KMB NOVAR 2600, Operating Manual

Page: 56 / 96

NOVAR 2600 Operating Manual
4.4.6.4 CHL – Capacitor Harmonic Load Factor
This quantity was designed and implemented in order compensation capacitors protection against
current overload to be possible simply. If appropriate alarm actuation is set the controller disconnects
the sections from a network as soon as the CHL-factor exceeds preset limit value.
Compensation capacitors’ service life depends on not exceeding of operation limits. One of the limits
is capacitors’s maximum current. This may be exceeded with voltage harmonic distortion due to
a capacitor’s inductance being a function of the frequency.
If voltage in not distorted (sinus), the capacitor current is
Ic =
U
Zc
=
U
1
2 πfC
= 2 πfCU
[ A ]
where :
Ic.... capacitor current [ A ]
U.... capacitor voltage [ V ]
Zc... capacitor impedance [ Ω ]
f.... frequency [ Hz ]
C... capacitor capacity [ F ]
If the voltage is distorted, the current flowing through a capacitor forms as the sum of current harmonic
component vectors
Ic
=
∑
i = 1
n
Ii
[ A]
and magnitude of each harmonic component is pursuant to the first formula
Ii = 2 πfi C Ui = 2 π ( f
f
∗ i ) C Ui
[ A ]
where :
i.... order of harmonic [ - ]
Ii.... current of i th harmonic component [ A ]
Ui... voltage of i th harmonic component [ V ]
fi.... frequency of i th harmonic component [ Hz ]
f
f
.... fundamental harmonic frequency [ Hz ]
According to the formula, the magnitude of current of each harmonic component is proportional to
a multiple of voltage and its order (Ui x i) of harmonic. Consequently, the total harmonic distortion,
which is defined as
THD
U
=
1
U 1
√
∑
i
=
2
N
Ui
2
∗
100
[ % ]
where:
THD
U
… voltage total harmonic distortion [ % ]
Ui......... voltage of i th harmonic component [ V ]
U
1
…..... voltage of fundamental harmonic component [ V ]
is not suitable as a criterion of capacitor current overload due to harmonic distortion, because it does
not respect distribution of harmonic components across their spectrum.
Therefore, the capacitor harmonic load factor is defined as follows
CHL
=
1
U
NOM
√
∑
i
=
1
N
i
∗
Ui
2
∗
100
[ % ]
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