Common faults of voltage transformers in switchgear

The important role of switchgear in the electrical industry is beyond doubt, but do you know about voltage transformers? It plays an important role in the switchgear. What should I do if the voltage transformer malfunctions? The following is a common fault analysis of voltage transformers in switchgear shared by technical personnel from Yubai New Electric.

What is a voltage transformer? A voltage transformer is a device that converts high voltage into a standard secondary voltage of 100V or lower in proportion, for use in protection, metering, and instrumentation. Simply put, it is a step-down transformer. However, we analyze and solve common faults of voltage transformers to ensure the safe operation of electrical equipment and reduce accidents. Voltage transformers are an indispensable electrical appliance in power transmission and supply systems such as power plants and substations. Precision voltage transformer is an instrument used in electrical testing laboratories to expand measurement limits, measure voltage, power, and electrical energy.

Prevent the impact as much as possible and eliminate accidents in their early stages.

According to regulations, a voltage above 250 volts is called high voltage. Here, we mainly refer to 10 kV complete sets of equipment, including switchgear, metering cabinets, capacitor cabinets, etc., as well as incoming and outgoing lines and transformers. Below is a common fault analyzed by technicians from Yubai New Electric with years of experience.

Fault phenomenon: The primary fuse of the voltage transformer is blown during operation.

Analyze the reasons:

(1) Due to faults such as inter turn, inter layer or inter phase short circuits, and one phase to ground faults inside the voltage sensor of the switchgear, it is possible for the fuse to melt.

(2) Secondary circuit failure, that is, when the secondary side of the transformer fails, the secondary side fuse is too large and causes the primary side fuse to melt.

(3) 10 kV unified grounding. When a 10 kV system is grounded, the ground voltage of the other two phases increases by three times the root. For voltage transformers with Y0/Y0 connections, the normal ground voltage of the two phases will become line voltage. Due to the increase in voltage, the current may increase and the fuse may melt.

(4) Ferromagnetic resonance occurs in the power system. In recent years, due to the significant increase in distribution lines, cables, and users, the electrical parameters of the 10 kV distribution system have undergone significant changes, gradually forming resonance conditions. In addition, some voltage transformers have poor excitation characteristics, so ferroresonance overvoltage often occurs. When the power system resonates, overcurrent will be generated on the voltage transformer, which not only causes the primary side fuse to break, but also often leads to voltage transformer burnout accidents.

Handling method:

When the primary fuse of the voltage transformer is blown, the isolation switch of the voltage transformer in the switchgear should be opened, and the secondary fuse should be removed to check whether it is blown. After eliminating the fault of the voltage transformer itself or the secondary fault, the qualified fuse can be replaced again to put the voltage transformer into operation.