-ETHOD OF OPERATION
6%
6
# ' #
-EASUREMENT SEQUENCE
4HE SEQUENCE FOR PROCESSING THE MEASURED QUANTI
TIES IS SHOWN SIMPLIFIED IN &IGURE
4HE INDICES FOR THE VOLTAGES ARE USED AS FOLLOWS THE
INDEX WHICH IS NOT A SUBSCRIPT IDENTIFIES THE FIXED
NON REGULATED VOLTAGE INDEX THE REGULATED VOLT
AGE OF THE GENERATOR &REQUENCY AND VOLTAGE BAL
ANCING MUST THEREFORE ALWAYS HAVE AN EFFECT ON VOLT
AGE 5 4HE ASSIGNMENT OF THESE INDICES IS IRRELEVANT
WHEN PARALLELING NETWORKS 4HE INDICES AS SUB
SCRIPTS IDENTIFY THE PHASES EG 5
,
IS THE PHASE
TO PHASE VOLTAGE BETWEEN PHASES , AND , OF THE
REGULATED SIDE 5
4HE MEASURED VOLTAGES 5
,
5
,
5
,
AND THE
MEASURED VOLTAGES 5
,
5
,
5
,
ARE CONTINU
OUSLY ENTERED AS NUMERICAL VALUES INTO A CIRCULATING
BUFFER 4HUS EACH OF THE SIX MEASURED QUANTITIES HAS
A CORRESPONDING SEQUENCE OF NUMERICAL SAMPLE VAL
UES IN THE CIRCULATING BUFFERS 4HESE SAMPLE VALUES
REPRESENT THE VARIATION OF THE ANALOG VARIABLE WITH RE
SPECT TO TIME
5
,
IS THE VOLTAGE 5
,
DISPLACED BY
^
AND
CONNECTED VIA A SEPARATE MEASURED VALUE INPUT VIA
SEPARATE SAMPLE AND HOLD ELEMENTS AND SEPARATE
ANALOG TO DIGITAL CONVERTER RANGES 4HE SAME AP
PLIES TO 5
,
AND 5
,
4HE VOLTAGES 5
,
AND 5
,
ARE USED IN THE DEVICE
FOR THE PHASE SEQUENCE CHECK 3INCE THEY ARE OF NO
SIGNIFICANCE WHEN DETERMINING THE PARALLELING CONDI
TIONS THEY CAN BE OMITTED
4HE VOLTAGES DISPLACED BY
^
WITH RESPECT TO ONE
ANOTHER MUST ALWAYS ADD UP TO ZERO 4HIS ENABLES
CONSTANT MONITORING OF THE MEASURING CIRCUITS IE
THE SEQUENCE FROM THE VOLTAGE TRANSFORMER CIRCUITS
UP TO THE MEASURED VALUE MEMORIES
4HE CONTINUITY OF THE MEASURED QUANTITIES IS ALSO
CHECKED 4HE DIFFERENCE BETWEEN TWO SUCCESSIVE
SAMPLE VALUES OF EACH MEASURED VOLTAGE IS CHECKED
TO SEE WHETHER IT FALLS BELOW A PERMISSIBLE VALUE
SINCE VOLTAGE JUMPS WOULD INFLUENCE DETERMINATION
OF FREQUENCIES AND PHASE ANGLES
4O ENSURE THAT HARMONICS DO NOT INFLUENCE THE RE
SULTS WHICH COULD LEAD TO AN OPERATION FAILURE THE
VOLTAGES DECISIVE FOR PARALLELING ARE FILTERED NUMERI
CALLY AND EACH STORED IN FURTHER FILTER BUFFERS
4HE MEASURED VOLTAGES ARE NOW EVALUATED BY
MEANS OF TWO DIFFERENT METHODS %ACH METHOD OPER
ATES WITH ITS OWN SETS OF MEASURED VALUES
4HE MAGNITUDES OF THE VOLTAGES ARE FIRST EXAMINED
AND COMPARED WITH THE PARAMETERIZED MINIMUM
AND MAXIMUM VALUES
4HE FIRST METHOD OPERATES ACCORDING TO THE ENVELOPE
CURVE PRINCIPLE 4HE INSTANTANEOUS VALUES OF THE EN
VELOPE CURVE ARE DETERMINED FROM THE BEAT FUNCTION
OF THE VOLTAGE DIFFERENCE 4HE TIME AT WHICH THE ENVE
LOPE CURVE REACHES A VALUE OF ZERO IS CALCULATED !
LOGICAL CLOSE COMMAND IS GENERATED TAKING INTO AC
COUNT THE PARAMETERIZED BREAKER OPERATING TIME
4HE SECOND METHOD OPERATES ACCORDING TO THE ZERO
CROSSING PRINCIPLE 4HE DIFFERENCE IN ANGLE IS DETER
MINED FROM THE ZERO CROSSINGS OF THE MEASURED VOLT
AGES 4HE SYNCHRONIZING INSTANT IS CALCULATED FROM
THE CHANGE IN THE ZERO CROSSINGS AND A LOGICAL CLOSE
COMMAND GENERATED TAKING INTO ACCOUNT THE PARA
METERIZED BREAKER OPERATING TIME
4HE TWO METHODS OF MEASUREMENT ARE BASED ON AU
TONOMOUS FIRMWARE BLOCKS AND MAKE DECISIONS IN
DEPENDENT OF ONE ANOTHER VIA THE RESPECTIVE CLOSE
COMMAND 3INCE THE ZERO CROSSING METHOD ENABLES
A HIGHER ACCURACY WITH RESPECT TO THE SWITCHING
ANGLE AN ANGLE WINDOW IS OPENED A FEW DEGREES
EARLIER FOR THE ENVELOPE CURVE METHOD SO THAT THE AC
CURACY OF THE CLOSE ANGLE IS DETERMINED BY THE ZERO
CROSSING METHOD WITHOUT HAVING TO RELINQUISH THE
HIGH RELIABILITY OF THE ENVELOPE CURVE METHOD
4HE LOGICAL CLOSE COMMANDS OF THE TWO METHODS ARE
EACH APPLIED TO DIFFERENT PORTS 4HESE CONTROL THE TWO
COIL POLES OF THE CLOSE RELAY IN A CROSSWISE MANNER
