The function can be enabled and disabled with the Operation setting. The corresponding parameter values are "On" and "Off".
SECRSYN has two parallel functionalities, the synchro check and energizing check functionality. The operation of SECRSYN can be described using a module diagram. All the modules in the diagram are explained in the next sections.
If Energizing check is passed, no further conditions need to be fulfilled to permit closing. Otherwise, Synchro check function can operate either with the U_AB or U_A voltages. The selection of used voltages is defined with the VT connection setting of the line voltage general parameters.
Energizing check
| Live dead mode | Description |
|---|---|
| Both Dead | Both line and bus de-energized |
| Live L, Dead B | Bus de-energized and line energized |
| Dead L, Live B | Line de-energized and bus energized |
| Dead Bus, L Any | Both line and bus de-energized or bus de-energized and line energized |
| Dead L, Bus Any | Both line and bus de-energized or line de-energized and bus energized |
| One Live, Dead | Bus de-energized and line energized or line de-energized and bus energized |
| Not Both Live | Both line and bus de-energized or bus de-energized and line energized or line de-energized and bus energized |
When the energizing direction corresponds to the settings, the situation has to be constant for a time set with the Energizing time setting before the circuit breaker closing is permitted. The purpose of this time delay is to ensure that the dead side remains de-energized and also that the situation is not caused by a temporary interference. If the conditions do not persist for a specified operation time, the timer is reset and the procedure is restarted when the conditions allow. The circuit breaker closing is not permitted if the measured voltage on the live side is greater than the set value of Max energizing V.
The measured energized state is available as a monitored data value ENERG_STATE and as four function outputs LLDB (live line / dead bus), LLLB (live line / live bus), DLLB (dead line / live bus) and DLDB (dead line / dead bus), of which only one can be active at a time. It is also possible that the measured energized state indicates “Unknown” if at least one of the measured voltages is between the limits set with the dead and live setting parameters.
Synchro check
- The measured line and bus voltages are higher than the set values of Live bus value and Live line value (ENERG_STATE equals to "Both Live").
- The measured bus and line frequency are both within the range of 95 to 105 percent of the value of f n.
- The measured voltages for the line and bus are less than the set value of Max energizing V.
- In the synchronous mode, the closing is attempted so that the phase difference at closing is close to zero.
- The synchronous mode is only possible when the frequency slip is below 0.1 percent of the value of f n.
- The voltage difference must not exceed the 1 percent of the value of U n.
- The measured difference of the voltages is less than the set value of Difference voltage.
- The measured difference of the phase angles is less than the set value of Difference angle.
- The measured difference in frequency is less than the set value of Frequency difference.
- The estimated breaker closing angle is decided to be less than the set value of Difference angle.
When the frequency, phase angle and voltage conditions are fulfilled, the duration of the synchronism conditions is checked so as to ensure that they are still met when the condition is determined on the basis of the measured frequency and phase difference. Depending on the circuit breaker and the closing system, the delay from the moment the closing signal is given until the circuit breaker finally closes is about 50...250 ms. The selected Closing time of CB informs the function how long the conditions have to persist. The Synchro check function compensates for the measured slip frequency and the circuit breaker closing delay. The phase angle advance is calculated continuously with the formula.
| ∠ U Bus | Measured bus voltage phase angle |
| ∠U Line | Measured line voltage phase angle |
| f Bus | Measured bus frequency |
| f line | Measured line frequency |
| T CB | Total circuit breaker closing delay, including the delay of the protection relay output contacts defined with the Closing time of CB setting parameter value |
| TPL | Output type dependent delay according to Table 2 |
| Output type | Recommended value for TPL |
|---|---|
| Mechanical relay output (PO) | 6 ms |
The closing angle is the estimated angle difference after the breaker closing delay.
The Minimum Syn time setting time can be set, if required, to demand the minimum time within which conditions must be simultaneously fulfilled before the SYNC_OK output is activated.
The measured voltage, frequency and phase angle difference values between the two sides of the circuit breaker are available as monitored data values U_DIFF_MEAS, FR_DIFF_MEAS and PH_DIFF_MEAS. Also, the indications of the conditions that are not fulfilled and thus preventing the breaker closing permission are available as monitored data values U_DIFF_SYNC, PH_DIF_SYNC and FR_DIFF_SYNC. These monitored data values are updated only when the Synchro check is enabled with the Synchro check mode setting and the measured ENERG_STATE is "Both Live".
Continuous mode
The continuous mode is activated by setting the parameter Control mode to "Continuous". In the continuous control mode, Synchro check is continuously checking the synchronism. When synchronism is detected (according to the settings), the SYNC_OK output is set to TRUE (logic '1') and it stays TRUE as long as the conditions are fulfilled. The command input is ignored in the continuous control mode.
Command mode
If Control mode is set to "Command", the purpose of the Synchro check functionality in the command mode is to find the instant when the voltages on both sides of the circuit breaker are in synchronism. The conditions for synchronism are met when the voltages on both sides of the circuit breaker have the same frequency and are in phase with a magnitude that makes the concerned busbars or lines such that they can be regarded as live.
In the command control mode operation, there are alarms for a failed closing attempt ( CL_FAIL_AL) and for a command signal that remains active too long ( CMD_FAIL_AL).
Closing is permitted during Maximum Syn time, starting from the moment the external command signal CL_COMMAND is activated. The CL_COMMAND input must be kept active for the whole time that the closing conditions are waited to be fulfilled. Otherwise, the procedure is cancelled. If the closing-command conditions are fulfilled during Maximum Syn time, a SYNC_OK pulse is delivered to the circuit breaker function. If the closing conditions are not fulfilled during the checking time, the alarm CL_FAIL_AL is activated as an indication of a failed closing attempt. The SYNC_OK pulse is not delivered if the closing conditions become valid after Maximum Syn time has elapsed. The closing pulse is delivered only once for each activated external command signal, and a new closing-command sequence cannot be started until the external command signal is reset and reactivated. The SYNC_INPRO output is active when the closing-command sequence is in progress and it is reset when the CL_COMMAND input is reset or Maximum Syn time has elapsed.
Bypass mode
SECRSYN can be set to the bypass mode by setting the parameters Synchrocheck mode and Live dead mode to "Off" or alternatively by activating the BYPASS input.
In the bypass mode, the closing conditions are always considered to be fulfilled by SECRSYN. Otherwise, the operation is similar to the normal mode.
Voltage angle difference adjustment
The vector group of the power transformer is defined with clock numbers, where the value of the hour pointer defines the low-voltage-side phasor and the high-voltage-side phasor is always fixed to the clock number 12, which is same as zero. The angle between clock numbers is 30 degrees. When comparing phase angles, the U_BUS input is always the reference. This means that when the Yd11 power transformer is used, the low-voltage-side voltage phasor leads by 30 degrees or lags by 330 degrees the high-voltage-side phasor. The rotation of the phasors is counterclockwise.
The generic rule is that a low-voltage-side phasor lags the high-voltage-side phasor by clock number * 30º. This is called angle difference adjustment and can be set for SECRSYN with the Phase shift setting.
