Hv Solid State Generation
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High Voltages Solid State
HV System
LIM/EHV/March 2007
1
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Solid State Switching Principle • • • • • • • •
HV System
The power systems engineers is interested in high voltages primarily for power transmission, and secondly for testing of his equipment used in power transmission in laboratory High voltage can be obtained locally from power generating plant through the use of solid state In many testing laboratories, the primary source of power is at low voltage (400 V three phase or 230 V single phase, at 50 Hz). From which high voltage can be obtained On board ship the same technology can be used to use high voltage Laboratory test are aimed to design the required high voltage Since insulation is usually being tested, the impedances involved are extremely high (order of M ohm and the currents small (less than an ampere). High voltage testing does not usually require high power. Thus special methods may be used which are not applicable when generating high voltage in high power applications. LIM/EHV/March 2007
2
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Solid State Switching Principle •
In the field of electrical eng. & applied physics, high voltages are required for several applications As: -a power supply (eg. hv dc) for the equipments such as electron microscope and x-ray machine. -Required for testing power apparatus – insulation testing. -High impulse voltages are required for testing purposes to simulate over voltages due to lightning and switching. • Sometimes, high direct voltages are needed in insulation test on cables and capacitors. Impulse generator charging units also require high dc voltages of about 100-200kV. • Normally for the generation of dc voltages of up to 100kV, electronics valve rectifiers are used and the output currents are about 100mA. The rectifier valves require special construction for cathode and filaments since a high electrostatic field of several kV/cm exists between the anode and cathode in the non-conduction period. • The ac supply to the rectifier tubes maybe of power frequency or maybe of audo frequency from an oscillator. The latter is used when a ripple of very small magnitude is required without the use of costly filters to smoothen the ripple. HV System
LIM/EHV/March 2007
3
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Half and Full Wave Rectifier •
Rectifier circuits for producing high dc voltages from ac sources maybe
b. c.
Half-Wave Full-Wave
o
The rectifier can be an electron tube or a solid state devices. Nowadays, single electron tubes are available for peak inverse voltages up to 250kV and semiconductor or solid state diodes up to 250kV.
o
For higher voltages, several units are to be used in series. When a number of units are used in series, transient voltage distribution along each unit becomes non-uniform and special care should be taken to make the distribution uniform.
HV System
LIM/EHV/March 2007
4
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RL
Vin
V out
Half Wave Rectifier
V
p V
AVG
0 T
Mean Load Voltage or Average Value of half wave output
HV System
LIM/EHV/March 2007
5
D1
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+ to
t1
t2
RL
D2
Full wave Rectifier Circuit Vp
figure 1.7 : Full-wave rectifier circuit V AVG to
t1
t2
Mean Load Voltage or Average Voltage Full-wave output HV System
LIM/EHV/March 2007
6
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Voltage Multiplier Circuits • Both full-wave as well as half-wave circuits can produce a maximum direct voltage corresponding to the peak value of the alternating voltage. • When higher voltages are required voltage multiplier circuits are used. The common circuits are the voltage double circuit • Used for higher voltages. • Generate very high dc voltage from single supply transformer by extending the simple voltage doubler circuit. HV System
LIM/EHV/March 2007
7
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Types of high voltages; • • • • • • •
HV System
High d.c. voltages High a.c. voltages of power frequency High a.c. voltages of high frequency High transient or impulse voltages of very short duration - lightning overvoltages Transient voltages of longer duration – switching surges
LIM/EHV/March 2007
8
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•
The voltage doubler circuit makes use of the positive and the negative half cycles to charge two different capacitors. These are then connected in series aiding to obtain double the direct voltage output. Figure shows a voltage doubler circuit.
•
In this case, the transformer will be of small rating that for the same direct voltage rating with only simple rectification. Further for the same direct voltage output the peak inverse voltage of the diodes will be halved.
HV System
Voltage doubler circuit
LIM/EHV/March 2007
9
To Be A World Class Maritime Academy
High Alternating Voltages • Required in laboratories and a.c. tests as well as for the • circuit of high d.c. and impulse voltage. • Test transformer are generally used. • Single transformer test units are made for high alternating voltages up to about 200 kV. • However, for high voltages to reduce the cost (insulation cost increases rapidly with voltage) and make transportation easier, a cascade arrangement of several transformers is used. • For higher voltage requirement, series connection or cascading of the several identical units of transformer is applied.
HV System
LIM/EHV/March 2007
10
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Cascade arrangement of transformers
HV System
LIM/EHV/March 2007
11
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1600 kV, 9.6 MVA Cascaded Power Transformer
HV System
LIM/EHV/March 2007
12
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Cascade arrangement of transformers • A typical cascade arrangement of transformers used to obtain up to 300 kV from three units each rated at 100 kV insulation. The low voltage winding is connected to the primary of the first transformer, and this is connected to the transformer tank which is earthed. • One end of the high voltage winding is also earthed through the tank. • The high voltage end and a tapping near this end is taken out at the top of the transformer through a bushing, and forms the primary of the second transformer. • One end of this winding is connected to the tank of the second transformer to maintain the tank at high voltage. • The secondary of this transformer too has one end connected to the tank and at the other end the next cascaded transformer is fed. HV System
LIM/EHV/March 2007
13
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Cascade arrangement of transformers • This cascade arrangement can be continued further if a still higher voltage is required. • In the cascade arrangement shown, each transformer needs only to be insulated for 100 kV, and hence the transformer can be relatively small. If a 300 kV transformer had to be used instead, the size would be massive. High voltage transformers for testing purposes are designed purposely to have a poor regulation. • This is to ensure that when the secondary of the transformer is short circuited (as will commonly happen in flash-over tests of insulation), the current would not increase to too high a value and to reduce the cost. In practice, an additional series resistance (commonly a water resistance) is also used in such cases to limit the current and prevent possible damage to the transformer. HV System
LIM/EHV/March 2007
14
To Be A World Class Maritime Academy
Cascade arrangement of transformers • •
•
•
What is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons. In the cascade arrangement shown, each transformer needs only to be insulated for 100 kV, and hence the transformer can be relatively small. If a 300 kV transformer had to be used instead, the size would be massive. High voltage transformers for testing purposes are designed purposely to have a poor regulation. This is to ensure that when the secondary of the transformer is short circuited (as will commonly happen in flash-over tests of insulation), the current would not increase to too high a value and to reduce the cost. In practice, an additional series resistance (commonly a water resistance) is also used in such cases to limit the current and prevent possible damage to the transformer. What is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons.
HV System
LIM/EHV/March 2007
15
To Be A World Class Maritime Academy
High D.C. Voltages • Generation of high d.c. voltages is mainly required in research work in the areas of pure and applied physics. • Needed in insulation test. • Use rectifier circuit (diode) to convert a.c. to d.c. • voltage. – vacuum rectifiers, semiconductor diodes HV System
LIM/EHV/March 2007
16
To Be A World Class Maritime Academy
Impulse High Voltage • Impulse voltages (IVs) are required in hv tests to simulate the stresses due to external and internal overvoltages, and also for fundamental investigations of the breakdown mechanisms. • Usually generated by discharging hv capacitors through switching gaps onto a network of resistors and capacitors. • In hv technology, a single, unipolar voltage is termed an impulse voltage. • Rectangular and wedge-shaped IVs are normally used for basic experiments while for testing purposes, double exponential IVs are used. • Standard test of impulse voltages can be represented as double exponential wave, and its mathematical equation is defined as follows; V = Vo [exp(-αt) – exp(-βt)] Where α and β are constants of microsecond values. HV System
LIM/EHV/March 2007
17
High Voltages Solid State
HV System
LIM/EHV/March 2007
1
To Be A World Class Maritime Academy
Solid State Switching Principle • • • • • • • •
HV System
The power systems engineers is interested in high voltages primarily for power transmission, and secondly for testing of his equipment used in power transmission in laboratory High voltage can be obtained locally from power generating plant through the use of solid state In many testing laboratories, the primary source of power is at low voltage (400 V three phase or 230 V single phase, at 50 Hz). From which high voltage can be obtained On board ship the same technology can be used to use high voltage Laboratory test are aimed to design the required high voltage Since insulation is usually being tested, the impedances involved are extremely high (order of M ohm and the currents small (less than an ampere). High voltage testing does not usually require high power. Thus special methods may be used which are not applicable when generating high voltage in high power applications. LIM/EHV/March 2007
2
To Be A World Class Maritime Academy
Solid State Switching Principle •
In the field of electrical eng. & applied physics, high voltages are required for several applications As: -a power supply (eg. hv dc) for the equipments such as electron microscope and x-ray machine. -Required for testing power apparatus – insulation testing. -High impulse voltages are required for testing purposes to simulate over voltages due to lightning and switching. • Sometimes, high direct voltages are needed in insulation test on cables and capacitors. Impulse generator charging units also require high dc voltages of about 100-200kV. • Normally for the generation of dc voltages of up to 100kV, electronics valve rectifiers are used and the output currents are about 100mA. The rectifier valves require special construction for cathode and filaments since a high electrostatic field of several kV/cm exists between the anode and cathode in the non-conduction period. • The ac supply to the rectifier tubes maybe of power frequency or maybe of audo frequency from an oscillator. The latter is used when a ripple of very small magnitude is required without the use of costly filters to smoothen the ripple. HV System
LIM/EHV/March 2007
3
To Be A World Class Maritime Academy
Half and Full Wave Rectifier •
Rectifier circuits for producing high dc voltages from ac sources maybe
b. c.
Half-Wave Full-Wave
o
The rectifier can be an electron tube or a solid state devices. Nowadays, single electron tubes are available for peak inverse voltages up to 250kV and semiconductor or solid state diodes up to 250kV.
o
For higher voltages, several units are to be used in series. When a number of units are used in series, transient voltage distribution along each unit becomes non-uniform and special care should be taken to make the distribution uniform.
HV System
LIM/EHV/March 2007
4
To Be A World Class Maritime Academy
RL
Vin
V out
Half Wave Rectifier
V
p V
AVG
0 T
Mean Load Voltage or Average Value of half wave output
HV System
LIM/EHV/March 2007
5
D1
To Be A World Class Maritime Academy
+ to
t1
t2
RL
D2
Full wave Rectifier Circuit Vp
figure 1.7 : Full-wave rectifier circuit V AVG to
t1
t2
Mean Load Voltage or Average Voltage Full-wave output HV System
LIM/EHV/March 2007
6
To Be A World Class Maritime Academy
Voltage Multiplier Circuits • Both full-wave as well as half-wave circuits can produce a maximum direct voltage corresponding to the peak value of the alternating voltage. • When higher voltages are required voltage multiplier circuits are used. The common circuits are the voltage double circuit • Used for higher voltages. • Generate very high dc voltage from single supply transformer by extending the simple voltage doubler circuit. HV System
LIM/EHV/March 2007
7
To Be A World Class Maritime Academy
Types of high voltages; • • • • • • •
HV System
High d.c. voltages High a.c. voltages of power frequency High a.c. voltages of high frequency High transient or impulse voltages of very short duration - lightning overvoltages Transient voltages of longer duration – switching surges
LIM/EHV/March 2007
8
To Be A World Class Maritime Academy
•
The voltage doubler circuit makes use of the positive and the negative half cycles to charge two different capacitors. These are then connected in series aiding to obtain double the direct voltage output. Figure shows a voltage doubler circuit.
•
In this case, the transformer will be of small rating that for the same direct voltage rating with only simple rectification. Further for the same direct voltage output the peak inverse voltage of the diodes will be halved.
HV System
Voltage doubler circuit
LIM/EHV/March 2007
9
To Be A World Class Maritime Academy
High Alternating Voltages • Required in laboratories and a.c. tests as well as for the • circuit of high d.c. and impulse voltage. • Test transformer are generally used. • Single transformer test units are made for high alternating voltages up to about 200 kV. • However, for high voltages to reduce the cost (insulation cost increases rapidly with voltage) and make transportation easier, a cascade arrangement of several transformers is used. • For higher voltage requirement, series connection or cascading of the several identical units of transformer is applied.
HV System
LIM/EHV/March 2007
10
To Be A World Class Maritime Academy
Cascade arrangement of transformers
HV System
LIM/EHV/March 2007
11
To Be A World Class Maritime Academy
1600 kV, 9.6 MVA Cascaded Power Transformer
HV System
LIM/EHV/March 2007
12
To Be A World Class Maritime Academy
Cascade arrangement of transformers • A typical cascade arrangement of transformers used to obtain up to 300 kV from three units each rated at 100 kV insulation. The low voltage winding is connected to the primary of the first transformer, and this is connected to the transformer tank which is earthed. • One end of the high voltage winding is also earthed through the tank. • The high voltage end and a tapping near this end is taken out at the top of the transformer through a bushing, and forms the primary of the second transformer. • One end of this winding is connected to the tank of the second transformer to maintain the tank at high voltage. • The secondary of this transformer too has one end connected to the tank and at the other end the next cascaded transformer is fed. HV System
LIM/EHV/March 2007
13
To Be A World Class Maritime Academy
Cascade arrangement of transformers • This cascade arrangement can be continued further if a still higher voltage is required. • In the cascade arrangement shown, each transformer needs only to be insulated for 100 kV, and hence the transformer can be relatively small. If a 300 kV transformer had to be used instead, the size would be massive. High voltage transformers for testing purposes are designed purposely to have a poor regulation. • This is to ensure that when the secondary of the transformer is short circuited (as will commonly happen in flash-over tests of insulation), the current would not increase to too high a value and to reduce the cost. In practice, an additional series resistance (commonly a water resistance) is also used in such cases to limit the current and prevent possible damage to the transformer. HV System
LIM/EHV/March 2007
14
To Be A World Class Maritime Academy
Cascade arrangement of transformers • •
•
•
What is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons. In the cascade arrangement shown, each transformer needs only to be insulated for 100 kV, and hence the transformer can be relatively small. If a 300 kV transformer had to be used instead, the size would be massive. High voltage transformers for testing purposes are designed purposely to have a poor regulation. This is to ensure that when the secondary of the transformer is short circuited (as will commonly happen in flash-over tests of insulation), the current would not increase to too high a value and to reduce the cost. In practice, an additional series resistance (commonly a water resistance) is also used in such cases to limit the current and prevent possible damage to the transformer. What is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons.
HV System
LIM/EHV/March 2007
15
To Be A World Class Maritime Academy
High D.C. Voltages • Generation of high d.c. voltages is mainly required in research work in the areas of pure and applied physics. • Needed in insulation test. • Use rectifier circuit (diode) to convert a.c. to d.c. • voltage. – vacuum rectifiers, semiconductor diodes HV System
LIM/EHV/March 2007
16
To Be A World Class Maritime Academy
Impulse High Voltage • Impulse voltages (IVs) are required in hv tests to simulate the stresses due to external and internal overvoltages, and also for fundamental investigations of the breakdown mechanisms. • Usually generated by discharging hv capacitors through switching gaps onto a network of resistors and capacitors. • In hv technology, a single, unipolar voltage is termed an impulse voltage. • Rectangular and wedge-shaped IVs are normally used for basic experiments while for testing purposes, double exponential IVs are used. • Standard test of impulse voltages can be represented as double exponential wave, and its mathematical equation is defined as follows; V = Vo [exp(-αt) – exp(-βt)] Where α and β are constants of microsecond values. HV System
LIM/EHV/March 2007
17
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