Electronic relay,static relay and functional circuits

Jun 2 • Notes • 11914 Views • 6 Comments on Electronic relay,static relay and functional circuits

Electronic Relay

It  is an electromechanical switch whose input is electrical with mechanical output.It is used to disconnect the faulty part of the circuit from the faulty part such that the due to the faulty part the whole circuit is not affected.It is achieved by comparing two quantities either in amplitude or in phase . The application of relay is decided by its characteristics and other factors like accuracy, operating time etc.

STATIC RELAY

static relay block diagram

A relay in which there is no armature or other moving element other and response is developed by electronic, magnetic and other components.The components that are used are capacitors,diodes,transistors etc. In this type of the relay the measurement is performed by the electronic or magnetic or it may be optical or any other component.

Any protective system is formed when it consists of the static and the electromechanical relays..

A comparator is widely used as the application of the relays are achieved by comparing the quantities.

Comparator

comparator circuit

Is basic function is to compare two quantities either in terms of amplitude or in phase. The relation in the amplitude or phase depends on the system conditions.For a value of the relation  or type and location of the fault the relay operates.

General equation of comparators

Let S and S₁ be the two input signal such that a tripping condition is indicated when the phase or the amplitude follows the threshold condition.The input signals are derived from the primary power system through current and voltage transformers. FIG pg 41

Let    S = K₁Å + K₂A ——-(1)

S = K₃Å + K₄B——–(2)

where K₁ and K₃ are scalar constants and K₂ and K₄ vector constants with angles θ₂ and θ₄ respectively.

Taking A as the reference vector and vector B to lag A by an angle Ø, above eqn reduces to

S= K₁IAI + K₂IBI{cos(θ₂– Ø) + jsin(θ₂ – Ø) ——–(3)

S₁ = K₃IAI + K₄IBI{cos(θ₄– Ø) + jsin(θ4 – Ø)——–(4)

Amplitude comparator

If the criteria for operation is given by ISI >= IS₁I, then at the threshold of operation

ISI = IS₁I, equating the moduli of expression eqn 2

{K₁IAI + k₂IBIcos(θ₂– Ø) }² +{K₂IBIsin(θ₂– Ø) }²

={K₃IAI + K₄IBIcos(θ₄– Ø) }² +{K₄IBIsin(θ₄– Ø) }² —–(4)

Now, by rearranging and dividing by (K₂² – K₃²) IAI²

IB/AI² + 2IB/AI[a₀ cosØ + b₀ sinØ] + c₀ = 0 ——(5)

where

a₀ = (K₁K₂ sinθ₂ – K₃K₄ cosθ₂) /  (K₁² – K₃²)

b₀ = (K₁K₂ sinθ₂ – K₃K₄ cosθ₂) /  (K₂² – K₄²)

c₀  = (K₁² – K₃²) / (K₂² – K₄²)

phase comparator

The two quantities to be compared are S and S₁. If α is the plane angle of input Sand β that of S₁, the relay operates when the product of S₁ and S₂ is positive.

All  characteristics of relays can be obtained with a symmetrical phase comparator with

(α – β) = 90⁰.

threshold condition, i.e.,

tan(α – β) = ∞

{(tanα – tanβ) / (1 + tanαtanβ)} = ∞

Now,            IB/AI² + IB/AI[a^‘0cosØ + b^‘₀ sinØ] + c^‘₀ = 0 ——4

where,            a^‘₀ = (K₁K₂ cosθ₄ + K₂K₃ cosθ₂) /  (K₂K₄ cos(θ_{2 –} θ₄)

b₀ = (K₁K₄ sinθ₄ + K₂K₃ sinθ₂) /  (K₂K₄ cos(θ_{2 –} θ₄)

c₀  = (K₁K₃) / (K₂K₄ cos(θ_{2 –} θ₄)

In most relays at lest one of constants K is 0 and two of them are often equal

level detection

The process of locating the X coordinate at which the data passes or reaches a given Y value. This is also called as  inverse interpolation

Finding a Level in Waveform Data

To find the single level operation  or the multilevel operation crossing the FINDLEVEL operation is used and FINDLEVELS respectively.The operations provide the advantage that it is quite helpful in reducing the effects of the noise.By the ascending or the descending values of the X coordinate value a range of the data can be easily..

FINDLEVEL finds the first level crossing which is located in the search range, starting at BEGINX and proceeding toward ENDX until crossing is found.

The search is performed sequentially.

The output are  two  numeric values: VFlag , VLevelX.

VFlag indicates whether the search is a success or failure

VLevelX contains the X coordinate of the level crossing.

finding the level in the waveform data

Logic &  training circuit

The Boolean algebra  are represented in the logic circuit.The  These Boolean algebra can be explained as set of elements, a set of operations and a number of unproved axioms . These  set of elements refer to binary number and operation means binary operations. A binary 1 can be represented by a switch that is closed or TRUE value and vice verse.

logic

On the principle of logic  the computer operates and  makes the use of  the TRUE and FALSE logic conditions of a logical statement .

It can be of  positive or negative polarity. The logic polarity is the type of the voltage used to represent the state of any statement

1)positive voltage can be represented by the state  1

2) negative voltage can be represented by 0.

Logic circuit are generally divided into two broad classes according to their polarity- positive and negative logic circuit.

Logic circuit

Logic circuits for digital system can be either combinational or sequential logic circuits.

A combinational circuit consists of the logic gates whose output are determined from the present combination of inputs without considering the previous inputs..

Sequential circuits employ memory elements in addition to logic gates. Their outputs are function of the inputs and the state of the memory elements.Sequential circuit depends upon the present inputs and the past inputs.

The logic gates accept signals from the inputs and generate signals to the outputs. This process changes the binary data from the given input data to the required output data.

Design Procedure:

1. The problem is given

2. The number of available input variables and the required output variables is determined.

3. The input and output variables are given  symbols.

4. The truth table that defines the required relationships between inputs and outputs derived.

5. The simplified boo lean function for each output is obtained.

6. The logic diagram is drawn.

Logic gates that are used in logic circuit

Complement, transfer, AND, OR, NAND, NOR, exclusive-OR, and equivalence are used as standard gates in digital design.

logic gates used in the logic circuits

Related Questions-Answers

1.what is the static relay and electronic relay.

The electronic relay is an electromechanical with electrical input and mechanical output.It is basically used to disconnect the faulty part of the circuit from the non faulty part.

The static relay is the one in which no moving element is present and response is developed by electronic, magnetic and other components.The components used are capacitors,diodes,transistors etc.

2.what is a comparator.explain

It is the basic function is to compare two quantities either in terms of amplitude or in phase. The relation in the amplitude or phase depends on the system conditions.For a value of the relation  or type and location of the fault the relay operates

3.How the level detection is done??

As per the explaination of the terms above in the notes the steps of the level detection are give below,

a)The search is performed sequentially.

b)The output are  two  numeric values: VFlag , VLevelX.

c)VFlag shows whether the search is failure or success

d) VLevelX contains the X coordinate of the level crossing.

4.Write the general equation of the comparators.

S and S₁ be the two input signal

Let    S = K₁Å + K₂A ——-(1)

S = K₃Å + K₄B——–(2)

where K₁ and K₃ are scalar constants

K₂ and K₄ vector constants with angles θ₂ and θ₄ respectively.

GATE Syllabus-

1. Gate Syllabus for Electronics and Communication Engineering 2014

2. Gate Syllabus for Electrical Engineering 2014

IES Syllabus-

1. IES Syllabus for Electronics and Telecomm

2. IES Syllabus for Electrical Engineering

3. IES Syllabus for General Ability

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