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25 - Synchronism-Check Relay


Description

This block models a generic 25 synchronism-check or sync-check relay. The primary application of this relay is in situations that require verification that synchronism exists prior to closing a circuit breaker. The model also includes the Voltage Check function which can be used for closing the circuit breaker on de-energized networks. The model works for 50 Hz or 60 Hz system.

Table of Contents

The figure below shows the tripping logic of the relay.


Details on the Synchronism-Check Model Functionality

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 the 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 misoperation when the simulation starts. A breaker operation time can also be defined to take into account the breaker operation delay.

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 VMax 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 (fBus – fLine) 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 VMin; Bus voltage and frequency within programmed limits.

B. Dead Bus Operation: The bus voltage is less than set value VMin; 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 VMin.

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

System Parameters


NameDescriptionUnitVariable = {Possible Values}
Frequency System frequency. Both 50 and 60 Hz are supported within the model.HzFreq_param = {50, 60}
Rated system voltageRated Line to Line rms voltageVVRMSLL_param = { [1, 1e8] }


Settings


NameDescriptionUnitVariable = {Possible Values}
Voltage difference thresholdVoltage difference limit for synchronizing

%

(% of V L-L)

dV_threshold_param={ [0.50, 50.00] }
Phase angle difference threshold

Phase angle difference limit for synchronizing

degdPhi_threshold_param={ [1.00, 90.00] }
Frequency difference thresholdFrequency difference limit for synchronizingHzdF_threshold_param={ [0.02, 0.25] }
Breaker close timeBreaker closing timesBreaker_delay={ [0, 60] }
Freeze timeThe initial time during which CloseCB will remain zero i.e. CB remains openstunf_param={ [0.10, 60.00] }
Voltage CheckVoltage Check functionality enable/disable-Volt_Check_param={0,1}
VMin

Threshold voltage below which Bus/Line considered to be dead/non-energized

%

(% of V L-L)

VMin_param={ [10.00, 80.00] }
VMax

Threshold voltage above which Bus/Line considered to be live/energized 

%

(% of V L-L)

VMax_param={ [50.00, 100.00] }


Inputs, Outputs and Signals Available for Monitoring

Inputs

NameDescription
VBusA 3-dimension bus voltage input for three-phase voltages, in the order of Va, Vb and Vc
VLineA 3-dimension line voltage input for three-phase voltages, in the order of Va, Vb and Vc
ResetThis is the relay reset signal. The relay will be reset when this signal becomes high (1).

Outputs

NameDescription
CloseCB

The CB close command. By default, it is low (0). it will become high (1) if  synchronism conditions are met, and the conditions keep being true for the certain time delay which is internally preset as 1 power cycle.

Note: The output CloseCB=0 => CB is Open

           The output CloseCB=1 => CB is Close

Sensors

NameDescriptionUnit
dVCalculated magnitude difference of bus and line voltage (Phase A)V
dPhiCalculated difference of bus and line phase angle (Phase A)deg
dfCalculated difference of bus and line frequencyHz


Typical Values for Parameters

The parameter section shows the possible values for each parameter. This section specifies typical values for a few parameters which would be useful as a start to work with the relay model. These values would change to fit the situation of the 25 relay model so they cannot be taken as sole values for each parameter.

NameDescriptionUnitTypical Values
Voltage difference thresholdVoltage difference limit for synchronizing

%

(% of V L-L)

2.0
Phase angle difference threshold

Phase angle difference limit for synchronizing

deg5.0
Frequency difference thresholdFrequency difference limit for synchronizingHz0.05
Breaker close timeBreaker closing times0
Freeze timeThe initial time during which CloseCB will remain zero i.e. CB remains opens0.3
Voltage CheckVoltage Check functionality enable/disable-Disabled
VMin

Threshold voltage below which Bus/Line considered to be dead/non-energized

%

(% of V L-L)

10.0
VMax

Threshold voltage above which Bus/Line considered to be live/energized 

%

(% of V L-L)

50.0


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


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