Shipping electrification is a promising way to reduce the environmental impact of the maritime industry and comply with the regulations imposed by the International Maritime Organization (IMO). However, the transition from traditional AC distribution systems to DC grids requires the use of power electronics components that can connect different energy sources and loads efficiently and safely. One of these components is the blocking diode, which plays a key role in preventing reverse currents and protecting the system from dangerous situations like arc flashing. In this article, we will explain what blocking diodes are, how they work, and why they are important for shipping electrification.
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What Is A Blocking Diode?
A blocking diode is a semiconductor device that allows the current to flow in one direction only. It has two terminals: an anode and a cathode. When the anode is connected to a positive voltage and the cathode to a negative voltage, the diode is forward-biased, and the current flows through it. When the polarity is reversed, the diode is reverse-biased, and the current is blocked. This property makes blocking diodes useful for preventing reverse currents in power supply systems.
What Is Reverse Current, And Why Is It Harmful?
Reverse current occurs when the output of a system has a higher voltage than the input, causing the current to flow back through the system. This can happen when power is disconnected from the system, and the input voltage suddenly drops. During this time, a higher voltage may be left at the output, which temporarily generates a reverse current.
Reverse current can damage internal circuits and power supplies such as batteries. Depending on the path from output to input, reverse current can damage cables and connectors. If the heat, developed by power dissipation over the device, exceeds the thermal limit of the device, it can cause the device to fail or even explode. Reverse current can also create dangerous situations like arc flashing, which is a phenomenon where an electric arc is formed between two conductors due to a high voltage difference. Arc flashing can cause severe burns, fires, and electrical shocks.
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How Do You Block Reverse Currents with Blocking Diodes?
Blocking diodes can be used to block reverse currents by placing them in series with the output of the system. For example, in a battery charging system, a blocking diode can be placed between the charger and the battery. This way, when the charger is on, the diode is forward-biased, and the current flows from the charger to the battery. When the charger is off, the diode is reverse-biased, and the current is blocked from the battery to the charger. This prevents the battery from discharging due to reverse current and protects the charger from damage.
Blocking diodes can also be used to prevent the feeding of short circuit current from the ship installation back to the shore supply. For example, there is a charging station on shore that provides power to a pantograph, which in turn provides an electrical connection to the vessel. The vessel side of the pantograph distributes the power to two switchboards. In these switchboards, blocking diodes can be used to prevent the current from flowing back to the shore supply in case of a short circuit on the vessel.
Conclusion
Blocking diodes are power supply key elements for shipping electrification. They allow the current to flow in one direction only and block the reverse current. This protects the system from damage and dangerous situations like arc flashing. Blocking diodes are essential for connecting different energy sources and loads in a DC grid and ensuring system selectivity and safety. Swartz Engineering is a leading provider of blocking diodes and other power electronics components for shipping electrification. Contact us today to find out more about our products and services.
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