Ballast Calculation - ABB i-bus KNX Product Manual

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ABB i-bus KNX
Device technology
2.2

Ballast calculation

The electronic ballast is a device for operating gas discharge lamps, e.g. fluorescent lamps. During normal
operation, it converts the mains voltage to an optimum operating voltage for the gas discharge lamps. Fur-
thermore, the electronic ballast enables the gas discharge lamps to ignite (start) via capacitor circuitry.
Using the original choke/starter circuitry, the lamps switch-on consecutively, with the electronic ballast all
fluorescent lamps switch on practically simultaneously. If switch-on occurs at the mains voltage peak, the
buffer capacitors of the electronic ballast cause a high but very short current pulse. When using several
ballasts on the same circuit, the simultaneous charging of the capacitors may result in very large system
inrush currents.
This peak inrush current I
tion of the respective circuit protection. In the following, the effects of the electronic ballast peak inrush cur-
rent and the associated limitation of the number of electronic ballasts on the Energy Actuator are exam-
ined.
The inrush current of the electronic ballast depends not only on the wattage but also on the type, the num-
ber of elements (lamps) and on the manufacturer. For this reason, the given maximum number of connect-
ible electronic ballasts per output can only relate to a defined type of electronic ballast. For a different bal-
last type, this value can only represent an estimation.
In order to properly estimate the number of electronic ballasts, the peak inrush current I
tive pulse width of the electronic ballast must be known. In the meantime, these values are stated by the
manufacturer in the technical data or are available on request.
Typical values for single element electronic ballasts with T5/T8 lamps are: Peak inrush current 15...50 A
with a pulse time of 120...200 µs.
The relays of the Energy Actuators have the following maximum starting values:
Max. peak inrush-current I
Max. peak inrush-current I
Max. peak inrush-current I
Caution
Do not exceed the threshold values.
Exceeding the value leads to destruction of the relay, e.g. due to welding.
Example
Electronic ballast 1 x 58 CF
Peak inrush-current I
Maximum number of electronic ballasts/output = 600 A/34 A = 17 ballasts
This number has been limited to 12 electronic ballasts in conjunction with a B16 miniature circuit break-
er. If more electronic ballasts are connected, the miniature circuit breaker may trip during switch on.
14 2CDC 505 084 D0203 | SE/S 3.16.1
is to be considered when designing the switch contacts as well as by the selec-
p
(150µs)
p
(250µs)
p
(600µs)
p
= 33.9 A (147.1 µs)
p
SE/S 3.16.1
600 A
480 A
300 A
and the respec-
p