Transcript Field Problems with Instrument Transformer Installations

Field Problems with Instrument
Transformer Installations
ElectriCities of North Carolina
Advanced Meter School
James Whitaker
Greenville Utilities Commission
Mark Wells
Town of Tarboro
Current Transformers


Proportionally steps down
the current level in the
meter circuit
Isolates meter personnel
and metering equipment
from high current flow
FORM 9S WIRING DIAGRAM
USING ONLY CTS
SECONDARY METERING
3 PHASE 4 WIRE WYE

SOME UTILITIES MAY
USE ONLY CTS AND NO
VTS
A
B
C
K
Y
Z
FORM
8/9S
SOLID STATE
METER
VOLTAGE
120 / 208
N
WHITE
ORANGE

THIS IS BY
PREFERENCE OR
POLICY
RED / BLACK
BLUE
ORANGE / BLACK
RED
BLUE / BLACK
BLACK
P P P N R
R
R
P
RED / BLACK
ORANGE
BLUE / BLACK
BLACK
ORANGE / BLACK
BLUE
/ BLACK
WHITE
RED

THE BILLING
MULTIPLIER WILL BE
DETERMINED BY THE
CT RATIO
A
+
B
+
C
+
120V
CT
120V
LINE
N
BLACK
CT
CT
120V
WIRING DIAGRAM
TRANSFORMER-RATED SOCKET TYPE
THREE PHASE, 4 WIRE WYE CT SERVICE
120-208 VOLT FM 8/9 S THREE ELEMENT SOLID STATE METER
FORM
NUMBER
S-8/9 S
Voltage Transformers
A voltage transformer
or VT steps down
higher voltage by
some ratio to a level
that is safer and
more practical to
meter.
FORM 9S WIRING DIAGRAM
USING VTS & CTS
SECONDARY METERING
3 PHASE 4 WIRE WYE USING SECONDARY VTS & CTS

THIS DIAGRAM USES
SECONDARY VTs TO
STEP DOWN THE
VOLTAGE TO 120V
FORM
8/9S
SOLID STATE
METER
VOLTAGE
277 / 480
A
B
C
K
Y
Z
N
MULTIPLIER =
CT x VT RATIO
WHITE
ORANGE
RED / BLACK
BLUE
ORANGE / BLACK
RED
BLUE / BLACK
BLACK
P P P N R


CTs ARE ALSO USED
THE BILLING
MULTIPLIER WILL BE A
COMBINATION OF VT
AND CT RATIO
R
R
P
RED / BLACK
VT
2.4 : 1
ORANGE
VT
2.4 : 1
BLUE
VT
BLUE / BLACK
BLACK
ORANGE / BLACK
VT
2.4 : 1
/ BLACK
WHITE
RED
A
+
B
+
C
+
CT
277V
CT
277V
LINE
N
GROUND
BLACK
CT
277V
WIRING DIAGRAM
TRANSFORMER-RATED SOCKET TYPE
THREE PHASE, 4 WIRE WYE SERVICE WITH VTS & CTS
277- 480 VOLT FM 8/9 S THREE ELEMENT SOLID STATE
METER
FORM
NUMBER
S-8/9 S
CT PROBLEMS


CT POSITIONED
BACKWARDS ON
PRIMARY
CONDUCTOR
THE METER WILL
RUN BACKWARDS
ON THIS PHASE
ANOTHER CT PROBLEM


WIRING REVERSED
AT SECONDARY
SIDE OF CT
SAME EFFECT AS
THE PREVIOUS
SLIDE, REVERSE
ROTATION ON THIS
PHASE
CT IMPROPER WIRING
POLARITY REVERSED


TEST SWITCH
CONNECTIONS
SAME THING,
REVERSE
ROTATION ON THIS
PHASE
CT INSTALLATION ISSUES


CT SHORTING BAR
LEFT IN THE
CLOSED POSITION
NO MEASURERMENT
OF CURRENT ON
THIS PHASE
LOOSE SCREW ?


CT CIRCUIT
SHORTED
NO OR LOW USAGE
ON THIS PHASE
OPEN CT CIRCUIT




BROKEN OR BURNED CT WIRING
BROKEN NEUTRAL CAN RESULT IN NO
REGISTRATION AT ALL
AGAIN, NO MEASUREMENT ON THAT
PARTICULIAR PHASE
POSSIBLE DAMAGE TO CT
OPEN VOLTAGE CIRCUIT



BROKEN VOLTAGE
WIRING
BAD VT = NO
VOLTAGE
NO MEASUREMENT
ON THIS PHASE
POSSIBLE TAMPERING


OPEN TEST
SWITCHES ON
CURRENT OR
VOLTAGE SIDE
NO MEASUREMENT
OF CURRENT ON
THESE TWO
PHASES
LOCKS HELP

USE SOME TYPE OF
METER BASE
LOCKING DEVICES
BILLING PROBLEMS

BILLING MULTIPLIER

CT RATIO 200:5=40

VT RATIO 288:120=2.4

40 X 2.4 = 96
WHAT IF ?



INSTALLATION CREW GIVES INCORRECT
INFORMATION TO THE BILLING
DEPARTMENT
SERVICE UPGRADE, CTS ARE CHANGED TO A
HIGHER RATIO AND THE CHANGE NEVER
GETS TO THE BILLING DEPARTMENT
BILLING MULTIPLIER IS WRONG!! LOSS OF
REVENUE
NEW MULTIPLIER





SERVICE AND CT UPGRADE
PREVIOUS BILLING MULTIPLIER WAS
96 (40X2.4=96)
NEW CTS 600:5 USING THE SAME VTS
WHAT IS THE NEW MULTIPLIER?
600:5=120 X 288:120=2.4 (120 X
2.4=288)
NEW BILLING MULTIPLIER IS 288
LOSS OF REVENUE


ALL OF THESE EXAMPLES AND MANY
OTHER PROBLEMS CAUSE A
TREMENDOUS AMOUNT IN REVENUE
LOSS EACH YEAR
WHAT CAN YOU DO TO CORRECT THIS
PROBLEM?
CT TEST PROGRAM


CHECK NEW INSTALLATIONS AS WELL AS
ANY UPGRADES AS THEY ARE DONE. THIS IS
WHEN A LOT OF ERRORS OCCUR AND THEY
ARE HARD TO CATCH BECAUSE THERE IS NO
BILLING HISTORY
HAVE A TEST SCHEDULE TO RECHECK CT
INSTALLATIONS PERIODICALLY
SAMPLE FIELD TEST




WIRE VERIFICATION
CT RATIO AND
ACCURACY
METER ACCURACY
TOTAL SYSTEM
ACCURACY
QUESTIONS ?