1 Configurations used at BMS[edit | edit source]
At our plants there are different types of HV-Pinning:
| plant type | power supply | Arc break | heating | electrode |
|---|---|---|---|---|
| PET-BO | PNC 20.000-20 | standard: no | LNG50 in generator cabinet | wire / jack |
| PET-BO | PNC 20.000-20 | optional: yes | LNG50 in ARC-Break | wire / jack |
| PET-CAST | PNC 30.000-60 | standard: yrs | LNG50 in ARC-Break | wire / jack |
| PA-BO | PNC 15.000-300 | standard: yes | HV-transformator and thyristor regulator, heating cartridge | pinbar |
2 Grounding scheme[edit | edit source]
The experience has shown that the commissioning teams check the installation in all conscience, but the depiction in the electrical drawings lets room for interpretation. So here is an explanation on the basis of a pattern from Fa. Heinzinger.
The energy which flows over the carbon brushes on both sides of the plant back to the generator should not flow only over the machine grounding, it should flow mainly over the shield of the HV-cable. The reason is that otherwise interference voltages will get back to the power supply of the generator and the high frequency (HF) parts of the disturbing signal don’t get on the shortest way over the shield of the HV cable back to the PNC power supply. Hence they can affect potential shifts, which cause damages on the electronic of the power supply.
Another error source is that multiple grounding on different points occur ground loops, which are additional resistors for the HF-parts and this also causes potential shifts.
3 Energy flow at flashover or short circuit on the electrode against ground (/roll)[edit | edit source]
The target of our grounding is to make the return of the energy to the power supply at a flashover very low-resistance for the high frequent parts of the appearing disturbing voltage. So that these parasitic currents don’t flow over the machine grounding (and the complete plant and electronic) back to the power supply, but instead over the shield of the HV-cable.
The following picture documentation explains how we can achieve that goal.
4 Design of the grounding connections[edit | edit source]
4.1 Connection in the generator cabinet[edit | edit source]
The grounding cable which comes from external to the generator cabinet must be directly connected to the designated grounding bolt in the lower area of the generator cabinet. The other internal grounding cables get star-shaped distributed from this point.
It must not happen, that external-coming grounding cables are connected on the cabinet rack and so get to the star point with a lower cross section.
With the copper stranded wire from Heinzinger the grounding is connected directly to the PNC power supply to reach low-resistance for HF parasitic currents.
A connection here is only allowed when it is factory-set and all grounding cables in the generator cabinet are connected from the central star point star-shaped. Moreover the jack of the PNC power supply is connected with a respective CU mesh stranded wire. At the newest generators this is the case.
Additional grounding cables on the backside jack of the PNC power supply except the factory-set CU stranded wire are not allowed and must be removed!
4.2 Connection of the carbon brushes to the roller shaft[edit | edit source]
Additional to the shown connection of the carbon brushes to the engine frame on both sides on the shaft journals of the chill roll is a CU mesh stranded wire necessary: from the carbon brushes to the grounding point of the HV-cable shield at the relative feed point of high voltage at the wire inductor.
The resistance between machine grounding of the roller and machine grounding of the inductor intake unit was at the line 6016SPV 3.5 ohms. This value is very high and shows that the quality of the grounding could be better. With the suggested CU mesh stranded wire this problem will be solved.
4.3 HV cable installation and route[edit | edit source]
WRONG:
Please do not route the cable as shown on the picture. There are about 10kV and extreme slew rates at flashover, so the data cables (Profibus, Encoder,..) will be disturbed (EMV).
The HV cable should be routed in grounded metal protective tubing and shorten to the minimal length.
5 HV Cable connections[edit | edit source]
Refer to Lemo HV Connector
6 HV Power Supply commissioning and function test[edit | edit source]
Refer to Pinning HV Powersupply
