The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
The operation of NSPTOV can be described using a module diagram. All the modules in the diagram are explained in the next sections.
Level detector
The calculated negative-sequence voltage is compared to the set Start value setting. If the value exceeds the set Start value, the level detector enables the timer.
Timer
Once activated, the timer activates the START output. The time characteristic is according to DT. When the operation timer has reached the value set by Operate delay time, the OPERATE output is activated if the overvoltage condition persists. If the negative-sequence voltage normalizes before the module operates, the reset timer is activated. If the reset timer reaches the value set by Reset delay time, the operate timer resets and the START output is deactivated.
The timer calculates the start duration value START_DUR, which indicates the percentage ratio of the start situation and the set operation time. The value is available in the monitored data view.
Blocking logic
There are three operation modes in the blocking function. The operation modes are controlled by the BLOCK input and the global setting in which selects the blocking mode. The BLOCK input can be controlled by a binary input, a horizontal communication input or an internal signal of the protection relay's program. The influence of the BLOCK signal activation is preselected with the global setting Blocking mode.
The Blocking mode setting has three blocking methods. In the "Freeze timers" mode, the operation timer is frozen to the prevailing value, but the OPERATE output is not deactivated when blocking is activated. In the "Block all" mode, the whole function is blocked and the timers are reset. In the "Block OPERATE output" mode, the function operates normally but the OPERATE output is not activated.