Free Expert Guides on Power Systems, Circuit Design & Electrical Troubleshooting

Single-Phase ReclosingAdvantage:When a single-phase-to-ground fault occurs on a line and three-phase auto-reclosing is applied, it results in higher switching overvoltages compared to single-phase reclosing. This is because three-phase tripping interrupts the current at zero-crossing, leaving residual charge voltages on the unfaulted phases—approximately equal to the peak phase voltage. Since the de-energized interval during reclosing is relatively short, the voltage on these unfaulted phases do

1.Causes of Damage to Agricultural H59/H61 Oil-Immersed Distribution Transformers1.1 Insulation DamageRural power supply commonly uses a 380/220V mixed system. Due to the high proportion of single-phase loads, H59/H61 oil-immersed distribution transformers often operate under significant three-phase load imbalance. In many cases, the degree of three-phase load imbalance far exceeds the limits permitted by operational regulations, causing premature aging, deterioration, and eventual failure of th

What lightning protection measures are used for H61 distribution transformers?A surge arrester should be installed on the high-voltage side of the H61 distribution transformer. According to SDJ7–79 "Technical Code for Design of Overvoltage Protection of Electric Power Equipment," the high-voltage side of an H61 distribution transformer should generally be protected by a surge arrester. The grounding conductor of the arrester, the neutral point on the low-voltage side of the transformer, and the

How to Implement Transformer Neutral Grounding Gap Protection Measures?In a certain power grid, when a single-phase ground fault occurs on a power supply line, both the transformer neutral grounding gap protection and the power supply line protection operate simultaneously, causing an outage of an otherwise healthy transformer. The main reason is that during a system single-phase ground fault, the zero-sequence overvoltage causes the transformer neutral grounding gap to break down. The resulting

1. System Configuration and Operating ConditionsThe main transformers at Zhengzhou Rail Transit’s Convention & Exhibition Center Main Substation and Municipal Stadium Main Substation adopt a star/delta winding connection with a non-grounded neutral point operation mode. On the 35 kV bus side, a Zigzag grounding transformer is used, connected to ground through a low-value resistor, and also supplies station service loads. When a single-phase ground short-circuit fault occurs on a line, a path

In power systems, transformers, as core equipment, are critical to the safe operation of the entire grid. However, due to various reasons, transformers are often exposed to multiple threats. In such cases, the importance of grounding resistor cabinets becomes evident, as they provide indispensable protection for transformers.Firstly, grounding resistor cabinets can effectively protect transformers from lightning strikes. The instantaneous high voltage caused by lightning can severely damage tran

Problems with Zero-Sequence Protection of 110 kV TransformersIn an effectively grounded system, the neutral-to-ground displacement voltage of a transformer is limited to a certain level, and the neutral-point gap protection does not operate. The purpose of installing gap protection is to prevent damage to transformer insulation caused by elevated zero-sequence voltage in non-effectively grounded systems. The discharge gap only operates when a single-phase ground fault occurs, all directly ground

Recently, the NSR-3611 low-voltage protection and control device and the NSD500M high-voltage measurement and control device—both developed by a Chinese protection and control equipment manufacturer—successfully passed the IEC 61850 Ed2.1 Server Level-A certification test conducted by DNV (Det Norske Veritas). The devices have been awarded the international Level-A certification by the Utilities Communication Architecture International Users Group (UCAIug). This milestone marks the manufacturer

1. What Is a Three-Phase Power Surge Protective Device (SPD)?A three-phase power surge protective device (SPD), also known as a three-phase lightning arrester, is specifically designed for three-phase AC power systems. Its primary function is to limit transient overvoltages caused by lightning strikes or switching operations in the power grid, thereby protecting downstream electrical equipment from damage. The SPD operates based on energy absorption and dissipation: when an overvoltage event occ

1.Introduction1.1 Basic Function and Background of GCBThe Generator Circuit Breaker (GCB), as the critical node connecting the generator to the step-up transformer, is responsible for interrupting current under both normal and fault conditions. Unlike conventional substation circuit breakers, the GCB directly withstands the massive short-circuit current from the generator, with rated short-circuit breaking currents reaching hundreds of kiloamperes. In large generating units, the reliable operati