What are the consequences of poor secondary grounding of a current transformer?

I. High-voltage intrusion, threatening personal and equipment safety

When the insulation between the primary and secondary sides breaks down due to aging, moisture, or overvoltage, high voltage (up to several kilovolts) from the primary side can directly enter the secondary circuit, which should be low voltage. If the secondary side is poorly grounded or not grounded, this high voltage cannot be discharged through the grounding path, leading to:

Secondary equipment (such as relays, energy meters, and monitoring devices) being burned out;

Operators may suffer electric shock when touching terminal blocks or instrument housings, which can result in injury or death in severe cases.

A typical case shows that in a substation, a lightning strike caused insulation damage, and the secondary side was not reliably grounded, allowing high voltage to enter the control room, burning out multiple pieces of equipment and causing serious electric shock injuries to maintenance personnel.

II. Misoperation or Failure to Operate Protection Devices, Affecting System Stability
Poor grounding can cause ground potential fluctuations or the formation of parasitic loops, distorting the current signals collected by relay protection devices:

Differential protection, distance protection, and other devices sensitive to current accuracy may maloperate or fail to operate;
In multi-point grounding, the ground grid potential difference will generate circulating current in the secondary circuit, interfering with normal sampling and leading to incorrect protection logic judgments.

This situation can easily cause unplanned power outages in actual operation, and even expand the scope of the accident.

III. Inaccurate Metering, Affecting Economic Operation and Electricity Billing
Poor grounding can lead to abnormal distribution of capacitance to ground in the secondary circuit, introducing measurement errors:

Increased deviation in electricity meter readings, resulting in over- or under-metering of electricity consumption over long-term operation;

In industrial and commercial users, this may lead to electricity bill disputes, affecting the economic interests of both the power supplier and the user.

Furthermore, lightning overvoltages can damage the electronic components of metering devices, especially in lightning-prone areas such as Xinjiang.

IV. Increased Risk of Core Overheating and Insulation Damage

Although primarily caused by secondary open circuits, poor grounding is often accompanied by loose contacts and terminal oxidation, indirectly increasing the risk of open circuits:

Once an open circuit occurs, magnetic flux saturation will induce voltages of up to several thousand volts on the secondary side, not only endangering safety but also accelerating insulation aging, ultimately leading to transformer burnout.

Existing cases show that oil-filled current transformers, due to poor grounding of the end screen, experienced prolonged partial discharge, eventually leading to equipment burnout or even explosion.

V. Increased Risk of Electrical Fires
Poor grounding prevents fault current from being effectively conducted to the ground, and local contact points may continuously heat up due to excessive resistance:

This can lead to arcing and discharge, igniting surrounding insulation materials; If the grounding wire itself is improperly selected (e.g., insufficient cross-sectional area), it may also overheat and burn out under abnormal current, further exacerbating the fault.