In main frequency capacitors the inherent losses are such that the internal heat which is generated can readily be dissipated by the surface area of the container. With higher frequencies, the KVAr output of the capacitor proportionately increases. This make it possible to obtain about 600 KVAr from a capacitor of dimensions which at 50 cycles would be more than what could be dissipated from the surface of the container without giving rise to harmful internal temperature. To prevent this overheating the water-cooling method is adopted. The calculations of KVAr from MFD rating of the Capacitor or vice versa can be done by a direct formula
KVAr = 2PIFCV2 x 1 0'
YESHA Medium Frequency Water Cooled Capacitors are low loss type with high dielectric strength. These capacitors utilize a Polypropylene/ Paper- Foil construction with a non-PCB Dielectric impregnant. Generally, unpainted aluminum case material is utilized. After winding the extended foil capacitor elements, one edge is soldered to a tinned copper tube, through which water is passed to dissipate the heat generated in the capacitor. For a successful joint between the foils and the tube, it is essential to have:
- Good electrical conductivity
- High thermal conductivity.
- High mechanical strength
- State whether any abnormal voltage rises are expected. If yes, what is the highest Voltage expected.
These points are of fundamental importance. Through years of experience YESHA has successfully developed special techniques to achieve these objectives. Capacitors can be made in three basic modes of construction viz.
1. The cooling pipe is connected to one electrode of the capacitor elements and it is also connected to the case is live. (This method is most widely used and is the preferred method)
The cooling pipe is connected to one electrode of the capacitor elements but it is isolated from the case. i.e., cooling pipe is one terminal but the case is dead. This is a dead can type design.
2. The cooling pope is isolated both from the capacitor elements and the container. (This method is not ideal)
The following criteria should be borne in mind while providing adequate water supply.
- Maximum permissible inlet temperature must not exceed, — 40°C.
- Maximum permissible outlet temperature must not exceed 45°C. Low temperature at inlet will increase efficiency and reduce the amount of water required. Flow of water must be such that difference between inlet and outlet temperature must not be more than 4°C.
- Maximum pressure of the water must not exceed 60 psi.
- Water must be clean and solids in water must not exceed 20 ppm the water must have a calcium carbonate substance of less than 100 ppm.
- P.H. of the water should be in the range of 7 to 8.3 and resistance should not be less than 2900 Ohms per cubic centimeter.
- Flow rate of the water should be 7 liters per minute: PLEASE NOTE flow rate faster than 7 LPM will not provide better cooling.