The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
The operation of PSPTUV can be described using a module diagram. All the modules in the diagram are explained in the next sections.
Level detector
The calculated positive-sequence voltage is compared to the set Start value setting. If the value drops below the set Start value, the level detector enables the timer. The Relative hysteresis setting can be used for preventing unnecessary oscillations if the input signal slightly varies from the Start value setting. After leaving the hysteresis area, the start condition has to be fulfilled again and it is not sufficient for the signal to only return to the hysteresis area.
The level detector contains a low-level blocking functionality for cases where the positive-sequence voltage is below the desired level. This feature is useful when unnecessary starts and operates are wanted to avoid during, for example, an autoreclose sequence. The low-level blocking is activated by default (Enable block value is set to “Enabled”) and the blocking level can be set with the Voltage block value setting.
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 undervoltage condition persists. If the positive-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.