How to change direction of three phase motor in Starters and VFD??

There are some applications where phase sequence required to be changed in 3-Phase motors. Mostly plants which don’t have their own power supply and take from Power Distribution companies phase sequence might change.

That Phase sequence can be easily changed in 3-Phase Induction motors by changing two phases from Input Source supply.

In Case of Star-Delta Starters 6 no. leads enter into motor so in that case Phase sequence can be changed by changing 2 no. of phases in each pair of 3-Phases.

Star-Delta Starter

Phase Sequence changed in Star-Delta Starter:-

In Case of DOL Soft-Starters Phase sequence can be changed by changing phases in Mains Supply.

Is there is requirement of changing Phase sequence in VFD’S????

Answer for the same in that there is no need of changing phase sequence. In Case of VFD there is no need of changing phase sequence as in that case 3-Phase supply is converted into DC supply thereafter that can be converted into AC supply again so that is why there is no need of changing phase sequence in VFD’S.

Three phase Motors Parameters calculations

It is very important to find  out electrical parameters for an electrical engineer.

Very time installation of motor required certain parameters calculations which are stated as below:-

Electrical Parameter to Find	Alternating Current
	Single-Phase	Three-Phase
Amperes when horsepower is known	HP x 746 E x Eff x pf	HP x 746 1.73 x E x Eff x pf
Amperes when kilowatts are known	KW x 1000 E x pf	KW x 1000 1.73 x E x pf
Amperes when KVA are known	KVAx 1000 E	KVA x 1000 1.73 x E
Kilowatts	I x E x pf 1000	1.73 x I x E x pf 1000
KVA	I x E 1000	1.73 x I x E 1000
Horsepower = (Output)	I x E x Eff x pf 746	1.73 x I x E x Eff x pff 746

As from above we can find out ampere a motor can take. Day to day checking motor ampere is very much required for an electrical engineer.

Three phase motor formula

There are following formula's which are very useful for an electrical engineer while doing calculation on various aspects for induction motors.


High Inertia Loads

t =	WK2 x rpm 308 x Tav.		WK2 = inertia in lb.ft.2 t = accelerating time in sec. T = Av. accelerating torque lb.ft..
T =	WK2 x rpm 308 x t

For calculating time required to accelerate an induction motor at a particular load formula-I will help the same

If you know want a particular motor to get accelerated at a given time then required torque can be calculated by using formula-II in above.

Both formulas are quite helpful while doing programming in Variable frequency drives and soft-starters.

Inertia reflected to motor = Load Inertia X (

Load rpm/Motor rpm

)X(Load rpm/Motor rpm)

Synchronous Speed, Frequency And Number Of Poles Of AC Motors

ns =

120 x f  P

f =

P x ns 120

P =

120 x f  ns

Relation Between Horsepower, Torque, And Speed

HP =

T x n 5250

T =

5250 HP  n

n =

5250 HP  T

Motor Slip

% Slip =

ns - n ns

x 100

Symbols

I	=	current in amperes
HP	=	output power in horsepower
n	=	motor speed in revolutions per minute (RPM)
ns	=	synchronous speed in revolutions per minute (RPM)
P	=	number of poles
f	=	frequency in cycles per second (CPS)
T	=	torque in pound-feet
EFF	=	efficiency as a decimal
PF	=	power factor as a decimal

Single phase and Three phase useful formula's

Rules Of Thumb (Approximation)

At 1800 rpm, a motor develops a 3 lb.ft. per hp

At 1200 rpm, a motor develops a 4.5 lb.ft. per hp

At 575 volts, a 3-phase motor draws 1 amp per hp

At 460 volts, a 3-phase motor draws 1.25 amp per hp

At 230 volts a 3-phase motor draws 2.5 amp per hp

At 230 volts, a single-phase motor draws 5 amp per hp

At 115 volts, a single-phase motor draws 10 amp per hp

Mechanical Formulas

Torque in lb.ft. =

HP x 5250 rpm

HP =

Torque x rpm 5250

rpm =

120 x Frequency No. of Poles

Temperature Conversion

Deg C = (Deg F - 32) x 5/9
Deg F = (Deg C x 9/5) + 32 

Single phase and three phase faults effects on human body and human body perception level

Can ever imagine how dangerous are electrical faults???

Let me give you one fact about electrical faults and their levels.

Temperature produced during electrical arc-flash can reach 35,000 _F (19,500 _C).

 These extremely high temperatures will easily melt copper conductors.

Copper expands by a factor of 67,000 times at such high temperatures

Usually such faults occurred during Short circuit of copper bus bars.

When Human comes directly short circuit with two phases.

The dangers associated with these faults are:-

1. High pressures

2. High level of Sound

3. Very high currents

These high pressures can easily exceed 100-1000  pounds per square foot. Such faults produce high sounds which seems like a bomb get blasted and even causes damages to ladders, Humans etc.

The sounds associated with these pressures can exceed 160 dB.

The electrical current levels associated with electrical shock are measured in milli-amperes or one-thousandth of an ampere (0.001 Amps).

Electrical current flows through the body’s nervous system, muscles, and the blood system. Current flow

can damage organs , Can cause burning of body and have long-term effects on the body, which may not be readily visible at the time of the shock event.

HT Fault currents are such high that immediately all body get burnt in seconds and only ashes remains

Electrical shock current levels:-

Current range (mA) Physiological effect Condition description:-

1mA Threshold of perception Detect a slight tingling sensation in hands or fingertips

1–9 mA       Let-go threshold:- Unpleasant sensation but muscle control not impaired.

9–25 mA     Muscular contraction:- Painful and hard or impossible to release energized object in hand

26–59 mA   Muscular contraction Breathing difficult

60–100 mA Ventricular fibrillation Heart stoppage, respiration inhibition, death possible

Difference between XLPE and PVC Cables

Both Cables are widely used in Industries:

PVC - stands for polyvinyl chloride 
XLPE - is cross linked polyethylene cable. 

Main Thumb rule for differentiation is that XLPE cables can be used for both HT and LT lines.
But PVC Cables can be used only for LT lines.

XLPE can withstand a higher temperature than PVC without detriment. This means that more current can be conducted for the same cross sectional area of copper. This means a big saving in cables costs. 

Visit link below for more details:-
http://electrialstandards.blogspot.com/2014/04/66kv-to-132kv-tests-requirement.html

http://electricalsystembasics.com/2014/04/xlpe-cables-advantages-oil-filled-paper-insulated-cables.html

XLPE Cables useful properties are :-

XLPE Cables construction:-

1.Temperature resistance
2. Stress rupture resistance 
3. Environmental stress crack resistance 
4. Resistance to U.V light
5. Chemical resistance
6. Oxidation resistance

 XLPE Cables can be useful for following applications:- 

1) XLPE cables work for the working voltage of 240 V to 500 KV . 
2) Conductor Material can be either Copper or Aluminium. 
3) XLPE cables can be either Single Core cables or Multi core cables depending upon the number of 
cores. 
4) They can be Unarmoured or Strip Armoured or Wire Armoured or Tape Armoured type depending upon the presence or absence of Armour . 
5) HT / LT Aerial Bunched Cables 


Polyvinyl chloride Cables

They are commonly abbreviated as PVC, insulated cables are widely used in various fields. 

PVC's Cables are generally have following Properties:-

1. Low cost
2. Chemical resistance 
3. High tensile strength
4. Better flexibility 

For electric cables the PVC is mixed up with plasticizers.

Low voltage copper conductor PVC cables are extensively used for domestic home appliances wiring, house wiring and internal wiring for lighting circuits in factories, power supply for office 
automation, in control.

PVC CABLES 
1) Power Cables upto 1.1 KV 
2) Multicore Cables upto 61 Cores 
3) Shielded instrumentation Cables 
4) FRLS / FR / HR / Fire Survival Cable 

YWY, AYFY, AYY, AYCY, A2XCY Cables Meanings

Its quit confusing sometimes to read Nomenclature of cables such as YWY or AYFY.

Below is Details of that Nomenclature which will help to read about cables nomenclatures and will ease out for Technical specifications of cables.

A = Appearing as a first letter denotes Aluminium Conductor.

Y = TROPODUR means PVC Insulation if appears any where in configuration but not at last if Y is written at last then it means TROPODUR Sheath.

2X = TROPOTHEN-X (Cross-linked Polyethylene) Insulation.

W = Round Steel Wire Armouring.

WW = Double Round Steel Wire Armouring.

F = Formed Steel Wire (Strip) Armouring.

FF = Double Formed Steel Wire (Strip) Armouring.

C = Metallic Screening (Usually of Copper).

CE = Metallic Screening (usually of Copper) over each individual core.

Gb = Holding Helix Tape (of Steel)

Wa = Aluminium Round Wire & Aluminium Formed Wire (Strip) Fa Armouring

b) Type Designations :

AYY Aluminium Conductor, TROPODUR Insulated, TROPODUR Outer Sheathed Heavy Duty 

Cables.

AYWY Aluminium Conductor, TROPODUR Insulated, Galvanised Round Steel Wire Armoured and TROPODUR Outer Sheathed Heavy Duty Cables.

AYFY Aluminium Conductor, TROPODUR Insulated, Galvanised Flat Steel Wire (Strip) Armoured and TROPODUR Outer Sheathed Heavy Duty Cable.

AYCY Aluminium Conductor, TROPODUR Insulated, Metallic Screened and TROPODUR Outer Sheathed Heavy Duty Cable.

A2XCY Aluminium Conductor, TROPOTHEN-X Insulated, Metallic Screened and TROPODUR Outer Sheathed Heavy Duty Cable.

AYCEFY Aluminium Conductor, TROPODUR Insulated, individual core metallic screened, Flat steel Wire (strip) Armoured and TROPODUR Outer Sheathed Heavy duty Cable.

A2XCEFY Aluminium Conductor, TROPOTHEN-X Insulated, individual cores metallic screened, Flat Steel Wire (Strip) Armoured and TROPODUR Outer Sheathed Heavy Duty Cable.

NOTE : If the first letter A is dropped in the above designations (i.e. YY, YWY, YFY etc.) they will denote corresponding types with Copper Conductors.

YWWGby…(Mining) Copper Conductor, TROPODUR Insulated, double round wire armoured and TROPODUR Outer Sheathed Heavy Duty Mining Cable.

YFFGby…(Mining) Copper Conductor, TROPODUR Insulated, double flat wire (strip) armoured and TROPODUR Outer Sheathed Heavy