3PR3 resistors are equipped with cast iron resistor elements 3PY6 which are installed in a steel sheet housing. Ceramic strips hold and insulate the resistor elements inside the housing. A heat shield separates the resistor zone from the terminal zone. Connecting pieces screwed to the resistor
elements supported on ceramic hold strips are used for connecting the cables.
Each resistor element can be provided with a connection. Changes or supplements regarding
the connections are easy, even retroactively. Elements WE4,7 through to WE90 are mechanically
sufficiently stable to be installed without additional fixature.
Elements WE125 through to WE700 are mounted with an acid-proof compound.
The resistors are available as standard banks, special banks or banks with double
elements in 5 box sizes.
Resistors with standard banks
The number of components for such units is already defined. A subsequent adjustment of the stepping is still possible at the place of installation within certain limits. A resistor set usually comprises several single or three-strand boxes. The terminal marking at the boxes is uniform so that the connection diagram of a resistor set is easy to set up. Standard bank units facilitate the warehousing of spare parts for larger systems.
Resistors with special banks
The number of components of these units is optimized for each individual application
where standard bank units are not economical or too large in size. Resistors with double banks For short-term and starting operations the use of double elements is often advantageous. Elements with the symbol DWE have double the storage capacity of standard WE elements. Compared with the
number of elements of WE units, the number of installable elements is reduced by 6 (3×2). The design is adjusted for each individual application. Standard sizes are not available.
1. Single-strand standard bank resistors with uniform number of WE elements.
2.Three-strand standard bank resistors with uniform number of WE elements.
3.Three-strand standard bank resistors with partly increased no. of WE elements.
Here, the first two resistor steps can be loaded with 1.4 times the current indicated in the tables. They are preferably used as end step for resistors in intermittent operation.
The resistors shall be installed horizontally such that the resistor elements between the ceramic strips are in upright position and the cooling air can rise freely between them. The load values indicated in the tables apply for natural air cooling. Care must be taken that the cooling air has unrestricted access from the bottom and can exit freely at the top. The place of installation must have good venting. In particular in case of indoor installation care must be taken that the ambient air does not heat to temperatures above 45°;C. The indicated loads result in temperature rises of up to 260 K. For a temperature rise of max. 200 K the load must be reduced by 25% (current value x 0.866). In particular in case of intermittent operation with high duty factor or continuous operation, additional
external venting with a fan can increase the rating and thus the admissible load.
The admissible loss for three stacked boxes is of about:
3PR3 0 4.0 kW
3PR3 2 6.0 kW
3PR3 4 8.0 kW
3PR3 6 11.0 kW
3PR3 8 13.0 kW
After taking off the side panel, the incoming cables can be inserted from below and directly
connected to the terminal connections of the resistor elements.
Cable diameter up to ……..1 x 150 mm²;
2 x 120 mm²;
Adm. continuous current….400 A
The heat dissipated by the resistors must be considered for connection. Lines or cables should be inserted into each box individually from the side such that they are not located in the area of the outflowing dissipated heat or heat radiation. For the maximum loads, DIN VDE 0298 T3/4 must be observed. Where required, lines or cables suited for elevated temperatures shall be used or the
ends of standard PVC cables/lines shall be covered with a heat-resistant insulating sleeve.
The resistors are maintenance-free. In case of strong dust formation, however, occasional cleaning with compressed air should be done to preserve the insulation against the grounded housing elements.