Diode stack (freewheeling / neutral point and clamping) PCS 6000 system power distribution cabinet PCDI0-01 3BHE031197R0001

　　Diode stack (freewheeling / neutral point and clamping)

　　A diode stack is aligned when all of the heat sinks are visually aligned with each another from the bottom isolator to the top isolator.

　　Checking vertical alignment

　　1. Align a 1-meter long spirit level (or wooden slat) vertically with the centers of the bottom and top isolators in the stack and then place against the following components:

　　• Freewheeling diode stack: heat sinks.

　　• Neutral point and clamping diode stacks: clamping capacitor busbars.

　　2. Visually check the vertical alignment of the heat sink slots.If the slots are not aligned, you need to realign the stack.

　　Realigning the stack

　　The following procedure aligns the heat sinks horizontally from the bottom to the top of the stack.

　　1. On the misaligned heat sinks, loosen the flexible busbar on the heat sink side by removing the M12 bolts with two 19 mm wrenches.

　　IMPORTANT! Carefully note the direction of bolts assembly, which is not always the same on each heat sink. If you drop a washer, bolt or nut into the power module or cubicle, remove it immediately.

　　2. Ensure that isolator at the bottom of the stack is centered by the centering pin to the frame.

　　3. Center the heat sink immediately above the bottom isolator with the center of the bottom isolator.

　　NOTE – The bottom isolator does not have a centering pin for the heat sink.

　　4. From bottom to top, gently move each misaligned heat sink back into position by hand.

　　NOTE – If you cannot move the heat sink, use the spreader tool to spread open the heat sinks above and below the heat sink and then try again.

　　NOTICE Applying too much force when you move the heat sink can scratch the semiconductor surface.

　　5. Visually verify the alignment of the stack.

　　6. If the stack is correctly aligned, tighten the stacks according to section 10.6.7,

　　Tightening the stacks, page 166.

　　7. Insert the M12 bolts that you removed from the flexible busbars (see step 1).

　　IMPORTANT! The direction of the bolt assembly is not the same on all heat sinks. Refer to the notes that you made in step 1 for the correction orientation. If you drop a washer, bolt or nut into the power module or cubicle, remove it immediately.

　　8. Tighten the M12 bolts with two 19 mm wrenches to the heat sinks according to section 10.4.1, Correct tightening torques of bolted connections, page 135.

　　. Effects of stack misalignment on semiconductors pole pieces

　　Below are different possible signs of stack misalignment (marked X), visible on semiconductors pole pieces. If repetitive semiconductor failures happen in a stack where similar observations as marked X are made, the necessity of replacing of all semiconductors in the stack should be evaluated with ABB technical support.

　　– Observation: All imprints of the above heat sink are centered on the pole piece of the semiconductor.

　　– Heat sink and semiconductors are well aligned.

　　– Observation: Imprints from above heat

　　sink are not centered on the IGCT pole piece.

　　– Possible cause: IGCT not fully inserted before the stack was tighten.

　　– Observation: Several imprints from above heat sink are not centered on the pole piece.

　　– Possible cause: Severe and repetitive misalignment of the above heat sink or missing centering ball.

　　– Observation: Imprint of centering ball on the diode pole piece.

　　– Possible cause: Diode not snapped into centering ball before stack tightening.

　　– Observation: Missing imprints from the heat sink on the semiconductor pole piece or non-homogeneous imprints to the touch

　　– Possible cause: Semiconductor tighten inside an already misaligned stack (pressure distribution not nominal).

　　– Observation: Missing imprints from the heat sink on the semiconductor pole piece or non-homogeneous imprints to the touch

　　– Possible cause: Semiconductor tighten inside an already misaligned stack (pressure distribution not nominal).

　　Tightening the stacks

　　IMPORTANT! The order in which the stacks are tightened (see Fig. 10–30) must be adhered to:

　　1) IGCT stack

　　2) Freewheeling diode stack

　　3) Neutral point and clamp diode stack

　　Figure 10–30 Order of tightening the clamping screws

　　1. Tighten all three stacks in the order given in Fig. 10–30 by tightening the clamping screw (see Fig. 10–31).

　　NOTICE The pressure plate can be damaged and a misalignment of a stack can occur if the clamping screw is not correctly inserted in the pressure plate.

　　2. Tighten the clamping screw until the pressure loading gauge is just released and the surfaces are even, then remove the pressure loading gauge (see Fig. 10–32).

3BHS600000_E80_RevF_Service_Manual_PCS6000 Using the spreading tool(1).pdf

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