What are the effects of excessively high or low DC bus voltage?

Excessive DC bus voltage can easily damage electrical components that operate under constant energization, such as instruments, relays, and indicator lights, due to overheating. Conversely, excessively low voltage can cause protective devices to malfunction or fail to operate. Generally, the permissible voltage variation range is 10%. DC bus voltage is a crucial parameter for DC power supply in a power system; both excessively high and low voltage can adversely affect the power system and electrical equipment. The following provides a detailed explanation:

Impact on Generators

• Magnetic Circuit Saturation: Increased current in the generator stator windings strengthens the air gap magnetic field. When this exceeds a certain level, it leads to magnetic circuit saturation, causing a sharp increase in excitation current and resulting in generator overexcitation.
• Increased Mechanical Stress and Losses: Excessive voltage increases copper and iron losses in the generator's stator and rotor windings, while also increasing mechanical stress and shortening the generator's lifespan.

Impact on Transmission Lines

• Increased Line Losses: Increased voltage reduces the current in transmission lines. According to the power loss formula P=I²RP=I²R (where PP is power loss, I² is current, and RR is line resistance), although the reduced current lowers the active power loss of the line itself, the loss characteristics of transformers and other equipment may increase the overall operating cost of the power system.
• Insulation Problems: Excessive voltage may break down the insulation of lines and transformers, causing insulation faults such as transformer winding insulation damage and line insulation breakdown.

Impact on Electrical Equipment

• Equipment Damage: For some voltage-sensitive electrical equipment, such as motors and electronic instruments, excessively high DC bus voltage may exceed their rated voltage, leading to damage to the winding insulation and even burnout of the equipment.
•  Malfunction of Protection Devices: Excessively high voltage may trigger malfunctions in protection devices, causing unnecessary power outages and affecting the normal operation of the power system.

Impact on Generators

• Reduced Output Power: Generator output power is related to voltage and current. When the DC bus voltage is too low, the generator's output voltage will also decrease accordingly, affecting the overall power supply capacity of the power system.
• Insufficient Excitation: The generator's excitation current is proportional to the voltage. Low voltage leads to insufficient excitation current, reducing the generator's generating capacity.

Impact on Transmission Lines

• Reduced Transmission Capacity: According to the power formula P=UIcos⁡φ (where P is active power, U is voltage, I is current, and cos⁡φ is the power factor), under a constant transmission power, a decrease in voltage will increase the current in the transmission line.
• Increased Line Losses: Increased current, according to P=I²RP=I²R, will significantly increase the active power losses in the line, reducing transmission efficiency and increasing transmission costs.

Impact on Electrical Equipment

• Malfunction: For inductive loads such as motors, low voltage reduces motor torque, preventing normal starting or operation and impacting production and daily life.
• Shortened Equipment Lifespan: Prolonged operation under low voltage accelerates the aging of electrical equipment, shortening its lifespan.

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