The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
The operation of FRPFRQ can be described using a module diagram. All the modules in the diagram are explained in the next sections.
Freq>/< detection
The frequency detection module includes an overfrequency or underfrequency detection based on the Operation mode setting.
In the “Freq>” mode, the measured frequency is compared to the set Start value Freq>. If the measured value exceeds the set value of the Start value Freq> setting, the module reports the exceeding of the value to the operate logic module.
In the “Freq<” mode, the measured frequency is compared to the set Start value Freq<. If the measured value is lower than the set value of the Start value Freq< setting, the module reports the value to the operate logic module.
df/dt detection
The frequency gradient detection module includes a detection for a positive or negative rate-of-change (gradient) of frequency based on the set Start value df/dt value. The negative rate-of-change protection is selected when the set value is negative. The positive rate-of-change protection is selected when the set value is positive. When the frequency gradient protection is selected and the gradient exceeds the set Start value df/dt value, the module reports the exceeding of the value to the operate logic module.
Operate logic
This module is used for combining different protection criteria based on the frequency and the frequency gradient measurement to achieve a more sophisticated behavior of the function. The criteria are selected with the Operation mode setting.
| Operation mode | Description |
|---|---|
| Freq< | The function operates independently as the underfrequency ("Freq<") protection function. When the measured frequency is below the set value of the Start value Freq< setting, the module activates the START and STR_UFRQ outputs. The time characteristic is according to DT. When the operation timer has reached the value set by the Operate Tm Freq setting, the OPERATE and OPR_UFRQ outputs are activated. If the frequency restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm Freq setting, the operate timer resets and the START and STR_UFRQ outputs are deactivated. |
| Freq> | The function operates independently as the overfrequency ("Freq>") protection function. When the measured frequency exceeds the set value of the Start value Freq> setting, the module activates the START and STR_OFRQ outputs. The time characteristic is according to DT. When the operation timer has reached the value set by the Operate Tm Freq setting, the OPERATE and OPR_OFRQ outputs are activated. If the frequency restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm Freq setting, the operate timer resets and the START and STR_OFRQ outputs are deactivated. |
| df/dt | The function operates independently as the frequency gradient ("df/dt"), rate-of-change, protection function. When the frequency gradient exceeds the set value of the Start value df/dt setting, the module activates the START and STR_FRG outputs. The time characteristic is according to DT. When the operation timer has reached the value set by the Operate Tm df/dt setting, the OPERATE and OPR_FRG outputs are activated. If the frequency gradient restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm df/dt setting, the operate timer resets and the START and STR_FRG outputs are deactivated. |
| Freq< + df/dt | A consecutive operation is enabled between the protection methods. When the measured frequency is below the set value of the Start value Freq< setting, the frequency gradient protection is enabled. After the frequency has dropped below the set value, the frequency gradient is compared to the set value of the Start value df/dt setting. When the frequency gradient exceeds the set value, the module activates the START and STR_FRG outputs. The time characteristic is according to DT. When the operation timer has reached the value set by the Operate Tm df/dt setting, the OPERATE and OPR_FRG outputs are activated. If the frequency gradient restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm df/dt setting, the operate timer resets and the START and STR_FRG outputs are deactivated. The OPR_UFRQ output is not active when this operation mode is used. |
| Freq> + df/dt | A consecutive operation is enabled between the protection methods. When the measured frequency exceeds the set value of the Start value Freq> setting, the frequency gradient protection is enabled. After the frequency exceeds the set value, the frequency gradient is compared to the set value of the Start value df/dt setting. When the frequency gradient exceeds the set value, the module activates the START and STR_FRG outputs. The time characteristic is according to DT. When the operation timer has reached the value set by the Operate Tm df/dt setting, the OPERATE and OPR_FRG outputs are activated. If the frequency gradient restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm df/dt setting, the operate timer resets and the START and STR_FRG outputs are deactivated. The OPR_OFRQ output is not active when this operation mode is used. |
| Freq< OR df/dt | A parallel operation between the protection methods is enabled. The START output is activated when either of the measured values of the protection module exceeds its set value. Detailed information about the active module is available at the STR_UFRQ and STR_FRG outputs. The shortest operate delay time from the set Operate Tm Freq or Operate Tm df/dt is dominant regarding the OPERATE output. The time characteristic is according to DT. The characteristic that activates the OPERATE output can be seen from the OPR_UFRQ or OPR_FRG output. If the frequency gradient restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm df/dt setting, the operate timer resets and the STR_FRG output is deactivated. If the frequency restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm Freq setting, the operate timer resets and the STR_UFRQ output is deactivated. |
| Freq> OR df/dt | A parallel operation between the protection methods is enabled. The START output is activated when either of the measured values of the protection module exceeds its set value. A detailed information from the active module is available at the STR_OFRQ and STR_FRG outputs. The shortest operate delay time from the set Operate Tm Freq or Operate Tm df/dt is dominant regarding the OPERATE output. The time characteristic is according to DT. The characteristic that activates the OPERATE output can be seen from the OPR_OFRQ or OPR_FRG output. If the frequency gradient restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm df/dt setting, the operate timer resets and the STR_FRG output is deactivated. If the frequency restores before the module operates, the reset timer is activated. If the timer reaches the value set by the Reset delay Tm Freq setting, the operate timer resets and the STR_UFRQ output is deactivated. |
| Operation mode in use | Available start duration value |
|---|---|
| Freq< | ST_DUR_UFRQ |
| Freq> | ST_DUR_OFRQ |
| df/dt | ST_DUR_FRG |
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.