Download ECP 11-0308 DUOBIAS Biased Differential

Document Number: ECP 11-0308
Date: 12/12/2016
DUOBIAS BIASED DIFFERENTIAL TRANSFORMER PROTECTION TEST FORM
Substation Name
Substation Number
Transformer
General Data
Relay Serial Number
Relay Article Number
Manufacturer
Manufacturer Type
Duobias M 200
CT Ratios HV
CT Ratio LV1
CT Ratio LV2
Trip Supply
V
Details of Aux DC Element
V
Interposing CTs
Transformer Rating
MVA
Transformer Ratio
Transformer Tapping Range
Bias Setting
Inspection of Site Wiring and Insulation Testing

To be carried out by appropriate Contractor.

Isolate the auxiliary supplies. Remove trip and intertrip links.

Measure the insulation resistance between each section of the wiring and other sections and to
earth. Apply short circuits to protect the status inputs and series resistors. Refer to relay manual.
Circuit Test
Ferrule Nos. / Description of Test Points
Insulation Resistance (M)
AN1
AN2
AN3
AN4
PSU
Mechanical Inspection
Mechanical inspection of the various DC relays is to be recorded on the Tripping
and Auxiliary Relays test form ECP 11-0305. Record here the mechanical
inspection of the Duobias M Relay
()
THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE
Version: 3.0
DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Settings Record
Record the relay settings in the tables below. All of these settings are to be provided by a Protection
Applications Engineer. This will normally be on a standard Reydisp Evo settings sheet and these
values must be checked, verified and recorded here by hand as a permanent commissioning record
to the setting of the relay. Note, use Spare rows to record other setting values as applicable eg
Circuit Breaker Fail logic if installed.
Setting Type
HV
LV A
Diff Initial Setting
%
Diff Bias Slope
%
LV B
Diff Bias Slope Limit
Diff Hi Sets
Mag Inrush Restraint
Level
%
Interposing CT
Multiplier
Interposing CT
Connection
REF
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A
A
A
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Table 1 - Mapping of Protection Function to Relays
Relay 1-16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Protection
Healthy
Curr Diff
Hi Set
Ref
Data
Stored
Hand
Reset
Unbalance
Diff
Trig
Storage
Local Datalink Baud Rate
Waveform Storage Pre-Trigger
Data Link Output
Table 2 - Mapping Table of Opto-inputs to Relays
Relay 1-16
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Secondary Injection Tests
Isolate the DC supplies for tripping and alarms from the relay and remove the trip and intertrip links.
The following settings should be used for the purpose of these tests:

W1 interposing CT multiplier 1.00

W1 interposing CT connection Yy0

W2 interposing CT multiplier 1.00

W2 interposing CT connections Yy0

Bias slope limit 4x

Differential highset 4x
Accuracy of Measurement
Inject all the relay current inputs with nominal current and record the values below.
Test
Applied Value (x In or Vn)
Relay Instruments Display (x In)
Winding 1 Line CT
Inputs
IA=1.00, IB =1.00, IC=1.00
IA =
IB =
IC =
Winding 2 Line CT
Inputs
IA=1.00, IB =1.00, IC=1.00
IA =
IB =
IC =
IA=1.00, IB =1.00, IC=1.00
IA =
IB =
IC =
IA=1.00, IB =1.00, IC=1.00
IA =
IB =
IC =
IA=1.00, IB =1.00, IC=1.00
IA =
IB =
IC =
W1 =
W2 =
1W3
Neutral Inputs
W1=1.00, W2 =1.00,
1W3=1.00,
1W4=1.00,1 W5 =1.00
1W4
1W5
1Voltage
VAUX = 1.00
VAUX =
REF W1
I = 0.200
I=
REF W2
I = 0.200
I=
REF W3
I = 0.200
I=
1Winding
3
Accuracy
1Winding
4
Accuracy
1Winding
5
Accuracy
Input(s)
=
=
=
1
If applicable the accuracy of the Instruments should be within 5% of injected value. If any
measurements are outside the stated ± 5% tolerance, the relay must be returned to the manufacturer.
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Checking the Bias Characteristic

Inject nominal current into W1 Red and W2 Red phase current inputs as shown in the test
circuit below.

The differential and restrain current meters should be monitored on the relay display.

Repeat the test with increasing bias current, up to 2.5 x the relay rating.

Record the results and check for accuracy in the table below.

Check that the bias currents on the display are as expected.
Initial and Bias Settings (%)
Bias Current (x In)
Initial
0
Bias
1
1.5
2
2.5
Operate Current
10
10
0.1
0.1
0.15
0.20
0.25
20
20
0.2
0.2
0.30
0.40
0.50
30
30
0.3
0.3
0.45
0.60
0.70
40
40
0.4
0.4
0.60
0.80
1.00
50
50
0.5
0.5
0.75
1.00
1.25
50
60
0.5
0.5
0.90
1.20
1.50
50
70
0.5
0.5
1.05
1.40
1.75
Selected Settings
Test Results
Phase A
Phase B
Phase C
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Inrush Inhibit

The magnetising inrush restraint feature can be checked by injecting the relay with 2nd
harmonic current into one set of inputs while fundamental is injected into another set of inputs. If
possible the test should be done three phase as all phases are blocked if one phase exceeds
the Inrush Inhibit Setting.

Check the 87 Inrush Inhibit setting is set to [Enabled].

Inject W1 inputs with a balanced three phase current of nominal amplitude and frequency. This
will operate all three phases of the biased differential function. The 87BD and phase LED’s will
be lit. Inject about 5% of nominal 2nd harmonic current into W2 inputs. Slowly raise the 2nd
Harmonic Current until the biased differential resets. The approximate levels of 2nd harmonic to
block operation are set out in the table below. Digital Test sets such as an Omicron 256-6 use a
ratio injection to test the relay inhibit, the Duobias M does not work like this as its setting is a
percentage of the operate current.
Inrush Inhibit Setting (% of Iop)
Recorded 2nd Harmonic Current
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Calculated % of I
operate
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Checking the Differential High Set (If applicable)
Switch on and increase the value of test current until the high set element operates. Record the
value below. Monitor the operate value using the relay instruments display. Test all three phases.
Condition
Operate
A
B
C
A-N
B-N
C-N
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Testing the Restricted Earth Fault Element
Refer to the calculated setting data and check that the relay has the correct settings for each of the HV
and LV REF protections. Measure the resistance of the REF series setting resistors and adjust each
one to match the REF setting data. Record the values in the table.
This should be done in two stages:
A - Current Injection by test set
Inject the REF inputs with the CT’s disconnected and record the pickup values in the table. The setting
resistor should be temporarily be shorted out to allow injection from digital test set.
B – Applied Voltage using Variac
Follow safety procedure to ensure no other personnel can come into contact with secondary wiring
during this test. Tests are carried out with the current transformers connected in idle shunt to the REF
parallel leg. Apply voltage across the REF parallel leg input via the test block or lead and connect an
a.c. voltmeter to verify the voltage applied. Slowly increase the applied voltage and note the voltage
required for the REF protection to operate on the voltmeter. Ensure that appropriate LED’s illuminate
and selected output relays operate.
Component/Element
Setting
Actual Value or Pickup
W1 REF Resistor


W2 REF Resistor


W1 REF Current Setting
x In
x In
W2 REF Current Setting
x In
x In
W1 Voltage Setting
V
V
W2 Voltage Setting
V
V
Note: In SPN currently a high impedance REF relay is used in parallel with the Duobias/resistor circuit.
This should be tested in accordance with test form ECP 11-0307. Settings should be arranged so that
both the high impedance relay and the Duobias REF elements operate as far as possible at the same
level of injected current.
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8 of 13
DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Proving Inputs and Outputs
The number of inputs and output contacts present will vary with model.
The easiest way to prove output contact operation is to use Reydisp Evolution. The relay output
contacts can be closed by selecting RELAY -> CONTROL -> CLOSE OUTPUT RELAY menus.
The status inputs must be tested by application of rated voltage. The “high” (operated) or “low”
(unoperated) state of each status input is most easily checked using the Instruments window of the
Reydisp Evolution software.
Refer to the record of settings in section 4 of this test sheet.
Primary Injection Tests
Primary injection is recommended to prove the relay connections, CT polarity and settings before
putting the protection scheme into service.
WARNING - It is important before carrying out any primary injection to ensure appropriate CTs
are shorted to avoid operation of any busbar type unit protection. If the injected primary current
is large enough, the bus zone protection may operate if the CTs are in the transformer turrets.
Biased Differential Protection
Sufficient primary current to prove the connections and settings is required so that a minimum
secondary current of about 10mA rms circulates in the relay inputs.
An external three-phase primary short is required on one side of the transformer, ideally the HV side.
Protection applications will advise on the expected current magnitude by reference to transformer
factory test certificates.
Apply 415 LVAC to the other side ensuring the primary current is injected through all of the biased
differential CTs.
The following procedure should be followed to check the ac scheme and settings are correct.
1. Use Reydisp evolution software to trigger a waveform record of the currents.
2. Retrieve the waveform record from the relay.
3. View the waveform record in Reydisp evolution.
4. Check the following current pairs are equal in magnitude, shown as a fraction of In in the waveform
display, and anti-phase, by placing the cursors on the peak relay currents:
a. W1 Ict Ia vs. W2 Ict Ia (and W3 if applicable)
b. W1 Ict Ib vs. W2 Ict Ib (and W3 if applicable)
c. W1 Ict Ic vs. W2 Ict Ic (and W3 if applicable)
If difficulty is experienced due to physical restraints, the differential element operation may be proven
using load current.
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Restricted Earth Fault (REF)
The CT polarities forming the REF must be proved, and the recommended way to achieve this is by
primary injection. Inject single phase or three phase current from a suitable primary test set through
earth and primary conductors. The results of these tests may be recorded in the table.
During these primary injection tests the injected current may be limited due to the impedance of the
neutral connection. Temporary shorts must be added to allow a definite result to be established.
Place a temporary short across the setting resistor to allow the secondary current to be measured.
Insert the test block with necessary shorts across from CT to relay side. Inject primary current
sufficient to allow measurement. Measure and record the REF spill current displayed by the
appropriate relay instrument. This spill current should be very small e.g. a few mA. Reverse the
connections to the secondary winding of the neutral CT and the spill current should become larger.
Repeat for other phases if necessary.
Condition
Primary Current A4
Ammeter Readings
LV Display
LV Line Current x In
A1
A2
A3
A4
A
B
C
A-N
B-N
C-N
Calculated CT Ratio  Primary Current / Secondary Current
Note: In SPN currently a high impedance REF relay is used in parallel with the Duobias/resistor
circuit. This should be tested in accordance with test form ECP 11-0307. Settings should be
arranged that both the high impedance relay and the Duobias REF elements operate as far as
possible at the same setting
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10 of 13
DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Trip Tests
Re-connect the auxiliary dc supplies for trip and alarm operations and insert the trip and intertrip links.
The differential protection should be operated by secondary injection to check that correct tripping (or
intertripping) and indication occurs.
Simulate the operation of each external contact that initiates a Duobias M status input. This can be
done by temporarily shorting across the operating contact. In each case check the appropriate LED
illuminates and that the correct tripping, intertripping and alarm initiation occurs.
Disconnect the dc power supply to the Duobias M relay and check the correct Protection Unhealthy
alarm contact operates.
Operate the differential protection and the REF protections in turn by primary or secondary injection
and check that the correct tripping and indication occurs.
Prove to diagram that trip functionality operates from all initiate positions and that the
Duobias LEDs and associated output relays close.
()
Prove to diagram that operation of all internal protection elements on Duo-Bias
triggers the correct LED and associated output relay
()
Prove operation transformer HV and LV trip relay(s) by initiation FROM and VIA
Duobias relay.
()
Prove correct functioning of Protection Unhealthy alarm.
()
Negative checks to diagram on all links associated with transformer protection
()
Alarms correctly initiated
Local
()
Telecontrol
()
Tests using Load Currents

Connect the laptop and check communications is established with the relay by downloading all
settings. Select INSTRUMENTS DISPLAY in Reydisp Evolution.

Under steady load conditions check for agreement between the relay ammeters and the software.

Record the on-load spills in the table.

If the secondary connections and the matching of the differential protection to the transformer ratio
and vector group connections is correct the readings 'OPERATE A, B, C' should be negligible for
all three phases.

Next unbalance the differential protection by a 180° reversed HV vector group compensation
setting. This may easily operate the relay and will trip.

A further confidence test could be done by increasing and decreasing in 30° steps until relay
operation occurs.

The operate currents "OPERATE A, B, C" should now be comparatively large.

Reset the HV vector group compensation setting back to the correct setting, re-check that the

'OPERATE A, B, C' currents are negligible. The 'RESTRAIN A, B, C' currents should be the greater
of the two sets by some margin. Record the values of operate and restrain currents in the table.
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11 of 13
DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Record Values in Amperes, ie LCD Reading x In
Metering Point Selected
Normal
A
B
Reversed
C
A
B
C
HV Line
HV Relay
LVA Line
LVA Relay
LVB Line
LVB Relay
Operate
Restrain
HV REF
LVA REF
LVB REF
HV CT Secondary Current
LVA CT Secondary Current
LVB CT Secondary Current
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DUOBIAS Biased Differential Transformer Protection Test
Form
Document Number: ECP 11-0308
Version: 3.0
Date: 12/12/2016
Comments
Test Equipment
Purpose
Make/Type
Serial Number
Certification
()
All tests have been completed satisfactorily
Contractor Commissioning Engineer (if applicable)
Organisation
Name
Date
Signature
UK Power Networks Commissioning Engineer
Name
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Signature
Date
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