GE Industrial Solutions AF-650 GP General Purpose Drive - Manual (Page 10)

4 How to Choose a Brake Resistor
The GE brake resistor programme consists of two types of resistors, flat packs and wire wound - see pictures below.
Illustration 4.1: Wire Wound
Illustration 4.2: Flat Pack
4.1.1 Flat Packs
The flat pack brake resistors ( see Illustration 4.2) for the AF-650 GP series is a safe and compact solution for the customer. At a constant load and free convection
the resistor is self protecting as a fuse. This means short circuit proof, no fault to frame, no melting of casing and self extinguishing. The casing is made of anodized
aluminum and is IP65 tight.
With the compact flat pack resistor, it is possible to mount the resistor on the rear of a AF-650 GP frequency converter.
The flat pack resistor portfolio covers the lower power range from 0.75 - 7.5 kW (200 - 240 V & 380 - 480 V) - and intended for horizontal applications (conveyors).
4.1.2 Wire Wound
The GE wire wound resistor (see Illustration 4.1) consist of fully welded wire wound ceramic resistors. The base material is a very high temperature (up to 700 °C)
resistant ceramic, called Corderite. This ensures a resistor which is suitable for pulse loads between 10 - 20 times or more compared to the nominal load, which
is used in frequent braking applications such as cranes, hoists and elevators.
To simplify the selection of the wire wound brake resistor GE has chosen to offer two sizes for each drive across the power range, from 0.37 kW to 355 kW (380 -
480 V).
The overall sizes are based on the duty cycle (10% and 40%) which is the proportion between the process time and the braking time. Thus if a 10% duty cycle
resistor is applied it is able to absorb/brake away the peak power for 10% of the period. The remaining 90% of the period will be used to deflect excess heat.
Depending on the size the periods for the wire wound resistors are 120, 300 and 600 seconds.
The following chapter lists the 10% and 40% brake resistors available for the AF-650 GP drives.
If the optimum brake resistor must be selected it is necessary to know how often and how much the motor is to brake. How to calculate this and application
examples can be found in chapter 6 and 7.
The enclosures comply with IP20.
As rule of thumb the 10% resistors are used for horizontal loads (e.g. conveyors, gantry cranes) and the 40% for vertical loads (e.g. cranes, hoists and elevators).
However to help choose the right sized brake resistor for an application the flow chart (illustration 3) provides guidance. Answer the questions in the diamond
shaped boxes and you are guided to either tables for selection of brake resistors or chapters about how to calculate inertia or duty cycle.
AF-650 GP Brake Resistor Design Guide
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