Fusing; Line Chokes - KEB Combivert F5 series Instruction Manual

General

1.5.4 Fusing

A circuit breaker or a disconnect switch with fuses must be provided as branch
circuit protection in accordance with the National Electric Code (NEC) and all
local codes.
The F5 is to be connected to the supply voltage using Class J fuses (BUSSMANN
type LPJ or equivalent) or using a magnetic trip circuit breaker with type D
characteristic. Ratings for the short-circuit protection device are specified per
unit size in the tables on pages 15-20.
The minimum voltage rating for protection devices used with 230V inverters shall be
250VAC. The minimum voltage rating for protection devices used with 460V inverters
shall be 600VAC.
Fuses should not be installed between the inverter and the motor. The output of the
inverter is short circuit protected and ground fault protected with a maximum trip value
(varies by housing size) of 250% of the rated output current. The tripping time is less
than 1 mSec. Repeated short-circuits faults can cause premature failure of the output
transistors. If the motor is operating in regenerative mode (2nd or 4th quadrant) and a
short circuit occurs, the inverter may not be able to limit the current before failure occurs.

1.5.5 Line Chokes

A line choke with minimum 3% impedance is required for all 230 V inverters 40hp
(size 19) and greater. A line choke with minimum 3% impedance is required for
all 460V inverters 100hp (size 23) and greater.
Installing a line choke will considerably extend the lifetime of the DC bus capacitors
especially on systems operating continuously at rated power.
A line choke with minimum 3% impedance should be installed when the power
available at the nearest distribution point is significantly greater (more than 200
times) than the rated power of the inverter.
Example: 5 hp COMBIVERT F5 S
2,000kVA / 6.6 kVA = 303 > 200 -> install 3% choke
Another method to determine whether a choke is required; if the line impedance
is less than 0.5%, then a choke should be used.
A line choke can be used to generally reduce conducted high frequency noise
eliminating nuisance trips. See section 3.2.1 on page 33 for more information.
10
= 6.6kVA, S
rated dist_xfrmr
=2,000 kVA.