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General Application of Induction Motors

The induction motor is the most popular machine that is widely employed in process and manufacturing industries. Alongside manufacturing facilities, it is the most popular machine for domestic purposes.

Deep Well Water Pumps

Deepwater wells use a special type of induction motor with a compact diameter and longer length.

Refrigerator and Compressors

Refrigerators and other compressuse split type induction motors in their working principle.

Small water pumps

Small water pumps use single phase induction motors.

Ceiling fan

Ceiling fans use single phase induction motors in their working.
The video below displays repairing of a single phase induction motor:

Washing machines

Many washing machines utilize single phase ac machines in their working.

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Hydroelectric Plants in India

 

Hydroelectric power is a major electrical power generation source.

Advantages:
Clean Fuel

The only fuel required for hydroelectric power generation is water. It is clean resource, has no pollutants, burning, or any sort of chemical reactions associated with it.

Small running charges

Compared to coal, gas, diesel power station and power stations, the hydroelectric station has very small running charges.

Renewable

Power generation through hydroelectric stations relies on the water cycle. Water comes through the reservoir, flows through penstock, passes through turbines, exits the station and joins some river. In fact, this water is renewable and it is never wasted.

 

Simple in construction

Unlike complex nuclear, steam, and diesel auxiliaries the hydro dams are simple in construction and operations.

Less maintenance

Equipment requires little to none maintenance.

Supplementary benefits

Alongside power generation, the reservoir has supplementary benefits. Entire list comprises flood control, irrigational water, drinking water.

Longer life

The expected life of a hydroelectric station is around 30 – 35 years after which it demands an upgradation. The actual process of renovation depends on the individual plant.

List of Hydro Power Plants in India

1. Tehri Dam

Operator: THDC Limited, Uttarakhand

Location: Uttarakhand

2. Koyna Hydroelectric Project

Operator: MAHAGENCO, Maharashtra State Power Generation Co Ltd.

Location: Maharashtra

3. Srisailam

Operator: APGENCO

Location: Andhra Pradesh

4. Nathpa Jhakri

Operator: Satluj Jal Vidyut Nigam

Location: Himachal Pradesh

5. Sardar Sarovar Dam

Operator: Sardar Sarovar Narmada Nigam Ltd

Location: Navagam, Gujarat

6. Bhakra Nangal Dam (Gobind Sagar)

Operator: Bhakra Beas Management Board

Location: Sutlej River, Bilaspur – Himachal Pradesh

7. Chamera I  

Operator: NHPC Limited

Location: Himachal Pradesh

8. Sharavathi Project

Operator: Karnataka Power Corporation Limited

Location: Karnataka

9. Indira Sagar Dam

Operator: Narmada Valley Development Authority

Location: Madhya Pradesh

10. Karcham Wangtoo Hydroelectric Plant

Operator: Jaypee Group

Location: Himachal Pradesh

11. Dehar (Pandoh) Power Project

Operator: Bhakra Beas Management Board

Location: Himachal Pradesh

12. Nagarjuna Sagar Dam Guntur

Operator: Andhra Pradesh Power Generation Corporation Limited

Location: Andhra Pradesh

13. Purulia Pass

Operator: West Bengal Electricity Distribution Company

Location: West Bengal

14. Idukki

Operator: Kerala State Electricity Board

Location: Kerala

15. Salal I & II  

Operator: NHPC Limited

Location: Jammu & Kashmir

16. Upper Indravati

Operator: Odisha Hydro Power Corporation

Location: Orissa

17. Ranjit Sagar Dam

Operator: Punjab State Power Corporation Limited

Location: Punjab

18. Omkareshwar

Operator: Narmada Hydroelectric Development Corporation

Location: Madhya Pradesh

19. Belimela Dam

Operator: Odisha Hydro Power Corporation

Location: Orissa

20. Teesta Dam

Operator: NHPC Limited

Location: Sikkim

 

Types and Classification of Faults on Electrical Power Systems

Question: How many types of faults exist on the power system and how they are classified?

Answer: Generally four types of faults exist and are classified into two categories.

Symmetrical faults: They give rise to symmetrical equal currents having a displacement of 120°.

Unsymmetrical faults: They gave rise to unsymmetrical currents having unequal displacements.

List contains:

  1. Line to line to line fault
  2. Line to ground
  3. Line to line
  4. Double line to ground

Types of Fault

Classification

Severity of Fault

3 Line

Symmetrical

Most Dangerous

Line to Line

Unsymmetrical Fault

More Dangerous

Line to Ground

Unsymmetrical Fault

Least Dangerous

Double Line to Ground

Unsymmetrical Fault

Dangerous than Line to Line and Line to Ground Fault

Power in DC and AC Circuits

Formulas of Power in DC, AC Single Phase and AC Three Phase Circuits

 

Back to basic, below are the simple Power formulas for Single Phase AC Circuit, Three Phase AC Circuits and DC Circuits. You can easily find electric power in watts by using the following power formulas in electric circuits.

Power Formulas in DC Circuits

P = V x I

P = I2 x R

P = V2 / R

Where:

P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Power Formulas in Single Phase AC Circuits

P = V x I x Cos Ф

P = I2 x R x Cos Ф

P = V2 / 2 (Cos Ф)

Where:

P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Cos Ф = Power Factor

Power Formulas in Three Phase AC Circuits

P = √3 x VL x IL x Cos Ф

P = 3 x VPh x IPh x Cos Ф

P = 3 x I2 x R x Cos Ф

P = 3 (V2 / R) x Cos Ф

Where:

P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Cos Ф = Power Factor

Basic Electrical Engineering Laws and Theorems

Ohm’s Law

Statement: The current flowing through any resistor is directly proportional to the voltage applied to it.

Mathematically, V = IR

Kirchhoff’s Current law

We all know that current is a basic feature of circuits which exists due to flow of charges. Kirchhoff’s current law explains the behavior of current at any junction.

Statement: The current flowing towards any junction (node) is equal to the current flowing away from that node.

Mathematically, ∑ Current In = ∑ Current out.

In other words, this law is also called the law of conservation of charge.

Kirchhoff’s Voltage law

Like Kirchhoff’s first law is focused on current at any junction, the voltage law explains the behavior of voltage around a loop.

Statement: The sum of voltage rise along a closed loop is equal to the sum of voltage drops around that loop.

Mathematically, ∑ Voltage rise = ∑ Voltage drop

In other words, this law is also called the law of conservation of energy.

Superposition principle

Many electrical circuits contain a single source powering different resistors. Sometimes a circuit contain multiple current and voltage sources. A superposition principle is applied to all circuits having multiple sources.

Statement: The voltage or current appearing across any component is equal to the sum of individual voltage or current of all independent sources.

Thevenin’s Theorem

Statement: Any complex electrical circuit can be reduced to a single voltage source having a single series resistor.

Practically, the Thevenin’s and Norton’s theorems are used in analysing the properties of electrical and electronic systems. They are employed in modelling transmission lines and large complex systems.

Norton’s theorem

Statement: Any complex electrical circuit can be reduced to a single current source having a single parallel resistor.

Maximum Power Transfer Theorem

Statement: if the value of load resistor is equal to the single resistor ( as calculated from Norton or Thevenin theorem) the load resistor will receive the maximum power.

Substitution Principle

Statement: Any electrical branch can be substituted with an equivalent electrical branch provided that current and voltage of both branches are same.

Millman’s Theorem

The Millman’s theorem is applied to the circuits which have several voltage sources in the parallel configuration. According to this theorem, the voltages source in parallel branches can be replaced by equivalent current sources and parallel resistors which can then be reduced to a single voltage source and a series resistors. The same is also true for several current sources in series configuration.

Transformer Rating in kVA, and not in kW or kVAR. Why?

Question: Why transformer rating is expressed in kVA instead of kW or kVAR?

Answer: At the time of manufacturing, the nature of load to be connected is not known. (i.e it is resistive, reactive, R, RL, RC, RLC or of any other type). Therefore it is beneficial to express power in terms of voltage and amps. This V & A represents the overall power delivered to any sort of load.

The power supplied to a resistive load is the product of voltage times current flowing through it.

In case of ac loads, the case is not same. Here the load is the sum of resistance and reactance. The power delivered to an AC load is neither real nor reactive, it is the apparent power which is expressed in terms of kVA.

Furthermore, two types of losses exist in Transformers:

  • Copper loess → They depend on current
  • Iron losses → They depend on the voltage

Since these losses depend on V & I only, a transformer is rated in terms of VA.

 

Types of MCB/MCCB

 

MCB/MCCB are widely used in electrical distribution system for ON/OFF Electrical supply and it also gives over current and short circuit protection. Selection of MCB/MCCB involves technical as well as Mechanical parameters. Not all the parameters are important but careless observation leads to wrong selection of MCB/MCCB or may increase cost unnecessarily.

Specifications of MCB/MCCB:
Current Related:

Frame Size (Inm): Amp
Rated current (In/ Ie): Amp
Ultimate short circuit breaking capacity (Icu): KA
Rated short-circuit breaking capacity (Ics): % of Icu

Voltage Related:

Rated voltage (Ve): Volt
Rated Insulation voltage (Vi): Volt
Rated impulse withstand voltage(Vimp): kV
No’s of Pole : SP,DP,TP,TPN,FP

Application Type:

Utilization Category/ Characteristic : B,C or D curve

Accessories:

Rotary Handle: Extended/ Direct
Alarm Contact
Shunt Trip
Under voltage Trip
Mechanical interlocking
Manual /Auto operation
Motorized Operation

Protection Type:

Protection : Over current / Short circuit
Trip Mechanism: Thermal / Magnetic / Solid / Microprocessor
Trip Mechanism adjustment : Fixed / Adjustable

Others:

Frequency;
Reference temperature (if different from 30°C);
Pollution degree;
Suitability for isolation;
Type of Mounting arrangement;
Electrical Life Cycles;
Mechanical Life Cycles;
Dimension: mm
Weight: Kg
Reference Standard: IEC: 60947-1/2, IS: 13947-1/2

Current Ratings:
Frame Size:

Breaker Frame Size indicates the basic framework of the Plastic shell of MCCB that can hold the highest rated current. It is the maximum current value for which the MCCB is designed (upper limit of the adjustable trip current range) and it also a deciding factor for physical dimensions of the device. There are varieties of current rating MCCB for the same series frame Size are available in the market.

For example, DX100 Frame Size MCCB are available in the market for the rated currents of 16A, 20A, 25A, 32A, 40A, 50A, 80A, 100A etc. Also for rated current of 100A MCCB of the frame size DX225 is also available.

Rated Current:

It is the current value above which overload protection is tripped and the circuit is disconnected.

For MCB, rated current is fixed, while in MCCB the rated current is adjustable.

Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A.

Voltage Ratings:
Ultimate short-circuit breaking capacity (Icu):

Breaking capacity can be defined as the maximum level of fault current which can be safely cleared.
It is the highest fault current that the MCCB can trip without being damaged permanently.
The MCCB will be reusable after interrupting a fault, as long as it doesn’t exceed this value.
It is indicate operation reliability of MCCB
This parameter may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application fault level may be 10kA.

Operating short-circuit breaking capacity (Ics):

It is expressed as a percentage ratio of Icu and tells you the maximum short-circuit current if a circuit breaker can break three times and still resume normal service.
The higher the lcs, the more reliable the circuit breaker
It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds this value, the MCCB will be unable to trip and another protection mechanism must operate.
If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
The Main difference between Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) that Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterwards.
For example, if a circuit breaker has an Ics of 25,000 Amperes and an Icu of 40,000

Amperes:

Any fault below 25kA will be cleared with no problem.
A fault between 25kA and 40kA will cause permanent damage when cleared.
Any current exceeding 40 kA can’t be cleared by this breaker.

Rated working voltage (Ve):

It is the continuous operation voltage for which the MCCB is designed.
This value is typically equivalent or close to a standard system voltage.
In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V.

Rated Insulation voltage (Vi):

It is the maximum voltage that the MCCB can resist according to laboratory tests.
It is higher than the rated working voltage, in order to provide a margin of safety during field operation.

Rated impulse withstands voltage (Vimp):

It is the value of transient peak voltage the circuit-breaker can withstand from switching surges or lighting strikes imposed on the supply.
This value characterizes the ability of the device to withstand transient over voltages such as lightning (standard impulse 1.2/50 μs).
Vimp = 8kV means Tested at 8 kV peak with 1.2/50μs impulse wave.

Number of Poles:

No of Pole for MCCB depends on Single Phase & Three Phase Power Controlling /Protection
Single Pole (SP) MCB:
A single pole MCB provides switching and protection for one single phase of a circuit. It is used for Single Phase circuit
Double Pole (DP) MCB:
A two Pole MCB provides switching and protection both for a phase and the neutral. It is used for Single Phase circuit
Triple Pole (TP) MCB:
A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral. It is used for Three Phase circuit
3 Pole with Neutral (TPN (3P+N) MCB):
A TPN MCB, has switching and protection to all three phases of circuit and additionally Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any protection and can only be switched. It is used for Three Phase circuit with Neutral
4 Pole (4P) MCB:
A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit. It is used for Three Phase circuit with Neutral.

Types and accessories of MCB/MCCB

 

Utilization category / Characteristic (B, C, D, K, Z curve):

Characteristic of Trip curves of MCCB tell about the trip current rating of MCCB.
MCB will trip instantaneously according to their Tripping Characteristic at 0.1 sec.
There are various type of MCCB:

  • Type B MCCB
  • Type C MCCB
  • Type D MCCB
  • Type K MCCB
  • Type Z MCCB

MCB trip curves

Type B MCCB:

Operating Current: This type of MCB trips between 3 and 5 times rated current (In).
Operating Time:04 To 13 Sec
For example a 10A device will trip at 30-50A.
Application: Domestic applications or light commercial applications where connected loads are primarily lighting fixtures, domestic appliances with mainly restive elements.
Suitable for: Restive Load application (Lighting , Small Motor)
Surge Current: The surge current level is relatively low.
Installation at: At Sub feeder of Distribution Board.

Type C MCCB:

Operating Current: This type of MCB trips between 5 and 10 times full load current.
Operating Time:04 To 5 Sec
Application: commercial or industrial type of applications, fluorescent lighting, motors etc where there could be chances of higher values of short circuit currents in the circuit.
Suitable for: Inductive Load application (Pumps, Motor, fluorescent lighting.)
Surge Current: The surge current level is relatively moderate level.
Installation at: At incoming / Outgoing of Distribution Board.

Type D MCCB:

Operating Current: This type of MCB trips between 10 and 20 times full load current.
Operating Time:04 To 3 Sec
Application: specialty industrial / commercial uses (Transformers or X-ray machines, large winding motors, discharge lighting, large battery charging). Where current inrush can be very high.
Suitable for: Inductive- Capacitive Load application (Pumps, Motor)
Surge Current: The surge current level is relatively High.
Installation at: At incoming of Distribution Board / Panels.

Type K MCCB:

Operating Current: This type of MCB trips between 8 and 12 times full load current.
Operating Time:04 To 5 Sec
Application: Suitable for inductive and motor loads with high inrush currents.
Surge Current: The surge current level is relatively High.
Installation at: At incoming of Distribution Board / Panels.

Type Z MCCB:

Operating Current: This type of MCB trips between 2 and 3 times full load current.
Operating Time:04 To 5 Sec
Application: These types of MCBs are highly sensitive to short circuit and are used for protection of highly sensitive devices such as semiconductor devices.
Surge Current: The surge current level is relatively too low.
Installation at: At Sub feeder of Distribution Board for IT equipment.

MCB/MCCB Accessories:
Rotary Handle:
  • It is used to extend ON/OFF handle of MCCB when Panel Door is closed.
  • It is also used to indicate ON/OFF or Trip Position
Shunt Trip:
  • Used for Remote Tripping
Alarm contact:
  • It gives Tripping Indication when MCCB Trip.
  • It does not give when MCCB is in normal condition (either ON or OFF)
Auxiliary contact:
  • It used for remote signaling and control purpose.
  • It is also give ON/OFF indication of MCCB at remote location.
Under Voltage Tripping:
  • It used to trip MCCB in under voltage condition (70 to 35% of rated Voltage).
Mechanical Interlocking:
  • It used to mechanical interlock of two MCCB on the same Panel.
Manual / Auto:
  • MCCB may have provision for Auto /Manual operation.
  • An “auto/manual” switch in front of Panel.
  • When set to the “Manual” position, lock out electrical control and when set to “auto”, lock out the manual control; remote indication
Motorized operation:
  • MCCB may have option for manual operation or with a motor mechanism for electrically controlled
Others:
Frequency:

MCB is designed and used in AC power system of 50 to 60Hz.
Electromagnetic force of magnetic release is related with power supply frequency so If Frequency is changed than electromagnetic fore of Magnetic element is changed hence MCCB tripping current will be different.
If we used MCCB for protection in DC circuits than specially design DC circuit MCCB should be used rather than normal type of MCCB.

Isolation:

MCCB is suitability for visible isolation. It is particularly important.
If a circuit breaker is turned off, it should indicate so visibly.
It should not be able to indicate otherwise if the contacts are not open. In other words, it offers proof of isolation.

Type of Mounting Arrangement:

According to mounting arrangement, MCBs can be divided into two categories.

DIN Rail Mount MCB:

  • The main advantage of this type of MCB is versatility
  • DIN rails are used by many different types of electrical and communications equipment, and they are mainstream in industrial settings.
  • They can be easily integrated into nearly any control or protection system.
  • A disadvantage of this type of MCB is that more work is required for installation, and plug-in MCBs may be a better choice for simple installations.

Plug-In MCB:

  • These MCBs are easy for installation. As name indicates, they just have to be plugged into a compatible electric panel.
  • Plug-in MCBs are suitable for applications that use circuit breakers exclusively- typically residential and commercial electrical distribution systems.
  • When using plug-in MCBs it is important that the breakers and the panel must match. It is not an issue when both are of the same brand.
Pollution degrees:
  • It determines in what kind of environment circuit breakers can be installed.
  • In a Domestic purpose where there is no dust no humidity, the circuit breaker is comfortable.
  • For Domestic purpose pollution degree 2 is suitable.
  • But in an outdoor public installation where there may be dust which cause leakage currents and lead to dangerous arcs.
  • For dusty pollution, humidity environment or outdoor type heavy-duty applications (incoming switchboards) pollution degree 3 is suitable.
Energy Class:
  • MCB need some time for tripping, In this time, fault current will create some energy which will exist in system. This energy is termed as release energy. For efficient MCB operation it should be in within limited.
  • On basis of amount of release energy it is classified in class 1, class 2 and class 3. Class 3 is best which allows maximum 1.5L joule/second.

Difference between MCB & MCCB

 

MCB is Miniature Circuit Breaker which is thermal operated and used for short circuit protection in small current rating circuit. Normally it is used where normal current is less than 100A.
MCCB is 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.

MAX44211 Output Protection

MAX44211-Output-Protection.jpg

Unwanted transients emanating from the power line back to the line-driver’s output and back-EMF generated by the coupling circuit when the load is disconnected and connected, and vice versa, create undesirable over-voltage conditions. Back-EMF is also generated when the line driver outputs are toggled from high to low impedance state, if significant current was flowing at the disconnect time. The MAX44211 power line communications driver most often is placed facing the power line with an isolating stage between them. In case of such over-stress conditions, external protection is required to protect the MAX44211 and downstream circuits.

The internal ESD clamping structure is present inside MAX44211 (see Figure) to protect the part from ESD or sub-microsecond events. When the application has hazards where these events can occur frequently and for comparatively longer time, it is recommended to have external protection circuitry. Failure to accommodate an output protection can result in over-stressing the outputs (OUT+/ OUT-) and eventually damage the part.

This application note provides insights and information on how to add external protection circuitry at the outputs of the MAX44211. A circuit using VAVDD = 15V is used in this application note.

The figure shows the internal ESD clamping protection structure.

Download PDF: MAX44211-Output-Protection

Source: Maxim Integrated