Snmek 1

1
KPB INTRA s.r.o.
How to order (demand) transformers correctly
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
2
How to order (demand) a transformer correctly

• Transformer type selection

• Measuring voltage or current transformer

VTS 12
CTS 12

• Indoor or outdoor environment

CTS 25
CTSO 38
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
3
How to order (demand) a transformer correctly

• Types of current transformers

• CTS 25
• Supporting type

• CTB 25
• Bushing type

• CTB 25
• Pass type

KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
4
How to order (demand) a transformer correctly

• Types of voltage transformers

• VTS 25
• Supporting type
• Earthed measuring phase earth
• E.g. 22000/v3//100/v3/100/3 V

• VTD 25
• Supporting type
• Unearthed measuring between phases
• E.g. 22000//100 V

KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
5
How to order (demand) a transformer correctly

• VTS 25
• Supporting type of
• earthed voltage transformer
• with fuse

• VTD 25
• Supporting type of
• unearthed voltage transformer
• with fuse

KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
6
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 

KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
7
How to order (demand) a transformer correctly

• Technical parameters of measuring transformers

• 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
CSN 40.5/95/200 kV acc. to GOST
Rated frequency 50 (60Hz)
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
8
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
• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
9
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
10
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
11
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
12
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
13
How to order (demand) a transformer correctly
The following parameters should be given for
individual windings

• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
14
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 transformers magnetic circuit will be
oversaturated This parameter is important for
protection of measuring instruments on the
transformers 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
15
How to order (demand) a transformer correctly
Example
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
16
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
17
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.

• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
18
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
19
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
20
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 factor

• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
21
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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
22
How to order (demand) a transformer correctly

• Technical parameters of measuring parameters

• 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.
CSN 40.5/95/200 kV acc. to GOST
Rated frequency 50 (60Hz)
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
23
How to order (demand) a transformer correctly
2.b.2 Rated conversion and number of secondary
windings

• E.g. VTS 25 - 10000/v3//100/v3/100/3 V or VTD 25
  - 22000//100 V
•  
• Instead of v3, 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/v3 V, 22000/v3 V, 35000/v3 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/v3 V, 110/v3 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
24
How to order (demand) a transformer correctly
Number of secondary windings
- is given by values after the double slash in
conversion   Examples   22000/v3//100/v3 V one
secondary winding 100/v3 V 11000/v3 //100/v3
/100/3 V two secondary windings -the 1st
measuring winding 100/v3 V -the 2nd
auxiliary winding 100/3 V 35000/v3 //100/v3
/100/v3 /100/3 V three secondary
windings -the 1st measuring winding 100/v3
V -the 2nd measuring winding 100/v3
V -the 3rd auxiliary winding 100/3 V 
Number of windings may be 1 , 2 , 3 or
exceptionally 4
KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
25
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
0.2,0.5,1 Accuracy classes for protection
transformers 3P and 6P Accuracy class for
auxiliary windings 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
26
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

• 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

• 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 lt 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
27
How to order (demand) a transformer correctly
Data which should be included in a demand
(summary)
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

• Voltage transformer type

• Conversion

• Insulation levels

• Rated frequency

• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
28
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
  transformers 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
29
How to order (demand) a transformer correctly
Potential solution of the problem called
ferro-resonance

• Increase of primary winding resistance

• Inconvenient as it increases instrument
  dimensions
• It increases production costs substantially
• It increases product price

• Undersaturation of magnetic circuit 0.4T

• It protects transformer against oversaturation
• It is necessary in some cases, e.g. for railway
  applications
• It increases instrument dimensions and product
  costs
• It limits some existing parameters of the
  instrument, e.g. output

• 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. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com
30
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
• knapek_at_kpbintra.cz
• Ing. Petr Novák Business Department Manager
  420 604 237 033
• novak_at_kpbintra.cz
• Ing. Josef Stejskal Technical Department
  Manager 420 603 862 464
• stejskal_at_kpbintra.cz
• www.kpbintra.com

KPB INTRA s.r.o. , dánská 477, CZ-68501
Bucovice, tel. [phone], fax 420 517
381 433, info_at_kpbintra.cz, www.kpbintra.com