NORD Drivesystems BU0505 - Manual (Page 28)

SK 54xE – Users Manual for Frequency Inverters
28 BU 0505 GB-1013
2.6 Brake resistor (BR)
CAUTION Danger of burns
The heat sink and all other metal components can heat up to temperatures above 70°C.
Touching such components may cause local burns to the affected parts of the body (hands, fingers, etc.).
To prevent such injuries, allow sufficient time for cooling down before starting work - the surface temperature
should be checked with suitable measuring equipment. In addition, keep sufficient distance from adjacent
components during installation, or install protection against contact.
During dynamic braking (frequency reduction) of a three-phase motor, electrical energy is returned to
the inverter. An external brake resistor can be used in order to prevent the FI from being shut down
due to overvoltage. With this, the integrated brake chopper (electronic switch) pulses the intermediate
circuit voltage (switching wave approx. 420 V/775 V(/825 V) DC, according to the mains voltage)
(115 V, 230 V/400 V(/500 V)) to the brake resistor. Here the excess energy is converted into heat.
For inverter powers up to 7.5 kW (230 V: up to 4.0 kW) a standard bottom-mounted resistor
(SK BR4-..., IP40) can be used. This can additionally be equipped with an optional temperature switch
(bi-metal, switching point 100
℃), in order to i
is enclosed. The resistor and the temperature switch are connected by means of flexible stranded
conductors. Approval: UL, cUL
Note: Brake resistors cannot be directly mounted below …-CP (ColdPlate) devices.
SK BR4-... Size 1 SK BR4-... Size 2
For frequency inverters above 3kW chassis resistors (SK BR2-..., IP20) are also available. These
must be mounted in the control cabinet, close to the frequency inverter. There is a temperature switch
on the braking resistor to provide protection against overload. Connection of the resistor and the
temperature switch is by means of screw terminals. Approval: UL, cUL
SK BR2-... Size 3 SK BR2-... Size 4 and above
Fig. 5: Top: bottom-mounted brake resistor SK BR4- Bottom: chassis brake resistor SK BR2-...
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