Model Overview

Sync-check relay is used for checking the conditions at circuit breaker closing. The purpose of the sync-check function is to find the instant when the voltages on both sides of the circuit breaker are in synchronism. The schematic for the relay operation is shown below:

The relay verifies that Bus frequency, voltage magnitude and phase angle match the Line frequency, voltage magnitude and phase angle before allowing the circuit breaker to be closed. The relay uses a three-phase Phase Lock Loop (PLL) to calculate the bus and line frequencies. Also, the model uses fundamental Phase A to Ground voltage as the operating quantity. The relay has a freezing time to avoid maloperation when the simulation starts. A breaker operation time can also be defined to take into account the breaker operation delay. The figure below shows the operation logic of the relay.

The relay works in both energized network and de-energized network, which will be discussed individually in the following sections.

Live Bus and Live Line

The function will compare the values of the bus and line voltage with the set values for V_Max which is a supervision to check whether both the bus and the line are live. 

Further, the Bus and Line voltages can be static or slipping with respect to each other:

1. When the voltages are static:

   If the magnitude of the frequency difference/slip frequency (f_Bus – f_Line) is less than or equal to 0.01 Hz—the relay presumes that voltages Bus and Line are “static” (not ‘slipping’ with respect to each other).

   In this case, if the voltage magnitude difference and angle difference are within the threshold bounds for a certain time i.e. Ton delay (internally pre-set as 1 power cycle),                                                                                                         

   then the network voltages are considered to be synchronized and a close command to the CB is delivered. (Output CloseCB will become high).                                                                                                                                             

   Note: If the voltages are static, breaker operate time will not be considered while issuing the CloseCB command.                                                                                                                                                                                                                          

2. When the voltages are slipping: 

   If the slip frequency magnitude is more than 0.01 Hz—the relay presumes that the voltages are not static and are slipping with respect to each other.

   In this case, if the condition that slip frequency is within the threshold limit fails, the CloseCB command will not be asserted.                                                                                                                                                                       

   On the other hand, if the slip frequency magnitude is less than the threshold limit, the relay logic will initiate the measuring and the evaluation of the instant at which both the voltages are synchronized, and the CB close command can be issued.

   Both voltages are thought of as revolving phasor-wise. If the voltage magnitude difference is within the threshold limit, there are two possibilities for the revolving phasors:                                                                                                               

   1. If the two phasors are approaching: 

      If the two phasors are approaching, CloseCB command will be issued at:

      

      where:  

      If the breaker delay is 0 s then the CB closing angle will be 0 deg.

      The figure below represents the CB closing in case when both the voltages are slipping and are approaching each other.                                                                                                                                                                                                                                                                                                                                                         

   2. If the two phasors are parting:

      If the two phasors are parting, CloseCB command will be issued at close in the range of

      • 
      • 

                               The figure below represents the CB closing in case when both the voltages are slipping and are parting from each other.

Dead Bus and/or Dead Line

In addition to normal conditions where both line and bus voltages are within live limits, the Voltage Check mode of operation, when selected, also allows the closing of the CB when the following conditions are met [2,3]:

A. Dead Line Operation: The line voltage is less than set value V_Min; Bus voltage and frequency within programmed limits.

B. Dead Bus Operation: The bus voltage is less than set value V_Min; Line voltage and frequency within programmed limits.

C. Dead Bus and Dead Line Operation: In this mode of operation both Line and Bus are dead i.e. both Line and Bus Voltages are less than set value V_Min.

Note: The frequencies on both sides of the circuit breaker are also measured. The frequencies must not deviate from the rated frequency more than +/-5Hz.

Mask and Parameters

General parameters

Settings

Inputs and Outputs

Inputs

Outputs

Available monitoring signals

References

1. Microgrid Controller Procurement Information, NREL-GHOST Model
2. User´s manual and Technical description of ABB SPAU 140 C Synchro-check relay
3. Line distance protection, ABB REL670 Technical manual
4. Line distance protection, ABB REL670 Application manual
5. Generator and Intertie Protection Relays SEL-700G Instruction manual