Knowledge Is Power SM
Apparatus Maintenance and Power Management
for Energy Delivery
Doble Testing
Current Transformers
(CT’s)
Test Procedure
•Short Primary Windings
•Ground all Secondary Windings
•Perform Overall Test in GST Ground Mode
•Perform Tap Test C1 and C2 (If Test Tap Installed)
CT Test Voltage
Liquid Filled
•15 kV and Above: 10 kV
•Below 15 kV: Test Voltage Equal to or Below
Nameplate Operating Line to Ground (L-to-G)
Voltage
Dry-Type
•15 kV and Above: 2 kV
10 kV*
•Below 15 kV: 2 kV
L-to-G Voltage *
10% to 25% Above Operating
L-to-G Voltage
* Note: Tip-Up Tests
Current Transformers (CTs)
H1 H2
X Windings
CT Without Test Tap
Current Transformers (CTs)
X1 X2 X3
CT Without Test Tap
Test Procedure
Test Procedure: CTs Without Test Taps
Test No. Energize Ground UST Guard
1 (Overall) Primary Secondary ---- ----
Test Procedure
Test No. 1: GST- Ground
H1 H2
High Voltage Lead
X1 X2 X3
CT Without Test Tap
Current Transformers (CTs)
H1 H2
C1 X Windings
C2
CT With Test Tap
Current Transformers (CTs)
H1 H2
C1
C2
X1 X2 X3
CT With Test Tap
Test Procedure
Test Procedure: CTs With Test Taps
Test No. Energize Ground UST Guard
1 (Overall) Primary Secondary ---- ----
2 (C1) Primary Secondary Tap ----
3 (C2) Tap Secondary ---- Primary
Test Procedure
Test No. 1: GST- Ground
H1 H2
High Voltage Lead
C1
C2
X1 X2 X3
CT With Test Tap
Test Procedure
Test No. 2: UST
High Voltage Lead H1 H2
Low Voltage Lead C1
C2
X1 X2 X3
CT With Test Tap
Test Procedure
Test No. 3: GST-Guard
H1 H2
Low Voltage Lead
High Voltage Lead C1
C2
X1 X2 X3
CT With Test Tap
Current Transformers - DTA
Current Transformers - DTA
Analysis
•Calculate Power Factor
•Compare Test Results to the Tabulated Data in the
Doble Test-Data-Reference-Book (TDRB)
Current Transformer
Supplementary Tests
Basic Principle
• Basic Theory for Power Transformer Tests
and Data Interpretation Also Applies to
CT’s
• Apply Test Voltage Across Full Winding
With the Highest Number of Turns:
• Minimizes Test Current
• No Step-Up Voltage
• Excitation Current Tests Can be Performed
at Multiple Test Voltages for Saturation
Curve
Doble
Current Transformer
Turn Ratio Test
Doble Transformer Turn Ratio Test
Doble TTR
Capacitor
HV Lead
CTRUE
UST Transformer
UST
LV Lead
IC IC/N
CTrue= CApparent=
10 kV x ω 10 kV x ω
Ratio N N = CTrue/CApparent
Doble Turns Ratio Test - CT
TTR Cap.
H1 H2
X1 X2 X3 Y1 Y2 Y3
UST UST
Meter Meter
C.True Measurement C.Apparent Measurement
Turns Ratio N N = CTrue/CApparent
Note: Test Voltage Based on Nameplate
Doble
Current Transformer
Excitation Current Test
Excitation Current Test - CT
H1 H2
X1 X2 X3 Y1 Y2 Y3
HV Lead Low Voltage Lead
UST
I & W Meter
Note: Test Voltage Limited to Rated Voltage of Secondary Winding
Excitation Current Test - CT
H1 H2
X1 X2 X3 Y1 Y2 Y3
HV Low Voltage
Lead Lead
UST
I & W Meter
Note: Test Voltage Limited to Rated Voltage of Secondary Winding
Recommended Test Voltage
Application Class designation Rated Test
voltage Voltage
(V) (kV)*
B-0.1 10 0.025
Metering B-0.2 20 0.025
B-0.5 50 0.050
B-0.9 90 0.090
B-1.8 180 0.180
B-1 C100 K100 T100 100 0.100
Relaying B-2 C200 K200 T200 200 0.200
B-4 C400 K400 T400 400 0.400
B-8 C800 K800 T800 800 0.800
C1000 K1000 T1000 1000 1.000
* Minimum output voltage of M4000 is about 0.025 kV and the voltage ramp step need to
be modified to 1 or 2 volts to prevent an Over voltage error from happen during voltage
ramping.
Doble
Current Transformer
Saturation Curve Test
Saturation Curve Test
• Use Same Procedure as Excitation Current Test
• Perform Test at Multiple Test Voltages
• 0.25% to 120% of Rated Voltage
• Print Test Data to Text File and Save
• Copy and Paste From Text File to a Spreadsheet
Application File (i.e. Excel)
• Graph Saturation Curve
Test Data Analysis - CT
Saturation curves in Figure 4 of C57.13-1993
Doble
Current Transformer
Polarity Test
Polarity Test
• Use Same Procedure as Doble Turns Ratio Test
• Observe the Capacitance Readings:
• If the Capacitance Value (Ratio Factor)
Compares to Calculated Value, Than HV Cable
and TTR Capacitor are of Same Polarity
• If Capacitance Value is Abnormally Low
(negative or inductive), Than HV Cable and
TTR Cap are Opposite Polarity
Test Data Analysis - CT
• Excitation Current: Comparison to Reference
• Change in I/W => Change in Insulation or Core
• Saturation Curve: Compares to Reference
• Similar or Above the Reference =>Ok.
• Below the Reference’s => Faster Saturation
(Design, Core, Insulation Problem)
• Turns Ratio: Compares to Class Accuracy
• Polarity: Matches Lead Identification
