Say P - active power
Q - reactive power.
f - frequency
V - line voltage.
Then the golden rule is,
P is directly related with f.
Q is directly related with V.
Even certain experienced staff think that parameters such as line voltage depends on the active power produced and frequency may drop if there is not enough reactive power. This is Totally WRONG.
In other words,
If you are going to change the frequency of the supply you must increase the amount of fuel (eg. steam/diesel/HFO/waterflow) which in turn increases the prime-mover (eg. diesel engine/ gas turbine/ steam turbine/ hydro turbine) speed. But speed governors are meant to regulate this type of frequency variation and to maintain the speed of the prime mover.
If you are going to change the terminal voltage of the supply you must increase the excitation given to the alternator.
But keep in mind that the above are purely applicable to generators running isolated/islanded. Parallel operation and infinite grid operation are bit different and certain parameters can not be independently controlled (for eg. voltage in infinite grid).
If multiple generators are running in parallel, only by increasing the excitation of all generators - the voltage can be increased, and vice versa. If not, only the reactive power share will change, not the output voltage.
The other important aspect of operating a power system is to do with the power factor. People confuse with whether the power factor must lead or lag. There is another belief, improving the power factor means we try to make the 0.9 to 0.8 lagging. In almost every practical power system (there are few exceptions) , the power factor should be lagging, BUT not necessarily each and every generating set. In other words, even when the system power factor is lagging - one machine may be running with a leading power factor, at the expense of another.
Saturday, July 24, 2010
Tuesday, July 13, 2010
A Bit of Automobile Technology
It would be nice to shift to a non-electrical topic for a change. A brief explanation would be provided about the recent past & current technology available in cars.
Different kinds of Transmission systems:
MT: Manual Transmission - The Coventional Gear selection system
AT: Automatic Transmission - The Automatic Gear selection system
ManuMatic/Tiptronic/GearTronic: Manu(al + Auto)matic system
CVT: Continuously Variable Transmission
Above the letters indicate the following:
1. P - Park
2. R - Reverse
3. N - Neutral
4. D - Drive
5. 2 - Second gear is maximum
6. L - Low/1st gear is maximum
Normally manual transmission employs a clutch but an auto transmission utilises a torque converter instead of clutch.
Few emission control systems:
CVCC: Compound Vortex Controlled Combustion by Honda for complying with emission standards
CC: Catalytic Converter used for treating toxic emissioons
Various ValveTrain systems:
VTEC: Variable Valve Timing and Lift Electronic Control by Honda
VVT-i : Variable Valve Timing with Intelligence developed by Toyota
SOHC: Single Over Head Camshaft system
DOHC: Double Over Head Camshaft system
Multiple Fuel delivery systems:
Carburettor:Conventional indirect injection
MFI: Mechanical Fuel Injection
EFI: Electronic Fuel Injection
Engine Efficiency Improvement systems:
Intercooler/Aftercooler:
Turbocharger/TurboSupercharger:
Passenger Safety systems:
ABS: AntiLock Braking System
EBD: Electronic Brakeforce Distribution
Emerging Aotomobile Design technologies:
HEV: Hybrid Electric Vehicle cosists of an IC Engine and Electric motors
Different kinds of Transmission systems:
MT: Manual Transmission - The Coventional Gear selection system
AT: Automatic Transmission - The Automatic Gear selection system
ManuMatic/Tiptronic/GearTronic: Manu(al + Auto)matic system
CVT: Continuously Variable Transmission
Above the letters indicate the following:
1. P - Park
2. R - Reverse
3. N - Neutral
4. D - Drive
5. 2 - Second gear is maximum
6. L - Low/1st gear is maximum
Normally manual transmission employs a clutch but an auto transmission utilises a torque converter instead of clutch.
Few emission control systems:
CVCC: Compound Vortex Controlled Combustion by Honda for complying with emission standards
CC: Catalytic Converter used for treating toxic emissioons
Various ValveTrain systems:
VTEC: Variable Valve Timing and Lift Electronic Control by Honda
VVT-i : Variable Valve Timing with Intelligence developed by Toyota
SOHC: Single Over Head Camshaft system
DOHC: Double Over Head Camshaft system
Multiple Fuel delivery systems:
Carburettor:Conventional indirect injection
MFI: Mechanical Fuel Injection
EFI: Electronic Fuel Injection
Engine Efficiency Improvement systems:
Intercooler/Aftercooler:
Turbocharger/TurboSupercharger:
Passenger Safety systems:
ABS: AntiLock Braking System
EBD: Electronic Brakeforce Distribution
Emerging Aotomobile Design technologies:
HEV: Hybrid Electric Vehicle cosists of an IC Engine and Electric motors
Monday, June 28, 2010
Half-a-loaf of Automotive Aerodynamics (AA)
what is aerodynamics?
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object as defined by wikipedia.
Aerodynamics of automobiles:
drag:
drag is a fluid dynamics term, sometimes called as air resistance or fluid resistance. It is defined as "forces that oppose the relative motion of an object through a fluid. Drag forces act in a direction opposite to the oncoming flow velocity". (wikipedia)
lift:
A fluid flowing past the surface of a body exerts a surface force on it. Lift is defined to be the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the surface force parallel to the flow direction.(wikipedia)
Note: In aircrafts Lift/drag ratio is expected to be higher. But this is not the case in automobiles where lift is to be reduced and drag too to be reduced. What is especially required in an autombile such as a racing car is the downforce (as opposed to the lift required in aircrafts).
Upper: non-aerodynamic car; Lower: aerodynamically improved design
From: http://www.generalamherst.com
A diffuser is seen in most racing cars:
Rear diffuser of Porsche - Courtesy: Wikipedia
Rear spoiler of Toyota - Courtesy: Wikipedia
Front Air Dam of Mazda - Courtesy: Mazda
Please visit hotrod for a fine detailed description of the role of aerodynamics in automobiles!
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object as defined by wikipedia.
Aerodynamics of automobiles:
drag:
drag is a fluid dynamics term, sometimes called as air resistance or fluid resistance. It is defined as "forces that oppose the relative motion of an object through a fluid. Drag forces act in a direction opposite to the oncoming flow velocity". (wikipedia)
| Shape and flow | Form drag | Skin friction |
|---|---|---|
 | 0% | 100% |
 | ~10% | ~90% |
 | ~90% | ~10% |
 | 100% | 0% |
lift:
A fluid flowing past the surface of a body exerts a surface force on it. Lift is defined to be the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is defined to be the component of the surface force parallel to the flow direction.(wikipedia)
Note: In aircrafts Lift/drag ratio is expected to be higher. But this is not the case in automobiles where lift is to be reduced and drag too to be reduced. What is especially required in an autombile such as a racing car is the downforce (as opposed to the lift required in aircrafts).
Upper: non-aerodynamic car; Lower: aerodynamically improved design
From: http://www.generalamherst.com
A diffuser is seen in most racing cars:
Rear diffuser of Porsche - Courtesy: Wikipedia
Rear spoiler of Toyota - Courtesy: Wikipedia
Front Air Dam of Mazda - Courtesy: Mazda
Please visit hotrod for a fine detailed description of the role of aerodynamics in automobiles!
Friday, May 28, 2010
Non-Conventional Renewable Energy (NCRE)
The term renewable energy now has become a magical word in energy. The world is constantly changing and so is the power sector. Nowadays people talk about 'deviating' from the 'conventional' energy sources such as thermal, hydro, nuclear etc and magically spell wind, solar, biomass, wave, tidal, geothermal, and so on.
Are those viable and financially feasible? what about the technical feasibility - such as reliability, stability issues?
Wind energy:
Wind takes the first priority when it comes to non-conventioanl renewable energy source. Though it is unrelaible at times, may have stability issues, voltage problems, might need reactive power compensation. Still it is CLEAN, Not forgetting that it needs a very high initial investment in comparative terms. Remember that open cycle gas turbines are the opposite. Their capital cost is in the lower limits in any commercial scale power systems.
A Horizontal axis wind turbine generator: from Howstuffworks
Solar Energy:
Solar PV
Solar energy is said to be abundant, though the fabrication of these photovoltaic semiconductors are not so easy. their Cost/Wattage is significantly high and the average payback period is well beyond 10 years.
Solar thermal
Biomass Energy:
Wave/Tide Energy:
Are those viable and financially feasible? what about the technical feasibility - such as reliability, stability issues?
Wind energy:
Wind takes the first priority when it comes to non-conventioanl renewable energy source. Though it is unrelaible at times, may have stability issues, voltage problems, might need reactive power compensation. Still it is CLEAN, Not forgetting that it needs a very high initial investment in comparative terms. Remember that open cycle gas turbines are the opposite. Their capital cost is in the lower limits in any commercial scale power systems.
Solar Energy:
Solar PV
Solar energy is said to be abundant, though the fabrication of these photovoltaic semiconductors are not so easy. their Cost/Wattage is significantly high and the average payback period is well beyond 10 years.
Solar thermal
Biomass Energy:
Wave/Tide Energy:
Industrial Automation
Industrial Automation is not a totally new concept. It has been practised in the industry for a long time. But the introduction of personal computers has revolutionised the automation industry providing easy access, custom software applications and so on.
Automation is a process where sensors/transducers are employed to 'sense' the signal, one or more controllers 'guiding' the operation involved and the desired output is achieved in the form of actuators/motors/physical parameters such as temperature/pH in a factory.
Sensors:
Pressure sensors
Position transducers
Proximity sensors
Temperature sensors
Humidity sensors
These sensors measure the relative humidity by converting the signals to desired voltage/current output.
Level sensors
Used to measure the level, for e.g. water level in a tank/ chemical level in a container.
Load cells
These are utilised to measure the weight in electronic form.
Inputs:
Analog input
4-20mA current input
0-10V voltage input
Digital inputs
push buttons
Controllers:
Process indicators
Timers
Counters
Temperature controllers - PID
PC-based controllers
Input-output modules
Programmable logic controllers (PLC): AC/DC inputs & outputs
Variable speed drives (VSD)/ Variable frequency drives (VFD)
Converters:
Converters are used to change the signal type from one to another. This conversion may take a form of analog signals to digital signals (ADC) or changing the signal medium such as RS232 serial type to RS485 two-wire type.
Actuators:
Based on the controller output, actuators would perform the desired action to change the controlled variable. These are mostly motion-oriented, for e.g. motors, solenoid valves, electromagnetic relays etc.
- Solenoid valves (electrically controlled valves)
- Motors such as steppers, servos, permanent magnet types
- Voltage-controlled electromagnetic relays
Software:
Automation configuration software (between h/w and s/w)
Automation display software ( to display the controlled parameters)
Supervisory control & Data acquisition (SCADA)
Automation is a process where sensors/transducers are employed to 'sense' the signal, one or more controllers 'guiding' the operation involved and the desired output is achieved in the form of actuators/motors/physical parameters such as temperature/pH in a factory.
Sensors:
Pressure sensors
Position transducers
- linear
- rotary
Proximity sensors
- capacitive proximity sensors
- inductive proximity sensors
- photoelectric proximity sensors
Temperature sensors
- Resistance Temperature Device (RTD)
- Thermocouple (TC)
- Thermistors
Humidity sensors
These sensors measure the relative humidity by converting the signals to desired voltage/current output.
Level sensors
Used to measure the level, for e.g. water level in a tank/ chemical level in a container.
Load cells
These are utilised to measure the weight in electronic form.
Inputs:
Analog input
4-20mA current input
0-10V voltage input
Digital inputs
push buttons
Controllers:
Process indicators
Timers
Counters
Temperature controllers - PID
PC-based controllers
Input-output modules
Programmable logic controllers (PLC): AC/DC inputs & outputs
Variable speed drives (VSD)/ Variable frequency drives (VFD)
Converters:
Converters are used to change the signal type from one to another. This conversion may take a form of analog signals to digital signals (ADC) or changing the signal medium such as RS232 serial type to RS485 two-wire type.
Actuators:
Based on the controller output, actuators would perform the desired action to change the controlled variable. These are mostly motion-oriented, for e.g. motors, solenoid valves, electromagnetic relays etc.
- Solenoid valves (electrically controlled valves)
- Motors such as steppers, servos, permanent magnet types
- Voltage-controlled electromagnetic relays
Software:
Automation configuration software (between h/w and s/w)
Automation display software ( to display the controlled parameters)
Supervisory control & Data acquisition (SCADA)
Sunday, May 16, 2010
Power Electronics
power semiconductor devices are as follows:
A p-n junction is the basic building block of a semiconductor. p indicates positive charges and n indicates negative charges.
Zener diode is a special diode which is utilised in the reverse-biased mode in voltage regulating apllications.
Schottky diode has very low forward voltage drop but at the same time weak reverse bias withstand capability.
High Amp power diodes are type of p-n jucntion diodes designed to handle high currnet with proper heat dissipation and easy mounting arrangements.
Rectificaion of AC to DC wave can be performed by diodes. A single diode can rectifiy half of an AC waveform, but a full bridge rectifier which contains 4 diodes in a special arrangement can result in fully-rectified DC waveform.
Transistors:
Bipolar transistors can be either pnp transistor or npn transistor.
In operation they employ both polarities of charges (i.e. electrons and holes) so the name bi-polar transistors. These are the conventional transistors.
A transistor can be used in a circuit as a switch which turns ON or OFF in specific conditions, or, as an amplifier which amplifies the signal fed into the transistor. Other evolutions of bipolar transistors are IGBTs, FETs, MOSFETs which have certain advantages depending on the application for which it is used for. For e.g. some of the above are fast-switching.
Thyristors :
Firing angle is the main aspect in the operation of a thyristor. A thyristor will start to conduct when a certain threshold current flows through its secondary circuit. These are mostly applied in high current switching.
HVDC -
Not forgetting the historical fact that there was an AC/DC war between Westinghouse & Edison , AC became predominant in transmitting power to long distances due to the inherent features of AC. Saying that, nowadays for ultra-long distance power transmission DC has been found more beneficial than AC. HVDC refers to high voltage direct current (dc) system. As the power generation is easy in AC form, in this HVDC system, it is then inverted into DC, transmitted over very long distance, and then converted back to conventional AC.
AC power--->Converter--->DC transmission line--->Inverter---->AC power
Here comes the ultimate importance of REAL high current low loss Power Electronic Converters and Inverters.
A 2000A 250 kV high voltage direct current (HVDC) thyristor valve rated 2000 A,250 kV dc at Manitoba Hydro's Henday converter station: Source unknown
FACTS -
Flexible alternating current (ac) transmission system is defined by the IEEE as "a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase power transfer capability."
To summarise the confusing AC/DC below provided is an application example.
1. AC to DC: rectifiers e.g. full bridge rectifier
2. DC to AC: inverters e.g. UPS in battery mode
3. AC to AC: transformers e.g. a 33/11kV power transformer
4. DC to DC: switching/chopping e.g. switch mode power supply
- p-n junction diode - conventional semiconductor-semiconductor junction diode
- schottky diode - faster switching, low forward voltage drop diode
- bipolar junction transistor (BJT) - conventional where both polarity charges operate (electrons & holes)
- field effect transistor (FET) - a unipolar transistor
- metal oxide semiconductor FET (MOSFET)
- Insulated gate bipolar transistor (IGBT)
- silicon controlled rectifier (SCR)
- triode for AC (TRIAC) - a bidirectional thyristor
A p-n junction is the basic building block of a semiconductor. p indicates positive charges and n indicates negative charges.
Zener diode is a special diode which is utilised in the reverse-biased mode in voltage regulating apllications.
Schottky diode has very low forward voltage drop but at the same time weak reverse bias withstand capability.
High Amp power diodes are type of p-n jucntion diodes designed to handle high currnet with proper heat dissipation and easy mounting arrangements.
Rectificaion of AC to DC wave can be performed by diodes. A single diode can rectifiy half of an AC waveform, but a full bridge rectifier which contains 4 diodes in a special arrangement can result in fully-rectified DC waveform.
Transistors:
Bipolar transistors can be either pnp transistor or npn transistor.
In operation they employ both polarities of charges (i.e. electrons and holes) so the name bi-polar transistors. These are the conventional transistors.
A transistor can be used in a circuit as a switch which turns ON or OFF in specific conditions, or, as an amplifier which amplifies the signal fed into the transistor. Other evolutions of bipolar transistors are IGBTs, FETs, MOSFETs which have certain advantages depending on the application for which it is used for. For e.g. some of the above are fast-switching.
Thyristors :
Firing angle is the main aspect in the operation of a thyristor. A thyristor will start to conduct when a certain threshold current flows through its secondary circuit. These are mostly applied in high current switching.
HVDC -
Not forgetting the historical fact that there was an AC/DC war between Westinghouse & Edison , AC became predominant in transmitting power to long distances due to the inherent features of AC. Saying that, nowadays for ultra-long distance power transmission DC has been found more beneficial than AC. HVDC refers to high voltage direct current (dc) system. As the power generation is easy in AC form, in this HVDC system, it is then inverted into DC, transmitted over very long distance, and then converted back to conventional AC.
AC power--->Converter--->DC transmission line--->Inverter---->AC power
Here comes the ultimate importance of REAL high current low loss Power Electronic Converters and Inverters.
A 2000A 250 kV high voltage direct current (HVDC) thyristor valve rated 2000 A,250 kV dc at Manitoba Hydro's Henday converter station: Source unknown
FACTS -
Flexible alternating current (ac) transmission system is defined by the IEEE as "a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase power transfer capability."
To summarise the confusing AC/DC below provided is an application example.
1. AC to DC: rectifiers e.g. full bridge rectifier
2. DC to AC: inverters e.g. UPS in battery mode
3. AC to AC: transformers e.g. a 33/11kV power transformer
4. DC to DC: switching/chopping e.g. switch mode power supply
