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# Description

This block models a generic 25 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.

# 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 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.

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.

## General parameters

NameUnitDescription

Frequency

Hz

System frequency. Both 50 and 60 Hz are supported within the model.

Rated system voltage

V

Line to Line rms voltage

Sample Time

s

Model time step

## Settings

NameUnitDescription

Enable

-

Enable and disable relay operation

Voltage difference threshold

%

(% of V L-L)

Voltage difference limit for synchronizing

Phase angle difference threshold

deg.

Phase angle difference limit for synchronizing

Frequency difference threshold

Hz

Frequency difference limit for synchronizing

Breaker close time

s

Breaker closing time

Freeze time

s

The initial time during which CloseCB will remain zero i.e. CB will be open

Voltage Check

-

Voltage Check functionality enable/disable

VMin

%

(% of V L-L)

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

VMax

%

(% of V L-L)

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

# Inputs and Outputs

## Inputs

NameDescription

VBus

A 3-dimension bus voltage input for three-phase voltages, in the order of Va, Vb and Vc

VLine

A 3-dimension line voltage input for three-phase voltages, in the order of Va, Vb and Vc

Reset

This is the relay reset signal. The relay will be reset when this signal becomes 1.

## Outputs

NameDescription
CloseCB

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

## Available monitoring signals

NameUnitDescription

dV

V

Calculated magnitude difference of bus and line voltage (Phase A)

dPhi

Deg

Calculated difference of bus and line phase angle (Phase A)

df

Hz

Calculated difference of bus and line frequency

# 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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