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The protections provided for 220 kV lines and bus bars are.

a. Bus bar differential protection. 

b. Distance protection. 

c. Overcurrent protection. 

d. Earth fault protection. 

There are two systems. 

a. Normal lighting with class IV power supply. 

b. Emergency lighting with class II power supplies and in control room with class I power supplies. 

The two main divisions of MAPS electrical system are.

a. Main output system. Output system supplies power to the grid. Generated voltage is stepped up to 220 kV from 16.5 kV and supplied to grid. 

b. Station service system. This system supplies the load inside the power station. The generated voltage is stepped down to 6.6 kV and 415 V from 16.5 kV and supplies to auxiliary loads. 

When class IV and class III power supply fails and DG’s cannot be started and also this condition prevails for 5 minutes then it is called station black out condition.  

The sources of power supply to class I bus are.

a. Through control UPS 240 V AC. 

b. Through control UPS 220 V DC backed by 220 V batteries. 

c. Through control UPS 48 V DC backed by 48 V batteries.

a. All safety related equipments are in control building, SRPH and are designed for SSE conditions. As per studies seismic condition is not there within 5 kms and nearest zone is away from 20 kms. 

b. Safety related equipments are separated from suitable fire barriers of 3 hrs rating by horizontal and vertical clearances and from turbine building which are houses high energy rotating equipments and where potential for fire is exist. 

c. Separate switchyard control is provided in case of non-availability of main control room with line and bus coupler protection and bus bar protections. Control room posses SUT, UT, GT, Generator and all classes of power supply control and protections. 

d. Protection panels of Generator, GT, and UT are separated from SUT in physical to have system flexibility. 

e. SCADA is provided in CER, TB and in switchyard separately. 

f. EMTR for each A and B groups are separated. 

g. Control supply for switchyard is separated from operating island. 

h. To reduce fault level in lighting circuits separate 280-kVA transformer is provided. 

Output of the generator is the function of volume, length, dia, airgap, and speed. 

Inverse time relay with definite minimum time is called IDMT

It is a self powered inverse time over current and earth fault relay, used for selective phase and earth fault protection in time graded systems for A.C. machines, transformers, feeders etc. A non-directional heavily damped induction disc relay, which has an adjustable inverse time/current characteristic with a definite minimum time. The relay has a high torque movement combined with low burden and low overshoot. The relay disc is so shaped that as it rotates the driving torque increases and offsets the changing restraining torque of the control spring. 

Sucking cooled hydrogen gas from the air gap, circulating in canals and removing the heat from the rotor. While sucking the gas, gas comes through the stator parts also and removes the heat from the stator parts. The heated gas circulated to the hydrogen for cooling purpose by the fans installed at rotor shaft. Thus the stator and rotor of the generator is cooled. This method is called Gas pickup method. 

Negative sequence can arise whenever there is any unbalance present in the system. Their effect is to set up a field rotating in opposite direction to the main field. 

If a machine is operating with an earthed neutral, a system earth fault will give rise to zero sequence current in the machine. 

EMF applied to secondary of current transformer (CT) which, when increased by 10% voltage causes the excitation current to increase by 50%. 

Directional phase or earth fault protection of ring-mains, parallel transformers, transformer feeders, parallel feeders etc., employing the time graded principle.; This relay comprises an inductive disc over current unit with wound shading coils and a directional high speed induction cup unit. The cup-unit contact is wired across the shading coils so that no torque is exerted on the disc of the over current unit until the cup unit contact closes. The inductive disc unit is thus directionally controlled and it operates only when the current flows in the tripping direction. The directional unit is a high speed, low inertia four pole induction cup movement designed to give a high, steady and non-vibrating torque. its current coil is connected in series with the operating coil of the induction disc unit. The directional unit is normally provided with voltage polarising coils.

When hydrogen concentration in air is more than 4% and less than 74% causes the explosion.

Earlier 25 Hz generally used. 

After developing of the high-speed turbine, 50/60 Hz standardized. 

Lifts the rotor by injection of oil at high pressure, when BGM is in service. Outlet pressure of JOP is 140 kg/cm² .  

This relay is used with on load transformer tap changers and induction regulators to provide close and accurate automatic voltage regulation on power systems of any voltage. 

When the regulated voltage moves outside a dead band, set by the sensitivity control, the volts high or volts low circuits are initiated and after a time delay, determined by the response characteristic, the appropriate tap changer control auxiliary relay closes its contact to initiate a tap change. 

(3) f constant but v and λ decreases

v = fλ

f = constant

so , v ∝ λ

in denser medium v decrease.

a) Same phase sequence. 

b) Voltage should in-phase and angle should not be more than 10°. 

c) Voltage value must be same and difference of 5% is allowed. 

d) Frequency should be same and difference of 0.1% i.e. 0.05 Hz is allowed. 

a. High thermal capacity 

b. Low electrical conductivity (Good insulator) 

c. Low viscosity 

d. Free of fire risk and non-toxic 

e. Simple heat exchanger i.e. it can be circulate easily and cooled by heat exchanger 

Classification of generator protection in nuclear power station.

1. MAIN ProStator 

E/f tection

Loss of Excitation

Pole slipping

Differential

Inter turn

Unbalance current

2. Backup Protection

Back up Impedance 

Over Voltage

Under Freq

Over freq.

3. STARTUP Protection

Phase o/c during startup

E/F during startup

4. EXCITATION Protection

Excitation transformer over current 

Rotor E/f. and Rotor o/v

48 V DC fail

more than 3 Bridge fail (¾ logic)

Manual channel fails

Transformer over temperature (Class –B) 

Generator Slipring wearing rate is 0.025 mm /1000 hrs.

24 kV, 3.15 Amps. 

IR It is the ratio of the DC voltage applied between the terminals and ground to the resultant current. When the DC voltage applied three components flow, 

a) A charging component flows into the capacitance of the winding. 

b) A polarization or absorption current involving in the insulation molecular mechanism. 

c) A leakage component over the surface between exposed conductor and ground which is highly dependent on the state of dryness of the winding.

The first two current components decay with time. The third component is determined by the presence of moisture or ground fault and relatively constant with time. Moisture may be with in the insulation or condensed on the end windings or connection surfaces, which are often dirty. If this leakage current is larger than the first two components then the total charging current will not change significantly with time. Thus to determine how dry and clean the winding, IR is measured after one minute and after 10 minutes. The ration of the 10 minutes reading over the oneminute reading is called the PI (Polarization Index). 

PI value detects relative condition of insulation with respect to moisture and other contaminants. 

It ensures an optimum solution for increasing current and to reduce losses. 

Oil has high thermal capacity than gas, but low thermal capacity than water. Ability to absorb heat is also less than waters. 

High viscosity of oil causes linear flow and poor surface heat transfer in small ducts. Large pumping power required. 

This relay is used to monitor the frequency of an electrical system. The relay are suitable for any application in industrial plants and to generators where definite time under or over frequency protection is required. 

The operating principle of the relay is the comparison of the time interval of the incoming frequency with that of a preset time derived from an accurate oscillator within the relay. The incoming frequency signal is connected to an INPUT CIRCUIT, which then drives an IMPULSE GENERATOR to produce a pulse at the beginning of each period of the input voltage. The preset time interval is obtained from an OSCILLATOR and COUNTER and adjustment is achieved using SELECTOR switches, which drive a DECODER circuit. A COMPARATOR compares the two-time interval and this triggers an adjustable TIMER which then operates the output relay and latched light emitting diode (LED) glows.  

Rotor windings are held by duraluminium wedges and by non-magnetic steel retaining rings in the overhang portion. 

To limit over voltage due to neutral shift. 

Aluminium bus bars are silver-plated at flexible connection to prevent the galvanic corrosion ant also for low contact resistance. 

Feeding DC current from slip ring to rotor winding

A small steam leak through CIES valves will keep the machine floating on to grid at low power. So even if turbine trip, relay picks up, there is no trip actually. So low forward power relay (0.54%) used to detect the condition.  

Phase segregated bus duct is better, since phase to phase faults are avoided.

Fault level is more in UT bus duct. Because the fault currents fed by the both generator and GT adds up within UT bus duct in case there is a fault in UT bus duct. 

Prevent vibrations transmitted from generator to IPBD.

Aluminium is nonmagnetic material. 

Short circuit forces are less. 

Transformers need protection against the risk of damage, which may be caused when the transformers are operated at flux density levels significantly greater than the design values. The over fluxing withstand time is generally found to be varying inversely with the working flux density in the core, having higher withstand times during extreme over fluxing conditions. 

The over fluxing condition can occur during system over voltage or under frequency conditions.

The basic operating principle is to produce an ac voltage, which depends upon the ratio between AC input voltage and the frequency. The AC input voltage is fed to a step-down transformer, which also provides isolation and the stepped down voltage is fed to a V/F ratio detector circuit. This circuit is a simple operational amplifier integrator with the provision for V/F pickup adjustment. The AC voltage is rectified by true RMS. to dc converter. This circuit gives a frequency output and this frequency increases rapidly with the increase in voltage. The frequency output is given to a curve shaping circuit, which involves counter and comparators. The counter counts the frequency output and the number of counts required for final trip condition is changed by the comparator circuits to get the required timing characteristic. 

Double frequency currents are induced in metal parts of rotor and overheating of retaining rings and non-magnetic wedges. 

Neoprene rubber bellows are used near the terminals of the equipment and also at building wall from indoor to outdoor area to allow thermal expansion and to minimise vibrations.  

Hydrogen picked up from stator core backspace, passes through ventilation canals on rotor and comes out through adjacent canals. Shaft fans aid the hydrogen flow. Heat from the hydrogen removed by 4 nos. of hydrogen coolers. (NAPW) 

To safe guard against the drastic consequences of failure to clear faults rapidly, many power supply authorities install 2 independent systems of protection for major transmission lines. There remains however the possibility of the circuit breaker itself failing to operate and this hazard is traditionally covered by remote breaker back-up.; CTIG relay is a 3 phase or 2 phase and earth fault instantaneous over current unit intended for use with a time delay to give back-up protection in the event of a circuit breaker failure. A particular feature of the CTIG relay is a fast reset, which enables the time delay to be set closer to the breaker trip-time. 

N = 120 f / P 

N – Speed in RPM 

f - Frequency in Hz 

P – Number of poles 

a. Rotor current limiter (3000 A) 

b. Rotor angle limiter (75° lag) 

c. Under excitation limiter. 

d. Stator current limiter (lead 10000 A) 

e. Stator current limiter (lag 10000 A) 

f. N – 2 limiter.

Silicagel breathers at either end. 

Brushes wear out unevenly, when run on barring gear speed. 

a. This for a vital link between generator, GT, UAT, SPPT, SET and neutral grounding transformer. 

b. The continuous enclosure operating at ground potential limits the leakage flux outside the enclosure to a very low value thereby eliminating the problem of inductive heating of magnetic materials in the vicinity of the busduct. 

c. Shielding effect of the enclosure reduced the electromagnetic forces under fault conditions between bus to bus to a great. 

d. The IPBD consists of high purity aluminium alloy bus supported by high strength porcelain insulator (24 kV class) within enclosure separates adjacent conductor by air. This eliminates phase to phase faults to a great extent. 

e. Practically negligible inductive heating on adjacent steel structure. 

f. High current carrying capacity. Because the conductors are of circular type having very little skin effect and has a very large cooling surface. 

g. Conductors are painted with epoxy Matt black paint results in heat dissipation and the temperature rise is small and current carrying capacity is improved. 

h. High dielectric strength as conductors are supported on porcelain insulators. 

i. Air tight, watertight and dust free bus conductors. Hence maintenance is nil. 

j. Separate parts erected IPBD. Hence changing parts makes it easy. 

By magnetic blow out coils, arc is elongated very fastly, so resistance of arc increases, soon becoming unstable and quenched by arc chutes.

Emf = 4.44 k_c k_d f ∅ T volts.

K_d = Distribution factor = sin m β/2 / m sin β/2

k_c/k_p = Coil span factor /Pitch factor = cos α/2 

k_f = Form factor = 1.11

∴Average emf induced / Cycle = ∅ N P/ 60 

= ∅ P ∗120 f /  60 * P

=2 f ∅ volt

If Z is the number of conductors = 2T (T = two sides of conductor) 

 emf induced = 2 f ∅ Z =2 f ∅ 2T = 4 f ∅ T

∴ RMS value of emf induced = form factor * emf

= 1.11 * 4 f ∅ T

= 4.44 f ∅ T volts.