Reasons for the fire in the power distribution circuit caused by the direct-type ammeter of the company’s Roots pump
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Everyone, in the company’s vacuum pump systems, the ammeters for the secondary pumps – rotoary pumps – are connected directly to the main circuit. High voltage can be generated as a result of high currents or poor contact with the ammeters, leading to excessive heat generation that affects the surrounding circuits and may even cause fires. Is this description accurate? Additionally, what are the requirements for using current transformers, and can they be removed?
Is such an approach reasonable? Are there any relevant electrical standards to regulate it?
Can an inductive ammeter be used? It doesn’t need to be connected directly in the main circuit; it is said that it can also be used in the secondary circuit.
Can a current transformer be used? What current level is required? Is it necessary for the current to be above 5A in order to use one?
For low-voltage electricity with a small current, the ammeter can be directly connected in series in the power distribution circuit； High voltage and large current are not permitted by the regulations, and there are no ammeters capable of measuring such high currents. The regulations stipulate that current transformers must be installed in circuits of 50A or higher.
Why do direct-connected ammeters tend to develop an open circuit, and why does high voltage occur once an open circuit is formed?
An inductive ammeter measures the current flowing through the main circuit wires by utilizing electromagnetic conversion in a coil; the induced current is multiplied by a current transformation ratio to determine the actual current value, and the ammeter is not directly connected to the main circuit wires. Therefore, a 5A ammeter is sufficient to measure very large currents, and this is achieved through current transformers with different transformation ratios; such devices are small in size, low in cost, easy to install, and do not require much space. The direct-wiring type must be connected in series in the main circuit wires; it is a foolish and wasteful approach to manufacture or install large ammeters.
There are several ways to measure current; one is to use a clamp ammeter to measure it directly； The second type is the series current transformer. By connecting an ammeter to the secondary side of the current transformer, it becomes possible to measure current. It should be noted that an ammeter cannot directly measure the current in the main circuit; conversion through a current transformer is necessary. Additionally, the rating of the current transformer must be sufficient to handle the maximum current in the circuit, to prevent the transformer from being damaged and posing a risk to safety ； Thirdly, a known resistor is connected in series with the circuit; by measuring the voltage across the resistor and then dividing this voltage by the resistance value, the current magnitude can also be determined, but this method is difficult to implement.