BASICS OF ELECTRICAL

ATOMS
All meters (solid, Liquid, Gas) are composed by minute particals called Malicules. There are two part in Atom, 1. Nucleus 2.Extra Nucleus a. Nucleus The Nucleus contains Protons and Neutrons Protons are positively charged particals and Neutrons have no particals b.Extra Nucleus Extra Nucleus contain only Electrons Electrons are negatively charged particals and moves around the Molicules with different orbits. The number of Protons are equels to Number of electrons in an Atom. Atomic Wieght = No. of Protons + No. of Neutrons Atomic Number = No. of Protons or No. of Electrons Normally the Number of Protons and Number of electrons are equles in a body. So the resultant charge is zero and the body electrically neutral. Charge The charge is Electrical energy possessed by protons or Electrons in an Atoms Unlike charges attract each other and like charges or repels each other. The Law of Conservation The Law of Concervation stats the algebraic sum of chares remain constant in a closed path. Therefore the charge can neither be created nor be distorted. The unit of the charge The charge on an electron is so small that is not convenient to select it as the unit charge. Normally Coulomb is the unit of charge. One Coulomb is equal to the charge on 6.28 X electrons. Each protons has positive charge = 1.6 X C. If 6.28 X Electrons remove from a neutral body then the body as positive charge 1 coulomb. If we say that a body has a negative charge of 1 C we should remove 6.28 X electrons from that body. Coulomb Inverse square Law The force two point charges is directly proportional to product of the two charges and inversely proportional to square of distance between two charges. F = 1/4π q1q2/ r - Distance between two charges ε0 – The permittivity of free space ε0 – 8.514 If charge placed in a material then Permittivity = ε0 εr εr – Relative permittivity of the material Electric Field The space around the charge in which the influence is felt is known as Electric field. Electric field Intensity The force experienced by an unit coulomb charge called Electric field Intensity. E = F/q F – Force in Newton q – Charge in Coulomb CURRENT AND VOLTAGE American physicists TOLMAN and STEWART experimentally con formed that the electric current in a conductor is a carried by electrons. The electrons in outer most orbit will less bound with nucleus and called free electrons. The free electrons move at random from one atom to other atom in the materials. Electro Motive Force An external force necessary to move the free electrons in definite direction is called Electro Motive Force. Faradays Law When ever a conductor cut the magnatic field an E.M.F induced in the conductor. E.M.F = BAL sinθ B – Magnatic density in webber A – Area of the conductor L – Length of the conductor. Theory of current (The Machanism of flow of current ) A metal piece contain a large number of free electrons moving in randam directin. The maxiumam speed the free electrons in the order of m/s. Due to e.m.f the electrons get accelerated and move in a definite direction. Due to electric field of moving electrons the electrons in the closed circuit also get accelerated and start to move. The direction of moving electrons can be find by Flamings Right hand rule. If E is the strength of the electric field applied from conductor closed circuit then the force on the electrons in the closed conductor F = e.E e- The charge on electrons in closed circuit. The acceleration produced on on electrons in a closed circuit a = F/m m – Mass of the electrons a = eE / m Due to acceleration the velocity of an electron increase but happens only short time τ. The electrons in a closed circuit contain The additional velocity acquired from e.m.f for τ time is called DRIFT VELOCITY. Vd = a τ =( eE / m) τ. Consider a wire of cross section ‘A’. Let ‘n’ be the number of free electrons per unit volume. The free electrons moves towards left with a constant drift velocity Vd. Numer of free electrons passed through the area of cross section per unit time = nAVd. Therefore the charge that flows per unit time = nAVde. This also called the current flows through the wire I= nAVde. This is relation between current and velocity I= nA E τ/ m. Electric current The rate of follow of charge in any cross section of a wire is defined as the electric current. I = Total charge flowing in a cross section / Time taken If charge dq flows through a wire in small time dt. The electric current = dq / dt. The unit of current is Ampere. One coulomb of charge flow through the wire in one second is called one Ampere. One ampere = 1 coulomb of charge (c) / 1 second (s) = 1 If there is no changes in rate of change of current and rate of change of time the the current is called steady current and if any one or both frequently change then the current called Alternating current .

Theory of Potential different

Consider a body in that one coulomb of negative charge is removed

Now the body is called positively charged body. Certain work was done to charge the body and it is stored in the body as potential energy.

AUTO RECLOSE

Auto Reclose Blocking Scheme
1. AR shall not be intiated under line is connected with generator bus unless proper analizes in the fulty line.
2. In case genarating power plant bus is connected to grid by medium and long lines,high-speed auto reclosing can be intiated by reverse direction (first chargeing the line from remote end and then reclose the CB at power plant end) for lines which restict the fult current to such a level that maximum shaft torques are with in the genarator specification under fault conditions.
3. AR shall not be intiated under the following conditions
a. BFP, BB protection trips
b. Direct transfer receiving Trips ( BF,PD)
c. SOTF Trips
d. Time delay trip
e. All type of communication failures ( 21 , 87L, BF,PD)
f. Both line & Bus side VT fuse failures

AR operate only zone -1 Ground to Earth Fault

Testing Tips CT

CT Testing

1. When your test the CT with CT analyzer remove the Metrosil connections.

Otherwise analyzer will show the more Ratio error and class fail.

2. Some ring type CT's core are connected with bus voltage. Take more care on dressing the wires.This wires are connect with RYB three phases.Therefore wires should be separate with appropriate air gap.

YOU TUBE LINK

TAN DELTA TEST EXPLANATION

You tube video links for CT http://www.youtube.com/watch?v=D6eXTDPwLzo&feature=related

http://www.youtube.com/watch?v=nUkYQ8Ah510&feature=related

CT DESINGING AREVA

CT AREVA DESIGNING DOCUMENTS DOWNLOAD

CT IEC - 60044-6 DOCUMENTS DOWNLOAD

SEC STANDERS ON CONTROL PANEL

1. Panel size should be 800 (W) X 800 (B) X 2200 (H)

2. Aux Power supply 127 V (AC), 220 V (AC) , 125 V (DC)

3.Group of terminals should identified by engraving labels.

4.The distance between TB and race way should be 80mm.

5. 10% spare terminals should provide.

6. The bottom of any relay and test block shall not be less than 300mm from floor level.

7. Not more then 2 LOR in the row and 15 cm between lockout and 10mm other relays.

8.VT secondary should ground at CVT junction box and CT secondary should ground at first interning point of protection panel. For metering CT secondary grounding at control panel.

9. Wiring size a) CT and VT and less than 2.5 Sq mm b) SCADA , SOE, ANNU not less than 0.8 Sqmm c) SCADA control output signal and other control wires not less then 1.5 Sq mm.

DESIGN TIP GIS

Inter lock bypass key should not bypass the SF6 minimum operating pressure interlock

DESIGN TIP BF II STAGE

1. The BF second stage (86BF) no need to use in close block circuit because breaker already trouble to open. Breaker 'b' contact already serious in closing circuit if breaker is in open condition it will not allow the closing command to CB.

2. The trip setting of Tie breaker should be less then the trip setting of other to Incomers

Because if any fault on tie breaker side then Tie breaker should trip first and save the incomer voltage.

Design Tip AUX RELAYS

TIMING FOR AUXILIARY RELAYS

1. High speed relay used for SOE, TFR 1ms

2. Other signals ANNU, SCADA 4 ms

3. BF initiation timers ( 0 - 100 ms)

4. High speed 85 DTTR, 85 PD relays 4 ms

5. DC supervision relays 100 ms

Design Tip AR BLOCK

Why 94BF -1, 86 BF -2 trip no need to block the AR relay ?

The breaker status contact is given to AR relay to monitor the breaker.

AR relay give the close command if CB is in open condition.

Breaker failure operate means CB in closed condition and failure to open for trip command.

AR relay automatically blocked when the CB is in closed condition.

Therefore separate close block no need from 94BF -1, 86 BF -2.

Transformer Protections

Transformer Protections

1. Transformer diffential protection

2. REF HV, REF LV

3. Dir O/C HV, LV , HVN, LVN (IOC, TOC) ,

4. O/C HV and LV Grounding

5. Mechanical Trip

a.BUZ relay Main Tank

b.BUZ relay OLTC

c. HV winding Temp High

d. LV winding Temp High

e. Main Tank PRD Opt

f. OLTC PRD Opt

g. Main tank oil Temp High

h. OLTC oil Temp High

6. O/C TW ( 51 TW-HS, 51 TW-LS)