Answer / t. eswara rao

Capacitors are used for compensating the inductive reactive
power in the system and bring the power factor to the unity.
But the question is what is problem if we connect them in star?
If we connect them in star , and any capacitor fails ,
it momentarily shorts the supply voltage and raises the
voltage levels across the remaining capacitor banks
connected in the remaining phases. This may lead to destroy
the other two capacitor banks also.

Answer / k.ravindran

When connected in delta, the voltage on each capacitor will
be the phase voltage.
When connected in star, the voltage on each capacitor will
be the phase voltage divided by root of 3.
If the capacitors are rated for the available phase
voltage, then they can be connected either in delta or in
star.

Answer / faraz ahmed

Wye connected capacitors connected to motors are not
appropriate because they are ungrounded and thus present a
potential difference on each phase of the capacitor which
contributes to the over-all deterioration of the capacitor.
As can be seen in fig.1 below, the failure of any one cell
of a Wye connected capacitor presents an unbalanced load to
the motor. This will effectively destroy the motor due to
unbalanced voltage, temperatures.
Example: If you have a 100HP motor and an unbalance of 5%,
this will cause a power loss of 25%. (100HP – 25% = 75HP).
If the motor was loaded to 85%, the motor now becomes
overloaded. The motor would run 113.5% overloaded, therefore
overheated and will eventually burn out.
Unprotected Wye connected capacitors should not be used for
Power Factor correction. The unbalance protection required
for this type of application is more costly than the
capacitors themselves and therefore not included with Wye
connected capacitors.
Wye connected capacitors do not circulate harmonics and thus
are much more vulnerable to failure due to harmonics.

Fig.1 - The total capacitance for the example above with a
failed cell would be 5kVAR
Delta connected three phase capacitors are more friendly to
the electrical environment. They not only provides
capacitance to each phase but also provides no voltage
unbalances (harmonics).
If a capacitor cell should fail for any reason in one phase,
we are going from a closed delta to an open delta
configuration and in this instance the voltages on each
phase stays the same (see fig.2 below). Failure of a
capacitor cell would only mean a drop in the kVAR on the
circuit. In other words, a 30kVAR delta connected three
phase capacitor with a failed cell would provide 20kVAr to
the electrical system instead of 30kVAR.
Delta connected capacitors unlike the Wye connected
capacitors are able to circulate harmonics currents within
the delta circuit. By doing so it reduces the harmonics on
the electrical system.


Fig.2 - The total capacitance for the example above with a
failed cell would be 20kVAR

Answer / miguel

kvar will be less.

Answer / pravin m sonwane

in medium voltage Delta connection or star ungrounded is
mostly used because of

1)Harmonic current is circulated in delta loop, hence no
damage to system

2)Across capacitors phase voltage is present.

3)more efficient configuration than other like star, star
grounded, star ungrounded, double star neutral may or may
not be isolated, double star with neutral grounded.

4)No zero sequence or third harmonic currents can flow in a
star-connected capacitor bank. Additionally, where one
series group per phase is used, the individual capacitor
fuses should be capable of interrupting the system
short-circuit phase-to-phase fault current.

5)The greatest use of A-connected banks is at 2400 V, since
this is the lowest standard capacitor voltage rating.

6)As zero sequence or third harmonic is absent, less
protection to bank is required. hence less costing in such
capacitor configuration.

Answer / sahil>m

Cy=3 C delta so value of cap will go high

Answer / sunil guru

if we convert the power from delta to star then the power
received is very less and not sufficient for compensating
purpose and making power factor at utility but while getting
star to delta power the power received is high and
advantageous.....

Answer / mira

because capacitors in delta provides reactive power 3 times
than that connected in star..such as in capacitor banks.

Answer / rabindra

the capacitance of the capacitor in case of star is 3-times
that in delta connection,so i think the capacitor may
destroy.

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