沧灿张5GN30RH东方马达

Air contamination is not as frequent a source of trouble as dirt, but can cause problems. A certain amount of air is always absorbed in the oil and causes no problem. Free bubbles in the oil that are in the high electric fields will be certain to cause breakdown. Some of the ways in which bubbles get in the oil are as follows:
1. On pumping oil into a transformer tank the oil, on striking the open oil surface, or a hard surface, captures air bubbles. This lowers the breakdown value of the oil markedly. Some of these bubbles float back to the surface and burst. Others are absorbed into the oil. Allowing the oil to stand for a day will bring it back to full test.? A useful technique is to let the oil flow almost parallel to the surface of a tank wall so that the stream spreads out without capturing bubbles. Then when the depth of oil is sufficient the hose is lowered beneath the surface of the oil.

?At the start of oil pumping there is often a certain amount of air trapped in the pumping system. This gets churned up into bubbles when pumping starts. If a spare drum of oil is available, this startup process can be done in it and the hoses then transferred to the transformer tank.

If a circulating pump is an integral? part of the tank assembly, this churning sometimes cannot be avoided. A compensating feature is that the pump will suck up bubbles along with the oil and take them out of the tank.

A leak in the negative pressure side of the pumping system will pull in air. This is broken into bubbles which end up in the transformer tank.

The core warms up during high average power transformer operation. It can then release air trapped in the laminations. These air bubbles can drift up through the transformer and enter the regions of high electric fields. Pearson transformer cores are impregnated with oil under vacuum to remove this air.

Water Contamination

As with air, oil contains a small amount of water which under normal laboratory room temperature and humidity, and over a long period of time, reaches an equilibrium that does not normally harm the oil. However, if the oil is in storage or in use in areas where the temperature and humidity are not held within bounds, water will condense and collect on the bottom of the container. Oil-breakdown value suffers under this condition.

Water is widely used for cooling. All too often mishaps occur and water is spilled in the oil or small undetected water leaks drip water into the oil. Where this is a factor it is best to specify a divided tank, so that the transformer compartment can be sealed against entry of moisture.

If water drops or puddles should exist on the bottom of a transformer tank or storage drum, and pumping should pickup some of this water, it will be broken up and emulsified with the oil. The water droplets can then stick to the surface of the transformer. High voltage operation under this condition will result in breakdown of the solid insulating material of the transformer.

If water is standing in the bottom of a container, the oil should be pumped off until a remainder which includes the water can be thrown away. Then a heater immersed in the oil for a long period (days) will gradually drive off the moisture. Other methods (all requiring special equipment) for removing moisture are:
1. Water absorbing filter.
2. Distillation type oil refiner.
3. Centrifugal type oil refiner.
4. Spraying heated oil into an evacuated chamber.

ACCIDENTAL OVER-VOLTAGES

It is possible for the pulse modulator to malfunction in such a way as to result in over-voltaging the transformer, as well as other important components such as the PFN and the switch.? Some of the possible causes are:

1. A combination of too-low load resistance and an inadequate PFN reverse charge removal circuit.
2. A switch that fires spontaneously during interpulse periods.
3. Continuous conduction of the switch.
4. Load resistance too high.
5. A combination of two or more problems listed above.

This list is only a partial one. There are undoubtedly many more possible sources of trouble.

Combination of Too Low Resistance and Inadequate Discharge Circuit for Removing Reverse Charge

This problem is covered (Vol. 5 p. 417 f.) of the M.I.T. Radiation Laboratory Series, Glasoe, etc., and is a problem that normally receives attention. One possible difficulty is that the reverse charge discharge circuit does not remove the reverse charge fast enough. It should do this even for complete load short circuit at full charging voltage. What can happen then is that the charging cycle can get well under way before the reverse charge is completely removed.

Successive pyramiding of the charging voltage can occur. A simple test that may help show whether this circuit is operating adequately is to momentarily short circuit the load. The peak charging voltage should not rise. If a full voltage test of this sort is ruled out, a low voltage test could be performed. This would show whether the discharge circuit is properly proportioned. It would not show whether the current capabilities of the discharge diode were adequate.

Switch Fires Spontaneously During Normal Interpulse Periods?

This problem is one of the most serious causes of component overvoltaging. It is also one that is difficult to avoid and difficult to cope with. With the tendency toward ever-higher peak and average pulse powers, the problem of securing a completely adequate switch becomes increasingly difficult. This is coupled with the necessity for keeping costs within limits so that completely adequate instrumentation and protective circuits are not always included as a matter of course in the design of the pulse modulator.

If a pulse switch has any tendency? toward spontaneous firing during the interpulse period and there is no positive type of protection included specifically for this malfunction, then the pulse transformer and other components will certainly be overvoltaged.

Consider the following explanation. If the switch closes while charging current is flowing, a normal or subnormal pulse voltage will appear at the load. Oftentimes the switch will then conduct continuously and the normal over current breaker protection will have to operate, but there will not necessarily (see below) be an overvoltage. If the switch should clear at? the end of the pulse as it normally? does, a new charging cycle is started.? But this new charging cycle starts with? finite current. For an initial charging current greater than zero, the next charging voltage crest will be higher.? Then if the switch is closed again at it's normal time a larger voltage pulse appears at the load.

Of course, if the switch has a tendency to close spontaneously for normal charging voltage, then it will be still more apt to close spontaneously at the higher than normal charging voltage. If this continues, enormous voltages can be generated.