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MEDIUM-VOLTAGE MEASURING CURRENT
TRANSFORMERS – USER MANUAL
MEDIUM-VOLTAGE
MEASURING CURRENT TRANSFORMERS
USER MANUAL
F.T.M. S. r. l. Fabbrica trasformatori di misura
Via Po, 3
20090 Opera – MI - Italy
Tel : +39 (0)2 576814
Fax : +39 (0)2 57605296
E-mail: [email protected]
Website: www.ftmsrl.it
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CONTENTS
1
INTRODUCTION
2
CHOICE OF DEVICES
2.1 SYSTEM SPECIFICATIONS
2.2 ENVIRONMENTAL CONDITIONS
2.3 SAFETY DISTANCES
3
TRASPORT
4
STORAGE
5
INSTALLATION
5.1 MECHANICAL ASSEMBLY
5.2 CONDENSATION PHENOMENA
5.3 CONNECTIONS TO THE MAIN CIRCUITS
5.4 GROUND CONNECTIONS
5.5 SEALING THE SECONDARY TERMINALS
6
COMMISSIONING
7
MAINTENANCE
8
STAFF TRAINING
9
TECHNICAL SPECIFICATIONS
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1. INTRODUCTION
This manual provides all the information needed to safely operate measuring current transformers
(CTs) suitable for installation and use in medium voltage systems (from 7.2 kV to 36 kV), and IEC
60044-1 compliant.
2. CHOICE OF DEVICES
Devices must be chosen so as to meet all the electrical parameters of the system in which they will
be installed, paying particular attention to the following:
2.1 SYSTEM SPECIFICATIONS
•
Power grid’s operating voltage
SERIES
AOC/ETO
MTA 7
MTA15/CTF17
MTA 24/CTA 24/CTP24/CTF24/STA/ETA/RTA24/DTA 24
RTA36
•
•
•
•
•
•
Operating voltage
From 0.72 kV to 24 kV
Up to 7.2 kV
From 7.2 kV to 17.5 kV
From 7.2 kV to 24 kV
From 7.2 kV to 36 kV
Rated primary current
¾ Limits as reported on the product’s technical datasheet
Rated secondary current
¾ All transformer series: 5A or 1A
¾ Special modifications on request
Short circuit thermal current and time
¾ All transformer series are guaranteed to bear 100 times the rated primary current for
1 second.
¾ Special modifications on request
Short circuit dynamic current
¾ All transformer series guarantee 2.5 times the short circuit thermal current.
¾ Special modifications on request
Frequency
¾ 50 – 60 Hz
Type of use
¾ Measure or protection
¾ All transformer series comply with the product’s standards.
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2.2 ENVIRONMENTAL CONDITIONS
Transformers may be subjected to the following environmental conditions, which need to be
carefully taken into account:
• Temperature
¾ All transformer series: from -5 °C to +40 °C
¾ Insulation class E
¾ Special modifications on request
• Altitude
¾ All transformer series: up to 1000 m a.s.l.
¾ Special modifications on request
• Humidity
¾ All transformer series:
o The mean relative humidity, measured over 24h, must not exceed 95%.
o The mean steam pressure, measured over 24h, must not exceed 2.2 kPa.
o The mean relative humidity per month must not exceed 90%.
o The mean steam pressure per month must not exceed 1.8 kPa.
¾ Special modifications on request
• Installation
¾ All transformer series: indoor installation
• Pollution levels
¾ All transformer series: installation is possible even in tropical climates
• Corrosive agents
¾ To be reported if present
• Dust and deposits
¾ To be reported if present
2.3 SAFETY DISTANCES
Safety distances to be complied with in CT installation are as provided by the standards on
medium tension insulated power systems.
3. TRASPORT
Transformers will be suitably packaged for transport according to the type of product and transport,
or to the modality agreed on with the customer.
On reception of the device, users are kindly asked to inspect it carefully to ensure the product is
undamaged.
4. STORAGE
Devices must be stored in clean and dry areas, between -20°C and +70°C (except as otherwise
specified).
Packaged units may be stacked one on top of another if allowed by and in conformity with the
packaging’s technical specifications.
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5. INSTALLATION
All installation operations must be carried out in compliance with all existing accident prevention
measures and the following instructions:
5.1 MECHANICAL ASSEMBLY
Before tightening, please ensure that the surfaces connecting the conductors and the
transformer’s primary and secondary terminals are clean and in good conditions. Also
ensure that the connections do not cause abnormal mechanical stress to the devices’
terminals.
The maximum and minimum tightening torques of the screw threads to be used for
connection to the primary and secondary terminals are as follows:
Terminals
Screw thread
Primary
Secondary
M12
M10
M6
Maximum torque
Nm
35
25
5
Minimum torque
Nm
15
10
3
Finally, check that no electrical insulation distance was altered during the connecting
operation.
5.2 CONDENSATION PHENOMENA
In order for the transformer to withstand the effects of high humidity and condensation, it is
advisable to ventilate and heat the installation switchboard, or to apply dehumidifying
devices to it.
5.3 CONNECTIONS TO THE MAIN CIRCUITS
The primary and secondary connections must be checked to ensure they are compatible with
the wiring diagram and the symbols present on the transformers.
The graphics printed on the transformers, showing how to connect them correctly, is as
follows:
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Single primary ratio CT
with a secondary winding
Single primary ratio CT
with two secondary windings
Primary
Primary
Secondary
Secondary
Double primary ratio CT
with the ratio change occurring on the
secondary winding and with a secondary
winding
Double primary ratio CT with the ratio change
occurring on the primary winding and with a
secondary winding
Primary
Primary
Secondary
The correct connections to obtain the different
primary burdens are as follows:
example: CT 100-200/5 A-A/A
Lowest primary ratio: 100/5 A/A,connect to the
secondary terminals: S1 and S2
Highest primary ratio: 200/5 A/A
connect to the secondary terminals: S1 and S3
Secondary
The correct connection to obtain the different
primary burdens, to be made using the copper
plates provided, is as follows:
example: CT 100-200/5 A-A/A
Lowest primary ratio: 100/5 A/A,connect the
primary terminals: C1 and C2
Highest primary ratio: 200/5 A/A
connect the primary terminals: P1 / C1
and the primary terminals: P2 / C2
Please pay maximum attention to the conditions of the CTs’ secondary
circuits, which must be connected to the burden or shorted at all times.
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5.4 GROUND CONNECTIONS
The support plates and one terminal per secondary winding must be connected to the
ground.
5.5 SEALING THE SECONDARY TERMINALS
All transformers are provided with a thermoplastic cap and fixing screws to protect and seal
the secondary clamps.
6. COMMISSIONING
To guarantee staff and device safety, please make sure, by checking the specifications on the label,
that the system’s electrical parameters do not exceed the transformer’s nominal parameters.
The data reported on the identification label are as follows:
1 Series / Type
2 Code
This is an 8-figure code, in which the first two figures represent the manufacturing year.
3 Insulation reference voltage / Power frequency withstand voltage / Impulse withstand
voltage, expressed in kV
0.72/3/- 1.2/6/- 7.2/20/60 - 12/28/75 – 17.5/38/95 – 24/50/125 – 36/70/170
(IEC standard-compliant values)
4 Short circuit thermal current and time
Expressed in kA and seconds
5 Short circuit dynamic current
Expressed in peak kA
6 Frequency
Expressed in Hz
7 Product’s reference standards.
8 Rated transformation ratio.
Rated primary current, A / Rated secondary current, A
9 Burden applied to the secondary terminals to which the accuracy class refers.
Expressed in VA
10 Accuracy class
11 Safety factor (if required)
12 Continuous thermal withstand value
Percentage referring to rated currents
13 Secondary terminals’ symbols
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7. MAINTENANCE
Before carrying out any operation, make sure that the CTs are not connected to the power grid or
powered in any way.
Check the tightening of the primary and secondary connections.
Ensure that the insulating resin surface shows no signs of deterioration such as carbonisation or
cracks.
Periodically remove any dust or other deposits that may accumulate on the transformers’ surfaces.
Avoid using solvents.
8. STAFF TRAINING
All installation, commissioning and maintenance operations must be carried out by trained staff.
Staff need to be trained in order for them to operate competently within the field.
9 TECHNICAL SPECIFICATIONS
For further information on the field of application and technical definitions, please refer to the
product’s standard:
IEC 60044-1
The products’ technical datasheets are available online at:
www.ftmsrl.it
In accordance with the existing law, F.T.M. S.r.l. expressly prohibits any reproduction, retransmission, republication,
or other use of all or part of this document without prior authorisation.
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