In power systems, current transformers (CTs) are widely used for primary measurement, control, and protection. When the secondary winding of a CT is open-circuited or when abnormal currents such as lightning current, resonant overcurrent, capacitor charging current, or inductor starting current flow through the primary side, overvoltages of several thousand volts or even tens of thousands of volts will be generated on the secondary side.
The hazards of overvoltage include damage to the insulation of the secondary system, overexcitation and burnout of the transformer, and endangering the lives of operating personnel. Specifically, the consequences of an open circuit in the secondary winding of a current transformer include: steep-wave high-amplitude overvoltages severely endangering equipment insulation and the lives of personnel; excessive core losses and severe overheating leading to overexcitation and burnout of the transformer; and residual magnetism in the core increasing measurement errors and even causing the secondary control and protection system to malfunction.
The protector is connected in parallel across the secondary winding of the CT. Under normal operation, it exhibits high resistance and minimal leakage current. Its main functions include overvoltage detection, instantaneous voltage limiting, delayed short-circuit protection of the secondary winding, audible and visual alarms, and passive contact signal output. Some models also feature differential lockout protection and automatic reset functions. Its working principle typically utilizes nonlinear components such as varistors, silicon controlled rectifiers (SCRs), or gas discharge tubes, which rapidly conduct upon detecting an overvoltage, limiting the voltage to a safe range or directly short-circuiting the secondary side.
This protector is suitable for abnormal overvoltage protection on the secondary side of various current transformers (CTs). Its applications include differential windings, overcurrent windings, measuring windings, busbar protection windings, and spare windings on the CT secondary side.