In power systems, voltage transformers (PTs) have different secondary voltage values, such as 100V and 100/√3V, which are related to the system's grounding method and the type of voltage being measured.
When the line voltage is 100V
- For neutral point directly grounded systems (high current grounded systems), three-phase three-winding five-limb voltage transformers or three single-phase voltage transformers connected in a Y0/y0/Δ configuration are typically used.
- When the primary line voltage is at its rated value, the secondary line voltage is 100V. For example, if the primary line voltage is 10kV, after the voltage transformer ratio is converted, the secondary line voltage is stabilized at 100V. This is used to connect measuring instruments, protection devices, etc., that require a line voltage of 100V, making it convenient for these devices to be designed and operated according to standardized voltage levels.
When the phase voltage is 100/√3V
- In a directly grounded neutral system, the secondary phase voltage is 100/√3V. Since the relationship between line voltage and phase voltage is Ul = 3Uph, and the line voltage is known to be 100V, the phase voltage is 100/√3V. In measurement and protection circuits, some components require a phase voltage signal, and this secondary voltage value can meet their operating requirements.
- For a neutral-point ungrounded system (low-current grounding system), when a single-phase ground fault occurs, the voltage of the faulty phase drops to zero, while the voltage of the non-faulty phases rises to the line voltage. At this time, the output voltage of the open delta winding of the voltage transformer is 100V, while the normal phase voltage on the secondary side is 100/√3V. This is because under normal operation, the three-phase voltages are symmetrical, and the phase voltage is 100/√3V after transformation by the voltage transformer. When a single-phase ground fault occurs, the 100V output from the open delta winding can be used to construct an insulation monitoring device to detect ground faults in the system.
- The secondary side of a voltage transformer has a winding with an output voltage of 100/3V, which is the residual voltage winding of the PT. In a three-phase PT, the secondary side is connected in an open delta configuration for relay protection in the event of a ground fault.
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in conclusion
Therefore, the statement that "the secondary voltage of a JDZW-35 Voltage Transformer is 100V or 100/√3V" is correct.
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