comparison b/w EHAV and HVDC economical comparison *------positive and negative corona pulses insulating materials: transformers and rotating machines

1. SUBMITTED TO- MR RAHUL SHARMA
Department of electrical engg
SUBMITTED BY-ASHUTOSH PARBHAKAR
1704506
306/17
Department of electrical engg
ashutosh parbhakar 306

2. Parameter EHVAC HVDC
Type of Transmission AC DC
Overall Losses High losses
Low losses.
There is no reactive power
loss.
Skin effect in the conductors,
dielectric loss heating
problems in an insulation of
conductors are absent.
I2R loss is very less. Line
charging and electric
resonance effects are absent.
Cost of Transmission High cost of
transmission
Only two conductors are
used for transmission and
DC cables are cheaper than
AC cables.
So low cost.
ashutosh parbhakar 306

3. Parameter EHVAC HVDC
Cost of Equipment Low cost of
equipment
Comparatively high
cost
Power Control Power cannot be
controlled
Power can be
controlled.
[But complex
converters control
circuits are required
Directionality of link Unidirectional
transmission
Bidirectional
transmission.
Transmitted power and
distance
Depends upon
distance
Independent of
distance
ashutosh parbhakar 306

4. The dc line is less costly compared with an 800 kV ac line. On the other
hand, the converter station cost offsets the gain in reduced cost of the
transmission line. Thus a short line is cheaper with ac transmission,
while a longer line is cheaper with dc.
ashutosh parbhakar 306

5.  Coronas may be positive or negative.
 This is determined by the polarity of the voltage on the highly
curved electrode. If the curved electrode is positive with respect
to the flat electrode, it has a positive corona; if it is negative, it
has a negative corona.
S.NO. Positive corona Negative corona
1 All the electrons are
attracted inward
toward the
nearby positive
electrode and the
ions are repelled
outwards.
All the electrons are
attracted outward
toward the near
by negative
electrode and the
ions are attracted
inwards.
2 - More intense corona
pulses are produced
3 More stable
discharge
More self-sustaining
dischargeashutosh parbhakar 306

6. S.NO. Positive pulses Negative pulses
4 Linearly sensitive to
changes in humidity
Humidity has little or
no effect
5 Produces less corona
than negative corona
Can only be sustained in
fluids that contain
electronegative
discharge
ashutosh parbhakar 306

7. 1.Insulating Oil:
Transformer oil act as liquid dielectric and coolant
2.Insulating paper:
Withstand the high electrical and physical stresses
experienced around a core and windings
3.Wood:
Used in areas which required higher mechanical and
lower electric strength and for making a variety of
insulation components like coil clamping ring, cleat,
support, core and yoke etc.
4.Insulating tape:
Insulating tape is used for various taping purposes . These
tapes are used in taping, banding, core bolt insulation,
places where required high strength and in banding of
transformer cores.
ashutosh parbhakar 306

8. The materials must have good mechanical characteristics
and high dielectric strength for reliable operation of the
machine. They should withstand thermal stresses and
mechanical vibrations.
Conductor:
Baked on enamel cotton covering or combination of both
(class A)- fibre glass coated with an organic varnish (class
B)- fibre glass coated with silicon varnish (class H).
Binders:
Paper backed mica, fibre glass, cotton tapes, synthetic
resin fabric tapes
Ground insulation:
Mica flakes bonded by resins
ashutosh parbhakar 306

9.  1. With the change of temperature the movement
of electrons in a material changes and hence it
affects the breakdown voltage of the material.
 2. Thickness i.e. geometric is very simple concept.
In an electrical material if the thickness of
material is increases its breakdown voltage is also
increased and hence the dielectric strength.
 3. The electric field has a direct relation with the
breakdown voltage or dielectric strength. An
increase in the electric field will result in
increased dielectric strength.
ashutosh parbhakar 306

10.  Impregnation in electrical engineering means
applying an impregnating agent in gaseous or fluid
form to a porous body in order to insulate it
electrically, i.e. that reliable protection against
electrical breakdown is provided even when the
thickness of the insulating layer is small.
 Applications of impregnation include solenoids and
transformers, electrical motors, Stators, coils and
rotors. This provides better electrical insulation and
prevents vibration. Impregnation increases the
thermal conductivity and helps to reach a better
environmental balance. Whether trickling, roll
dipping, hot dipping, vertical dipping or potting – our
solutions ensure a reliable process to guarantee a high
quality and continuous impregnation result.
ashutosh parbhakar 306

11. ashutosh parbhakar 306