A Note On Magnetic Materials

Limitation of design

• Saturation
• Temperature Rise
• Insulation
• Efficiency
• Mechanical Parts
• Commutation
• Power Factor
• Consumers Spec
• Standard Spec

Machine Design Facts

Q) Why electrostatic machines are not used and not electromagnetic machines are used?

Ans) Because of use of maximum energy density funda.

Q) What is Basic Structure of machine:

Ans:

• Magnetic Circuit
• Electrical Circuit
• Dielectric Circuit
• Thermal Circuit
• Mechanical Circuit

considering all above a successful designer brings out an economic and technical compromise.

Electrical titbits

Q) What is efficiency of Electric Locomotive compared to Steam?

Ans) Steam loc 6 %, Electric Loco 45 %

Q) Which load forms sizeable base load for grid?

Ans) Electric Traction

Q) What is effect of low frequency on motor?

Ans) It improves commutation of DC machines and p.f. and efficiency is also increased.

Q) What is advantage of DC series motor vs ac series motor?

Ans) DC series motor develops more starting as well as running torque for same size than ac motor.

What we use for Magnetic calculations

1. Basic Formula etc.

2. Total mmf calculation

• mmf for airgap
• Net length of iron
• mmf for teeth
• real & apparent flux densities

3. Leakage calculation

Some material science facts for Electrical Engineers

Q) Why Silicon ( 3 to 5 % ) is added to steel for making Transformer core lamination?

Ans) Higher content of silicon raises the resistivity of material and thus reduces the eddy current losses.

Q) Why Cold Rolled Steel is used?

Ans) Because it permits high flux densities 1.8 Wb/sq.m

This reduces the amount of material. For HR its just 1.3 Wb/sq.m

Insulations for HR:- Kaolin, Varnish

Insulation for CR:- Phosphate base.

Motor Design

Lighting Basics

Step towards Smart Grid

Through Ditrsibution Automation and Control (DAC), Following needs to be regulated:-

• DSM:- Demand side management.
• DLS:- Discretionary Load Switching = customer load management.
• Peak load pricing
• Load shedding
• Load reconfiguration.
• Voltage regulation
• TLM ( Transforner load management)
• FLM( feeder load management)
• Capacitor control
• Fault detection, isolation.
• Condition and state monitoring
• Load studies
• Customer meter reading
• Remote connect/disconnect.

Smart grids used AI ( artificial intelligence) these days.

Latest Tech Innovations in Electrical Engineering

• Grid - Scale storage

Till now pumped storage or compressed air storage technology was there, which costs about Rs 40,000 per unit.

Now flow batteries, liquid-metal batteries, flywheels and ultracapacitors have come up which costs Rs 10,000 per unit.

• Digital Power Conversion

Silicon carbide/ gallium nitrite high speed switches for high freq. power handling, They are energy efficient and nano and can replace today's bulky transformers.

• Compressorless AC and Electrochromic windows

Thery dehumidify air with desiccants instead of refrigeration cycle. Window shading w.rt temperature is also coming up.

• Clean Coal

Till now carbon capture and sequestratyion (CCS) costs Rs 500,000 per KW. New tech will make 90 % of CO2 capture @ Rs 100,000 per KW.

• Biofuels and Electrofuels

Cane/Corn ethanol are available. Cellulosic and algae based biofuels are also coming up @ Rs 100 per gallon.

• Others:- Gen IV nuke reactors, Small , shrouded wind turbines, Solid-oxide fuel cells, ground-source heat pumps.

What is used to make LEDs?

Material Formula and its type

Magnetism of different materials

Some facts on protection

HRC fuse breaking capacity:- 80 KA

SF6 breaking capacity:- 30 KA

ACB breaking capacity :- 50 KA

hence fuses are used for S.C. protection and Relays for O.L. protection.

T1 and T2 reduce the fault current ( say from 400 A to 10 A ) which is the utility of these transformers.

Protections used in 132 KV/ 6.9 KV switchyard:-

• Lightening arrestor 120 KV, 10 KA

• IDMT O/C Relay + IDMT E/F Relay ( 51 + 51 N)

• IDMT O/C Relay + Instantaneous Relay + IDMT E/F Relay ( 51 + 50 + 51 N)
• Transformer Differential Relay(87)
• Restricted E/F Relay + Standby E/F Relay (64 R + 51 G)

Some notes on SubStation Relays

Trip Circuit Supervision Relay ( VAX ) :- 21 ( After closing only) 31 ( Preclosing and After Closing).
Application :- After Cl;osing or continuous supervision of the trip circuit or circuit breaker.
Detection:-
1.Failure of Trip Supply
2.Open Circuit of trip Coil or trip circuit wiring
3.Failure of mechanism to complete the tripping operation.

A CTZM Relay is used at ACB in PCC which feeds the MCC and the delay settins are provided there at.

When 10 MVA primary side SF6 primary side SF6 breaker operates, there should be an interlock to open the breaker on secondary side ( to prevent closing on load T/F) but this is not provided and is done manually.

CBCT :- Core Balance Current Transformer, Used for Unbalanced Current Protection.

Some questions answered.

Q)What is the difference between Screw Compressor and Reciprocating Compressor?
Ans) Screw Comp. is a constant torque load device. The output( i.e. air flow is also const.). unlike reciprocating comp, current of Screw Comp is much less fluctuating.

Q)Why three intermediate tap positions ( 11A,11B and 11C) are provided?
Ans) For Mechanical convenience.

Q) What re three MODES of CB/Feeder?
Ans) 1.Service :- Both Control and Power Supply will be there.
2.Test :- Only control Supply and no power supply.
3.Isolation:-Neither Control Now Power Supply.

Q)Where you find two diaphragms in transformer?
Ans) In the EXTRA VENT provided just below level og conservator.

A Lecture on Dielectrics

3A - Dielectric Materials

Some Rapid Fire Questions on Electrical Engineering

Q) Which machines have parabolic characteristics?

Ans) Fans and Pumps

Q) Which machine has linear load characteristics?

Ans) Screw Feeders

Q) What is difference between NEMA and IEC?

Ans) NEMA is American and IEC is Indian standard.

Power Management in Factories

There are three types of loads:-

• Load which cannot afford any power failure. ( on a small capacity DG set ;say 250 KVA)
• Load which can tolerate 2 min inturruption. ( on a small capacity DG set ;say 250 KVA)
• Load which can tolerate 30 min interruption. ( on a high capacity DG set ;say 4 MVA)

Motor Facts

Upto 30 KW DOL starters are used, above that, y-Delta starters are used.

For motors rated 55 KW+, motor heaters are used.

For motors rated /. 90 KW, PTC Thermisters are used.

For all motors rated 90 KW +, the vendor should furnish following data soon after submission of T-S curves and G D sqaure value of the driven equipment:- (This data is required for selection of proper motor protection relay).

• Thermal Withstand Curve: Hot and Cold.
• Stator Time Constant.
• Stalling Current.
• Stall Withstand:Hot and Cold
• Starting Current.
• Acceleration Time.