Short Circuit Protection Devices - Daikin PE-ADDA200 Service And Installation Manual

7.1.3

Short Circuit protection devices

Short circuit protection is achieved by means of external fuses or automatic circuit breakers. Semiconductor
fuses ensure the power module is not damaged in case of short circuit, however other protection devices such
as circuit breakers or general type fuses can be used, provided that the system is designed to limit damage to
the inverter only, ensuring safety of personnel and machinery.
Protection Devices shall be selected on the basis of their:

Rated Current

Rated Voltage

Operating i 2 t

Arc Voltage
 Peak Let-Through Current

Interrupting Capacity
Rated Current: The Rated Input Currents of the VFD is given in Tab. 2. Note that in case of unbalanced supply
voltage, the current in one phase can exceed the given rated current. Please refer to the guidelines provided by
the manufacturer of the protection device to apply the correct derating to the rated current.
Rated Voltage: The rated voltage of the protection device shall be selected in accordance to the mains voltage.
Operating i 2 t: The operating i
fully protected or if it is allowed to be damaged in case of a fault. To avoid any damage to the power modules,
this value must be smaller than the i
The i 2 t of the power modules depends on their initial junction temperature (T
overcurrent (t). As the temperature increases, the operating i
of the semiconductor modules. It is normally enough to compare the i
the cold semiconductor module. Of course, in the specific operating conditions, the former must be smaller than
the latter. In case the protection device has a higher I
guaranteed. However, proper system design may allow the power module to be damaged without any other
consequences to the other equipment.
Arc Voltage: a certain voltage develops across the fuse during opening, which depends on the applied voltage,
the circuit impedance and the point of initiation of the short-circuit. The maximum peak voltage plotted against
the applied voltage is typically given by the protection device manufacturers. The resulting voltage across each
rectifier module shall be less than their maximum non repetitive blocking voltage (max 1700 V @ T
to the chosen topology and the presence of RC snubbers and surge suppressors in the input stage of the VFD, it
can be considered that this requirement is always met.
Peak Let-Through Current: under short-circuit conditions, semiconductor fuses limit the peak fault current. For
each fuse, the worst-case peak let-through current is typically given as function of the symmetrical prospective
rms fault current. In any condition, such peak let-though current must be less than the surge overload current
(half sine wave peak value) of the semiconductor module, given in Fig. 8.
Daikin Applied Europe S.p.A
SERVICE and INSTALLATION MANUAL
Compressor Inverter PE-ADDA200
2 t of the protection device determines whether the semiconductor power module is
2 t value of the semiconductor to be protected (see Tab. 2).
2 t, integrity of the semiconductor power module cannot be
Page 16 of 51
) and on the duration of the
VJ
2
t of the fuses generally decreases faster than that
2
t of the cold protection device with that of
Rev. 0.3
= 25°C). Due
VJ