SOME FEATURES OF AC DRIVES

1. Controlled Starting Current -- When an AC motor is started "across the line," it takes as much as seven-to-eight times the motor full-load current to start the motor and load. This current flexes the motor windings and generates heat, which will, over time, reduce the longevity of the motor

2. Reduced Power Line Disturbances -- Starting an AC motor across the line, and the subsequent demand for seven-to-eight times the motor full-load current, places an enormous drain on the power distribution system connected to the motor.
3. Lower Power Demand on Start -- If power is proportional to current-times-voltage, then power needed to start an AC motor across the line is significantly higher than with an Adjustable Speed AC Drive. This is true only at start, since the power to run the motor at load would be equal regardless if it were fixed speed or variable speed.

4. Controlled Acceleration -- An Adjustable Speed AC Drive starts at zero speed and accelerates smoothly on a customer-adjustable ramp. On the other hand, an AC motor started across the line is a tremendous mechanical shock both for the motor and connected load. This shock will, over time, increase the wear and tear on the connected load, as well as the AC motor

5. Adjustable Operating Speed -- Use of an Adjustable Speed AC Drive enables optimizing of a process, making changes in a process, allows starting at reduced speed, and allows remote adjustment of speed by programmable controller or process controller.

6. Adjustable Torque Limit -- Use of an Adjustable Speed AC Drive can protect machinery from damage, and protect the process or product (because the amount of torque being applied by the motor to the load can be controlled accurately). An example would be a machine jam. An Adjustable Speed AC Drive are set to limit the amount of torque so the AC motor never exceeds this limit.

7. Controlled Stopping -- Just as important as controlled acceleration, controlled stopping can be important to reduce mechanical wear and tear -- due to shocks to the process or loss of product due to breakage.

8. Energy Savings -- . Centrifugal fans and pumps follow a variable torque load profile, which has horsepower proportional to the cube of speed and torque varying proportional to the square of speed Energy savings can be sufficient to pay back the capitalized cost in a matter of a couple of years (or less), depending on the size of the motor.

9. Reverse Operation -- Using an Adjustable Speed AC Drive eliminates the need for a reversing starter, since the output phases to the motor can be electronically changed without any mechanical devices. The elimination of a reversing starter eliminates its maintenance cost and reduces panel space.

10. Elimination of Mechanical Drive Components -- Using an Adjustable Speed AC Drive can eliminate the need for expensive mechanical drive components such as gearboxes. Because the AC Drive can operate with an infinite variable speed.

Electrical Q & Ans; A Part-1

1)     Why ELCB cannot work if Neutral input of ELCB does not connect to ground?

• ELCB is used to detect earth leakage fault. Once the phase and neutral are connected in an ELCB, the current will flow through phase and that same current will have to return neutral so resultant current is zero.
• Once there is a ground fault in the load side, current from phase will directly pass through earth and it will not return through neutral through ELCB. That means once side current is going and not returning and hence because of this difference in current ELCB will trip and it will safe guard the other circuits from faulty loads. If the neutral is not grounded fault current will definitely high and that full fault current will come back through ELCB, and there will be no difference in current.

2)     What is the difference between MCB & MCCB, Where it can be used?

• MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit.
• Normally it is used where normal current is less than 100A.
• MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition. Under voltage and under frequency may be inbuilt.
• Normally it is used where normal current is more than 100A.

3)     Why in a three pin plug the earth pin is thicker and longer than the other pins?

• It depends upon R=ρL/A where area (A) is inversely proportional to resistance (R), so if  area (A) increases, R decreases & if R is less the leakage current will take low resistance path so the earth pin should be thicker. It is longer because the The First to make the connection and last to disconnect should be earth Pin. This assures Safety for the person who uses the electrical instrument.

4)     Why Delta Star Transformers are used for Lighting Loads?

• For lighting loads, neutral conductor is must and hence the secondary must be star winding and this lighting load is always unbalanced in all three phases.
• To minimize the current unbalance in the primary we use delta winding in the primary So delta / star transformer is used for lighting loads.

5)      What are the advantages of star-delta starter with induction motor?

• The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting current is reduced to 3-4 times of current of Direct online starting  Hence the starting current is reduced , the voltage drops during the starting of motor in systems are reduced.

6)     What is meant by regenerative braking?

• When the supply is cut off for a running motor, it still continue running due to inertia. In order to stop it quickly we place a load (resistor) across the armature winding and the motor should have maintained continuous field supply so that back e.m.f voltage is made to apply across the resistor and due to load the motor stops quickly. This type of breaking is called as “Regenerative Breaking”.

7)     When voltage increases then current also increases then why we need of over voltage relay and over current relay? Can we measure over voltage and over current by measuring current only?

• No. We cannot sense the over voltage by just measuring the current only because the current increases not only for over voltages but also for under voltage (As most of the loads are non-linear in nature).So, the over voltage protection & over current protection are completely different.
• Over voltage relay meant for sensing over voltages & protect the system from insulation break down and firing. Over current relay meant for sensing any internal short circuit, over load condition, earth fault thereby reducing the system failure & risk of fire. So, for a better protection of the system. It should have both over voltage & over current relay.

8)     If one lamp connects between two phases it will glow or not?

• If the voltage between the two phases is equal to the lamp voltage then the lamp will glow.
• When the voltage difference is big it will damage the lamp and when the difference is smaller the lamp will glow depending on the type of lamp.

9)     What are HRC fuses and where it is used?

• HRC stand for “high rupturing capacity” fuse and it is used in distribution system for electrical transformers

10)  Mention the methods for starting an induction motor?

• The different methods of starting an induction motor
• DOL:direct online starter
• Star delta starter
• Auto transformer starter
• Resistance starter
• Series reactor starter

11)  What is the difference between earth resistance and earth electrode resistance?

• Only one of the terminals is evident in the earth resistance. In order to find the second terminal we should recourse to its definition:
• Earth Resistance is the resistance existing between the electrically accessible part of a buried electrode and another point of the earth, which is far away.
• The resistance of the electrode has the following components:
  (A) the resistance of the metal and that of the connection to it.
  (B) The contact resistance of the surrounding earth to the electrode.

12)  Why most of analog o/p devices having o/p range 4 to 20 mA and not 0 to 20 mA?

• 4-20 mA is a standard range used to indicate measured values for any process. The reason that 4ma is chosen instead of 0 mA is for fail safe operation.
• For example: A pressure instrument gives output 4mA to indicate 0 psi  up to 20 mA to indicate 100 psi or full scale. Due to any problem in instrument (i.e) broken wire, its output reduces to 0 mA. So if range is 0-20 mA then we can differentiate whether it is due to broken wire or due to 0 psi.

13)  Two bulbs of 100w and 40w respectively connected in series across a 230v supply which bulb will glow bright and why?

• Since two bulbs are in series they will get equal amount of electrical current but as the supply voltage is constant across the Bulb (P=V^2/R).So the resistance of 40W bulb is greater and voltage across 40W is more (V=IR) so 40W bulb will glow brighter.

14)  What happen if we give 220 volts dc supply to bulb or tube light?

• Bulbs or devices for AC are designed to operate such that it offers high impedance to AC supply. Normally they have low resistance. When DC supply is applied, due to low resistance, the current through lamp would be so high that it may damage the bulb element

15)  What is meant by knee point voltage?

• Knee point voltage is calculated for electrical Current transformers and is very important factor to choose a CT. It is the voltage at which a CT gets saturated.

16)  What is reverse power relay?

• Reverse Power flow relay are used in generating stations’ protection.
• A generating station is supposed to feed power to the grid and in case generating units are off, there is no generation in the plant then plant may take power from grid. To stop the flow of power from grid to generator we use reverse power relay.

17)  What will happen if DC supply is given on the primary of a transformer?

• Mainly transformer has high inductance and low resistance. In case of DC supply there is no inductance, only resistance will act in the electrical circuit. So high electrical current will flow through primary side of the transformer. So for this reason coil and insulation will burn out
• When AC current flow to primary winding it induced alternating flux which also link to secondary winding so secondary current flow in secondary winding according to primary current.Secondary current also induced emf (Back emf) in secondary winding which oppose induced emf of primary winding and thus control primary current also.
• If DC current apply to Primary winding than alternating flux is not produced so no secondary emf induced in secondary winding  so primary current may goes high and burn transformer winding.

18)  Different between megger and contact resistance meter?

• Megger used to measure cable resistance, conductor continuity, phase identification where as contact resistance meter used to measure low resistance like relays, contactors.

19)  When we connect the capacitor bank in series?

• We connect capacitor bank in series to improve the voltage profile at the load end in transmission line there is considerable voltage drop along the transmission line due to impedance of the line. so in order to bring the voltage at the load terminals within its limits i.e (+ or – %6 )of the rated terminal voltage the capacitor bank is used in series

20)  What is Diversity factor in electrical installations?

• Diversity factor is the ratio of the sum of the individual maximum demands of the various subdivisions of a system, or part of a system, to the maximum demand of the whole system, or part of the system, under consideration. Diversity factor is usually more than one.

21)  Why humming sound occurred in HT transmission line?

• This sound is coming due to ionization (breakdown of air into charged particles) of air around transmission conductor. This effect is called as Corona effect, and it is considered as power loss.

22)  Why frequency is 50 hz only & amp; why should we maintain the frequency constant?

• We can have the frequency at any frequency we like, but then we must also make our own motors, transformers or any other equipment we want to use.
• We maintain the frequency at 50 Hz or 60hz because the world maintains a standard at 50 /60hz and the equipments are made to operate at these frequency.

23)  If we give 2334 A, 540V on Primary side of 1.125 MVA step up transformer, then what will be the Secondary Current, If Secondary Voltage=11 KV?

• As we know the Voltage & current relation for transformer-V1/V2 = I2/I1
  We Know, VI= 540 V; V2=11KV or 11000 V; I1= 2334 Amps.
  By putting these value on Relation-
  540/11000= I2/2334
  So,I2 = 114.5 Amps

24)  What are the points to be considered for MCB (miniature circuit breaker selection)?

• I(L)x1.25=I(MAX) maximum current. Mcb specification is done on maximum current flow in circuit.

25)  How can we start-up the 40w tube light with 230v AC/DC without using any choke/Coil?

• It is possible by means of Electronic choke. Otherwise it’s not possible to ionize the particles in tube. Light, with normal voltage.

26)  What is “pu” in electrical engineering?

• Pu stands for per unit and this will be used in power system single line diagram there it is like a huge electrical circuit with no of components (generators, transformers, loads) with different ratings (in MVA and KV). To bring all the ratings into common platform we use pu concept in which, in general largest MVA and KV ratings of the component is considered as base values, then all other component ratings will get back into this basis. Those values are called as pu values. (p.u=actual value/base value).

27)  Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

• Link is provided at a Neutral common point in the circuit from which various connections are taken for the individual control circuit and so it is given in a link form to withstand high Amps.
• But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only. So if any malfunction happens the fuse connected in the particular control circuit alone will blow off.
• If Fuse is provided in Neutral and if it is blowout and at the same time Supply is on than due to open or break Neutral Voltage is increase and equipment may be damage.

28)  If 200w, 100 w and 60 w lamps connected in series with 230V AC , which lamp glow brighter? Each lamp voltage rating is 230V.

• Each bulb when independently working will have currents (W/V= I)
• For 200 Watt Bulb current (I200) =200/230=0.8696 A
• For 100 Watt Bulb current (I100) =100/230=0.4348 A
• For 60 Watt Bulb current (I60) =60/230=0.2609 A
• Resistance of each bulb filament is (V/I = R)
• For 200 Watt Bulb R200= 230/0.8696= 264.5 ohms
• For 100 Watt Bulb R100= 230/0.4348 = 528.98 ohms and
• For 60 Watt Bulb R60= 230/0.2609=881.6 ohms respectively
• Now, when in series, current flowing in all bulbs will be same. The energy released will be I²R
• Thus, light output will be highest where resistance is highest. Thus, 60 watt bulb will be brightest.
• The 60W lamp as it has highest resistance & minimum current requirement.
• Highest voltage drop across it X I [which is common for all lamps] =s highest power.
• Note to remember:
• Lowest power-lamp has highest element resistance.
• And highest resistance will drop highest voltage drop across it in a Series circuit
• And highest resistance in a parallel circuit will pass minimum current through it. So minimum power dissipated across it as min current X equal Voltage across =s min power dissipation

29)  How to check Capacitor with use of Multi meter.

• Most troubles with Capacitors either open or short.
• An ohmmeter (multi meter) is good enough. A shorted Capacitor will clearly show very low resistance. A open Capacitor will not show any movement on ohmmeter.
• A good capacitor will show low resistance initially, and resistance gradually increases. This shows that Capacitor is not bad. By shorting the two ends of Capacitor (charged by ohmmeter) momentarily can give a weak spark. To know the value and other parameters, you need better instruments

30)  What is the difference between Electronic regulator and ordinary rheostat regulator for fans?

• The difference between the electronic and ordinary regulator is that in electronic regulator power losses are less because as we decrease the speed the electronic regulator give the power needed for that particular speed .But in case of ordinary rheostat type regulator the power wastage is same for every speed and no power is saved. In electronic regulator triac is employed for speed control. by varying the firing angle speed is controlled but in rheostat control resistance is decreased by steps to achieve speed control.

31)  What will happen when power factor is leading in distribution of power?

• If there is high power factor, i.e if the power factor is close to one:
• Losses in form of heat will be reduced,
• Cable becomes less bulky and easy to carry, and very cheap to afford.
• It also reduces over heating of transformers.

32)  What the main difference between UPS & amp; inverter?

• Uninterrupted power supply is mainly use for short time. Means according to ups VA it gives backup. Ups is also two types: on line and offline. Online ups having high volt and amp for long time backup with high dc voltage. But ups start with 12v dc with 7 amps. but inverter is start with 12v,24,dc to 36v dc and 120amp to 180amp battery with long time backup

33)  Which type of A.C motor is used in the fan?

• It is Single Phase induction motor which mostly squirrel cage rotor and are capacitor start capacitor run.

34)  What is the difference between synchronous generator and asynchronous generator?

• In simple, synchronous generator supplies’ both active and reactive power but asynchronous generator (induction generator) supply’s only active power and observe reactive power for magnetizing. This type of generators is used in windmills.

35)  What is the Polarization index value?

• Its ratio between insulation resistance (IR)i.e meager value for 10min to insulation resistance for 1 min. It ranges from 5-7 for new motors & normally for motor to be in good condition it should be Greater than 2.5 .

36)  What is Automatic Voltage regulator (AVR)?

• AVR is an abbreviation for Automatic Voltage Regulator.
• It is important part in Synchronous Generators; it controls the output voltage of the generator by controlling its excitation current. Thus it can control the output Reactive Power of the Generator.

37)  Difference between a four point starter and three point starters?

• The shunt connection in four point starter is provided separately from the line where as in three point starter it is connected with line which is the drawback in three point starter

38)  What happens if we connect a capacitor to a generator load?

• Connecting a capacitor across a generator always improves power factor, but it will help depends up on the engine capacity of the alternator, otherwise the alternator will be over loaded due to the extra watts consumed due to the improvement on pf.
•  Don’t connect a capacitor across an alternator while it is picking up or without any other load

39)  Why the capacitors work on ac only?

• Generally capacitor gives infinite resistance to dc components (i.e., block the dc components). It allows the ac components to pass through.

40)  Why the up to dia 70mm² live conductor, the earth cable must be same size but above dia 70mm² live conductor the earth conductor need to be only dia 70mm²?

• The current carrying capacity of a cable refers to it carrying a continuous load.
• An earth cable normally carries no load, and under fault conditions will carry a significant instantaneous current but only for a short time most Regulations define 0.1 to 5 sec before the fuse or breaker trips. Its size therefore is defined by different calculating parameters.
• The magnitude of earth fault current depends on:
• (a) the external earth loop impedance of the installation (i.e. beyond the supply terminals)
• (b) the impedance of the active conductor in fault
• (c) the impedance of the earth cable.
• i.e. Fault current = voltage / a + b + c
• Now when the active conductor (b) is small, its impedance is much more than (a), so the earth (c) cable is sized to match. As the active conductor gets bigger, its impedance drops significantly below that of the external earth loop impedance (a); when It is quite large its impedance can be ignored. At this point there is no merit in increasing the earth cable size
• i.e. Fault current = voltage / a + c
• (c) is also very small so the fault current peaks out.
• The neutral conductor is a separate issue. It is defined as an active conductor and therefore must be sized for continuous full load. In a 3-phase system,
• If balanced, no neutral current flows. It used to be common practice to install reduced neutral supplies, and cables are available with say half-size neutrals (remember a neutral is always necessary to provide single phase voltages). However the increasing use of non-linear loads which produce harmonics has made this practice dangerous, so for example the current in some standard require full size neutrals. Indeed, in big UPS installations I install double neutrals and earths for this reason.

Selection of 3P-TPN-4P MCB & Distribution Board

Type of breakers based on number of pole:

• Based on the number of poles, the breakers are classified as

1. SP – Single Pole
2. SPN – Single Pole and Neutral
3. DP – Double pole
4. TP – Triple Pole
5. TPN – Triple Pole and Neutral
6. 4P – Four Pole

1.     SP ( Single Pole ) MCB:

• In Single Pole MCCB, switching & protection is affected in only one phase.
• Application: Single Phase Supply to break the Phase only.

2.     DP ( Double Pole ) MCB:

• In Two Pole MCCB, switching & protection is affected in phases and the neutral.
• Application: Single Phase Supply to break the Phase and Neutral.

3.     TP ( Triple Pole) MCB:

• In Three Pole MCB, switching & protection is affected in only three phases and the neutral is not part of the MCB.
• 3pole MCCB signifies for the connection of three wires for three phase system (R-Y-B Phase).
• Application: Three Phase Supply only (Without Neutral).

4.     TPN (3P+N) MCB:

• In TPN MCB, Neutral is part of the MCB as a separate pole but without any protective given in the neutral pole (i.e.) neutral is only switched but has no protective element incorporated.
• TPN for Y (or star) the connection between ground and neutral is in many countries not allowed. Therefore the N is also switches.
• Application: Three Phase Supply with Neutral

5.     4 Pole MCB:

• 4pole MCCB for 4 wires connections, the one additional 4^th pole for neutral wire connection so that between neutral and any of the other three will supply.
• In 4-Pole MCCBs the neutral pole is also having protective release as in the phase poles.
• Application: Three Phase Supply with Neutral

Difference between TPN and 4P (or SPN and DP):

• TPN means a 4 Pole device with 4th Pole as Neutral. In TPN opening & closing will open & close the Neutral.
• For TPN, protection applies to the current flows through only 3 poles (Three Phase) only; there is no protection for the current flow through the neutral pole. Neutral is just an isolating pole.
• TP MCB is used in 3phase 4wire system. It is denoted as TP+N which will mean a three pole device with external neutral link which can be isolated if required. 
• For the 4 pole breakers, protection applies to current flow through all poles. However when breaker trips or manually opened, all poles are disconnected.
• Same type of difference also applies for SPN and DP.

Where to Use TP, TPN and 4P in Distribution panel:

• For any Distribution board, the protection system (MCB) must be used in the incomer. For a three phase distribution panel either TP or TPN or 4P can be used as the incoming protection.
• TP MCB: It is most commonly used type in all ordinary three phase supply.
• TPN MCB: It is generally used where there are dual sources of incomer to the panel (utility source and emergency generator source).
• 4P MCB: It is used where is the possibility of high neutral current (due to unbalance loads and /or 3^rd and multiple of 3^rd harmonics current etc) and Neutral / Earth Protection is provided on Neutral.

Where to use 4 Pole or TPN MCB instead of 3 Pole (TP) MCB.

• Multiple Incoming Power System:
• When we have a transformer or a stand-by generator feeding to a bus, it is mandatory that at least either of the Incomers or the bus coupler must be TPN or 4-Pole Breaker please refers IS 3043.
• In multi incomer power feeding systems, we cannot mix up the neutrals of incoming powers to other Power Source so we can use TPN or 4P breakers or MCB instead of TP MCB to isolate the Neutral of other power sources from the Neutral of incomer power in use.
• We can use 4 Pole ACB instead of TP for safety reasons .If there is power failure and DG sets are in running condition to feed the loads, if there is some unbalance in loads(which is practically unavoidable in L.V. distribution system ), depending of quantum of unbalance, there will be flow of current through Neutral. During this time, if Power Supply Utility Technicians are working, and if they touch the neutral conductors(which is earthed at their point ) they will likely to get electric shock depending on the potential rise in common neutral due flow of current through Neutral conductor as stated above. Even fatal accident may occur due the above reason. As such, it is a mandatory practice to isolate the two Neutrals.
• We can use 4-pole breakers or TPN Breakers when the system has two alternative sources and, in the event of power failure from the mains, change-over to the standby generator is done. In such a case, it is a good practice to isolate the neutral also.
• 4 pole circuit breakers have advantages in the case when one of the poles of the device will get damage, and it also provides isolation from neutral voltage.
• Normally, Neutral is not allowed to break in any conditions, (except special applications) for human & equipment safety. So for single incomer power fed systems, 3P breaker is used, where only phases are isolated during breaking operations.
• Where We have dual Power like in DG & other electricity supply sources ,it is required to isolate neutral, where neutral needs to be isolated  in internal network TPN MCB or 4P MCB can be used.

Where to use 4 Pole MCB instead of TPN MCB

• Any Protection Relay used on Neutral (Ground Fault Protection of Double ended System):
• The use of four poles or three poles CB will depend on system protection and system configuration.
• Normally in 3phase with neutral we just use 3pole CB and Neutral is connected on common Neutral Link but if application of 3pole will affect the operation of protective relay then we must use 4pole CB.
• System evaluation has to be required to decide whether three-pole circuit breakers plus neutral link can be used or four-pole breakers are required.
• If unrestricted ground fault protection is fitted to the transformer neutral, then the bus section circuit breaker should have 4-poles and preferably incomer circuit breakers should also have 4-poles because un cleared ground fault located at the load side of a feeder have two return paths. As shown in fig a ground fault on a feeder at the bus section “A” will have a current return path in both the incomers, thus tripping both Bus. The sensitivity of the unrestricted ground fault relay is reduced due to the split current paths.

• For System Stability :
• In an unbalanced 3phase system or a system with non-linear loads, the neutral gives the safety to the unbalanced loads in the system and therefore It must not be neglected. In perfectly balanced conditions the neutral functions as a safety conductor in the unforeseen short-circuit and fault conditions. Therefore by using 4-pole MCB will enhance the system stability.
• 4 Poles will be decided after knowing the Earthing Systems (TT, TN-S, TN-C, IT).

(1) IT (with distributed neutral) System:

• The Neutral should be switched on & off with phases.
• Required MCB: TPN or 4P MCB.

(2) IT (without distributed neutral) System:

• There is no neutral.
• Required MCB: TP MCB.

(3) TN-S System:

• Required MCB: TP MCB because even when neutral is cut off system remains connected with Ground.

(4) TN-C System:

• Required MCB: TPN or 4P only, because we cannot afford to cut neutral doing so will result in system loosing contact with Ground.

(5) TN-C-S System:

• Neutral and Ground cable are separate
• Required MCB:  TP MCB Because Neutral and Ground cable are separate.

(6) TT System: 

• Ground is provided locally
• Required MCB:  TP MCB because ground is provided locally.
• Conclusion: Its compulsory to use TPN in TN-C system rest everywhere you can use MCB.

Nomenclature of Distribution Board:

• Distribution Box can be decided by “way” means how many how many single phase (single pole) distribution. Circuit and Neutral are used.

1)     SPN Distribution Board (Incoming+ Outgoing)

• 4way (Row) SPN = 4 X 1SP= 4Nos (Module) of single pole MCB as outgoing feeders.
• 6way (Row) SPN = 6 X 1SP= 6Nos (Module) of single pole MCB as outgoing feeders.
• 8way (Row) SPN = 8 X 1SP= 8Nos (Module) of single pole MCB as outgoing feeders.
• 10way (Row) SPN = 10 X 1SP= 10Nos (Module) of single pole MCB as outgoing feeders.
• 12way (Row) SPN = 12 X 1SP= 12Nos (Module) of single pole MCB as outgoing feeders.
• Normally single phase distribution is mainly used for small single phase loads at house wiring or industrial lighting wiring.

2)     TPN Distribution Board (Incoming, Outgoing)

• 4way (Row) TPN = 4 X TP= 4nos of 3pole MCB as outgoing feeders =12 No of single pole MCB.
• 6way (Row) TPN = 6 X TP= 6nos of 3pole MCB as outgoing feeders =18 No of single pole MCB.
• 8way (Row) TPN = 8 X TP= 8nos of 3pole MCB as outgoing feeders =24 No of single pole MCB.
• 10way (Row) TPN = 10 X TP= 10nos of 3pole MCB as outgoing feeders =30 No of single pole MCB.
• 12way (Row) TPN =12 X TP= 12nos of 3pole MCB as outgoing feeders =36 No of single pole MCB

How to save Electrical energy at Home

How to save  Electrical energy at Home

In our home we use lot of electrical equipment like Tv, Freeze, Washing machine,Mp3 player. music system, computer laptop. But we have not adequate knowledge for how to use this electrical equipment in proper way Due to this ignorance we are paying more electricity Bill which we are not actually use.
Do you know in actual we are consuming more electricity or paying more amounts what we actually not use it?
According to the energy auditors we can easily save between 5 and 10% of their energy consumption (and costs) by changing our behavior such as switching electrical equipment off at the mains rather than leaving it on standby, turning off lights when they’re not being used
By saving Electrical energy will directly reflected to saving money so it is very necessary to under stood ghost unit or amount which we are paying without using the appliances.
The major appliances in your home — refrigerators, clothes washers, dishwashers — account for a big chunk of your monthly utility bill. And if your refrigerator or washing machine is more than a decade old, you’re spending a lot more on energy than you need to.
Today’s major appliances don’t hog energy the way older models do because they must meet minimum federal energy efficiency standards. These standards have been tightened over the years, so any new appliance you buy today has to use less energy than the model you’re replacing. For instance, if you buy one of today’s most energy-efficient refrigerators, it will use less than half the energy of a model that’s 12 years old or older.

Lighting

• Get into the habit of turning lights off when you leave a room. —-Saving Energy 0.5 %
• Use task lighting (table and desktop lamps) instead of room lighting.
• Take advantage of daylight
• De-dust lighting fixtures to maintain illumination—–Saving Energy 1 %
• Compact fluorescent bulbs (CFL):

1. CFL use 75% less energy than Normal bulbs.
2. CFL are four times more energy efficient than Normal bulbs.
3. CFL can last up to ten times longer than a normal bulb.

• Use electronic chokes. in place of conventional copper chokes.—-Saving Energy 2 %
• Get into the habit of turning lights off when you leave a room.
• Use only one bulb for light fittings with more than one light bulb, or replace additional bulbs with a lower wattage version.
• Use energy-saving light bulbs that can last up to ten times longer than a normal bulb and use significantly less energy. A single 20- to 25-watt energy-saving bulb provides as much light as a 100-watt ordinary bulb.
• Use tungsten halogen bulbs for spotlights—they last longer and are up to 100% more efficient.
• Fit external lights with a motion sensor.
• Use high frequency fittings for fluorescent tubes because they cut flicker and are even more efficient than energy-saving light bulbs. They are suitable for kitchens, halls, workshops and garages.

Save on Your Fridge & Freezer:

• Defrost your fridge regularly.
• Check that the door seals are strong and intact.
• Don’t stand Freezer’s Back Side too near the Wall.
• Avoid putting warm or hot food in the fridge or freezer—it   requires more energy to cool it down.
• Clean condenser coils twice a year.
• Get rid of old refrigerators!  They use twice the energy as new Energy Star® models.
• Keep refrigerators full but not overcrowded.
• Defrost your fridge regularly. When ice builds up, your freezer uses more electricity. If it frosts up again quickly, check that the door seals are strong and intact.
• Do not stand the fridge next to the oven or other hot appliances if you can help it. Also ensure there is plenty of ventilation space behind and above it.
• Keep the fridge at 40°F and the freezer at 0°F. Empty and then turn your fridge off if you go on a long vacation (but make sure you leave the door open).
• Aim to keep your fridge at least three-quarters full to maintain maximum efficiency. A full fridge is a healthy fridge.
• Avoid putting warm or hot food in the fridge or freezer—it requires more energy to cool it down.

AIR CONDITION UNIT

• For Home Purpose use Window unit Instead Of Split Unit.
• For Office and Commercial Purpose Use Split AC instead of Window unit.
• Consider installing a programmable t. Just set the times and temperatures to match your schedule and you will save money and be comfortably cool when you return home.
• Get air conditioner maintenance each year.
• Checks the condenser coils, the evaporator coils, the blower wheel, the filter, the lubrication and the electrical   contacts.
• Replace worn and dirty equipment for maximum efficiency.
• Replace air conditioner filters every month.
• Turn off central air conditioning 30 minutes before leaving your home.
• Consider using ceiling or portable fans to circulate and cool the air.
• Try increasing your air conditioner temperature. Even 1 degree higher could mean significant savings, and you will probably not notice the difference.
• Keep central air conditioner usage to a minimum—or even turn the unit off—if you plan to go away.
• Consider installing a programmable thermostat. Just set the times and temperatures to match your schedule, and you will save money and be comfortably cool when you return home.
• Get air conditioner maintenance each year—ensure your service person checks the condenser coils, the evaporator coils, the blower wheel, the filter, the lubrication and the electrical contacts. Replace worn and dirty equipment for maximum efficiency.
• Replace air conditioner filters every month.
• Buy the proper size equipment to meet your family’s needs—an oversized air conditioner unit will waste energy.
• If you have a furnace, replace it at the same time as your air conditioner system. Why? Because it is your furnace fan that blows cool air around your home, and a newer furnace fan provides improved air circulation all year round, plus saves energy costs.

Water Heater:

• Check your hot water temperature. It does not need to be any higher than 140°F for washing purposes.
• Plug the basin or bath when you run any hot water.
• Use a timer to make sure the heating and hot water are only on when needed.
• Insulate your hot water pipes to prevent heat loss, and your water will stay hotter for longer. Plus, you will also use less energy to heat it. And simply fitting a jacket onto your hot water tank can cut waste by up to three quarters.
• Take showers—a bath consumes 5 times more hot water. Buy a low-flow showerhead for more efficiency and it will pay for itself in no time.
• Avoid washing dishes under hot running water, and do not pre-rinse before using the dishwasher.
• Repair dripping hot water taps immediately
• Make sure hot water taps are always turned off properly.

Washing Machine:

• Wash full loads of Washing Machine—you will use your machine less often, saving time, and it is more energy-efficient.
• Wash at a lower temperature or the economy setting to save even more.
• Use the spin cycle, and then hang washing out rather than tumble drying—your clothes and linens will smell fresher!
• If you need to tumble dry, try a lower temperature setting.
• Use your dryer for consecutive loads, because the built-up heat between loads will use less energy.

Oven/Electrical Cooker:

• Make sure your oven door closes tightly.
• Use a microwave rather than conventional oven, when possible.
• Keep the center of the pan over the element, and keep the lid on when cooking on the stovetop.
• Only boil the amount of water that you need—just ensure there is enough water to cover the heating element. Turn the element or electric kettle down as soon as it reaches the boiling point.

COMPUTER / LAPTOP

• Buy a laptop instead of a desktop, if practical. —-Saving Energy 5 %.
• If you buy a desktop, get an LCD screen instead of an outdated CRT.
• Use sleep-mode when not in use helps cut  energy costs by approx  40%.
• Turn off the monitor; this device alone uses more than half  the system’s  energy.
• Screen savers save computer screens, not energy.
• Use separate  On/Off switch Socket Instead of One.
• Laser printers use more electricity than inkjet printers.

FAN:

• A ceiling fan in operation through out night will gobble up 22 units in a month.
• There is a wrong notion that fan at more speed would consume more current.
• Fan running at slow speed would waste energy as heat in the regulator.
• The ordinary regulator would take 20 watts extra at low speed.
• The energy loss can be compensated by using  electronic   regulator

Buy efficient electric appliances:

• They use two to 10 times less electricity for the same functionality, and are mostly higher quality products that last longer than the less efficient ones. In short, efficient appliances save you lots of energy and money.
• In many countries, efficiency rating labels are mandatory on most appliances. Look Energy Star label is used.
• The label gives you information on the annual electricity consumption. In the paragraphs below, we provide some indication of the consumption of the most efficient appliances to use as a rough guide when shopping. Lists of brands and models and where to find them are country-specific and so cannot be listed here, but check the links on this page for more detailed information.
• Average consumption of electric appliances in different regions in the world, compared with the high efficient models on the market

Ghost consumers:

• Identify the “ghost consumers” which consume power – not because they are in use, but because they are   plugged in and are in stand-by mode.
• The TV consumes 10 watt power When It’s is in Stand by Mode.

Ex.  TV is in stand-by-mode  for 10 hours a Day.
Energy Consumption  /  Day= 10 X 10 = 100 Watts. = 0.1 KWH.
Energy consumption /  Month= 1X100X30=3000 Watts=3KWH ( Unit) .
Energy Consumption in Rupees. = 3 X 4 = 12 Rs/Month.

• The TV consumes 5 watt power when we  don’t  plug out from switch Board.

Ex.  TV is in un Plug Mode for 10 hours a Day.
Energy Consumption  /  Day= 5 X 10 = 50 Watts. = 0.05 KWH.
Energy consumption /  Month= 1X50X30= 1500 Watts=1.5 KWH ( Unit) .
Energy Consumption in Rupees. = 1.5 X 4 = 6 Rs/Month.

• The cell phone charger uses 3 watt per hour when plugged.
• Mosquito mats consume 5 watts per hour.
• If you use an electric geyser, do not leave it in thermostat mode, for it causes standing losses of 1-1.5 units

Calculate Size of Contactor, Fuse, C.B, O/L  of DOL Starter

• Calculate Size of each Part of DOL starter for The System Voltage 415V ,5HP Three Phase House hold Application Induction Motor ,Code A, Motor efficiency 80%,Motor RPM 750 ,Power Factor 0.8 , Overload Relay of Starter is Put before Motor.

Basic Calculation of Motor Torque & Current:

• Motor Rated Torque (Full Load Torque) =5252xHPxRPM
• Motor Rated Torque (Full Load Torque) =5252x5x750=35 lb-ft.
• Motor Rated Torque (Full Load Torque) =9500xKWxRPM
• Motor Rated Torque (Full Load Torque) =9500x(5×0.746)x750 =47 Nm
• If Motor Capacity is less than 30 KW than Motor Starting Torque is 3xMotor Full Load Current or 2X Motor Full Load Current.
• Motor Starting Torque=3xMotor Full Load Current.
• Motor Starting Torque==3×47=142Nm.
• Motor Lock Rotor Current =1000xHPx figure from below Chart/1.732×415

Locked Rotor Current
Code	Min	Max
A	1	3.14
B	3.15	3.54
C	3.55	3.99
D	4	4.49
E	4.5	4.99
F	5	2.59
G	2.6	6.29
H	6.3	7.09
I	7.1	7.99
K	8	8.99
L	9	9.99
M	10	11.19
N	11.2	12.49
P	12.5	13.99
R	14	15.99
S	16	17.99
T	18	19.99
U	20	22.39
V	22.4

• As per above chart Minimum Locked Rotor Current  =1000x5x1/1.732×415=7 Amp
• Maximum Locked Rotor Current =1000x5x3.14/1.732×415=22 Amp.
• Motor Full Load Current (Line) =KWx1000/1.732×415
• Motor Full Load Current (Line) = (5×0.746)x1000/1.732×415=6 Amp.
• Motor Full Load Current (Phase)=Motor Full Load Current (Line)/1.732
• Motor Full Load Current (Phase)==6/1.732=4Amp
• Motor Starting Current =6 to 7xFull Load Current.
• Motor Starting Current (Line)=7×6=45 Amp

(1) Size of Fuse:

Fuse  as per NEC 430-52
Type of Motor	Time Delay Fuse	Non-Time Delay Fuse
Single Phase	300%	175%
3 Phase	300%	175%
Synchronous	300%	175%
Wound Rotor	150%	150%
Direct Current	150%	150%

• Maximum Size of Time Delay Fuse =300% x Full Load Line Current.
• Maximum Size of Time Delay Fuse =300%x6= 19 Amp.
• Maximum Size of Non Time Delay Fuse =1.75% x Full Load Line Current.
• Maximum Size of Non Time Delay Fuse=1.75%6=11 Amp.

(2) Size of Circuit Breaker:

Circuit Breaker as per NEC 430-52
Type of Motor	Instantaneous Trip	Inverse Time
Single Phase	800%	250%
3 Phase	800%	250%
Synchronous	800%	250%
Wound Rotor	800%	150%
Direct Current	200%	150%

• Maximum Size of Instantaneous Trip Circuit Breaker =800% x Full Load Line Current.
• Maximum Size of Instantaneous Trip Circuit Breaker =800%x6= 52 Amp.
• Maximum Size of Inverse Trip Circuit Breaker =250% x Full Load Line Current.
• Maximum Size of Inverse Trip Circuit Breaker =250%x6= 16 Amp.

(3) Thermal over Load Relay:

• Thermal over Load Relay (Phase):
• Min Thermal Over Load Relay setting =70%xFull Load Current(Phase)
• Min Thermal Over Load Relay setting =70%x4= 3 Amp
• Max Thermal Over Load Relay setting =120%xFull Load Current(Phase)
• Max Thermal Over Load Relay setting =120%x4= 4 Amp
• Thermal over Load Relay (Phase):
• Thermal over Load Relay setting =100%xFull Load Current (Line).
• Thermal over Load Relay setting =100%x6= 6 Amp

(4) Size and Type of Contactor:

Application	Contactor	Making Cap
Non-Inductive or Slightly Inductive ,Resistive Load	AC1	1.5
Slip Ring Motor	AC2	4
Squirrel Cage Motor	AC3	10
Rapid Start / Stop	AC4	12
Switching of Electrical Discharge Lamp	AC5a	3
Switching of Electrical Incandescent Lamp	AC5b	1.5
Switching of Transformer	AC6a	12
Switching of Capacitor Bank	AC6b	12
Slightly Inductive Load in Household or same type load	AC7a	1.5
Motor Load in Household Application	AC7b	8
Hermetic refrigerant Compressor Motor with Manual O/L Reset	AC8a	6
Hermetic refrigerant Compressor Motor with Auto O/L Reset	AC8b	6
Control of Restive & Solid State Load with opto coupler Isolation	AC12	6
Control of Restive Load and Solid State with T/C Isolation	AC13	10
Control of Small Electro Magnetic Load ( <72va span="">	AC14	6
Control of Small Electro Magnetic Load ( >72VA)	AC15	10

• As per above Chart
• Type of Contactor= AC7b
• Size of Main Contactor = 100%X Full Load Current (Line).
• Size of Main Contactor =100%x6 = 6 Amp.
• Making/Breaking Capacity of Contactor= Value above Chart x Full Load Current (Line).
• Making/Breaking Capacity of Contactor=8×6= 52 Amp.

Electrical Thumb Rules (Part 1)

Electrical Thumb Rules For:

• Cable Capacity
• Current Capacity of Equipment
• Earthing Resistance
• Minimum Bending Radius
• Insulation Resistance
• Lighting Arrestor
• Transformer
• Diesel Generator
• Current Transformer
• Quick Electrical Calculation
Cable Capacity

• For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire in Sq.mm
  Ex. For 2.5 Sq.mm = 6×2.5 = 15 Amp, For 1 Sq.mm = 6×1 = 6 Amp, For 1.5 Sq.mm = 6×1.5 = 9 Amp
• For Cable Current Capacity = 4X Size of Cable in Sq.mm, Ex. For 2.5 Sq.mm = 4×2.5 = 9 Amp.
• Nomenclature for cable Rating = Uo/U
• where Uo = Phase-Ground Voltage, U = Phase-Phase Voltage, Um = Highest Permissible Voltage

Current Capacity of Equipment

• 1 Phase Motor draws Current = 7Amp per HP.
• 3 Phase Motor draws Current = 1.25Amp per HP.
• Full Load Current of 3 Phase Motor = HPx1.5
• Full Load Current of 1 Phase Motor = HPx6
• No Load Current of 3 Phase Motor = 30% of FLC
• KW Rating of Motor = HPx0.75
• Full Load Current of equipment = 1.39xKVA (for 3 Phase 415Volt)
• Full Load Current of equipment = 1.74xKw (for 3 Phase 415Volt)

Earthing Resistance

• Earthing Resistance for Single Pit = 5Ω, Earthing Grid = 0.5Ω
• As per NEC 1985 Earthing Resistance should be < 5Ω.
• Voltage between Neutral and Earth <= 2 Volt
• Resistance between Neutral and Earth <= 1Ω
• Creepage Distance = 18 to 22mm/KV (Moderate Polluted Air) or
• Creepage Distance = 25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius

• Minimum Bending Radius for LT Power Cable = 12 x Dia of Cable.
• Minimum Bending Radius for HT Power Cable = 20 x Dia of Cable.
• Minimum Bending Radius for Control Cable = 10 x Dia of Cable.

Insulation Resistance

• Insulation Resistance Value for Rotating Machine = (KV+1) MΩ.
• Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).
• Insulation Resistance Value for Equipment (<1kv strong=""> Minimum 1 MΩ.
• Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV.
• Insulation Resistance Value for Panel = 2 x KV rating of the panel.
• Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ
• Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.
• Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000
• Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).
• Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

Lighting Arrestor

Arrestor have Two Rating:

1. MCOV=Max. Continuous Line to Ground Operating Voltage.
2. Duty Cycle Voltage. (Duty Cycle Voltage > MCOV).

Transformer

• Current Rating of Transformer = KVA x 1.4
• Short Circuit Current of T.C /Generator = Current Rating / % Impedance
• No Load Current of Transformer =< 2% of Transformer Rated current
• Capacitor Current (Ic) = KVAR / 1.732xVolt (Phase-Phase)
• Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW,
• Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.
• The diversity they would apply to apartments is around 60%
• Maximum HT (11kV) connected load will be around 4.5MVA per circuit.
• 4No. earth pits per transformer (2No. for body and 2No. for neutral earthing),
• Clearances, approx.1000mm around TC allow for transformer movement for replacement.

Diesel Generator

• Diesel Generator Set Produces = 3.87 Units (KWH) in 1 Litter of Diesel.
• Requirement Area of Diesel Generator = for 25KW to 48KW = 56 Sq.meter, 100KW = 65 Sq.meter.
• DG less than or equal to 1000kVA must be in a canopy.
• DG greater 1000kVA can either be in a canopy or skid mounted in an acoustically treated room
• DG noise levels to be less than 75dBA at 1 meter.
• DG fuel storage tanks should be a maximum of 990 Litter per unit. Storage tanks above this level will trigger more stringent explosion protection provision.

Current Transformer

Nomenclature of CT:

• Ratio: input / output current ratio
• Burden (VA): total burden including pilot wires. (2.5, 5, 10, 15 and 30VA.)
• Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30).
• Accuracy Limit Factor:
• Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor.Example: 1600/5, 15VA 5P10  (Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10)
• As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accu­rate to 0.3 percent if the connected secondary burden if imped­ance does not exceed 0.1 ohms.
• As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A).

Quick Electrical Calculation

1HP = 0.746KW	Star Connection
1KW = 1.36HP	Line Voltage = √3 Phase Voltage
1Watt = 0.846 Kla/Hr	Line Current = Phase Current
1Watt = 3.41 BTU/Hr	Delta Connection
1KWH = 3.6 MJ	Line Voltage = Phase Voltage
1Cal = 4.186 J	Line Current = √3 Phase Current
1Tone = 3530 BTU
85 Sq.ft Floor Area = 1200 BTU
1Kcal = 4186 Joule
1KWH = 860 Kcal
1Cal = 4.183 Joule

Electrical Thumb Rules (Part 2)

Electrical Thumb Rules

Useful Electrical Equations

• For Sinusoidal Current: Form Factor = RMS Value/Average Value =1.11
• For Sinusoidal Current: Peak Factor = Max Value/RMS Value = 1.414
• Average Value of Sinusoidal Current (I_av) = 0.637 x Im (Im = Max.Value)
• RMS Value of Sinusoidal Current (I_rms) = 0.707 x Im (Im = Max.Value)
• A.C Current = D.C Current/0.636.
• Phase Difference between Phase = 360/ No of Phase (1 Phase=230/1=360°, 2 Phase=360/2=180°)
• Short Circuit Level of Cable in KA (I_sc) =
  (0.094 x Cable Dia in Sq.mm) /√ Short Circuit Time (Sec)
• Max.Cross Section Area of Earthing Strip (mm2) = √(Fault Current x Fault Current x Operating Time of Disconnected Device ) / K
  K = Material Factor, K for Cu = 159, K for Al = 105, K for steel = 58 , K for GI = 80
• Most Economical Voltage at given Distance = 5.5x√((km/1.6)+(kw/100))
• Cable Voltage Drop (%) =
  (1.732 x current x (RcosǾ+jsinǾ) x 1.732 x Length (km) x 100) / (Volt(L-L) x Cable Run.
• Spacing of Conductor in Transmission Line (mm) = 500 + 18 x (P – P Volt) + (2 x (Span in Length)/50).
• Protection radius of Lighnting Arrestor = √h x (2D-h) + (2D+L).
  Where h= height of L.A, D-distance of equipment (20, 40, 60 Meter), L=V x t (V=1m/ms, t=Discharge Time).
• Size of Lightning Arrestor = 1.5x Phase to Earth Voltage or 1.5 x (System Voltage/1.732).
• Maximum Voltage of the System = 1.1xRated Voltage (Ex. 66KV = 1.1 × 66 = 72.6KV)
• Load Factor = Average Power/Peak Power
• If Load Factor is 1 or 100% = This is best situation for System and Consumer both.
• If Load Factor is Low (0 or 25%) = you are paying maximum amount of KWH consumption. Load Factor may be increased by switching or use of your Electrical Application.
• Demand Factor = Maximum Demand / Total Connected Load (Demand Factor <1 li="">
• Demand factor should be applied for Group Load
• Diversity Factor =
  Sum of Maximum Power Demand / Maximum Demand (Demand Factor >1)
  Diversity factor should be consider for individual Load
• Plant Factor (Plant Capacity) = Average Load / Capacity of Plant
• Fusing Factor = Minimum Fusing Current / Current Rating (Fusing Factor>1).
• Voltage Variation (1 to 1.5%) = ((Average Voltage – Min Voltage) x 100)/Average Voltage
  Ex: 462V, 463V, 455V, Voltage Variation= ((460 – 455)  x 100)/455 = 1.1%.
• Current Variation (10%) = ((Average Current – Min Current) x 100)/Average Current
  Ex: 30A,35A,30A, Current Variation = ((35-31.7) x 100)/31.7 = 10.4%
• Fault Level at TC Secondary
  = TC (VA) x 100 / Transformer Secondary (V) x Impedance (%)
• Motor Full Load Current = Kw /1.732 x KV x P.F x Efficiency