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KPB INTRA s.r.o.
How to order (demand) transformers correctly
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
1. Transformer type selection
a.
Measuring voltage or current transformer
VTS 12
b.
CTS 12
Indoor or outdoor environment
CTS 25
CTSO 38
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
c.
Types of current transformers
CTS 25
CTB 25
CTB 25
•Supporting type
•Bushing type
•Pass type
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
c.
Types of voltage transformers
VTS 25
•Supporting type
•Earthed measuring phase – earth
•E.g. 22000/√3//100/√3/100/3
VTD 25
V
•Supporting type
•Unearthed measuring between phases
•E.g. 22000//100 V
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
VTS 25
VTD 25
•Supporting type of
•earthed voltage transformer
•with fuse
•Supporting type of
•unearthed voltage transformer
•with fuse
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Functions and types of fuses

A fuse is used to protect adjacent equipment in case of transformer destruction

An appropriate type of fuse corresponds to each type of transformer
JT6
600 mA
VTS 12 – 1 pc
VTD 12 – 2 pcs
JT6
300 mA
VTS 25 – 1 pc
VTD 25 – 2 pcs
Bussman2
3.15 A
VTS 38
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2. Technical parameters of measuring transformers
a. Measuring current transformer
2.a.1
Insulation levels
Insulation voltage/Testing voltage/Testing impact voltage
e.g.
25/50/125 kV
36/70/170 kV
acc. to IEC 60044-1
38.5/80/180 kV
acc. to ČSN
40.5/95/200 kV
acc. to GOST
Rated frequency 50 (60Hz)
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2.a.2
Rated conversion and number of secondary windings
E.g. 100//5 A or 250//1/1 A
• If switch-over type is required, the primary current is to be stated in conversion in the form of
e.g. 100-200//5 A (one branch) or 50-100-200//5 A (two branches)
•
Rated conversion consists of rated
a.
b.
Primary current
Secondary current
Note:
It is appropriate to separate the primary current from the secondary one with a double slash // in the notation in
order to increase clarity.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2.a.2.a
Primary current
Selection from series in accordance with standards
10,12.5,15,20,25,30,40,50,60,75 A
An atypical current, e.g. 65 A or 630 or 515 A should be consulted with the designer.
2.a.2.b
Secondary current
Only 5 A or 1 A (or 2 A) is acceptable according to standards
Other values, e.g. 2.5 A should be consulted with the designer
(accuracy may not always be guaranteed as we do not have the necessary measuring equipment)
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Number of secondary windings
- Is given by the values after a double slash in conversion
Examples
400//5 A
One secondary winding 5A
150//5/1 A
Two secondary windings, first winding - 5 A , second winding 1 A
700//1/1/1 A
Three secondary windings (all 1A)
150-300//5//5 A
Two secondary windings (both 5A) with one branch
on secondary winding
Number of windings may be 1 , 2 , 3 or exceptionally 4
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Basic diagrams of winding of measuring current transformer
Single core type
Three-core type
Two-core type
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Basic diagrams of winding of measuring current transformer
Single core type with one branch
Three-core type with one
branch on each core
Two-core type with one
branch on each core
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
The following parameters should be given for individual windings:
I.
Rated load (burden) in VA
E.g. 15 VA
II.a) Accuracy class for measuring windings
0.2 ( 0.2S)
0.5 (0.5S)
II.b) Accuracy class for protection winding 5P or 10P
5P corresponds to 1 % error at rated current passing
10P corresponds to 3 % error at rated current passing
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
III.a)
Instrument security factor FS for measuring windings
It is stated as FS , e.g. FS5 or FS10
It expresses the ratio of resulting exciting current with respect to rated current at which
the transformer’s magnetic circuit will be oversaturated
This parameter is important for protection of measuring instruments on the transformer’s
secondary side
The real instrument security factor for measuring instruments is always lower than the
value stated in the label, e.g. for FS5, the max. factor is 4.999
In the case of passing a primary current higher than a quintuple of the primary current, a
current lower than 25 A will appear in the secondary circuit at conversion to 5A
(quintuple of 5A)
Or, in the case of conversion to 1 A, a current lower than 5 A will appear in the secondary
circuit (quintuple of 1A)
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Example
Primary
current
Secondary
current
100
5
200
10
300
15
400
20
500
24.995
600
24.995
[A]
25
sekundární proud [A]
[A]
30
20
15
10
5
0
100
200
300
400
500
600
prim ární proud [A]
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
III.b)
Instrument security factor for protection windings
Accuracy limit factor:

Ratio of rated primary overcurrent at a given precision and rated primary current
Follows always after accuracy class
E.g. 5P10 or 10P20 (instrument security factor is either 10 or 20)

Real instrument security factor of protection windings is always higher than the stated
value.

It must be guaranteed for transformer winding that measuring error will not exceed
10 % in the case of passing overcurrent in the value of a multiple of instrument security
factor 10%

It is important for correct operation of protections

There is a risk of protection failure if it has been set incorrectly (higher instrument
security factor than that stated on the label (transformer will be oversaturated before
protection activation)
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Example:
Transformer 50//5 A
Accuracy class in combination with instrument security factor 10P10
The transformer will measure with max 10% error if a current of 500 A
is passing, i.e. measured current will be at least 450 A
Instrument security factor 10
guarantees correct
functioning of protection
winding up to tenfold the
rated current. However,
rated load in VA may not be
exceeded as this could affect
the instrument security
factor.
80
70
sekundární proud [A]
60
50
10%
40
30
20
skutečný proud ε=10%
ideální proud za předpokladu ε=0%
10
0
0
100
200
300
400
500
600
700
800
primární proud [A]


E.g. If the above-mentioned burden is 10 VA and instrument protection factor 10, the instrument
security number will be reduced to 7 upon winding loading with a burden with output of 15 VA
Load (burden) may be increased by too long a supply line (several tens of meters) between the
protection and terminal board or by too small a cross section of wires, which is why this fact should be
considered when dimensioning rated burden of protection winding.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2.3
Short-circuit currents
2.3.a)
Rated short-time thermal current
Ith - rated short-time thermal current: effective value of primary current that the
transformer withstands for 1 second with secondary winding short circuit without
damage to the transformer.
Also times other than 1 second such as 0.5 s, 2 s, 3s may be agreed upon.
2.3.b)
Rated dynamic current
Idyn - rated dynamic current: peak value of primary current which the
transformer withstands without electric or mechanical damage caused by
electrodynamic force in the case of secondary winding short-circuit.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly

Rated dynamic current (1s) corresponds to a 2.5 multiple of short-term thermal current
Ith short-circuit duration 1s. Short-circuit conditions in the mains will be specified by the
specialized designer.

If a different short-circuit duration time than one second is stated, it is necessary to state this
fact in a request or an order!
Idyn = 2.5 x Ith

These short-circuit currents should be written in a request as follows: Ith/Idyn kA,
the value is to stated in kA, e.g. 16/40 kA.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Data which should be included in a request (summary)
 Current transformer type
 Conversion
 Insulation levels
 Rated frequency
 Parameters of individual windings – burden/accuracy class/instrument security fac
 Short-circuit currents Ith/Idyn
 Official verification (calibration) – if requested
 Non-standard modifications
 E.g. tropical design, PR super-structures, different base
boards, etc.

Such data must be specified for each winding separately as specification should be
unambiguous and complete in order to allow offering of precisely the required type
of the instrument transformer
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Example of incorrectly specified demand
Frequently the customer describes an instrument with the following parameters:
CTS 25 100//5/5
15 VA 0.5 FS5
It is apparent from conversion that it is a two-winding current transformer; however, parameters of the other winding are not
specified and we can only estimate that the other winding is the same as the first one. If the same windings are concerned, it is
advisable, because of the unambiguous character of the specification, to state the type as follows:
CTS 25 100//5/5
15 VA 0.5 FS5
15 VA 0.5 FS5
Please always state complete data in order to prevent any misunderstanding!
An example of a correctly specified demand
CTS 25 300//5/5/5 A
25/50/125 kV
50 Hz
25/63 kA
15 VA 0.2 FS5
10 VA 0.5 FS10
15 VA 5P10
Official verification for the first winding
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2. Technical parameters of measuring parameters
b. Measuring voltage transformer
2.b.1
Insulation levels
Insulation voltage/Testing voltage/Testing impact voltage
E.g.
25/50/125 kV
36/70/170 kV
acc. to IEC 60044-1
38.5/80/180 kV
acc. to. ČSN
40.5/95/200 kV
acc. to GOST
Rated frequency 50 (60Hz)
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
2.b.2
Rated conversion and number of secondary windings
E.g. VTS 25 - 10000/√3//100/√3/100/3 V or VTD 25 - 22000//100 V
•
Instead of √3, it is possible to write V3 (VTS 25 22000/V3//100/V3
Note:
It is appropriate to separate the primary current from the secondary one by a double slash //
in the notation in order to increase clarity.
2.b.2.a
Standardized levels of primary voltages
Standard voltage levels in the Czech Republic
Earthed type: 11000/√3 V, 22000/√3 V, 35000/√3 V
Unearthed type: 11000 V, 22000 V, 35000 V
2.b.2.b
Standardized values of secondary voltages (measuring zone)
Standard voltage levels in the Czech Republic
Earthed type – measuring and protection winding: 100/√3 V, 110/√3 V
Unearthed type – auxiliary winding: 100/3 V, 110/3 V
Note: In the case that an unearthed transformer is used as a supply of low output of low voltage,
it is also possible to select different secondary voltages, e.g. 220 V, 231 V, 380 V, 400 V, 500 V, etc.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Number of secondary windings
- is given by values after the double slash in conversion
Examples
22000/√3//100/√3 V
11000/√3 //100/√3 /100/3 V
one secondary winding 100/√3 V
two secondary windings
-the 1st measuring winding 100/√3 V
-the 2nd auxiliary winding 100/3 V
35000/√3 //100/√3 /100/√3 /100/3 V three secondary windings
-the 1st measuring winding 100/√3 V
-the 2nd measuring winding 100/√3 V
-the 3rd auxiliary winding 100/3 V
Number of windings may be 1 , 2 , 3 or exceptionally 4
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Parameters for individual windings
Each winding should include data as follows:


Burden size in VA
Accuracy class 0.2, 0.5, 1, 3P, 6P
Accuracy classes for measuring windings are:
Accuracy classes for protection transformers:
Accuracy class for auxiliary windings:
0.2,0.5,1
3P and 6P
6P
If a measuring transformer contains more measuring windings,
it is necessary to take into account the fact that individual windings
affect each other so that a sum of their output may reach a maximum of
the output of the transformer with one winding
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Example
Transformer VTS 25 output with one measuring secondary winding can reach an output
of 30 VA in accuracy class 0.2
1. The same transformer VTS 25 with two measuring windings reaches only max. output
1st winding 15 VA in class 0.2
2nd winding 10 VA in class 0.2
2. The same transformer VTS 25 with three measuring windings reaches only max. output
1st winding 5 VA in class 0.2
2nd winding 5 VA in class 0.2
3rd winding 5 VA in class 0.2
Note: For spatial reasons, it is usually impossible to reach the maximum limit for a given accuracy class
by the sum of individual windings, e.g.
15 VA + 10 VA < 30 VA
Please consider whether it is necessary to require high outputs, e.g.
50VA in class 0.2 or 30 VA and 30VA in class 0.2
for a two-winding measuring voltage transformer.
These requirements increase demands for instrument design and
the transformer is less resistant to the phenomenon called ferro-resonance.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Data which should be included in a demand (summary)
 Voltage transformer type
 Conversion
 Insulation levels
 Rated frequency
Correctly specified demand:
VTS 25 22000/V3//100/V3/100/3 V
25/50/125 kV
50 Hz
30 VA 0.5
50 VA 6P
Official verification not required
 Parameters of individual windings – burden/accuracy class
 Official verification (calibration) if required
 Non-standard modifications
E.g. Tropical modification, PR superstructures, different base boards, etc.
Such data must be specified for each winding separately as specification should be
unambiguous and complete in order to allow offering of precisely the required type
of the instrument transformer.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Ferro-resonance
The phenomenon called “ferro-resonance” appears in electric networks.
Causes of its occurrence:

Presence of capacitors (cable supply lines, capacitor batteries, etc.)

Effect of inductivity of chokes and the transformer’s own inductivity

Occurrence of oversaturation and impacts at transient phenomena

Oscillation of electric power between instrument capacitances and inductivity
Consequences:

Disturbing insulation of measuring voltage transformers

Progressive instrument destruction

In some cases, even sudden explosion of the instrument
Note: This phenomenon will appear more frequently in future as a consequence of replacement
of existing analog voltmeters with electronic ones because electronic voltmeters have a lower burden
and thus also lower damping effects, which means that the existing transformers are less
resistant with respect to this phenomenon.
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Potential solution of the problem called ferro-resonance
1. Increase of primary winding resistance
•
•
•
Inconvenient as it increases instrument dimensions
It increases production costs substantially
It increases product price
2. Undersaturation of magnetic circuit 0.4T
•
•
•
•
It
It
It
It
protects transformer against oversaturation
is necessary in some cases, e.g. for railway applications
increases instrument dimensions and product costs
limits some existing parameters of the instrument, e.g. output
3. Use of resistor connected in open triangle with auxiliary windings MTN
(68 Ohm/ 200W (TR305 manufacturer: Tesla Blatná)
•
•
It reduces ferro-resonance effects
Low costs with respect to instrument purchase price
Note: In the case that resistor
connection would result in
non-activation of parallel
protection or signalling
relay, it is possible to reduce
consumption by connecting
two resistors in series.
connection
diagram
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com
How to order (demand) a transformer correctly
Thank you for your attention. Should you have any questions please feel free to contact:
Ing. Robert Knápek - Executive: +420 603 481 128
[email protected]
Ing. Petr Novák – Business Department Manager: +420 604 237 033
[email protected]
Ing. Josef Stejskal – Technical Department Manager: +420 603 862 464
[email protected]
www.kpbintra.com
KPB INTRA s.r.o. , Ždánská 477, CZ-68501 Bučovice, tel.: +420 517 380 388, fax: +420 517 381 433, [email protected], www.kpbintra.com