The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
The operation of PDNSPTOC can be described by using a module diagram. All the modules in the diagram are explained in the next sections.
I2/I1
The I 2/I 1 module calculates the ratio of the negative and positive sequence current. It reports the calculated value to the level detector.
Level detector
The level detector compares the calculated ratio of the negative- and positive- sequence currents to the set Start value . If the calculated value exceeds the set Start value and the min current check module has exceeded the value of Min phase current , the level detector reports the exceeding of the value to the timer.
Min current check
The min current check module checks whether the measured phase currents are above the set Min phase current. At least one of the phase currents needs to be above the set limit to enable the level detector module.
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 fault disappears 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 timer" 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.