    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 11

    STATIC RELAYS

    BATCH 11
    K.S.BHARATHWAJ 107114042
    K.S.LAHARI 107114043
    K.SREEDHAR BABU 107114044
    KAUSHIK RAAM A.G 107114045
    RELAYS: A RECAP

    A relay (protective) is a device that detects the fault and initiates the operation
    of the circuit breaker to isolate the defective element from the rest of the system.
    The relays detect the abnormal conditions in the electrical circuits by constantly
    measuring the electrical quantities which are different under normal and fault
    conditions.
    Electrical Relayscan be divided into mechanical action relays called
    Electromechanical Relays and those which use semiconductor transistors,
    thyristors, triacs, etc, as their switching device called Solid State Relays or
    SSRs.
    WHAT ARE STATIC RELAYS ?

    Solid State Relay (Static Relay) is anelectrical relayin which


    the response is developed by electronic/magnetic/optical or
    other components, without mechanical motion of components.
    A static relay consists of :
    An input circuit that measures the value of desired property
    Acomparatorcircuit that compares the measured value to a pre-set
    threshold
    An optional time delay circuit that controls the timing of the switch
    action after the input has reached the threshold
    A power supply for the static relay circuits
    The static components of a
    static relay are shown in the
    figure beside. Here the
    relaying quantity, i.e., the
    output of a CT or PT of a
    transducer is rectified by the
    rectifier. The rectified output
    is given to a measuring unit
    constitute of comparators,
    level detectors, and logic
    circuits. The output is
    actuated when the dynamic
    input, i.e. the
    The output of relaying
    the measuring unit is fed to the output unit devices after it is
    quantity
    amplifiedattains
    by the the threshold
    amplifiers. The output unit activates the trip coil only when the
    value.
    relay operates. The relaying quantity such as the voltage and current is rectified
    and measured. When the quantity under measurement attains certain well-
    defined value, the output device is energized and hence, the circuit breaker trip is
    triggered.
    The static relay can be arranged to respond to electrical
    inputs. The other types of input such as heat, light, magnetic
    field, traveling waves, etc., can be suitably converted into
    equivalent analog and digital signal and then supplied to the
    static relay
    Bridge rectifiers convert a sinusoidal
    voltage into full-wave rectified pulses at
    twice the input frequency. The problem here
    is that these voltage pulses start and end
    from zero volts which means that they will
    fall below the minimum turn-on voltage
    requirements of the SSRs input threshold
    causing the output to turn on and off
    every half cycle.
    The electrical separation between the input
    control signal and the output load voltage is
    accomplished with the aid of an opto-
    With no input signal applied, no load current flows through the SSR as it is effectively
    OFF (open-circuited) and the output terminals see the full AC supply voltage. With the
    application of a DC input signal, no matter which part of the sinusoidal waveform,
    either positive or negative the cycle is going through, due to zero-voltage switching
    characteristics of the SSR, the output only turns-on when the waveform crosses over
    the zero point.
    When the DC input voltage signal is removed,
    the output does not suddenly turn-off as once
    triggered into conduction, the thyristor or
    triac used as the switching device stays ON
    for the remainder of the half cycle until the
    load currents drops below the devices holding
    current, at which point it switches OFF. Thus
    the high dv/dt back emfs associated with
    switching inductive loads in the middle of a
    sine wave is greatly reduced.
    Then the main advantages of the AC solid state relay over the
    electro-mechanical relay are its zero crossing function which turns
    ON the SSR when the AC load voltage is close to zero volts, thus
    suppressing any high inrush currents as the load current will
    always start from a point close to 0V.
    ADVANTAGES

    1.More accurate and fast in operation


    2. No moving parts.
    3.VA ratings of CT and PT is comparatively lower.
    4.Low power consumption.
    5.Resetting time and overshoot can be reduced.
    6.Very compact.
    7.Superior characteristics and accuracy.
    8.Several functions can be accommodated in a static relay
    DISADVANTAGES

    1.Reliability cannot be predicted


    2.Construction is not very robust.
    3.Easily affected by surrounding interference.
    4.Auxiliarty DC supply is required
    5.Affected by voltage transients

    For integrated protection and


    monitoring systems
    programmable microprocessor
    controlled static relays are
    preferred.
    COMPARISON WITH ELECTRO-MAGNETIC
    RELAY
    While the solid state relay and electro-mechanical relay are
    fundamentally similar in that their low voltage input is
    electrically isolated from the output that switches and controls
    a load, electro-mechanical relays have a limited contact life
    cycle, can take up a lot of room and have slower switch
    speeds, especially large power relays and contactors. Solid
    state relays have no such limitations.
    Low powerconsumption as low as 1mW.
    No moving contacts; hence associated problems of arcing, contact bounce,
    erosion, replacement of contacts.
    No gravity effect on operation of staticrelays. Hence can be used in vessels, i.e.,
    ships, aircrafts etc.
    A single relay can perform several functions like over current, under voltage,
    single phasing protection by incorporating respective functional blocks. This is not
    possible in electromagneticrelays.
    Static relay is compact.
    Superior operating characteristics and accuracy.
    Static relay can think,programmableoperation is possible with static relay.
    Effect of vibration is nil, hence can be used in earthquake-prone areas.
    Simplified testing and servicing. Can convert even non-electrical quantities to
    electrical in conjunction with transducers.
    APPLICATIONS

    1.Ultra high speed protection of EHV AC transmission lines


    utilizing distance protection.
    2.In over current and earth fault protection schemes
    3.As main element in differential relay

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